Green Manuring-A Basic Component of Organic Farming
With the advent of high yielding crop varieties, expanded area under irrigation and greater use of fertilizers and other inputs, Asia has changed within the last 20 years from a region of food scarcity to a region of food sufficiency. Increased fertilizer use has been estimated to contribute to about one-fourth of the increased rice production. In some countries, fertilizer prices were subsidised, thereby enabling farmers to apply production-maximising doses. During the same period, use of organic manures including green manure, declined substantially. But fossil fuel-based inorganic fertilizers are becoming more expensive. Another issue of great concern is the sustain ability of soil productivity as lands are intensively tilled to produce higher yields from a single crop and higher total annual yields under intensive cropping system. The soil organic matter and nitrogen levels vital to sustained crop production are often limiting in the soils of East, South and South East of Asia. Hence, there is an urgent need to identify alternate nitrogen sources to supplement inorganic fertilizers. Occurrence of multi-nutrient deficiencies and overall decline in the productive capacity of soils under intensive fertilizers use have been widely reported. All these factors have created a renewed interest on organic manures. Green manuring is a low cost but effective technology in minimising the investment cost of fertilizers and in safeguarding the productive capacity of the soil.
The practice of green manuring is as old as the art of manuring crops. The first serious test was made in 1882 at Kanpur Agricultural Station in Uttar Pradesh and was followed at Nagpur and Damraon in 1882 and 1897 respectively. The European planters of India were the pioneers in giving a systematic practice of green manuring as far back as 1890 in the coffee estates of southern India. It is a well known fact that N, for which soils have the greatest hunger, is a costly plant nutrient. This can be cheaply obtained by the inclusion of leguminous crops in rotations and their ploughing under:
Crops grown for the purpose of restoring or increasing the organic matter content in the soil are called green manure crops. Their use in cropping system is called 'Green Manuring' where the crop is grown in situ or brought from outside and incorporated.
Green leaf manuring consist of gathering green biomass from nearby location and adding it to the soil. In both, the organic material should be worked into the soil while they are fairly young for easy and rapid decomposition.
Legumes are usually utilised as green manure crops as they fix atmospheric nitrogen in the root nodules through symbiotic association with a bacterium, rhizobium and leave part of it for utilization of the companion or succeeding crop.
Objectives of Green Manuring
The main objective of green manuring is to add nitrogen to the companion or succeeding crop and to add to or sustain organic matter in the soil.
Subsidiary Objective of Green Manures
Legumes are inter-sown in the main standing crop a little before or after harvest with a view to utilize the nitrates that might form during the off season or the left over moisture in the soil profile. This may otherwise be lost. Such subsidiary crops are called 'Catch Crops'. The catch crops are ploughed in as green manures or grazed off.
Green manure crops may be sown in young orchards with the object of shading the soil surface and preventing the rise of temperature. Otherwise the tender roots of fruit plants may be affected by the high soil temperature. In plantation crops like tea and coffee, Gliricidia is used as shade crop first and then incorporated as green manure.
Green manure crops are sometimes grown with the objective of clothing the surface with a vegetative cover, especially in hill slopes during the rainy season to avoid soil erosion and runoff. This may also be done to check wind erosion. The crop chosen should be capable of covering the surface at the time of commencement of rainy or windy season. Later it is used as green manure.
Some legumes are also are grown for taking a few cuttings of green fodder for cattle in early stage. For example, Philippesara seeds are broadcasted in the standing rice crop (3-5 days before harvest) in coastal Andhra Pradesh. The early growth supplies fodder for cattle and the latter growth is used for green manure purpose.
Advantages of Green Manuring
• Green manuring has a positive influence on the physical and chemical properties of the soil.
• It helps to maintain the organic matter status of arable soils
• Green manure serves as a source of food and energy for the soil microbial population which multiplies rapidly in the presence of easily decomposable organic matter.
• The enhance activities of soil organisms not only cause rapid decomposition of the green manure but also result in the release of plant nutrients in available forms for use by the crops.
• Green manuring improves aeration in the rice soils by stimulation the activites of surface film of algae and bacteria.
• Many green manure crops have additional used as sources of food, feed and fuel.
Soil Structure and Tilth Improvement
• Green manuring builds up soil structure and improves tilth.
• It promotes formation of crumbs in heavy soils leading to better aeration and drainage.
• Depending on the amount humus formed, green manuring increases the water holding capacity of light soils.
• Green manure crops form a canopy cover over the soil and reduce the soil temperature and protect the soil from the erosive action of rain and water currents.
Fertility Improvement of Soils
• Green manure crops absorb nutrients from the lower layer of soils and leave them in the soil surface layer when ploughed in, for use by the succedding crops.
• Green manure crops prevent leaching of nutrients to lower layers.
• Leguminous green manure plants harbour nitrogen fixing bacteria, rhizobia, in the root nodules and fix atmospheric nitrogen.
• Green manure crops increase the solubility of lime phosphates trace elements etc., through the activity of the soil microorganisms and by producing organic acids during decomposition.
• A crop of green manure on an average is reported to fix 60-100 kg nitrogen/ha in single season under favourable conditions.
Amelioration of Soil Problems
• Green manuring helps to ameliorate soil problems. Sesbania aculeata (dhaincha), when applied to sodic soils continously for four or five seasons, improves the permeability and helps to leach out the harmful sodic salts. The soil becomes fit for growing crops.
• Green leaf manure from sources as Argemone mexicana and Tamarindus indica has a buffering effect when applied to sodic soils.
Improvement in Crop Yield and Quality
• Green manuring increasing the yield of crops to a extent of 15 to 20 per cent compared to no green manuring.
• Vitamin and protein, content of rice have been found to be increased by green manuring of rice crop.
Certain green manure like pongamia and Neem leaves are reported to have insect control effects.
Classification of Green Manures
It can be mainly classified into two groups viz., legumes and non-legumes and further sub-divided under two groups in each viz., green manure and green leaf manure.
Green manure Green leaf Green manure Green leaf manure manure
(eg)Dhiancha (eg) Gliricidia (eg) Sunflower (eg) Calotropis
Sunhemp Cassia Buck wheat Adathoda
Kolinji Pongamea glabra Thespesia
The legume and non-legume green manures are differentiated as follows:
• Fix free nitrogen from the atmosphere
• Physical condition of the soil is improved by cultivation and incorporation.
• They are more succulent than the non-legumes and less soil moisture is utilised for their decomposition.
• They serve as cover crops by their vigorous growth and weeds are smothered e.g. clover, dhaincha and cowpea.
• Free nitrogen is not fixed by non-legumes except in specific plants which have root nodules produced by bacteria or fungi, e.g. casuarina, Elasagnus and Cycas.
• They are not as succulent as legumes and hence require more soil moisture and time for decomposition
Characteristics Desirable in Legume Green Manure Crops
• Multipurpose use
• Short duration, fast growing, high nutrient accumulation ability
• Tolerance to shade, flood, drought and adverse temperatures.
• Wide ecological adaptability
• Efficiency in use of water
• Early onset of biological nitrogen fixation
• High N accumulation rates
• Timely release of nutrients
• Photoperiod insensitivity
• High seed production
• High seed viability
• Ease in incorporation
• Ability to cross-inoculate or responsive to inoculation
• Pest and disease resistant
• High N sink in underground plant parts.
Leguminous Green Manures
Some common leguminous green manure plant species are listed below:
Local name Botanical name
Sesbania Sesbania speciosa
Dhaincha Sesbania aculeata
Sunnhemp Crotlaria juncea
Wild Indigo Tephrosia purpurea
Pillipesara Phaseolus trilobus
Cowpea Vigna unguiculata, (Syn.V.sinensis)
Clusterbean (Guar) Cyamopsis tetragonoloba
Greengram (Mungbean) Vigna radiata, (Syn. Phaseolus aureus)
Blackgram Vigna mungo. (Syn. Phaseolus mungo)
Berseem Trifolium alexandrinum
Madras Indigo Indigofera tinctoria
Some of the common shrubs and trees used as green leaf manures are the following:
Cassia auriculata, Derris indica, Ipomoea cornea, Thespesia populnea, Azadirachta indica, Glyricidia maculata, Leucaena leucocephala, Calotropis gigantea, Delonix regia, Delonix elata, Jatropha gossypifolia, Cassia tora, Cassia occidentalis, Tephrosia purpurea, Tephrosia candida, Dodonea viscosa., Hibiscus viscosa, Vitex negundo.
Choice of Green Manure Species
Various nitrogen-fixing leguminous and non-leguminous species - particularly trees, creepers and bushes - can be used as green manures. The criteria for selection of plants as green manure is given in Table 2. Using grain legumes for green manuring brings quick economic benefits but, as they tend to accumulate nutrients in the grain, which is then harvested, their positive effect on subsequent crop yields is usually low. Mixtures of green manure crops are often more successful than sole crops, as they are less susceptible to pest attacks and combine different characteristics needed for improving the fallow land, such as quick soil cover and deep rooting.
As legume growth depends on the presence of suitable Rhizobium strains, inoculation may be necessary. Plant growth and organic N2-binding can be hindered by water stress, unfavourable pH, lack of other nutrients (particularly P, Ca, Mo and Zn) and/or Mn toxicity. Applying mineral or organic fertilisers (including rock phosphate, lime and ashes) can help to improve legume establishment.
Also species in the natural vegetation should be considered for improved fallow, particularly those that are protected by local farmers, e.g. Acioa barterii, Chlorophora excelsa, Alchornea cordifolia, Anthonota macrophylla and Dialium guineense in southern Nigeria. Also tropical grasses such as Pennisetum purpureum. Panicum maximum or Tripsacum laxum can produce large biomass and accumulate phosphorus and potassium more quickly than most legumes.
