GREEN MANURING

India has changed from a region of food scarcity to food sufficiency by increased fertilizer use with subsidized prices, but use of organic manures including green manure, declined substantially. Inorganic fertilizers are becoming more expensive, therefore sustainability of soil productivity has become a question. Hence, alternate sources to supplement inorganic fertilizers are thought. Green manuring are low cost and effective technology in minimising cost of fertilizers and safeguarding productivity.

Green manure crops

Crops grown for the purpose of restoring or increasing the organic matter content in the soil are called Green manure crops

Green manure incorporated field

Green Manuring

Use of Green manure crops in cropping system is called 'Green Manuring' where the crop is grown in situ or brought from outside and incorporated when it is purposely grown.

Green leaf manuring

Consists of gathering green biomass from nearby location and adding to the soil.

Greenleaf Manure Incorporation in Rice Field

Objectives of green manuring

To add N to the companion or succeeding crop and add or sustain organic matter in the soil.

Subsidiary objective
a. Catch Crops

Legumes are inter-sown in standing crop before or after harvest, to utilize nitrates or the left over moisture

b. Shade crops

Sown in young orchards with the objective of shading the soil surface and, preventing the rise of temperature. Otherwise tender roots of fruit plants may be affected by the high soil temperature. In plantation like tea and coffee, Glyricidia is used as shade crop first and incorporated as green manure.

c. Cover crops

Green manure crops 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 run off.

d. Forage crops

Legume are grown for taking cutting of green fodder for cattle in early stages and later as GM. Pillipesara seeds can be broadcasted in the standing rice crop
(3-5 days before harvest).

Classification of green manures

Green manures
Legumes		Non-legumes
Green manure	Green leaf manure	Green manure	Green leaf manure
(eg)Daincha	(eg) Gliricidia	(eg) Sunflower	(eg) Calotropis
Sunhemp	Cassia	Buck wheat	Adathoda
Kolinji	Pongamia glabra		Thespesia

Characteristics desirable in legume green manure crops

1. Multipurpose use
2. Short duration, fast growing, high nutrient accumulation ability
3. Tolerance to shade; flood, drought and adverse temperatures.
4. Wide ecological adaptability
5. Efficiency in use of water
6. Early onset of biological nitrogen fixation
7. High N accumulation rates
8. Timely release of nutrients
9. Photoperiod insensitivity
10. High seed production
11. High seed viability
12. Ease in incorporation
13. Ability to cross-inoculate or responsive to inoculation
14. Pest and disease resistant
15. High N sink in underground plant parts.

Leguminous green manures

Local name

Sesbania                                
Dhaincha                                
Sunhemp                               
Wild Indigo                           
Pillipesara                              
Cowpea                                  
Cluster bean (Guar)                
Green gram (Mung bean)       
Berseem                                 
Madras Indigo

Common shrubs and trees used as green leaf manures

Non-conventional green manures

1. Leguminous or non-leguminous annuals, shrubs and trees providing large biomass and can supply considerable quantity of plant nutrients
2. Initial set back may be seen in crops after the incorporation of organic residues with wide C-N ratio
3. High lignin content which resist easy decomposition and release of higher proportion of organic acids during decomposition adversely affect establishment of young seedlings can be overcome by extra addition of N or use suitable microbial inoculants.

Forms of green manuring

1. Improved fallow, i.e. replacing natural fallow vegetation with green manure
2. Alley cropping: quickly growing trees, shrubs (usually legumes) or; grasses are planted in rows and are regularly cut back
3. Integration of trees into crop land, as found in several traditional farming systems,
4. Relay fallowing by sowing bush legumes among the food crops
5. Live mulching, in which the rows of food crops are sown into a low but dense cover crop of grasses or legumes, strips of the cover crop are removed by hand or killed by herbicides when the food crops are to be sown, thus reducing soil tillage operations to zero;
6. Shaded green manures (in fruit orchards, coffee plots, multistorey kitchen gardens etc)