Introduction
Green manuring is the practice of incorporating green plant tissues into the soil for improving the soil productivity. It is a low cost but effective technology in minimizing the investment cost of fertilizers and in safeguarding the productive capacity of the soil.
Criteria for selection of green manure crops
- The green manure crops must develop good foliage (പച്ചിലപ്പടര്പ്പ്, ഇല) and rapid growth.
- They should have deep root system.
- They should be able to grow well on poor soils.
- Water requirement of green manure crops should be less.
- Must have legumes (പയര് വര്ഗ്ഗം)to fix atmospheric nitrogen.
- Should be of short duration.
- Should be succulent (നീരുള്ള), non-fibrous and non-woody in nature.
Benefits of green manuring
- Adds nutrients and organic matter to the soil.
- Improves physical, chemical and biological properties of the soil.
- Serves as 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 for use by the crops.
- Promotes formation of crumbs leading to better aeration and drainage in the soils.
- Builds up soil structure and improves tilth (ഉഴുവല്).
- Improves water holding capacity of soils.
- If green manure crop is a legume, it adds lot of nitrogen to the soil by fixing atmospheric nitrogen.
- Uptake plant nutrients from the lower layers and adds them in the surface soil when turned under.
- Green manure crops act as cover crop and reduce the soil temperature and protect the soil from erosion, crust formation and suppress the growth of weeds.
- Help in conserving nutrients by taking up soluble nutrients which might otherwise been lost due to leaching or erosion.
- Prevent leaching of nutrients to lower layers.
- Helps in reclaiming the saline (ഉപ്പുള്ള) and alkali soils.
- Many green manure crops have additional use as sources of food, feed and fuel.
- They increase the yield of crops.
Methods of green manuring
Broadly the practice of green manuring can be divided into two types.
- In-situ green manuring
- Ex-situ green manuring/Green leaf manuring
In-situ green manuring
It is a system by which green manure crops are grown and incorporated in to the soil of the same field in which it is grown.
Leguminous green manuring crops
- Sunnhemp : Crotalaria juncea
- Daincha : Sesbania aculeate
- Sesbania : Sesbania speciosa
- Indigo : Indigofera tinctoria
- Wild Indigo : Tephrosia purpurea
- Cow pea : Vigna unguiculata/V. sinensis
- Green gram/Mung : Phaseolus aureus/Vigna radiata
- Black gram/Urd : Phaseolus mungo/Vigna mungo
- Horse gram : Macrotyloma uniflorum
- Cluster bean/Guar : Cyamopsis tetragonaloba
- Berseem : Trifolium alexandrium
Sunhemp
Malayalam Name(s): Chanaka, Chanambu, Dhunam, Kattuthanatalakatta, Pulivanni, Sanam, Wuckoonar
English name(s): Bengal Hemp, Brown Hemp, Indian Hemp, Madras Hemp, Sun Hemp
Description: Annual erect herbs to 2.3 m tall; stems striate, silky-pubescent. Leaves 3-8 x 0.5-1.5 cm, oblong-elliptic to oblanceolate, base usually acute, apex obtuse to subacute, apiculate, clothed on both sides with appressed hairs; petiole to 3 mm long; stipules minute. Inflorescence teminal, racemose, many-flowered, 15-30 cm long. Flowers yellow, 1.5-2 cm long; pedicels c. 5 mm long; bracts 3-4 mm long, lanceolate; bracteoles linear. Calyx c. 1.8 cm long, fulvous hairy, teeth linear-lanceolate. Petals 1.5-2 cm long; standard c. 2 cm long and broad, ovate, veined red, silky without; wings shorter than keel and standard. Pods sessile, 2.5-3x 1-1.3 cm, oblong-cylindrical, fulvous silky hairy. Seeds 8-15, c. 4 mm long, obliquely-cordiform.
Habit : Herb
Flowering & Fruiting : July-September
Habitat : Dry deciduous forests, also grown as green mannure in the plains
Distribution : India; now spread to most tropical countries.