Agronomy of Green Manure Crops
It is adaptive to different soil conditions and can come up in sandy, loamy, alluvial, clayey and alkaline soils. Though the growth is very slow in the first 30 to 40 days, it picks up subsequently making rapid growth. It withstands salinity to some extent. It has no serious pests or diseases. The plant has greyish appearance with soft hairs on the stem and leaves. The stem is pithy, but if allowed to grow for more than four or five months, it becomes woody making it difficult to be pulled out or even to be harvested with sickle.
There are different methods of growing Sesbania speciosa in rice field. Three or five days prior to the harvest of rice crop, seeds at 50 kg/ha are sown as broadcast. These seeds get thrust into the soil while labourers move during harvest of rice crop. With the available soil moisture, the Sesbania seeds germinate. This method is very easy to follow as it involves no preparatory cultivation for raising green manure crop. In another method, after ploughing the field, Sesbania seeds are broadcasted at 35 to 50 kg/ha. A good stand of crop can be obtained by Irrigation, Where two crops of rice are taken, three weeks old seedlings of Sesbania can be grown along the borders of the field during the first crop season and utilised as green manure for the second crop. Such border planting of Sesbania at a spacing of 5 to 10 cm in one hectare will give about 5000 to 8000 kg of green matter for the second crop. For this purpose, at the time of raising rice nursery for the first crop, 0.75 kg of seeds of Sesbania may be sown in 2.5 cents (100 sq.m) of nursery. While transplanting rice seedlings, Sesbania seedlings are also pulled out and planted along the borders of the field.
Each plant of Sesbania gives about 400-600 g of seeds. For sowing one hectare for green manure purpose, 50-60 kg seeds will be necessary. Hence, if about 125 to 150 vigorous plants are left among the border plants, sufficient seeds could be obtained from these plants. The yield of green matter varies depending upon the duration of growth. A 60 days crop will yield about 10,000 kg/ha of green matter while 90, 120, 150 days crop will yield 20,000, 50,000 and 60,000 kg/ha of green matter, respectively. For one hectare of rice crop, 6,250 kg of green matter will be sufficient.
Sesbania Aculeata (Dhaincha)
It is a quick growing succulent green manure crop. It adapts itself to varying conditions of soil and climate. It can be grown even under adverse conditions of drought, water logging, salinity, etc. It comes up even in alkaline soils and corrects alkalinity if grown repeatedly for four to five years. Bacterial nodules are formed in plenty on the roots. The plant has a soft stem. It makes good growth in two to four months and produces abundant green matter ranging from 10 to 20 tonnes per hectare, depending upon the age at harvest. Recommended seed rate is 20 to 25 kg/ha, though higher seed rate help in producing plants with thin stem. The stem gets woody and fibrous after three months of growth.
As a pure crop, 25 to 30 kg/ha seeds are sown and the plants ploughed in for single crop rice. Though the initial growth is slow, it picks up fast and grows vigorously by later.
It is an aquatic leguminous crop which have nodules both on the stem and roots. It was introduced in lndia in the 1980's from the International Rice Research Institute, Philippines. It is a tropical legume which thrives well under flooded and water logged conditions, producing aerial nodules on the stem. Due to its profuse stem nodulation, it gives ten times more nodules than most of the legumes. This can be grown either prior to rice crop or in between two rice crops. Though naturally propagated by seeds, seedlings and root stem cuttings can also be used as planting material.
The normal seed rate is 30 to 40 kg/ha. To get early, uniform germination and vigorous seedlings, seeds have to be scarified with concentrated sulphuric acid for 15 minutes. Summer (April-July) is the best season for getting higher biomass and better seed production. The photosensitive nature of this crop (short day) restricts its usage during winter. Intercropping one row of 30 days old seedlings for every 1.5 metre in rice fields could produce three to five tonnes of biomass in 30 days after transplanting. Rice yields are not affected due to intercropping.
Crotalaria Juncea (Sunnhemp)
It is a very quick growing green manure-cum-fibre crop. It comes up well in loamy and heavy soils. This crop can be cut even when it is 45 days old. It does not withstand heavy irrigation or continuous water logging. There are a number of varieties varying in duration ranging from 75 to 150 days. The general appearance of the crop is greyish to greenish. The tall, robust and late duration varieties are used for fibre extraction also. The seed rate is 25 to 40 kg/ha and the yield of green matter may vary ranging from 12,000 to 25.000 kg/ha depending upon the environmental conditions and duration of the crop.
Tephrosia Purpurea (Wild Indigo)
It is a slow growing green manure crop. It is not grazed by cattle and so no protection is needed in the field. Further, if the crop is continuously raised for two to four seasons in the same field, it becomes self sown in the subsequent years and, thereafter, there is no need of any fresh sowing of seeds in the same field. It is suitable for light soils. It does not withstand water stagnation. It is a perennial undershrub, growing wild in sandy or gravelly waste lands. But it is grown as an annual crop for green manure purpose. It is hardy and drought resistant and suited for summer fallows. It comes up well in loamy soils and could be grown in light soils.
The seeds are sown as broadcast in the standing crop of rice just a week before harvest as catch crop. The seeds have a waxy, impermeable hard seed coat and do not quickly germinate. To hasten germination, the seeds are to be pounded with sand or steeped in hot water at 55C for two to three minutes. The seed rate is 25 to 40 kg/ha, while the green manure yield varies from 3500 to 6000 kg/ha.
This is a perennial shrub. It is found wild and in cultivated lands. There are two types which closely resemble each other and are generally found grown as indigo (Madras Indigo and Bengal Indigo). The seed rate is 25 to 30 kg/ha and the yield of green matter varies from 10,000 to 12,000 kg/ha.
This is a leguminous cover crop with the ability to cover the ground within a short period. It is also a self sown crop. The cultivation of calopogonium as a cover crop is the cheapest and most effective method to check soil erosion and the growth of obnoxious weeds in plantations of pepper, orange, coconut etc. It also enriches the soil and conserves soil moisture. It is an annual/perennial, with creeping or climbing habit. It is not grazed by cattle. The plant is capable of growing to a length of about 2.5 m in the course of about 16 weeks and to strike root at every one of nearly 25 nodes over this length, though only about 50 per cent of these nodes actually develop roots in the field. Each plant has three leader shoots and about eight main lateral shoots from each leader shoot. In addition to the large volume of leafy growth over the ground, the plants are found to develop a large volume of roots in the ground. The luxurious surface growth of the Plant protects the soil from the splash effects of rain drops during the monsoon months.
The chief merit of Calopogonium as a cover crop, in addition to the ease with which it can be established in a very short period, is that it dries up during the summer months and offers no competition to the plantation crops for the limited soil moisture. The leave shed by the cover crop during the summer months provide a dry mulch which could effectively reduce soil temperature and surface evaporation during the season. Another desirable attribute of Calopogonium is that it re-establishes itself during the rainy season and covers the soil within a short period. Profuse seeding is yet another virtue of calopogonium. This results in the cover crop establishing itself every year with the summer showers from the self sown seeds. The seed rate for establishing the cover crop in the beginning is 8 to 10 kg/ha and the yield of green matter is 5000 kg/ha.
Phaseolus Trilobus (Phillipesara)
This is a dual purpose crop yielding good fodder for cattle and green manure for land. It is a herbaceous creeper growing into a short dense cover crop when grown thick. Though it does not produce a bulky yield, it is capable of being cut twice or thrice before being ploughed into the field. The harvested material is used as forage. Seeds are also used as a minor pulse. It comes up under varying conditions of soil but prefers loamy and clayey soils. Initially, adequate soil moisture is essential for its early growth. One or two irrigations given during its growth period will help in producing bumper harvest forage crop. After this harvest, the crop can be ploughed into the soil. It is able to withstand drought and also excessive soil moisture. The seed rate is 20-25 kg/ha and the yield of green matter is 10,000 to 12,000 kg/ha.
It serves as a cover crop as well as a good fodder crop. It is a drought tolerant legume and a self propagating crop and so it needs no replanting. It is a slow growing perennial creeper which is hardy and aggressive in nature. It is a shade loving crop and persists in soil. It has cracked pods.
Macroptilium Atropurpureum (Siratoo)
It is a good cover crop. It is a highly drought resistant perennial legume. It forms a good mixture with pasture grasses. It is suitable for sandy loam to red loamy soil. It is a slow growing crop. It has prostrate stem. It sheds its leaves. It has to be replanted each year. The biomass produced by this plant is more than that of Centrosema.
It is used as a good soil cover and also as forage crop. It is a perennial drought resistant, spreading type. It is capable of growing on sandy soils. It is a compatible mixture with cultivated pasture grasses. It produces low biomass.
Pueraria Phaseoloides (Kudzu)
It is a hardy, perennial leguminous cover crop. It comes up in poor, rough soils and steep slopes. It is a creeper. It has prostrate stem. It sheds its leaves in winter. It has to be replanted each year. It is a fast growing vine propagated through cuttings. It does not withstand water logging. It is superior to Centrosema in biomass production. It comes up in hot summer and autumn.
Dolichos Lab Lab var. Lignosus
It is an excellent cover crop. It has a diffuse branching forming a dense cover. It has profuse seeding habit. It does not tolerate winter.
Agronomy of Green Leaf Manure Shrubs and Trees
Green leaf manuring is the application of green leaves gathered from shrubs and trees growing in waste lands to the fields where crops are to be raised. Green leafy material is gathered from all sources by farmers for manuring purpose. Different kinds of shrubs growing on tank bunds, waste lands, field bunds, garden lands, etc. are used. In addition, loppings from miscellaneous trees are also gathered for use as green leaf manure. Green leaves have the same effect as green manure on the land and the crop.
The common shrubs growing in waste lands are Cassia auriculata, Dodonia viscosa, Calotropis gigantea, etc.
Leguminous trees like Pongamia glabra and Cassia siamea can be planted in waste lands, for augmenting the supply of green leaves. The trees do not require any attention after they get established and start growing.
