Green Manures And Green Leaf Manures

Green Manures And Green Leaf Manures

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 sustainability 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 Southeast of Asia. Hence, there is an urgent need to identify alternate nitrogen sources to supplement inorganic fertilizers.

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Occurrence of multi-nutrient deficiencies and overall decline in the productive capacity of soils under intensive fertilizers use has 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 and 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.

Definition

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 consists 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.

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Subsidiary Object of Green Manures

(a) Catch crops: 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 ploughed in as green manures or grazed off. Utilizing the nitrates formed in the soil or residual moisture is a primary object of Green Manuring is only incidental.

(b) Shade crops: 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.

(c) Cover crops: Green manure crops are sometimes grown with the object of clothing the surface with a vegetative cover especially in hill slopes during the rainy weather to avoid soil erosion and runoff. This may also 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.

(d) Forage crops: Some legumes are also grown for taking a few cuttings of green fodder for cattle in every stages. 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 later growth is used for green manure purpose.

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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 enhanced 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 of use by the crops. Green manuring improves aeration in the rice soils by stimulating the activities of surface film of algae and bacteria. Many green manure crops have additional use as sources of food, feed and fuel.

(i) Soil structure and tilth improvement: Green manuring builds up soil structure and improves tilth. It promotes formation of crumps 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.

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(ii) 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 succeeding 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. Single crop of green manure on an average is reported to fix 60–100 kg nitrogen/ha in single season under favourable conditions.

(iii) Amelioration of soil problems: Green manuring helps to ameliorate soil problems. Sesbania aculeata (dhaincha), when applied to sodic soils continuously 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 such as Argemone mexicana and Tamarindus indica has a buffering effect when applied to sodic soils.

(iv) Improvement in crop yield and quality: Green manuring increases the yield of crops to an extent of 15–20 per cent compared to no-green manuring. Vitamins and protein content of rice have been found to be increased by green manuring of rice crop.

(v) Pest control: Certain green manure like Pongamia and Neem leaves are reported to have insect control effects.

The legume and non-legume green manures are differentiated as follows:

(i) Legumes: Legumes 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.

(ii) Non-legumes: Free N 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.

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Agronomy of Green Manure Crops

1. Sesbania speciosa (sithagathi):

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 30–40 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. After ploughing the field, Sesbania seeds are broadcasted at 35–50 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 5–10 cm in one hectare will give about 5000–8000 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 of nursery.

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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 kg seeds will be necessary. Hence, if about 125–150 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.

Season: Grown all seasons, March–April sowing is best

Soil: Grown in all types of soil conditions

Seed rate: 30–50 kg/ha for green manure, seed purpose 15 kg/ha

Seed treatment: Mix seeds with specific rhizobium strain @ 5 pkts/ha

Spacing: Broadcasted and for seed purpose adopt 45 × 20 cm

Irrigation: Once in 15–20 days

Harvest: Incorporate the green matter 45–60 DAS and for seed, collect the seeds on 130 DAS

Yield: Green biomass-10–18 t/ha, Seed 400–600 kg/ha

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2. Sesbania aculeata (Daincha):

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-five years. Bacterial nodules are formed in plenty on the roots. The plant has a soft stem. It makes good growth in two-four months and produces abundant green matter ranging from 10–20 t/ha, depending upon the age at harvest. Recommended seed rate is 20–25 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, 25–30 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.

Season: Grown all seasons when sufficient moisture is available, March–April sowing is best for seeds production

Soil: Grown in all soil conditions

Seed rate: 25–30 kg/ha for green manure, seed purpose 20 kg/ha

Seed treatment: Mix seeds with specific rhizobium strain @ 5 pkts/ha

Spacing: Broadcasted, for seed purpose adopt 45 × 20 cm

Irrigation: Once in 15–20 days

Harvest: Incorporate the green matter within 45–60 DAS and collect seeds from 100 DAS

Yield: Green biomass-20 t/ha, Seed-500–600 kg/ha

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3. Sesbania rostrata (Manila agathi):

It is a leguminous crop, which has nodules both on the stem and roots. It was introduced in India during 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 30–40 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 rice could produce 3–5 t of biomass in 30 days after transplanting. Rice yields are not affected due to intercropping.

