Green manures

GREEN MANURES 

Green manuring can be defined as a practice of ploughing or turning into the soil undecomposed green plant tissues for improving physical structure as well as soil fertility. Green manuring, wherever feasible, is the principal supplementary  means of adding organic matter to the soil. The green-manure crop supplies organic matter as well as additional nitrogen, particularly if it is a legume crop, due to its ability to fix nitrogen from the air with the help of its root nodule bacteria. The green-manure crops also exercise a protective action against erosion and leaching.  Green manure to be incorporated in soil before flowering stage because they are grown for their green leafy material, which is high in nutrients and protects the soil. Green manures will not break down in to the soil so quickly, but gradually,  add some nutrients to the soil for the next crop.  The nutritional potentials and nutritional contents of some important green manures are given in the Table 5 and 6 respectively. 

Table 1 : Nutrient potential of green manures 

Green manure	Biomass (tones)	N accumulobase   (Kg/ha)
Sesbania aculeate	22.50	145.00
S. rostrata	20.06	146.00
Crotalaria juncea	18.40	113.00
Tephrosia perpura	6.80	6.0
Green gram	6.50	60.20
Black gram	5.12	51.20
Cow pea	7.12	63.30

Table 2 : Nutrient content of important green matures

Crop	Nutrient content (% on dry weight basis)
Green manure	N                                        P                                        K
Sesbania aculeate	3.3	0.7	1.3
Crotalaria juncea	2.6	0.6	2.0
Sesbania speciosa	2.7	0.5	2.2
Tephrosia purpurea	2.4	0.3	0.8
Phaseolus trilobus	2.1	0.5	-
Green leaf manure
Pongamia glabra	3.2	0.3	1.3
Glyricidia maculeata	2.9	o.5	2.8
Azadirachta Indica	2.8	0.3	0.4
Calatropis gigantecum	2.1	0.7	3.6

ADVANTAGES OF GREEN MANURES: 

Usage of green leaf manure is advantageous both for crops and soil.

The advantages are:

1. As they decompose rapidly, it is easy to retain the organic matter in the soil.

2. Green manures improve both physical and chemical properties of the soil.

3. They provide energy to microbes.

 4. They provide nutrients to the standing crop and also to the next crop.

5. Addition of green manure crops to the soil, acts as much and prevent soil erosion.

6. Leaching of nutrients in light soils can be prevented by addition of green manure.

7. Cultivating green manure crops can control weeds.

 8. Majority of green manure crops being legumes, use of nitrogenous fertilizers can be minimized.