Sesbania aculeate (Dhaincha)
It is a small tree in the genus Sesbania belongs to the family Fabaceae. It can grow on saline soil. The plant has a great number of uses, including as green manure, rice straw, wood and fodder. It can be used like industrial hemp for rope, fish nets, sackcloth and sailcloth. Its fibers are similar to those of birch trees and show promise as a source of paper fiber. Like other legumes, it can be planted to improve the soil via nitrogen fixation. The quantity of nitrogen fixed is 75 to 80 kg per ha.
Sesbania rostrata (New Dhaincha)
This is a small semi-aquatic leguminous tree, in the genus Sesbania. It forms a symbiotic relationship with Gram-negative Rhizobia which leads to the formation of nitrogen fixing nodules on both stem and roots. It is mainly used as green manure to improve soil fertility due to its fast growth, high biomass production and ability to convert large amounts of atmospheric nitrogen into a usable form for plants. Other applications include production of high quality forage for livestock and it is a source of fuel-wood. The quantity of nitrogen fixed is 150 to 180 kg per ha.
Indigo ( Indigofera tinctoria)
Indigofera tinctoria, also called true indigo, is a species of plant from the bean family that was one of the original sources of indigo dye. It has been naturalized to tropical and temperate Asia, as well as parts of Africa, but its native habitat is unknown since it has been in cultivation worldwide for many centuries. Today most dye is synthetic, but natural dye from I. tinctoria is still available, marketed as natural coloring where it is known as tarum in Indonesia and nila in Malaysia. In Iran and areas of the former Soviet Union it is known as basma. The plant is also widely grown as a soil-improving groundcover.
True indigo is a shrub one to two meters high. It may be an annual, biennial, or perennial, depending on the climate in which it is grown. It has light green pinnate leaves and sheafs of pink or violet flowers. The plant is a legume, so it is rotated into fields to improve the soil in the same way that other legume crops such as alfalfa and beans are.
Tephrosia purpurea (Wild indigo or Kolingi)
This species of flowering plant in the pea family, Fabaceae that has a pantropical distribution. It is a common wasteland weed. In many parts it is under cultivation as green manure crop. Used as a fish poison. The leaves and seeds contain tephrosin, which paralyzes fish. Larger doses are lethal to fish, but mammals and amphibians are unaffected. It is also used traditionally as folk medicine. It resists drought but does not withstand water stagnation. The seed have a waxy, impermeable hard seed coat and do not quickly germinate. To hasten germination, the seeds are to be abraded with sand or steeped in hot water at 55°C for two to three minutes.
Cow pea (Vigna unguiculata/V. sinensis)
Cowpea (Vigna unguiculata (L.) Walp.) is cultivated widely in the tropics and has multipurpose uses: as food for human beings, fodder for livestock and atmospheric nitrogen fixers. Cowpea grains rich in protein are consumed in different forms in several parts of the tropics. The average grain yield of cowpea in West Africa is approximately 492 kg ha−1, which is much lower than its potential yields. This low productivity is due to a host of diseases, insects, pests, parasitic weeds, drought, poor soils and low plant population density in the farmer’s field. Despite a large number of cowpea accessions (about 15,000) maintained at the International Institute of Tropical Agriculture (IITA), recent studies demonstrated that genetic diversity in cultivated cowpea is low. Researchers, however, found a high level of random amplified polymorphic DNA marker diversity in landraces from Malawi. However, ex situ collection of cowpea and wild Vigna germplasm from different parts of the world were assembled in the IITA gene bank. These genetic resources have been explored to identify new traits and to develop elite cowpea varieties. Many cowpea varieties with high yield potential have been developed and adopted by the farmers. Efforts are continuing to develop better-performing varieties using conventional breeding procedures, while molecular tools are being developed to facilitate progress in cowpea breeding (Agbicodo et al., 2010).
Green gram / Mung (Phaseolus aureus / Vigna radiata)
Black gram / Urd : Phaseolus mungo / Vigna mungo
Vigna mungo, the black gram, urad bean, mash kalai, uzhunnu parippu, ulundu paruppu, minapa pappu, Uddu (in Kannada) or black matpe is a bean grown in South Asia. Like its relative, the mung bean, it has been reclassified from the Phaseolus to the Vigna genus. The product sold as black lentil is usually the whole urad bean, whereas the split bean (the interior being white) is called white lentil. It should not be confused with the much smaller true black lentil (Lens culinaris).
