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| Sesbania Rostrata (image credit: b inxee) |
In agriculture, green manures refers to the plants or crops that are grown and turned into the soil to improve its quality.
The green manure plants are cut and then plowed into the soil or they can be simply left in the ground for an extended period of time till tillage.
Green manures also increase the efficiency of fertilizer use of crops when applied in combination with inorganic fertilizers.
Green manuring was first practised in China around 1100 BC.
In India, around 6.2 million has was reported under green manuring in 1989. Around 80 percent of which was located in 6 states: 1. Uttar Pradesh, 2. Andhra Pradesh, 3. Madhya Pradesh, 4. Karnataka, 5. Odisha and 6. Punjab.
Characteristics of Green Manuring Crops
1. Capable of growing quickly and acculumating sufficient fixed nitrogen in 4 to 6 weeks.
2. Tolerant to adverse climatic conditions such as drought, water logging, and high and low temperatures.
3. Pest and disease tolerant.
4. Should posses adequate Rhizobium nodule potential and must be an effective nitrogen fixer.
5. Easy to incorporate and quickly decomposable.
Among the green manure plants, Sesbania rostrata is being preferred. It bears stem nodules in addition to the root nodules. The amount of Nitrogen contributed by Sesbania rostrata plant in terms of Nitrogen fertilizer equivalence ranges from 80–120 kg/ha. In a field trial, comprising different green manure crops, it was found out that Sesbania rostrata produced the highest biomass per hectare (20–25 tons/ha) and accumulated a maximum of 150–220 kg N/ha.
The common leguminous green manure crops used in tropical regions and their N content are given below in the table.
| Crop | Scientific Name | Biomass | Nitrogen percentage (Moist) |
|---|---|---|---|
| Sunnhemp | Crotalaria juncea | 21.2 | 0.43 |
| Dhaincha | Sesbania aculeata | 20.0 | 0.43 |
| Dhaincha | Sesbania rostrata | 19.6 | - |
| Pillipesara | Phaseolus trilobus | 18.3 | 1.10 |
| Mungbean | Phaseolus arvensis | 8.0 | 0.53 |
| Cowpea | Vigna sinensis | 15.0 | 0.49 |
| Guar | Cyamposis tetragonoloba | 20.0 | 0.34 |
| Senji | Melilotus alba | 28.6 | 0.57 |
| Khesari | Lathyrus sativus | 12.3 | 0.54 |
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Agriculture