A brief description of some of the most common shrubs and trees utilised for the collection of green leafy material is given below.
Glyricidia (Glyricidia Maculata Syn. G. sepium)
It is a shrub type of plant that comes up well in moist situations. Under favourable conditions of soil and climate, it takes up a tree habit. It is a quick growing tree and often used for shade and green leaf manure in tea, coffee and cocoa plantations. It can be planted on alternate field bunds of wetland, 1 to 2 m apart, or as a thick hedge by close planting in three to four rows at 0.5 m spacing or along field border as tall shrubs giving support to the fence line or along farm roads on both sides for the production of green leaf. For green leaf purposes, the shrub could be kept low by pruning or lopping at convenient heights. The shrub is pruned two to three times a year and it withstands repeated loppings. It has no root effect on the crops grown by the side. When the shrubs are regularly lopped the height is restricted to 2-3m and they do not affect the growth of cultivated crops with their shade effect.
Glyricida can be propagated by planting stem cuttings or seedlings raised in nurseries. The establishment of seedling is better compared to stem cutting. The seeds are sown in well prepared nursery and the seedlings transplanted when they are about 30 to 60 days old. Within two years after planting, the plants are ready for lopping. Each plant gives 5 to 10 kg of green leaves annually. When the individual rice fields are about of 0.1 ha each 375 to 400 plants can be planted on the bunds of one hectare of land and this will produce 2500 to 3500 kg of green leaves annually.
It is a quick growing, profusely branching, and highly drought resistant weed. It gives abundant green leafy material in short time. It is multiplied by means of mature stem cuttings. Stem cuttings of about 0.3 m long with three or four nodes and axillary buds are planted at a distance of 1 to 2 m all along the wide field bunds, irrigation channels and fences. As many as 1800 - 2000 cuttings can be accommodated in one ha as border planting and two to three loppings can be taken in a year. Each plant will give about 5 to 7 kg of green matter per lopping.
It is a very common plant, found coming up in waste lands, hill slopes, plain sea shores, etc., almost in the wild condition. It is a hardy plant. The plant is propagated through seeds. The seeds get dispersed and plants grow naturally without any efforts. When the plants start to flower in off-season, they are cut and applied to the fields.
Derris Indica (Syn. Pongamia Glabra)
It is a leguminous, moderate sized ever green tree. It grows in coastal forests, on river banks and on tank bunds mostly along streams, wastelands and road sides. Trees are established by means of planting two to three months old seedlings, 4 to 5 m apart. Loppings may be taken once or twice a year. A tree yields approximately 100 to 150 kg of green material per lopping.
Azadirachta Indica (Neem)
It is a profusely branching, large evergreen tree and gives plenty of foliage. It comes up in all types of soil. The trees are grown along field borders, rivers banks, roads, waste lands and also in garden lands and homestead gardens. Trees are established by planting seedlings. at a spacing of 5 to 6m. One or two loppings in a year are taken in favourable seasons, each lopping weighing about 150 to 200 kg of green matter.
It is also an evergreens tree which thrives in all types of soils. The trees are grown in garden land areas, gardens and also in waste lands. A spacing of 4 to 5 m is adopted. It is propagated by stem cuttings. It establishes very quickly and produces a number of branches. Two or three loppings of green leaves are taken in a year during favourable seasons. A tree will give as much as 100 to 150 kg of green matter per lopping.
The leguminous green manure crops have the ability to fix gaseous nitrogen from the air with the aid of rhizobia which live in nodules on the roots of the legume plants. The bacteria live symbiotically in nodules, with the plants providing food and energy for the organisms which, in turn, benefit the host plant by fixing nitrogen from the air. Consequent on this symbiotic relationship the leguminous plants succeed in enriching the soil nitrogen status only in the presence of proper nodule bacteria. As many soils do not contain the appropriate strains of bacteria, it becomes necessary to inoculate the legume seeds with the specific strains of rhizobia in order to ensure better growth of the host plant and effective nitrogen fixation by the nodule organisms. Without Rhizobium bacteria, the leguminous green manure crops may deplete the soil of nitrogen like any other non-leguminous plants instead of replenishing the soil nitrogen store. Among the root nodule bacteria (rhizobia), there are several types and strains which are specific for different legumes. For best results, appropriate strains of Rhizobium bacteria for each legume should be present. It may be that poor and ineffective forms of many of the strains of rhizobia are present in normal soils. They may produce nodules that provide little or no nitrogen. Therefore, it becomes necessary to inoculate the legume seeds with beneficial strains of proper root nodule bacteria.
The process of nitrogen fixation begins as soon as or shortly after the formation of nodules, and continues as long as the nodules remain firm and healthy. The maximum nitrogen fixation is found to take place at the flowering stage of the host plant. The percentage of nitrogen progressively decreases as the seed formation proceeds and the nitrogen percentage in the nodules approximates to that of the root by the time the seed is ripened.
Conditions for Fixation of Nitrogen
• The presence of appropriate strains of rhizobia in the soil
• The level of moisture in the soil
• The initial nitrogen level in the soil
• The presence of other available plant nutrients in the soil
• The pH of the soil (pH 5 to 9 is conducive for N fixation)
• The stage of growth and conditions of the green manure crop
When the soil is rich in nitrogen, the root nodule bacteria do not fix nitrogen from air but feed on the soil nitrogen. The legumes, then, act just like any other non-leguminous crops. Under such circumstances, it would be advantageous to grow cereals along with legumes in the ratio of 1:3 so that the cereals would be depleting the soil of its nitrogen and the legume would thrive on the atmospheric nitrogen. The requirements for successful nitrogen fixation are proper inoculation with efficient strains of bacteria, adequate supply of available phosphate, lime and moisture, good drainage and a neutral soil reaction.
Bacterial Inoculation of Legumes
It has been proved that there is a definite increase in the total nitrogen content of legumes when inoculated with specific bacterial culture of the right type and efficiency. Inoculation is the process of mixing the most appropriate bacteria with seeds at sowing time so that maximum benefits are derived from the symbiotic association of plant and bacteria. Inoculation is generally done by treating the specific pure cultures with seeds by using gum or rice kanji. The following indications normally reflect the need for rhizobial inoculation.
• When the growth of a recent crop of legume is poor
• When the recently grown legume crop had sparse nodulation on the tap root and upper side roots with widely scattered small nodules on the lower regions of root system.
• When legume is being grown on land that is poor due to lack of care or unfavourable natural conditions.
The uses of inoculation could be summed up as follows:
• It prevents nitrogen starvation
• It lessens the dependence of legumes on soil nitrogen
• It improves~ the quality of crop
• It increases crop yield
• It ensures a nitrogen rich leguminous green manure crop.
Method of Application of Green Manure
The method of application varies from place to place depending upon other agronomic practices followed. In the case of green manuring, when plants are grown in the same field where they are to be incorporated, the plants are cut at the proper stage to the ground level, placed in the furrows and covered by the next furrow. With the availability of labor saving implements like green manure trampler, the plants are trampled by working the implement and later on levelling the field. This practice is possible where rice is transplanted. In broadcast crop, a suitable modification is necessary and usually the green manure crop is incorporated during the first weeding. In the case of green leaf manuring, the plants brought from outside source are spread over the field and trampled in by the use of implements or by human labour. In some cases, as in the green manuring of sugarcane. The incorporation is done during intercultivation operation.
Decomposition of Green Manure
The green manure applied to soil undergoes a series of chemical changes and only after these biochemical changes the nutrients contained in the plants become available and the humus is synthesized. Hence, as in the case of any other bulky organic manure, the nutrients become available slowly and steadily for a prolonged period of time. The green matter applied to the soil is acted upon by many types of microorganisms such as bacteria, fungi, actinomycetes and macroorganisms like protozoa, worms and insect larvae and several intermediate and end products are formed during the decomposition. The type of decomposition and the products formed are found to be controlled by the following important factors:
(1) Organisms present: The type and nature of microorganisms whether fungi or bacteria, aerobic or anaerobic, autotrophic or heterotrophic organisms, will decide the type of decomposition.
(2) Temperature: Optimum temperature of about 30-35ºC is necessary for the normal decomposition processes and the rate of decomposition will be modified at low or high temperature.
(3) Aeration: The various stages of the decomposition process are decided by the presence or absence of air. Hence, there is aerobic decomposition in the presence of air and anaerobic decomposition in the absence of air.
(4) Moisture supply: The moisture content of the green matter and the soil decide the rate and type of decomposition. Optimum moisture is necessary for the normal rate of decomposition. In low moisture supply, decomposition will be slowed down.
(5) Soil factors: The various physical, chemical and biological properties of the soil will influence the rate and type of decomposition. In general, decomposition will be rapid in a fertile soil than in a non-fertile soil.
(6) Nature of green manure: The composition of the green manure, its age, maturity and C/N ratio will also influence the rate and type of decomposition. The young plants will decompose more rapidly than well-matured plants. Similarly plants having greater amount of nitrogen will decompose more rapidly than those having higher content of carbon compounds.
Putting all the above influencing factors together, the decomposition can be broadly studied under two categories.
(i) Aerobic decomposition
(ii) Anaerobic decomposition or putrification
The plant material incorporated into the soil is made up of numerous compounds. But, for studying the decomposition processes the various compounds can be roughly brought under three groups:
(1) Carbon compounds consisting of carbohydrates, fats, oils, organic acids, lignin and other cyclic organic compounds.
(2) Nitrogen compounds consisting of proteins, amino acids and other non-protein nitrogenous substances and
(3) Mineral salts.
In this process of decomposition the most important deciding factor is the aeration in the soil and sufficient quantity of air is always necessary for the normal rate of aerobic decomposition.
Changes in the Carbon Compounds
The various carbon compounds are attacked by the organisms and all of them are found to be converted finally to carbon dioxide and water. For example, if glucose is attacked by the aerobic bacteria, carbon dioxide and water are produced.