Horse gram (Macrotyloma uniflorum)
Horse gram is native to tropical southern Asia and has been found in archaeological sites in India, starting from 2500 BC. It was probably first domesticated in India, and is now grown as a legume from India to Myanmar. It is also grown for fodder and as a green manure crop in tropical countries in southeastern Asia, and in northern Australia.
Horse gram powder does wonders in treating various health issues such as asthma, bronchitis, urinary problems, jaundice, peptic ulcer, haemorrhoids and even menstrual problems. It is also beneficial for extracting phlegm, and controlling fever.
Cluster Bean / Guar (Cyamopsis tetragonaloba)
Guar (Cyamopsis tetragonoloba [L.] Taub.), also known as cluster bean, has traditionally been used as a fodder and vegetable crop. Because of its ability to fix nitrogen and because it has a smaller seed than other legumes, it is also used as green manure. Galactomannan gum, a polysaccharide derived from guar seeds that results in highly viscous aqueous solutions at low concentrations, has long been used in many industrial applications (Dhugga et al., 2004).
Guar is a drought-hardy, deep-rooted, annual legume grown in the summer season. The name guar is believed to have arisen from the Sanskrit words gau and ahaar, which mean cow and fodder respectively. In the earlier literature, C. tetragonoloba was known as Dolichos fabaeformis or C. psoralioides (Stephens, 1998). It belongs to the tribe Galegae of the family fabaceae; which has three species, of which C. tetragonaloba is the only economically important one. The haploid chromosome number of guar is 7 (Patil, 2004).
In India, guar is mainly grown in the dry habitats of Rajasthan, Haryana, Gujarat, and Punjab and to a limited extent in Uttar Pradesh and Madhya Pradesh. Guar is also grown in Pakistan as a cash crop, and to a limited extent in other parts of the world such as Australia, Bangladesh, Brazil, Myanmar, South Africa, southwestern USA, and Sri Lanka.
Berseem(Trifolium alexandrium)
Trifolium alexandrinum (Egyptian clover, berseem clover) is an annual clover cultivated mostly in irrigated sub-tropical regions, and used as leguminous crop. It is an important winter crop in Egypt, where it may have been cultivated since ancient times, and was introduced into northern India in the early nineteenth century. It is also grown in the United States and Europe.
The plant reaches 30 to 100 cm (12 to 39 in) tall with erect or ascending stems. There are two types of berseem clover, single-cut and multi-cut. Single-cut varieties, like Balady, feature a high growing point and feature poor recovery once harvested. Multi-cut varieties, like Frosty, feature a lower growing point allowing for multiple harvests from a single sowing. 
Berseem clover is generally frost-sensitive and should be planted only after potential for frost has passed. The exception is Frosty berseem clover which was developed by Grassland Oregon, Inc. and released in 2016. This variety is capable of surviving temperatures as low as 5 degrees Fahrenheit.
Forage - Berseem clover is capable of producing up to 8 tons of forage in a single growing season. Berseem clover is similar in forage quality to that of alfalfa.
Green Manure - Berseem clover can also be used as a cover crop suppressing weeds or as a green manure crop providing nitrogen to following crops. As a green manure crop, berseem is capable of providing as much as 280 lbs./acre of nitrogen to following crops.
b) Non-leguminous Green Manuring Crops
Crops like maize, sorghum, barley and oats can be used as green manure crops.
B. Ex-situ Green Manuring / Green Leaf Manuring
The practice of collecting green leaves from all the available sources and incorporating them in the soil is called as green leaf manuring.