Season: Grown all seasons. February–May sowing biomass yield is more, March–May sowing is best for seeds production

Soil: Black and red soils suitable, Saline alkaline soils not suitable

Seed rate: 40 kg/ha for green manure, seed purpose 7–8 kg/ha

Seed treatment: Seeds to be scarified with concentrated H2SO4 (100 ml/kg) by soaking for 10 minutes then wash thoroughly (10–15 times). Mix seeds with specific rhizobium strain @ 5 pkts/ha

Spacing: Broadcasted, for seed purpose adopt 45 × 20 cm

Irrigation: Once in 15–20 days

Nipping: For seed purpose, it should be done 60 DAS to increase branching and seed yield

Harvest: Incorporate the green matter within 45–50 DAS and seeds can be collected from 100 DAS (3–4 harvest)

Yield: Green biomass–20 t/ha, Seed–500–600 kg/ha

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4. 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 75–150 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 25–40 kg/ha and the yield of green matter may vary ranging from 12,000–25,000 kg/ha depending upon the environmental conditions and duration of the crop. The further details are given in the section 15.11:

Season: Grown in all seasons, March–April sowing is best for seeds production

Soil: Loamy soils are suitable

Seed rate: 25–40 kg/ha for green manure, seed purpose 20 kg/ha

Seed treatment: Mix seeds with specific rhizobium strain @ 5 pkts/ha

Spacing: Broadcasted or 30 × 10 cm, seed purpose adopt 45 × 20 cm

Irrigation: Once in 30 days

Harvest: Incorporate the green mater within 45-60 DAS and for seed production, collect the seeds from 150 DAS

Yield: Green biomass 13–15 t/ha, Seed–400 kg/ha

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5. 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 2–4 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 under shrub, growing wild in sandy or gravelly wastelands. 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 55°C for 2–3 minutes. The seed rate is 25–40 kg/ha, while the green manure yield varies from 3500–6000 kg/ha.

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Season: Grown all seasons, March–April is best for seeds production

Soil: Grown all soils, sandy soils are suitable

Seed rate: 25–40 kg/ha for GM, seed purpose 10 kg/ha

Seed treatment: Soak the seeds in concentrated sulphuric acid (100 ml/kg seed) for 30 m and then thoroughly wash the seeds in water for 10–15 times and shade dry

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Spacing: Broadcasted, for seed purpose adopt 30 × 10 cm

Irrigation: Once in 30 days Harvest Incorporate within 60 DAS and for seed collect from 150 DAS

Yield: Green biomass 3.5–5 t/ha, Seed–400–500 kg/ha

6. Indigofera tinctoria:

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 25–30 kg/ha and the yield of green matter varies from 10,000–12,000 kg/ha.

7. Calapogonium mucunoides:

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.

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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 raindrops during the monsoon months.

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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 8–10 kg/ha and the yield of green matter is 5000 kg/ha.

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8. Phaseolus trilobus (Pillipesara):

This is a dual-purpose crop yielding good fodder for cattle and green manure for land. It is an 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 of 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 10,000–12,000 kg/ha.

9. Centrosema pubescens:

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.

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10. 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.

11. Stylosanthes hamata:

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.

12. 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.

13. 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.

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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.

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The common shrubs growing in waste lands are Cassia auriculata, Dodonia viscosa, Calotropis gigantea, etc. Leguminous trees like Pongamia glabra and 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.

1. 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, 1–2 m apart, or as a thick hedge by close planting in 3–4 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 2–3 times a year and it withstands repeated lopping. It has no root effect on the crops grown by the side. When the shrubs are regularly lopped, the height is restricted to 2–3 m and they do not affect the growth of cultivated crops with their shade effect. Glyricidia 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 30–60 days old. Within two years after planting, the plants are ready for lopping. Each plant gives 5–10 kg of green leaves annually. When the individual rice fields are about 0.1 ha each, 375–400 plants can be planted on the bunds of one hectare of land and this will produce 2500-3500 kg of green leaves annually.

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2. Ipomoea cornea:

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 1–2 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.

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3. Cassia auriculata:

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.

4. 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.

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5. Azadirachta indica (Neem):

It is a profusely branching, large ever-green 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 seedling at a spacing of 5–6 m. One or two loppings in a Year are taken in favourable seasons, each lopping weighing about 150–200 kg of green matter.

6. Thespesia populnea:

It is also an ever-green 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 4–5 m is adopted. It is propagated by stem cuttings. It establishes very quickly and produces a number of branches. Two or three lopping of green leaves are taken in a year during favourable seasons. A tree will give as much as 100–150 kg of green matter per lopping.

7. Delonix elata (Vadanarayan):

It is a tropical ever green tree, which thrives in all types of soils. Generally, it is propagated by stem cuttings. In a year, 2–3 lopping can be taken during favourable seasons. It has some medicinal values.

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