C6H1206+602 BACTERIA ----> 6 CO2 + 6 H2O + ENERGY
In the same way, if starch, cellulose, and hemicellulose are present, they will be converted finally to carbon dioxide and water. This conversion is found to be performed by a group of bacteria, fungi and actinomycetes capable of living only under aerated condition. But the various organisms capable of decomposing the carbonaceous material require sufficient quantity of energy and nutrients. They find sufficient energy from the decomposition of carbohydrates but there may be insufficiency of nitrogen and phosphorus and in such cases, nitrogen and phosphorus should be added to favour all the activities of the organisms. In the case of young plants there may be sufficient quantities of nutrients and hence the rate of decomposition of carbonaceous material Will be carbondioxide and water but this conversion is not so quick and simple as seen from the reaction.
Limitations in Raising Green Manure Crops
Though there are several advantages of green manuring, it is not being practised on a large scale by the farmers due to certain limitations,
• Non-availability of water resources may restrict raising of green manure crops.
• Non-availability of good quality seeds poses a problem.
• Allotment of 6-8 weeks exclusively for growing a green manure crop is not preferred by farmers in intensive cropping system.
• In North India, where rice is grown after a wheat crop, the farmers are not able to carry out field operations in the peak summer months of May and June.
• As the benefits of green manuring are not as spectacular as those usually derives from direct application of inorganic fertilisers, farmers are not convinced about the usefulness of green manuring.
• Sensitivity of certain leguminous green manure crops to photoperiodism is a constraint.
• Vegetative growth is retarded by early flowering during a short, dry season, resulting in less biomass production.
• A green manure crop may compete for time, labour and water, the cost of which must be balanced against the cost of inorganic fertilisers.
• Poor germination of certain green manure seeds is also a problem.
• Incorporation of green manure crops under certain situations may be difficult and costly.
• Green manuring represents a cheap and effective way of improving the soil fertility as long as water conditions permit and green manuring is not advisable where water is a limiting factor since the succeeding crop will suffer due to dearth of water.
• For a green manure crop, a legume is preferable as it adds atmospheric nitrogen which is a distinct addition to the soil.
• In tropical regions like India, more than the physical effects such as nitrogen supply, releasing the unavailable nutrient and chelating actions seem to be the important effects of green manures.
• Green manure crops serve as cover crop in the soil erosion areas and aids in conservation of moisture.
• It acts as a good amendment for the reclamation of problem soil like alkali soil.
• Young green leaves can be incorporated immediately after planting but older crops has to be buried 4-8 weeks ahead of the planting.
• The optimum dose of green manure is from 4000-6000 kg per hectare.
• Green manures should be buried in the proper stage of their growth i.e., at flowering stage which coincides at the 8th week as it contains maximum nitrogen and less of carbon.
• Optimum depth of burying green manure is at 10-15 cm.
• Green manuring is practically as efficient as ammonium sulphate/urea for rice on equal nitrogen basis.
• Green manuring, in conjunction with artificials, especially with phosphate, increases the yields economically.
• It is quite clear from the review of work that more than its value as supplier of nitrogen, there are beneficial effects for the increased yield of succeeding crops.
• It has the potential to improve the low fertility status of soil
• A considerable reduction in the investment on fertiliser, the cost of which is increasing, could be achieved by green manuring.
• Green manuring can be an important component of low external input sustainable agriculture (LEISA) without sacrificing the level of productivity.
Biological Pest Management
Organic and Natural farming, which aim at 'cooperating rather than' confronting with the nature has been hailed as the only answer to bring sustainability to agriculture. In organic farming systems pest control strategies are largely preventative, rather than reactive. Organic farming is not a single method but rather a variety of techniques which are aimed at reducing costs, preserving the environment and protecting human health by eliminating the use of toxic farm chemicals. Masonobu Fukuoka of Japan, considered as the father of Organic farming, has been consistently recording yields of many crops which are comparable to the best yields obtained in Japan, by not using HYVs, chemical fertilizers or pesticides. Use of pesticides and chemical fertilizers does not necessarily lead to better farming than using natural agricultural methods.
In the conventional agriculture pests are often controlled with man made chemicals which have following harmful effects:
1. Chemicals kill useful insects which eat pests.
2. Chemicals can be very bad for the health of people who use them and people who eat food with small amounts of these chemicals still attached.
3. These chemical can stay in the environment and in the bodies of animals causing problems for many years (discussed in detail in chapter 1).
4. They are very simple chemicals and insect pests very quickly, over a few breeding cycles, become unaffected by them.
5. Many farmers in developing countries cannot afford to buy man made chemicals.
Pests-insects, disease causing pathogens, weeds and nematodes are estimated to cause an annual loss of about 33-35 per cent of the potential food production world-wide. In lndia, according to very conservative estimate, the annual crop losses due to these pests amount to a staggering Rs 25,000 crores. In order to increase agricultural production, many changes have been adopted in the recent past such as use of dwarf high yielding cultivars, higher fertilizer use, increased irrigation sources, intensive cropping, large areas under single crop, extension of new crops in non-conventional areas, large scale movement of seeds etc. All these change have often led to serious pest problems. The new high yielding cultivars in use today are often more susceptible to pests than the old varieties were. Abundant irrigation and nutrient supply has enabled crops to be grown throughout the year-providing ideal conditions for the pests to multiply. Abandoning many time to planting etc. has further aggravated the problem. With the result, not only the infestation of known major pests has increased, but also hitherto unimportant or unknown pests have emerged as major pests.
The current pest control technology relies heavily on pesticides. The pesticide consumption world-wide which was 148,000 metric tonnes in 1966 has increased to over 302,000 metric tonnes in 1976, the most significant increase being for herbicides which increased from 51,000 to 181,000 metric tonnes. In India, it was nearly 200 metric tonnes in 1955 and about 75,000 tonnes in 1985 and may reach l00,000 tonnes in 1990 and 200,000 tonnes in 2000 AD. Pesticide residues in agricultural commodities are the issue of major concern besides their harmful effects on wild life, and other desirable flora and fauna. Equally worrying thing is about development of resistance in pests to pesticides. There are innumerable instances of insect pests, fungi and weed species showing resistance to pesticide for which they were previously susceptible. Outbreak of American bollworm Heliothis armigera in cotton crop in Andhra Pradesh in areas where synthetic pyrethroides were liberally used is indicative of things to come in the future. Such developments have negative impact as it makes room for using higher rate of encourages people to look for chemicals which are more toxic than the ones used previously.
Due to the dangers of using chemical pesticides, there has been a considerable resurgence of interest amongst the scientists to look for alternative methods of pest control. Slowly but steadily there has been growing appreciation about the role of pest resistant cultivars, biological control agents and cultural methods in pest control. These non-chemical or 'bio-environmental' methods are the major components in the integrated management of pests.
The non-chemical methods of pest management certainly form the major components of Organic farming. Management for integration of non chemical methods of controlling insect pests, disease, weeds and nematodes is essential for successful organic farming.
Cultural control is the deliberate manipulation of the environment to make it less favourable for pests by disrupting their reproductive cycles, eliminating their food or making it more favourable for their natural enemies. The following are just a few examples of the diverse ways in which the method can be used.
Sanitation includes the removal or destruction of breeding refuges and over wintering sites of pests. Removing diseased plants (rouging) or pruning infested parts is important in disease management. To prevent introduction of inoculum, all means of carrying the pathogen should be looked into e.g., seeds or propagating material, water, plant debris, farm-yard manure, implements etc. Collection and destruction of egg masses could be very useful practice in insect management in orchards. Care need to be taken to use well composted manure, as high composting temperature, is expected to damage disease inoculum, weed seeds etc.
The government laws or quarantine play great role in preventing the introduction of pests by propagating material. The seed certification programmes adopted by the various countries have proved immensely useful in containing the spread of pests.
While it is difficult of check the spread of diseases through irrigation water, systematic weed control along irrigation canals will help in stopping the spread of weed seeds. Similarly, machinery used in an infested field, unless cleaned properly, will aid in spread of disease pathogens and weed seeds. Disinfestation of smaller tools and movement of farm vehicles from less diseased to severely infected fields are general methods of preventing spread of diseases by man and machinery.
Pest population may often be effectively suppressed by destruction of their alternate plant hosts, many may in fact be weeds.
The parasitic weed Striga will continue to thrive on sorghum stubbles even after harvest. Unless pulled out, this may be a potential source of infestation in the coming years. Destruction of infested young shoots of sugarcane and the stubbles even after harvest helps a great deal in keeping the incidence of sugarcane borer at a very low level.
In many developing and under-developed countries, tillage still is the only known method of controlling weeds. The practice however is rapidly being replaced in much of the developed countries with herbicides.
Frequent shallow ploughings given before planting are very effective in controlling annual weeds. This techniques of sowing crop seed in the relatively weed-free soil is termed as 'state seed bed' techniques which is being very widely used in many crops. Being less expensive, this can form an important component of integrated weed management system in many places. However, it may bring back the buried weed seeds on to the surface. Alternatively, a very low dose of a contact herbicide may take care of weeds without disturbing the soil further. Deep ploughing particularly in summer months is very effective against deep rooted perennial weeds as it would expose the underground vegetative parts to hot weather.
With soil tillage, other pests are also killed mainly due to exposure or debris destruction. For example, the wheat sawfly in North Dakota has been reduced by as much as 75 per cent by cultivation. Summer tillage of wheat destroys wheat streak virus reservoirs and viruse's vector the wheat curl mite. Tillage, however, need to be timed to coincide with the susceptible stages of the insects.
