green manuring


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Green manuring is the practice of growing lush plants on the site into which you want to incorporate organic matter, then turning into the soil while it is still fresh. The plant material used in this way is called a green manure (GM). Generally the practice of green manuring is adopted in two ways: a) In-situ green manuring b) Green leaf manuring What is green manuring?

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In-situ green manuring In this system the short duration legume crops are grown and buried in the same site when they attain the age of 60-80 days after sowing. This system of on-site nutrient resource generation is most prevalent in northern and southern parts of India where rice is the major crop in the existing cropping systems.

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Common legume crops for in-situ green manuring

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Green leaf manuring Green leaves and tender plant parts of the plants are collected from shrubs and trees growing on bunds, degraded lands or nearby forest and they are turned down or mixed into the soil 15-30 days before sowing of the Crops depending on the tenderness of the foliage or plant parts.

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The most common shrubs/trees used for green leaf manuring are given below :

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Status of GM crops in India At present only 6.7 million hectares are in green manure which accounts for 4.5 per cent of net sown area (142 million ha) of the country (Agril. Statistics at a Glance, 2005). The practice of green manuring is most common in rice growing states like A.P., U.P., Karnataka, Punjab and Orissa which contribute 41, 16, 11, 6 and 5 per cent to the total area under green manuring in India respectively. Whereas, the share of Gujarat (3%), M.P. (3%), Himachal Pradesh (2%) and Haryana (1.7%) is not very encouraging and concerted efforts are to be made out at all levels to bring more area under green manuring that too in irrigated area if nutritional need of organic farming is to be made. [Source : Bisen et al., 2008]

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Biomass potential of GM crops The benefits deriving from green manure crops are directly related to the amount of biomass and nutrients added in soil. Biomass production of green manure crops varies widely according to the species of the legumes, environmental conditions, soil fertility and crop management practices and age of green manure crops

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Nutrient compositions of common green manures

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Nutrient potential of GM crops Almost all GM crops which are used for in-situ or ex-situ green manuring contain all the plant nutrients which are essential for completing the life cycle of any plant grown in community. Among the different GM crops, dhaincha (Sesbania aculeata) and Sunhemp (Crotalaria juncea) have higher accumulation of major and micro nutrients on account of more biomass production and better nutrient composition compared to food legumes which are inferior due to low contents of nutrients coupled with less dry matter production. Water hyacinth has great nutrient potentials and it could contribute 198 kg N, 63.0 kg P2 O5, 125.3 kg K2O and 350 g Zn, 3290 g Fe, 133 g Cu and 2940 g Mn when about 70 q/ha dry matter is added in the soil and could serve as better source of plant nutrients through ex-situ green manuring .

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Biomass and nutrient potentials of different green manures and weeds

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Techniques for good benefits from GM Crops The maximum benefit from green manuring can be obtained through better knowledge of suitable sowing time of GM crops, age or stage of GM crop for burial and time interval between burial and sowings of next crop.

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15 Stage of GM crop at burial Knowledge of time of burial of GM crops is of utmost importance for deriving maximum benefits. The chemical composition of most plants changes identically during growing season. During early period of crop growth its content of N, protein and water soluble constituents are maximum, while the amount of fibre, cellulose, hemicelluloses, lignin and the C: N ratio are also less. Therefore, tissues of immature plants usually decompose more rapidly as compared to those of matured plants. Singh et al. (1992) reported that the GM crops are to be buried in the soil when they are 2 months old and two weeks delay in the incorporation reduced their N content and increased the C: N ratio, cellulose, hemicelluloses and lignin contents.

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16 Time interval between burial of GM sowing of next crop Knowledge of time interval between burial of GM crops and sowing of next food crop for just to facilitate the complete decomposition of the turned in green matter is essential. Ghose et al. (1960) reported that the time interval was not so important when succulent green manure crop of eight weeks age was buried because transplanting of paddy immediately after burying of green manure crop was as good as any other treatment. But it was necessary to give time interval of 4-6 weeks before planting paddy when the GM was 12 weeks of age.

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17 Criteria for selection of green manures plants Various nitrogen fixing leguminous and non-leguminous species particularly tree, creepers and bushes can be used as green manures

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18 The criteria for selection of plants as GM crops

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19 Integrated nutrient management in rice (Oryza sativa)- wheat (Triticum aestivum) cropping system RD, Recommended dose [Source : Patra et al., 2000]

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20 Yield components of rice and wheat as influenced by integrated nutrient management (average data of 3 years) [Source : Patra et al., 2000]

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21 Effect of integrated nutrient management on yield and economics of rice-wheat cropping system (average of 3 years) * Rice equivalent; Cost of input (Rs/kg) : N, 8.15; P, 19.15; K, 6.30; Value of produce (Rs/q): Rice, 415; wheat, 600 rice; wheat straw, 25.00 [Source : Patra et al., 2000]