- Glyrcidia : Glyrcidia maculata
- Subabul : Leucaena leucocephala
- Agase : Sesbania grandiflora
- Pongamia : Pongamia glabra
- Eupatorium : Chromolaena odorata
- Neem : Melia azadiracta
- Cassia : Cassia siamea
- Ipomea : Ipomoea carnea
- Yekka : Calotropis gigantia
Glyrcidia ( Glyrcidia maculata)
Gliricidia sepium, often simply referred to as its genus name Gliricidia, is a medium size leguminous tree belonging to the family Fabaceae. Common names include quickstick, mata ratón; cacao de nance, cachanance; balo in Panama; piñon Cubano in the Dominican Republic; madreado in Honduras; kakawate in the Philippines; madre xacao or madre de cacao in the Philippines and Guatemala; madero negro in Nicaragua; undirmari in Marathi and wetahiriya in Sinhala). It is an important multi-purpose legume tree, with a native range from Mexico to Colombia, but now widely introduced to other tropical zones.
- Gliricidia sepium is a medium-sized tree that grows 10–12 m (33–39 ft) high. The bark is smooth, and its color can range from a whitish gray to deep red-brown.
- The flowers are located on the end of branches that have no leaves. These flowers have a bright pink to lilac color that is tinged with white. A pale yellow spot is usually at the flower's base.
- The tree's fruit is a pod about 10–15 cm (4–6 in) long. It is green when unripe and becomes yellow-brown when it reaches maturity. The pod produces four to ten round brown seeds.
- G. sepium is native to tropical dry forests in Mexico and Central America. In addition to its native range it is cultivated in many tropical and subtropical regions, including the Caribbean, northern parts of South America, central Africa, parts of India,parts of Sri Lanka, parts of Myanmar and Southeast Asia.
- The tree grows well in acidic soils with a pH of 4.5-6.2. The tree is found on volcanic soils in its native range in Central America and Mexico. However, it can also grow on sandy, clay, and limestone soils
Uses
G. sepium was spread from its native range throughout the tropics to shade plantation crops such as coffee. Today it is used for many other purposes including live fencing, fodder, firewood, green manure, intercropping, and rat poison.[9] Its use expanded following the widespread defoliation of Leucaena by psyllid in the 1980s. In the charsutri method of paddy cultivation, leaves of glyricidia are incorporated in soil during ploughing.
Fodder
G. sepium is used as cut and carry forage for cattle, sheep, and goats. Its high protein content allows it to complement low-quality tropical forages. G. sepium can tolerate repeated cutting, every 2 to 4 months depending on the climate. Cutting G. sepium causes it to retain its leaves during the dry season when many forage crops have lost their leaves. In some cases it is the only source of feed during the dry season.
Intercropping
G. sepium trees are used for intercropping in part because they fix nitrogen in the soil and tolerate low soil fertility, so when they are interplanted with crops they can boost crop yields significantly, without the need of chemical fertilizers.
G. Sepium tolerates being cut back to crop height, and can even be coppiced, year after year. When the trees are cut back, they enter a temporary dormant state during which their root systems do not compete for nutrients needed by the crops, so the crops can establish themselves.
These properties also enable G. Sepium to be used as green manure.
Subabul : Leucaena leucocephala
Agase : Sesbania grandiflora
Sesbania grandiflora, commonly known as vegetable hummingbird, West Indian pea, Jayanti, agati, or katurai, is a small tree in the genus Sesbania in the legume family. It has edible flowers and leaves commonly eaten in Southeast Asia and South Asia.Description
Sesbania grandiflora is a fast-growing tree. The leaves are regular and rounded and the flowers white, red or pink. The fruits look like flat, long, thin green beans. The tree thrives under full exposure to sunshine and is extremely frost sensitive.
It is a small soft wooded tree up to 3–8 m (10–26 ft) tall. Leaves are 15–30 cm (6–12 in) long, with leaflets in 10–20 pairs or more and an odd one. Flowers are oblong, 1.5–10 cm (1–4 in) long in lax, with two to four flower racemes. The calyx is campanulate and shallowly two-lipped. Pods are slender, falcate or straight, and 30–45 cm (12–18 in) long, with a thick suture and approximately 30 seeds 8 mm (0.3 in) in size.
Origin and distribution
It is native to Maritime Southeast Asia (Malaysia, Indonesia, Philippines, Brunei) to Northern Australia, and is cultivated in many parts of South India and Sri Lanka. It has many traditional uses. It grows where there is good soil and a hot, humid climate.