Depth of ploughing is also an important factor as burial to at least 8 cm is necessary to control Cephalosporium stripe of wheat, to atleast 15cm for the bent grass nematode and to atleast 25-30 cm for sorghum downy-mildew. Although the long term effects of reduced tillage have not been studied adequately, some adverse effects are known. For example, army worms and corn stalk borers often increase in crops grown under reduced tillage and surface accumulation of crop residues under reduced tillage conditions increases the infestations of termites, slugs, some nematodes and diseases.
Application of Manures and Soil Amendments
Application of soil amendments would change the rhizosphere environment by affecting porosity, aeration, temperature, water holding capacity etc. Healthy crop plants have a greater chance of fighting with pests than under nourished plants. Besides, soil amendments as such or their decomposition products may have a direct effect. More than thirty disease mainly root rots have been reported to be significantly controlled by application of organic amendments.
Incorporation of various kinds of organic amendments to soil also holds promise in long-term control of nematodes. Use of chopped shoots, straw, saw dust, animal manure, cakes etc. have resulted in significant reduction nematodes population. In India, oil cakes of linseed, mustard, peanut, castor bean, mahuva, (Madhuca indica) and neem (Azadirachta indica) have proved very effective for nematode control in a variety of crops.
All plant feeding insects have specific nutrient requirements. The incidence of corn leaf hopper (Dalbulis maidis) which transmit corn stunt pathogen was reduced at low N levels and at high planting densities .Poor nutrition to crops is also known to affect the reproductive ability of some insects feeding on them.
Increased application of plant nutrients, although, increase the growth of both weeds and crop plants, it benefits crop more. However, increased application of nitrogen is known to reduce Striga incidence in cereals. However, other methods of weed control must accompany increased supply of nutrients as weeds are known to deplete large quantities of nutrients from soil, thereby depriving the crop plants of the precious and costly input.
Cropping patterns have undergone drastic changes over the years. Provision of irrigation, development of short duration, photo-insensitive, high yielding varieties of crops have resulted in growing of more number of crops in a year. Consideration of potential pest problems while choosing crops/crop sequences would go a long way in pest management. Following are some of the examples.
Good crop rotation with non-host plants would result in reduction of pest population either directly by toxic action of the non-host crops or indirectly by depriving them of the food the host plant would have offered had it been grown continuously. Several soil borne diseases of cereal crops are successfully controlled by a crop rotation period of 2-3 years. Soil pathogens that can be controlled by a 3 to 4 year rotation with non-host crops include organisms causing cabbage black rot, bacterial leaf blight of bean and cabbage black leg. Gartic, onion, beet root and Lucerne are suggested as good rotational crops in controlling Fusarium wilt of melons and cucumber. Crop rotation is one of the most important measures for controlling plant parasitic nematodes and frequently it appears to be the only economical method for controlling this pest. Effective rotation is widely practised for control of the golden nematode of potatoes, the soybean cyst nematode and the root rust nematode.
Each crop has its own characteristic weeds and they thrive well when the same crop is grown successively. Monoculture of the cereals and use of hormone herbicides have led to serious problems of grass weeds in many parts of the world. In a 3-year study, high populations of Xanthium pensylvanicum were associated with soybean than with corn regardless of weed control measures. Scirups maritamus a difficult-to-control weed in a continuously flooded low land field was effectively controlled when the rice was rotated with an upland crop.
Rotation is most effective against soil pests (e.g. white grubs, wire worms etc.), which take several years to reach maturity. Until synthetic organic insecticides became available, rotating corn with such crops as oats, clover and soybean was a standard procedure for controlling corn rootworms in mid western United States. In white ant infested areas crops like sugarcane, wheat and chillies should be avoided; instead tobacco or onions maybe grown.
Chief obstacles to success of crop rotations are the pronounced longevity of inoculum/weed seed in soil and frequently wide host ranges of pests. Often populations of a pest other than the target pest may increase on the alternative crop. Some crops used in rotation may often be of very low economic values.
The practice of attracting pests to small plantings of crops, which are then destroyed or sprayed with a toxicant has been quite successful against some plant nematodes, parasitic weeds and insect pests.
A susceptible crop such as sorghum or sudan grass may be grown before the main crop season to induce germination of Striga seeds before it is destroyed. Crops such as groundnut, linseed, cowpea, cotton, sunflower etc. form good rotational crops as they induce germination but are not parasitized by Striga.
Some nematodes may also be controlled by trap crops. Highly susceptible crops are allowed to grow in infested fields until the second stage larvae enter the roots and begin to develop. The crop will be destroyed before nematodes mature.
In all these, the plant destruction must properly be timed and implemented, lest the population of pest may increase many-fold.
Inter row space is a potential place for weeds which can be put to better use by intercropping. Intercropping in broad spaced crops such as pigeonpea, sugarcane, cotton, maize, sorghum with fast canopy forming plants, reduce the weed emergence and competition substantially.
Lower incidence of insect pests were found on legumes intercropped with maize. Intercrops of clover, spinach, beans and tomato reduced incidences of Brevicoryne brassicae andPlutella xylostella in cabbage substantially. Incidence of Heliothis armigera reduced in chickpea when grown in association with barley, mustard or wheat.
Intervening strip of non-suitable crop prevent movement of insect pests from one strip of a crop to another. Also adjacent strips share unspeciaIized natural enemies which would move when insect pests build up on the neighbouring strips. The abandonment of strip farming in Peru some years back has been given as the reason for boll worm outbreak on cotton there and certainly re-diversifying the cotton agro-ecosystem has now greatly reduced the incidence of the pest.
Time of Planting
Pest outbreaks occur at particular soil and climatic conditions and planting can be so adjusted that such outbreaks do not coincide with the susceptible stage of the crop.
With diseases, it is reported that the incidences of chickpea wilt and root rot of pea were considerably reduced when the planting was delayed. There are also reports of early sown wheat escaping rust damage and pearl millet sown before 15th July recording less incidence of ergot in North India.
Maize sown late suffers little from damage by maize borer as by then the egg parasite Trichogramma is able to keep down the population of the pest. Maize grown in winter is free from borer attack as this pest hibernates during winter. Rice is reported to suffer less from borer attack if transplanted early (before middle of June). Early Maturing cotton varieties(Bikaneri norma, H-777 and F-414) have become popular in Punjab and Haryana as they escape pink bollworm attack.
Late sown crop in winter is expected to have less problems with nematodes as they are inactive during this period.
Late planting of wheat reduces infestations of important weeds such as Chenopedium album, wild oats (Avena spp) and Phalaris minor. However, the limitation is altered planting time may not always be the best one for obtained higher yields.
The scab of potato is suppressed by irrigating potato at the time of tuber formation. Wet weather diseases such as halo-blight and anthracnose of beans, early blight and charcoal rot of potatoes can be checked by furrow rather than sprinkler irrigation. Diseases which are favoured by high moisture at the soil surface like damping off or collar rot can be minimized by planting crops in ridges or raised beds. Irrigation often makes it possible to avoid a pest by allowing the crop to be grown out-of-season.
It is a well-known fact that transplanted rice faces very less weed problem compared to other methods which is mainly due to pudding and impounding of water. Flooding upto 10 to 20 cm early in the season reduced the infestation of many weeds including Echnochloa crus-galli but may increase problems with other weeds such as blue green algae. Under irrigated conditions, planting crop-seed in the moisture zone in an otherwise dry seed bed and delaying the first irrigation reduces the weed infestations quite substantially.
Drip irrigation, by virtue of providing water at the base of the plant, results in far lesser weed problem than would be expected from other methods of irrigation. Similarly, overhead sprinkler irrigation in potato effectively controlled potato moth .
Weeds and crop seeds germinate almost simultaneously and they start competing with each other for water, nutrients and space. Selection of vigorous growing crop cultivar, closer row spacing, higher crop seed rate, proper time and method of fertilizer application etc. are some of the husbandry practices which are likely to play a vital role in weed management. There is much meaning in the saying that good crop is the best weed killer.
Among winter cereals, barley is reported to be more competitive than wheat or oat .Maize is having the highest weed suppressing ability (92%) followed by pearl millet (88%), sorghum (81%) and Setaria (73%). Amongst noncereals, cowpea (88%) is more competitive than groundnut (62%), castor (51%) and pigeonpea (54%). Similarly, Cyperus rotundusinfests lower yield loss in maize and sorghum as compared to groundnut, soybean, and grain legumes.
The high yielding dwarf cultivars of wheat and rice are more vulnerable to weeds and more time is spent in weed removal than in traditional cultivars.
Higher plant population of the crop can put pressure on availability of space for weed growth from relatively early stages of crop growth. Narrow row spacing, higher seed rate and cross sowing all have suppressing effect on weeds.
Close planting tend to produce microenvironment ideal for some fungal diseases, while with others, the same environment may prevent diseases by discouraging an insect vector from feeding. Dense seeding of many crops reduces the losses in yield caused by pathogens and insect pests by providing more plants per hectare.
Physical and Mechanical Control
Despite major advances in chemical control, hand removal of weeds still remains to be the most practical method of weed control in many developing countries of the world for a variety of reasons. Although back-breaking and laborious hand weeding is quite effective if employed at the right time.
Such manual destruction of other pests is not practicable although, it could be followed to some extent in controlling of some insect pests in orchards, like collecting and destructing the egg masses, mechanical exclusion of insects by placing impenetrable barriers around the host plant etc.
Flaming with propane burners of infested plants or weeds was practiced widely in western countries before the introduction of chemical pesticides, Burning rice straw has been reported to result in reduced incidence of stem rot of rice caused by Sclerotium oryzae . Burning crop residues under direct seeding and reduced tillage conditions has shown to reduce infestation of several pests including weeds.
It involves covering soil surface with polythelene sheets to increase the soil temperature which would be lethal to soil borne pathogens, insect-pests, nematodes, weed seeds etc. It was first practised successfully in Israel for the control of Verticillium dahliae and Fusarium oxysporum. A treatment period 30-40 days appears to be adequate to control many diseases.