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22 Influence of organic sources of nitrogen on productivity of rice [Source : Hemalatha et al., 2000]

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23 Time of sowing and harvest of green-manure and rice [Source : Hemalatha et al., 2000]

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24 Influence of organic sources of nitrogen on yield and quality of rice [Source : Hemalatha et al., 2000]

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25 Influence of organic sources of nitrogen on post-harvest soil-available N, P, K (kg/ha) and organic carbon content (%) [Source : Hemalatha et al., 2000]

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26 Grain yield (kg/ha) of rice and wheat as influenced by green-manuring and nitrogen levels applied in rice [Source : Nair and Gupta, 1999]

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27 Effect of green-manuring and nitrogen levels on total NPK uptake (kg/ha) by rice and succeeding wheat crop [Source : Nair and Gupta, 1999]

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28 Effect of green-manure of legumes on green-matter production and nitrogen addition (mean data of 2 years) Figures in parentheses indicate N level of previous crop [Source : Thakur et al., 1999]

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29 Impact of green-manuring crop and nitrogen on yield and yield attributes of rice-wheat system (pooled data of 2 years) Figures in parentheses indicate dhaincha green matter yield, greengram grain and haulm weight and cowpea fodder yield, respectively. [Source : Thakur et al., 1999]

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30 Effect of different treatments on total yield in terms of rice equivalent and economics of rice-wheat cropping system (pooled data of 2 years) [Source : Thakur et al., 1999]

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31 Change in physico-chemical properties of soil on soil-depth basis N, Available nitrogen (kg/ha); P, available P2O5 (kg/ha); K available K2O (kg/ha); OC = Organic carbon [Source : Thakur, et al., 1999]

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32 Effect of system rice intensification on grain yield (q/ha), straw yield (q/ha) and test weight (g) of rice [Source : Division of Agronomy, SKUAST-K, 2006]

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33 Effect of green manuring alone and in combination with FYM and NPK on biological yield, grain yield and straw yield (q/ha) of rice [Source : Division of Agronomy, SKUAST-K, 2006]

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34 Sesbania germinating in rice field SKUAST-K, Shalimar Campus

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35 Effect of green manuring alone and in combination with FYM and NPK on plant height and yield attributes of rice [Source : Division of Agronomy, SKUAST-K, 2006]

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36 Effect of green manureing alone and in combination with FYM and NPK on status of available NPK (kg/ha) and organic carbon (%) in rice field [Source : Division of Agronomy, SKUAST-K, 2006]

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38 Nitrogen fixation The main benefit of using a legume as a green manure is that legumes fix nitrogen from the atmosphere and convert it into a form that is available to other plants. Legumes from a symbiotic association with soil bacteria called rhizobium. These bacteria colonize the root hairs of the legumes and multiply causing swellings, which become nodules. The bacteria benefit from the relationship by obtaining carbohydrates (plant sugars) from the legume. The growing legume benefits from the nitrogen that is captured from the air and converted into ammonium legume benefits from the nitrogen that is captured from the air and converted into ammonium within the nodules.

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43 Effect of green manuring on soil productivity The physico-chemical properties of soils are affected significantly due to addition of organic matter in the form of green manures particularly in plots receiving green manuring through Sesbania rostrata and Crotalaria juncia. Consequently, marked improvement in soil structures, infiltration rate, bulk density and water holding capacity of soil. Enhances soil fertility Green manures recycle nutrients and add organic matter to the soil. They help prevent nutrients being washed out of the soil. The nutrients are taken up by the green manure and held inside the plant. When the nutrients are needed for the next crop, the plants are dug into the soil or used as mulch on top of the soil. This helps to increase crop yields. Legumes and other nitrogen fixing plants, which take nitrogen from the air to the soil are particularly beneficial.

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Supplement for nutrients Different green manures and grain-legumes are used to increase the nitrogen content and texture of the soil. Among the green manures Sesbania aculeata accumulated the largest amount of biomass and nitrogen contribution and among the grain legumes, cowpea ranks first both in terms of grain yield and biomass addition. The available green manure crops and utilization pattern are as follows :

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Nutrient potential of green manures [Source : Sharma, 2004]

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Improved soil structure Green manures improve soil structure, letting more air into the soil and improving drainage. Green manures help sandy soil hold more water and not drain so quickly. Prevention of soil erosion Green manures help to stop the soil being carried away by wind and rain. The roots penetrate the soil and hold it in place.

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Weed control Green manures help to control weeds. Bare soil can become quickly overgrown with weeds, which can be difficult to remove. Green manures cover the ground well and stop weeds growing beneath them, by competing for nutrients, space and light.