Medicinal uses
The leaf extract may inhibit the formation of advanced glycation end-products. The leaf extract contains linolenic acid and aspartic acid, which were found to be the major compounds responsible for the anti-glycation potential of the leaf extract.
Culinary uses
The flowers of S. grandiflora are eaten as a vegetable in South Asia and Southeast Asia, including Laos, Thailand, Java and Lombok in Indonesia, Vietnam, Maldives, Sri Lanka, and the Ilocos Region of the Philippines.
The young pods are also eaten. In Sri Lanka, agati leaves, known as Katuru murunga in Sinhala language, are sometimes added to sudhu hodhi or white curry, a widely eaten, thin coconut gravy.
Pongamia(Pongamia glabra)
Found in East Asia, Pongamia pinnata or Pongnam is a tropical, fast-growing, medium to large tree usually growing about 15-25 m in height and 50-80cm in bole diameter. It has a broad crown of drooping branches, straight or crooked bole, extensive lateral roots, and creamy white or pink flowers that form into clusters. It is a tree with multiple uses, particularly valued for being a source of oil, wood, medicines, dye, etc. Aside from such functions, Pongnam is planted as an ornamental and is used in soil conservation and soil erosion control practices. It is capable of fixing atmospheric nitrogen thus it can be used as green manure. There are no edible uses. However, there are several medicinal uses of this plant. Plant parts, in different forms, are used in the treatment or as relief from various conditions such as but not limited to dyspepsia, hemorrhoids, rheumatism, skin diseases, bronchitis and cough, herpes, diabetes, spleen enlargement, sores, and ulcers. Root juice, in particular, is used to clean teeth. Seed oil is used as lubricant, varnish, water-paint binder, and in soap manufacturing. Fiber obtained from the bark is made into ropes, twines, or strings. The wood is not durable but can be used in cabinet making, posts, agricultural implements, tool handles, cartwheels, paper making, etc. It is also used as fuel wood. Established plants are resistant to drought. Propagation method is through seed and germination takes place within 1-5 weeks of sowing.
Physical Characteristics
- Pongamia pinnata is an evergreen Tree growing to 20 m (65ft) by 20 m (65ft) at a fast rate.
- It can fix Nitrogen.
- Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: acid, neutral and basic (alkaline) soils and can grow in very alkaline and saline soils.
- It can grow in full shade (deep woodland) semi-shade (light woodland) or no shade. It prefers moist or wet soil.
Eupatorium (Chromolaena odorata) കമ്മ്യൂണിസ്റ്റ് പച്ച
Included in the top 100 of the world’s most invasive species, this flowering shrub is native to north and central America, and has been introduced to parts of Asia, Africa and Australia. It spreads very rapidly after disturbances like fire or clearing of land for agriculture, and suppresses the growth of native understorey species.
It is a perennial herb that has wind dispersed seeds, that can also attach to fur, clothes, etc and this facilitates long distance seed dispersal. Leaves release a pungent odour when crushed, and are used as traditional medicine in Indonesia, Malaysia, Thailand and Nigeria. However, it is toxic to cattle, and can cause allergies in humans.
Management and control
Manual slashing is commonly used, especially in fields, but this is a temporary measure, as the seeds remain in the soil and regrowth is common. Chemical control using herbicides like Triclopyr is effective, but has detrimental effects on native species and soil ecology. Biological control by a leaf-feeding moth, Pareuchaetes pseudoinsulata, and by a gall-forming fly Cecidochares connexa has shown significant success in some part of Africa, Indonesia and the Pacific islands.
Neem (Melia azadiracta)
Azadirachta indica, commonly known as neem, nimtree or Indian lilac, and in Nigeria called dogoyaro or dogonyaro, is a tree in the mahogany family Meliaceae. It is one of two species in the genus Azadirachta, and is native to the Indian subcontinent and most of the countries in Africa. It is typically grown in tropical and semi-tropical regions. Neem trees also grow on islands in southern Iran. Its fruits and seeds are the source of neem oil.