A mulching period of 2-6 weeks with clear polythene sheets has been reported to give effective control of many annual weeds including Phalaris spp. Orobanche, Sinapis alba etc. Irrigation prior to solarisation has a complementary effect as moisture imbibed seeds are more sensitive to heat than dry seeds. The limitation however, is that normally weed seeds upto about 5 cm depth are only affected implying that deep preparatory cultivation would nullify the effect. Although the technique is limited by the cost of treatment, it may be made use of in controlling weeds in nursery areas, in high value crops etc.
With nematodes, effective control of Pratylenchus thornei in potatoes and of Ditylenchus dipsaci in garlic was obtained in Israil with solarisation for 4 and 8 weeks respectively.
The classical example of use of flooding is for the control of banana wilt. Chlamydospores of Fusarium are killed by restricted supply of oxygen in the water stagnated fields. Other fungi showing significant control by flooding are Verticillium dahliae in cotton, Sclerotinia sclerotiorum in cauliflower and fungus causing black tobacco and bacterial blight of cotton Flooding also effectively controls many arable weeds and that is the reason for reduced weed infestation in transplanted rice as compared to direct seeded rice, as has been discussed earlier.
Many plant parasitic nematodes are reported to be susceptible to flooding. However, a flooding period of 4-8 months is required for effective control of root knott nematodes, which is naturally a limiting factor.
Although still grossly underused, biological control is gaining world recognition as a primary and often essential component of successful integrated pest management.
Classical biological control involves deliberate introduction and establishment of natural enemies in areas where they did not previously occur. The approach is used largely against pests of foreign origin.
In addition to deliberate introduction of biocontrol agents, proper attention needs to be given for conservation and augmentation of natural enemies, that already exist in an area. This need to be treated as an important element in species (an example is Trichogrammatid egg parasitoids). Phago-stimulants are applied~ to the plants to increase the ingestion of leaves sprayed with microbial agents.
For discouraging the activity of hyperparasites, parasitoids should be released at a time when the activity of hyperparasitoids is the least.
Legislation: The Government of India banned the export of frogs, because 90% of the food of frogs is agricultural pests. It has been estimated that catching frogs for export led to the survival of 200,000 tonnes of pests thereby requiring farmers to spend more on pest control. Legislation is required to ban all such actions which directly or indirectly kill beneficial insects.
Conservation of Biodiversity
Biodiversity should be documented and properly inventoried, so that it can be utilized better. Otherwise, several species facing the threat of extinction will be wiped out before they are studied and named. It will also helps as plan conservation measures.
Conservation of Natural Enemies
Several ways of conservation of natural enemies have been attempted in the past. The use of relatively safer pesticides, and their selective use could conserve the biotic agents. Several other methods of enrichment and conservation of natural enemies include providing artificial structures (nesting boxes for wasps and predatory birds, burlap traps for C. montrouzieri), planting or retaining food and shelter plants of biotic agents on the bunds (retaining pollen and nectar bearing flowering plants Euphorbia, wild clover, etc. to provide supplementary food to parasitoids and predatory; rice gall midges and plant hoppers and their natural enemies survive on weeds like, Cyperus during off season and later shift to rice crop providing early suppression of the pests), placing bundles of rice straw for attracting spiders, retention of crop stubble, grass weed heaps for maintaining predator population, collecting egg masses of borers and putting them in a bamboo cage cum percher (which permits escape of egg parasitoids and allow the predatory birds to perch, and trap and kill the hatching larvae) are effective. ln addition to nest boxes, nesting material perching sites and water pans, retaining bushes (Acalypha, Hibiscus, crotons, etc.) helps retention or predatory birds in the desired area. Controlling ants (which interfere with the activity of biotic agents), avoiding complete trash burning (to conserve sugarcane pyrilla parasitoids), regular removal of fallen fruits (to increase the effectiveness of egg parasitoids due to overall lowering of population of the pests), strip cutting of alfalfa (to increase biotic agents in the adjoining crops), use of trap crops (planting castor around tobacco attracts S. litura to deposit the egg masses which are either collected or T. remus in released), use of semiochemicals or kairomones (to increase the searching ability and retention of the parasitoids, of gall midge, lafhopper and other pests from wild hosts to rice), use of organic manures instead of chemical fertilizers (to conserve predaceous arthropods such as carabid beetles and enhance the efficiency of plant disease antagonists), synchronizing the release of parasitoid with the availability of appropriate stage of the host and enacting suitable legislation (to prevent indiscriminate killing of beneficial organisms) have been suggested from time to time. Percent parasitism of yellow stem borer (Scirpophaga incertulas) egg masses is significantly more in transplanted rice than direct seeding, which indicates the importance of the method of planting in attracting natural enemies.
The natural occurrence of diseases caused by microorganism is common in both insect and weed populations and is a major natural mortality factor in many situations. For many practical reasons however, use of microorganisms for pest control involve their culture in artificial media and later introduction of comparatively large amounts of inoculum into the field at an appropriate time and place. The technique is possible only with those microorganisms that can be readily cultured in artificial media and more over than can be induced to produce spores or other suitable resting stages which permit storage and application. Many fungi and bacteria can be handled in this way but insect viruses have the limitation that they have to be raised in living insects. This is unfortunate as insect viruses probably have greater potential for pest control than any other group of microorganisms because of their virulence and selectivity.
As these biocontrol agent is (microbial pathogens) are applied on the targeted pests in much the same way as chemical pesticides, they are often termed as biopesticides or natural pesticides. Microbial phytotoxins, allelochemicals and other biocides of plant origin are also discussed here.
Bacillus thuringensis a bacterial pathogen infecting a wide range of insect pests is the most common microbial insecticide in use today. The disease agents marketed by several companies and is registered for use against the insect caterpillar pests that attack a wide variety of vegetables, flower and ornamental crops. Unlike most chemical insecticides, it can be used on edible products upto the time of harvest. It is selective in action and does not harm parasites or predators of pests of any extent.
Another bacterium B. popilale is also commercially available for insect control which is effective against the white grubs Popillae japonica and Hototrichia spp.
Amongst insect pathogenic fungi, commercial preparations of Verticillium lecanii are now available for control of aphids, thrips and whitefly under glass house conditions Effectiveness out of doors is unlikely to be reliable because of the requirement for high humidity for infection to take place.
Several mycoherbicides have been registered in the USA for commercial use of weed control. One such is the formulation of soil-borne fungus Phytophthora palmivora for selective control of strangler (milk weed) vine Morrenia odorata in citrus groves. Marketed under the trade name 'Devine', it causes lethal root rots of its host plant and persists saprophytically in the soil for extended periods of time.
Extensive research during the last two decades has demonstrated that several plant secondary metabolities (allelochemicals) as well as fungal and microbial foxins posses good pesticidal activity. Biolophos is a natural phytotoxin isolated from the fermentation broth of Streptomyces hygroscopicus and S. viridochromogenes and exhibits strong herbicidal activity against a wide range of grass and broad leaf weeds following application to their foliage. It is currently being marketed in Japan under the trade name Herbiaceae. Neem has long been known to have insecticidal properties and applications of neem extracts have been recommended for deterring insect attack, particularly locuss. Vikwood Ltd., USA has formulated a neem seed extract 'Margosan O'. The National Chemical Laboratories, Pune in India has also been successful in developing neem formulations with antifeedant/insecticidal properties.
The allelochemical from marigold-terthicyl was found to be highly nematicidal. Another compound cucurbitacins has also be found to be equally effective in controlling nematode populations.
Self Sustainability of Organic Farming
In many respects, organic farming is a way of life as much as it is a method of farming. The profitability of organic farms depends on the higher prices that their products command in the market place. Organic agriculture is not based exclusively on short-term economics, but also considers ecological concepts. It utilizes appropriate technology and appropriate traditional farming methods. This form of farming can also be called sustainable agriculture. The principals of this method are:
1. Organize the production of crops and livestock and the management of farm resources so that they harmonize rather than conflict with natural systems.
2. Use and development of appropriate technologies based upon an understanding of biological systems.
3. Achieve and maintain soil fertility for optimum production by relying primarily renewable resources.
4. Use diversification to pursue optimum production.
5. Aim for optimum nutritional value of staple food.
6. Use decentralized structures for processing, distributing and marketing of products.
7. Strive for equitable relationships between those who work and live on the land.
8. Create a system, which is aesthetically pleasing for those working in this system and for those viewing it from the outside, e. g., It should rather than scare the landscape of which it forms a part.
9. Maintain and preserve wildlife and their habitats.
Self Sustainable System
If the production system is solely dependant on the external inputs as in the case of conventional agriculture, the balance of the system disturbs as the buffer capacity exhaust. The results of this dependence of conventional agriculture are clearly visible in terms of decreasing production and environmental degradation. Although the organic farming is self dependant in terms of nutrient supply and plant protection, yet in addition to this so technologies are incorporated in the system which decrease the dependence on external supply sources for other inputs like water, energy etc. the system sustainability increase several times and it become more eco-friendly.
In the development of a more self-sufficient and sustaining agriculture, a deep understanding of the nature of agro-ecosystems needs the following principles:
1. They should function and to be design in such a way that they can manage agro-ecosystems.
2. They should be productive.
3. They should be obtained after conservation of natural resources.
4. They should be culturally sensitive and socially acceptable.
5. They should be economically viable.
Plants and animals communities together make agro-ecosystems which interact with their physical and chemical environments. They are modified by people to produce food, fibre, fuel and other products for human consumption and processing. An area used of agricultural production, looks as a complex system in which ecological processes found under natural conditions, such as nutrient cycling, predatory/prey interactions, competition, symbiosis and successional changes. By understanding these ecological relationships and process agro-ecosystems can be manipulated to improve production and to produce more sustainably, with fewer negative environmental or social impacts, and fewer external inputs. .
The design of such systems is based on the application of the following ecological principles.