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48 48 Place in farming system Green manures in rotation : Growing green manures as part of a crop rotation is an important part of an organic farming system. These help to build soil fertility and are particularly useful when grown before crops, which need a lot of nutrients. Green manures can be used in rotation : 1. Whenever there is no crop in the ground, rather than leaving the land bare and allowing weeds to grow and nutrients to leach out of the soil. 2. As break crops, when these is only a short time between main crops.

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49 49 Green manures as mulch Green manure plants can be cut and left on the soil surface as a mulch. Mulching releases nutrients slowly but has some advantages : 1. Mulching helps to prevent weed growth 2. Mulching protects the soil from erosion 3. Mulching keeps the soil moist by reducing evaporation

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50 50 Green manures in agroforestry Agroforestry is the practice of growing trees and/or shrubs together, with crops and/or animals. The trees/shrubs act as long term green manures and the leaves can be used to digging in or as a mulch. The regular pruning of agroforestry trees such as Leucaena (Leucaena leucoephata), Mother of cocoa (Glyricidia sepium) and Calliandra (Calliandra calothyrsus) during the crop growing period provides large amounts of green material for digging into the soil and reduces competition with the main crop. The material can also be used as a mulch. It is spread on the top soil, usually between crop rows or before a crop has been planted. As well as improving the soil in the ways described above, trees and shrubs also provide food, fodder, fuel wood, erosion control and other benefits.

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51 51 Digging in green manures Before a crop is sown, the green manure is dug back into the soil. Here it decomposes and the nutrients held inside green manure plants are released. 1. The plants take a short time, usually about two weeks, rot down into the soil before the next crop is sown. 2. Green manures should not be ploughed in as this buries the plants and the nutrients too deep. They should be turned in just under the soil surface. 3. Digging is easier if the plants have been chopped into small pieces before digging. This also helps to prevent the problem of regrowth, if this occurs.

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52 52 The choice of green manure When choosing which green manure plant to use, you should consider the following points : 1. A green manure must suit the local climate, and the soil that it is to be sown in. This will help to keep the green manure healthy and to keep pests and diseases to a minimum. 2. Fast growing and leafy green manures are often preferred as they provide more nutrients when dug in. 3. Green manures should not be closely related to the following crop as they could attract pests and diseases which may affect the following cop. 4. It is important to know whether seed is easily available and affordable. 5. The length of time that land is free and how long the green manure will take to grow. 6. Plants which can be grown as a green manure include legumes and non-legumes. Legumes have nodules on their roots which contain bacteria. These bacteria take nitrogen from the air. This is known as nitrogen-fixation. Plants use this to grow, but this extra nitrogen is also made available to future crops when the legumes are dug into the soil. The ability of legumes to fix nitrogen makes them very good green manures.

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53 53 Sustainability For more than a decade it has been accepted that green manures and cover crops would only be accepted by small farmers if they could be grown on land that had no opportunity cost, could be intercropped with other produce, grown under tree crops or on fallow land and be cultivated in periods of expected drought or extreme cold. They would also be favoured if they involved no extra labour or out of pocket cash expense.

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54 Essential precautions Broadcast or sow the seeds after the harvest of main crop, preferably in the water sign/zodiac of the ascending period of the month. Slash the green manure crops shoots and incorporate them into the soil. Slashing and incorporation of green manure crop should be done while the soil has adequate moisture. If there is no moisture an irrigation is essential. Without moisture incorporation is difficult and if done, it will not be effective. Meanwhile moisture is a critical factor for the microbes to act over the incorporate material. sow or transplant the next crops 1-2 weeks after the incorporation of the green manure, since in the initial stage of decomposition there will be a release heat of decomposition that is very unfavorable for germination and the growth of young plants. Use disc harrow to incorporate the green manure crop. Discs harrow have become the implement of choice for incorporating all the heaviest perennial stands. Disc harrow implements adequately mix the legume residues into the soil, promoting even decomposition and nutrient release near to the soil surface.

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55 55 Conclusions A number of conclusions can be drawn from the examples given above : The variety of sustainable green manure and crop cover systems already established in traditional as well as more recently introduced agricultural system is remarkably diverse. Green manures and cover crops have been adopted on a wide scale despite the seemingly prohibitive conditions. The fact that virtually every system referred to has some elements of these conditions confirms their predictive value. Thus, programmes to introduce new green manure and cover crop systems should teach farmers not only how these species can be used to improve their soil but that they have other uses as well. Tremendous potential still exists for the development of new green manure and cover crop system. Scope of potential systems for using green manure and cover crops still need to be investigated, most notably the major possibilities of using them for animal feed; the potential latent in new as yet untried species, including trees and non-legumes, and the value of combining of green manures and cover crops rather than using individual species. Experience leads us to believe that, with the possible exception of very intensive farming systems such as irrigated vegetable and rice, green manure and cover crop systems can probably be introduced into many, if not most of the world’s small scale farming systems.

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