Cassia (Cassia siamea)
Siamese Cassia is a small to medium sized tree, up to 15-20 m tall, with a short bole and low branching high crown. Leaves pinnate, alternate, rachis 25-30 cm long, with a marked furrow, 8-13 pairs of leaflets of different size. Leaflets oblong, rounded at the base and at the apex, slightly retuse. Upper side dark green and shining, underside dull-green, shortly haired. Flowers yellow, up to 3.5 cm long, in dense racemes at the end of the shoots, and in their axils.
Growing Season and Type
- It prefers well drained , moist soil.
- It starts flowering and fruiting at the age of 2-3 years. Once established, it flowers precociously and abundantly throughout the year.
- Young plants are subjected to browsing damage by domestic animals.
- It has a spreading root system, and competes strongly with other species.
- It prefers full sun to Partial shade.
- It prefers acidic to neutral Ph.
Ipomea (Ipomoea carnea)
Yekka (Calotropis gigantia)
Green manuring practices
- Green manure crop can be grown in any type of soil provided there is sufficient rainfall or alternatively availability of irrigation water.
- For leguminous green manure crop, the seeds should be inoculated with the proper strain of bacteria. Molybdenum seed treatment could also enhance N fixation.
- The green manure crop should be sown with a higher seed rate than usual so that there will be a good canopy produced very quickly.
| Seed rate and biomass production of green manure crops. | |||
| Sl. No. | Green manure crop | Seed rate (kg/ha) | Biomass yield (t/ha) |
| 1 | Sunnhemp | 25-40 | 21 |
| 2 | Daincha | 20-25 | 26 |
| 3 | Cow pea | 25-30 | 15 |
| 4 | Indigo | 25-30 | 12 |
| 5 | Wild Indigo | 25-40 | 16 |
| 6 | Green gram | 15 | 10 |
| 7 | Black gram | 15 | 10 |
| 8 | Cluster bean | 12-15 | 10 |
- The production of green manures is limited by the deficiency of essential nutrients in the soil.
- The application of phosphatic fertilizers improves the growth of leguminous crop markedly and promotes the fixation of nitrogen by profuse nodulation.
- The best stage at which the crop should be incorporated into soil is when it reaches the flowering stage. For example sunhemp is ready for turning in at the age of 7-8 weeks whereas, daincha is ready for incorporation when it is 5-6 weeks old.
- Incorporation of green manure crops should be done at least 3-4 weeks before sowing or planting of main crop.
- Incorporation of green manure crop is done in the different ways. In some cases, the plants are cut close to the ground and the green material is put in the furrows opened by a mould board plough and is later buried. One of the methods is to plank the material down with a heavy plank or log and then plough the field. The other method is to mix the uprooted or cut plant material (green leaf manure) by means of disc harrow.
- Immediately after ploughing the material, care should be taken to cover it with soil by using suitable implements to ensure proper decomposition. Proper covering of material with the soil is especially necessary if the soil moisture supply is deficient.
- Under certain favorable circumstances, green manure crop such as daincha can be sown in between the rows of main crops. When daincha is sufficiently grown, it can be uprooted and mixed with the soil by inter cultivation.
- Under limited moisture supply conditions, it is advisable to go for green leaf manuring by growing the green manure crops in one field and add the green material to another field. By adding this, the moisture required for growing the green manure crop is saved.
| Nutrient content of green manures. | ||||
| Sl. No. | Name | Nutrient content (%) | ||
| Nitrogen | Phosphorus | Potassium | ||
| 1 | Sunhemp | 0.89 | 0.12 | 0.51 |
| 2 | Daincha | 0.68 | 0.13 | 0.40 |
| 3 | Cowpea | 0.71 | 0.15 | 0.58 |
| 4 | Green gram | 0.82 | 0.18 | 0.52 |
| 5 | Black gram | 0.82 | 0.18 | 0.52 |
| 6 | Horse gram | 0.91 | 0.18 | 0.65 |
| 7 | Glyricidia | 0.68 | 0.16 | 0.30 |
| 8 | Pongamia | 0.16 | 0.14 | 0.49 |
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