1. Enhance recycling of biomass and optimizing nutrient availability and balancing nutrient flow.
2. Securing favorable soil conditions for plant growth, particularly by managing organic matter and enhancing soil biotic activity.
3. Minimizing losses due to flows of solar radiation, air and water by way of microclimate management, water harvesting and soil management through increased soil cover.
4. Species and genetic diversification of the agro-ecosystem in time and space.
5. Enhance beneficial biological interactions and synergisms among agro-biodiversity components thus resulting in the promotion of key ecological processes and services.
These principles can be applied by way of various techniques and strategies. Each of these have different effects on productivity, stability and resiliency within the farm system, depending on the local opportunities, resource constructions and, in most cases, on the market. The ultimate goal of agroecological design is to integrate components so that overall biological efficiency improved, biodiversity is preserved, and the agro-ecosystem productivity and its self-sustaining capacity is maintained. The goal is to design a quit of agro-ecosystems within a landscape unit, each mimicking the structure and function of natural ecosystems.
Peripherals for Self-Sustainability
From a management perspective, the agroecological objective is to provide a balanced environments, sustained yields, biologically mediated soil fertility and natural pest regulation through the design of diversified agro-ecosystems and the use of low-input technologies intercropping, agroforestry and other diversification methods mimic natural ecological processes, and that the sustainability of complex agro ecosystems lies in the ecological models they follow. By designing farming systems that mimic nature, optimal use can be made of sunlight, soil nutrients and rainfall.
Agroecological management must lead management to optimal recycling of nutrients and organic matter turnover, closed energy flows, water and soil conservation and balance pest-natural enemy populations. The strategy exploits the complementaries and synergisms that result from the various combinations of crops, tree and animals in spatial and temporal arrangements.
In essence, the optimal behaviour of agro-ecosystems depends on the level interactions between the various biotic and abiotic components. By assembling a functional biodiversity it is possible to initiate synergisms which subsidize agro ecosystems processes by providing ecological services such as the activation of soil biology, the recycling of nutrients the enhancement of beneficial arthropods and antagonists, and so on. Today, there is a diverse selection of practices and technologies available, and which very in effectiveness as well as in strategic value. Key practices are those of a preventative nature and which series of mechanisms.
Various strategies to restore agricultural diversity in time and space include crop rotations, cover crops, intercropping, crop/livestock mixtures, and so on, which exhibit the following ecological features.
Temporal diversity incorporated into cropping systems, providing crop nutrients and breaking the life cycles of several insect pests, diseases, and weed life cycles.
Complex cropping systems in which two or more crop species are planted with in sufficient spatial proximity to result in competition or complementation, thus enhancing yields.
An agricultural system where trees are grown together with annual crop and/or animals, resulting in enhanced complementary relations between components increasing multiple use of the agro-ecosystem.
The use of pure or mixed stands of legumes or other annual plant species under fruit trees for the purpose of improving soil fertility, enhancing biological control of pests, and modifying the orchard microclimate.
Animal integration in agro-ecosystems aids in achieving high biomass output and optimal recycling.
All of the above diversified forms of agro-ecosystems share in common the following features:
1. Maintain vegetative cover as an effective soil and water conserving measure, met through the use of no-till practices, mulch farming, and of cover crops and use other appropriate methods.
2. Provide a regular supply of organic matter through the addition of organic matter (manure, compost, and promotion of soil biotic activity).
3. Enhance nutrient recycling mechanisms through the use of livestock systems based on legumes, etc.
4. Promote pest regulation through enhanced activity of biological control agents achieved by introducing and/or conserving natural enemies and antagonists.
Research on diversified cropping systems underscores the great importance of diversity in an agricultural setting. Diversity is of value in agro ecosystems for a variety of reasons.
I. As diversity increases, so do opportunities for coexistence and beneficial interactions between species that can enhance agro-ecosystem sustainability.
2. Greater diversity often allows better resource-use-efficiency in an agro ecosystem. There is better system-level adaptation to habitat heterogeneity, leading to complementarily in crop species needs, diversification of niches, overlap of species niches, and partitioning of resources.
3. Ecosystems in which plant species are intermingled possess an associated resistance to herbivores as in diverse systems there is a greater abundance and diversity of natural enemies of pest insects keeping in check the populations of individual herbivore species.
4. A diverse crop assemblage can create a diversity of microclimates within the cropping system that can be occupied by a range of non-crop organisms - including beneficial predators, parasites, pollinators, soil fauna and antagonists - that are of importance for the entire system.
5. Diversity in the agricultural land scape can contribute to the conservation of biodiversity in surrounding natural ecosystems.
6. Diversity in the agricultural landscape can contribute to the conservation of biodiversity in surrounding natural ecosystems.
7. Diversity in the soil performs a variety of ecological services such as nutrient recycling and detoxification of noxious chemicals and regulation of plant growth.
Diversity reduces risk for farmers, especially in marginal areas with more unpredictable environmental conditions. If one crop does not do Well, income from others can compensate.
Integration of Aquaculture
In recent years, aquaculture-the keeping or breeding of organisms, which live in fresh or salt water - has become a subject of growing interest. Within the framework of small holder agriculture at issue here, attention must be focused on fish farming in ponds and fish breeding in rice fields. Fish provides protein, which is of exceptionally high quality from the biological point of view; they are also highly efficient in converting feed. Moreover, fish production is an enterprise that - in contrast to many other forms of animal husbandry-competes little or not at all with the production of food for humans. All these factors give pond-based fish farming a position of considerable importance as an enterprise in small holder agriculture.
Fish breeding in rice fields, as has long been practiced in Southeast Asia, is a close to ideal form of land use, with cereal and animal protein being produced from the same area of land. Depending on the way the rice is grown, the following production methods can be used:
1. One generation fish following a single rice harvest per year (rice-fish rotation).
2. Fish farming between two cultivation periods, in the case of 2-3 rice harvests per year.
3. Fish farming simultaneously with rice growing (rice-fish culture).
In all cases, the fish culture remains secondary to the culture.
However, other forms of fish breeding have gained considerably greater importance. These range from extension management in natural waters (stocking with young fish, no additional feeding) to intensive fish farming in specially created ponds (high stocking rate, artificial feeding only). An interesting and important example is the carp polyculture of China. Various carp species with different feeding habits live in different zones of a pond fertilized with domestic refuse and sewage and animal excrements. The water plants floating on the surface as well as any green feed added are eaten by the grass carp. Silver carp filter the plankton out of the water, and common carp eat the insect larvae, worms and snails on the bottom of the pond. This system can also be combined with the keeping of ducks.
Although various techniques of low-external-input agriculture have been described here separately, it is essential to recognize that eco-farming involves the complex integration of several of these techniques in a manner which makes the most efficient use of locally available resources. The combination of techniques, which is most suitable for a particular farm at any point in time depends on the specific situation of that farm, in terms of not only the natural conditions but also the sociological and economic situation of the farm family. As these conditions change, so too do the appropriate eco-farming techniques.
Indigenous Organic Farming Practices
Within an indigenous farming system, it is difficult to distinguish the individual organic-farming measures visualized by agricultural scientists, because man, animals, forests, grasslands and fields are inseparable components of a single agro-ecosystem. For example, agroforestry is a relatively new concept in agricultural science, but it is not at all new to smallholders in the tropics, most of whom regard trees as a integral part of their farming systems. Particularly in densely populated Southeast Asia and in the dryland of India, indigenous farmers have developed highly productive and sustainable land-use systems in which agroforestry, multiple cropping, use of biological symbionts, mulching, composting, integrated plant protection, integration of fish and other livestock, and other organic farming measures are inextricably combined. ln less densely populated parts of the tropics and subtropics, the indigenous farming systems represent a less intensive form of resource use, but the techniques and strategies applied by the farmers to gain a more or less secure livelihood are equally dependent on their detailed ecological knowledge.
Various elements of organic farming in traditional systems, e.g. the burning of vegetative growth before planting to enhance soil fertility, are not immediately evident to an observer trained in formal agricultural science and even be regarded as harmful until the underlying principles are understood. There has also been a tendency among western scientists to regard the farming practices of different ethnic groups as representative of stages in an evolutionary development of agriculture. Only now are scientists beginning to realize that techniques once regarded as "primitive" (e.g. minimum tillage) reflected local adaptations to rainfall intensity, soil texture and erosion risks. They are organic farming techniques; ecologically appropriate for a specific site.
Soil and Water Conservation
Soil and water conservation practices are based on the following principles:
1. Soil Conservation measures includes reduction of splash erosion, detachment and transport of soil practices; and Control of run-off - to check sheet, rill and gully erosion
2. Rain water management includes collection storage and conservation of rainwater
The choice and design of soil and water conservation measure for agricultural lands depend mainly on the soil, land slope, rainfall and wind characteristics of the area. The measures adopted are broadly classified as:
1. Agronomical and biological measures; and
2. Engineering measures.
Often, both engineering and biological methods are used together but differ for arable and non arable lands.
Increase in Crop Yield
The yields of wheat crop by mulching with straw was increased in acidicred loam, sierozem and laterite soils by 14.3, 24 and 29 per cent over unmulched treatment under different conditions. Mulching showed better effect on pea crop in acidic red-loam, medium black and laterite soils and increased the grain yield by 77.6, 43 and 40 per cent, respectively. Trials were repeated in different agro-climatic conditions (Bangalore red sandy loam, Ranchi acidic red, Poona medium black, Hissar sierozem, Delhi and Barrackpur aIluvial soils) on wheat, pea, moong and maize crop (Gaur, 1975; Gaur and Mukherjee, 1980). The previous year's findings were confirmed showing the beneficial effect of wheat or paddy straw orkaranj leaves mulch at 10 tonnes/ha on the crops. The grain yield of wheat was increased by 66 to 67 per cent in sierozem and Barrackpur alluvial soil, by 31.6 per cent in red sandy loam, 14.3 per cent in acidic red loam and 4.2 per cent in medium black soil. Pea grain yield was increased by 77.6, 29.4,13.4 and 9.6 percent in acidic red loam, red sandy loam, medium black and Barrackpur alluvial, soil respectively. The grain yield of moong and maize was increased significantly in Delhi alluvial soil due to wheat straw mulch by 31.7 and 110.5 per cent, respectively. The incorporation of mulched material used on previous crop - maize, in soil increased the grain yield of wheat crop by 16.1 per cent. Nitrogen uptake by both these crops was increased and mulching had favourable effect on the population of soil bacteria, fungi and actinomycetes. The population of nitrogen fixers and phosphate solubilisers were increased several-folds.
The direct utilization of organics low in nitrogen, i.e. high C/N ratio material may not always be feasible in intensive agriculture and particularly in culture of cereal crops. The utilization of organic materials in soil in case of cereals requires proper understanding of the technology by the farmer. While growing legume crops which have got host-Rhizobiumsymbiosis system i.e. fixing of nitrogen in the nodules by rhizobia for the supply to plant, is not affected with nitrogen immobilization processes which generally occurs when organic matter low in nitrogen is ploughed in the soil. On the other hand, this benefits the process of nitrogen fixation. More over, the beneficial effects can be obtained by improvement of soil conditions, nitrogen immobilization and greater supply of carbon dioxide to plants for production of sufficient photosynthates. This method of recycling can be carried out by ploughing straw one week before sowing with small dosage of nitrogen (10-20 kg N/ha) and phosphate (90kg P205/ha) as recommended for leguminous crops.
Nodulation in groundnut crop was improved due to application of wheat straw at 2,5 and 10 tonnes per hectare in Delhi alluvial soil. Ped yield was significantly increased by 66 and 95 per cent due to application of 2 and tonnes straw per hectare by this method. Growth of plants was favourably influenced by 5 tonnes straw application. The residual effect of straw incorporation after groundnut increased the wheat grain yield by 3.9 to 36.8 per cent. Maximum residual effect was obtained with 10 tonnes straw applied per hectare. The practice can be followed in legume-cereal rotation. The straw gets decomposed during the growth period of legume crops and residual effect can be observed on the following crop. This has been confirmed with other legume crops (lentil, peas and moong).
Control of Pest and Disease
Mulches provide extra benefits in disease prevention and control soil microlife. The warm moist conditions under the mulch also break down many of the dormant overwintering organisms.
After a mulch is removed the soil will be in a much better condition than if it had been left bare. The combination of worm and other activity, favourable physical conditions and a lack of rain impaction gives most soils that crumbly brown-sugar texture beloved by gardeners and plants. Mulches on empty ground as a winter cover against soil erosion and leaching will also produce a good tilth without the digging and raking otherwise required.
Many diseases such as rose blackspot overwinter on layer of mulch is applied on top of this infective material after leaf-fall it is sealed in and cannot be splashed back onto the plant to restart the cycle in spring. Thus disease prevention may be an unnoticed side-effect, as when horse manure is applied to roses, and when strawberries and gooseberries are strawed. Mulching can also protect indirectly against mildews, which are often aggravated, if not caused, by insufficient water; a moisture-retaining mulch will reduce attacks.
Apart from encouraging the soil microlife with nutrients, warmth and moisture a mulch also forms a good home for many larger creatures. Woodlice, for example, process the material and break it down; they then provide a basic food source for shrews, birds and hedgehogs, which help to control other more harmful bugs.
Mulches will further assist in the control of some pests such as per midge, gooseberry sawfly and raspberry bettle. Many pests such as these can be brought to the surface to be picked off or left for the birds, if the area is well watered and then covered overnight with a sheet of black plastic or old carpet. Sheets of impenetrable mulch can be even more effective. If they are a put down before the pupae emerge, the pests are trapped underneath, die and are converted to soil fertility, sward the next day, especially in hot conditions, unless you wish to kill the grass as well.
Gardeners use a mulch for its appearance. An attractive covering is certainly pleasing to the eye and acts as an excellent foil to plants. The problem of cost against aesthetic value can be answered by using a thin layer of an attractive mulch on top of a cheaper or more effective kind. Mulches also come into their own where it is desirable to keep plants clean. Thin fabric or horticultural paper laid on the ground are excellent materials to protect salaaming, especially spinach, from soil splash. Gravel can also be used for this purpose.
Drawbacks of Mulching
Mulches do have a following few drawbacks,
1. Certain pernicious ones are found in the mulch habitat. Slugs and snails like the moist conditions beneath, though they are reluctant to move around on top of a dry mulch. Many bugs are a mixed blessing, such as woodlice and millipedes, which attack crops as well as processing dead material.
2. Warm moist conditions may encourage fungal or other diseases, so that the crowns of herbaceous plants rot or the emergent growths suffer from damping off or a neck rot. To prevent neck or crown not in susceptible plants leaves a clear space free of mulch about the plant. To prevent the mulch encroaching on a valued plant use a ring of wire netting as a miniature snow fence.
3. Too thick or unperforated an impermeable mulch may restrict soil aeration; while this may not damage established plants during city periods, wet anaerobic (oxygen-starved) conditions during the dormant season can rapidly cause root die-back and death. Anaerobic conditions can also change the composition of the soil microlife, leading to decreased beneficial activity and reduction of fertility.
4. The most direct damage to plants from mulches generally comes from birds spreading them on top of low-growing thymes and other susceptible carpeting plants.
5. A hidden danger is where the sites of dormant plants are not marked and shoots might unwittingly be trodden on.
Straw (and hay) is the commonest bulk mulching material, especially for soft fruit, and for keeping strawberries clean. Straw is low in nutrient value but does not cause nitrogen robbery. Straw makes an excellent quick-drying pathway and is a mulch in most parts of the productive garden. In the vegetable garden it is more suitable for larger transplants, as the birds more it around and it can smother seedlings. When used as a temporary mulch it causes a weed problem afterwards.
This involves opening of trenches of 30 cm depth and 15 cm width across the slope at vertical intervals of 30 cm. Sorghum stubbles/red gram/cotton stalks are stacked vertically in these trenches. The stalks should protrude up to 10 cm above the ground. These vertical mulches act as intake points and divert run-off water to sub soil layers.
This is ideally suited to soils with high clay content and low infiltration rate, Vertical mulch conserves moisture better than other methods during drought periods,
Live Vegetative Barriers
Under this mulching method, subabul is planted in the field and gliricidia on the contour keylines. They act as vegetative barriers and effective mulch. When subabul and gliricidialeaves are cut and spread in the field, it improves soil moisture and also supplies about 20 to 30 kg nitrogen per hectare.
Agroforestry/Alternate Land Use Systems
Alternative land use/agroforestry is defined as an effective economic utilization of land without harming the natural resources structures based on land capability. This involves the addition of a perennial component which has drought tolerance, can with stand the aberrations of monsoon and imparts stability to production.
The need of agroforestry based organic farming is not only to improve micro-climate and increasing availability of organic residue but also to bring million of hectares of economically-marginal or environmentally-sensitive cropland, forest and waste lands into sustainable use.
Agroforestry or multi-story farming is a form of multiple cropping which essentially involves a vertical arrangement of crops (plants growing one above the other), whereas the dominant concept of intercropping is one of horizontal arrangement (plants growing beside each other). The integration of trees and shrubs with field crops eliminates the spatial separation between field and forest. A structural diversity of vegetation is sought which approaches the optimum for that site (structure of the climax vegetation). As in intercropping, the plants are combined in space and time in such a way that they compete as little as possible for nutrients, water and light, but rather complement each other in their differing requirements so as to achieve an optimal output per unit area. Scientific research in interrelationships and practical methods of agroforestry is still in its infancy.
Trees not only preserve soil fertility; they also make an important contribution to the economy of the farm household. As trees provide various products such as firewood, timber and fodder, the integration of trees into farming systems can reduce household expenditures for these products or can provide an additional source of cash income. If trees and shrubs are planted in home gardens and adjacent fields, their products can be collected quickly at the convenience of the household members. This considerably reduces the time and energy that particularly women and children must spend collecting firewood and increases the flexibility of timing this activity, The contribution of trees to improving working conditions should also not be underrated: the physical efficiency of workers under the climatic conditions created by trees is considerably higher than in the open field.
Organic farming requires the supply of crop nutrients and protection of crops with organic inputs. Therefore, the supply of nutrients is essentially through the application of organic matter in the form of farmyard manure, green manure and compost. Availability of nutrient-rich organic matter in adequate quantities to meet the crop requirements is a major constraint limiting large scale adoption of organic farming. Where as chemical fertilizers contain crop nutrients in a concentrated form, the nutrient content of most organic manures is low. Therefore, the quantity of any manure required to be applied to get a satisfactory crop yield is very high. It is usually in tons per ha as against the kg per ha of fertilizers required. Sources of organic matter are limited in dry areas of India. As the number of farmers practicing organic matter are limited in any given locality is very few at present, they are able to collect farmers take to organic farming, there is likely to be a serious shortage of organic matter. Therefore, on-farm production of organic matter and its careful use within the farm are crucial factors determining the viability of organic farming by a large number of farmers in a dry area. In this regard trees, if included appropriately in the farming system, can be of immense benefit. They can (a) add nutrients and organic matter to the soil, (b) reduce nutrient and organic matter losses from the soil and (c) decrease the requirement of chemicals for crop protection by reducing the incidence of pests, diseases and weeds in crop fields.
1. Selection of a suitable land-use model.
2. Identification of trees or shrubs that are not relished by livestock.
3. Level of competition between bushes and crop for soil water and light is minimal.
4. Consider the farmers' preference for trees.
5. Improved planting spot (dug out pit).
6. Undertake in situ water harvesting (individual basin) measures.