In agriculture, organic matter is considered the backbone of cultivated soils. In the early 1970s the organic matter in the soil was around 0.7 per cent, which has now declined to 0.2 to 0.3 per cent, particularly in the intensive crop cultivation region like northern India. The continuous use of fertilisers and pesticides has altered the biological properties of soil. Microbial activity in soil has decreased. Soil aeration, porosity and water-holding capacity have been affected due to the reduced organic matter.

Chemical fertilisers only provide one or two major nutrients, while the soils are becoming deficient in micro-nutrients. Our efforts should be on gradual reduction of chemical use while sustaining productivity. An important way is the use of bulky organic manures, which can improve the organic content of soil, thereby enhancing its physical, chemical and biological properties. Organic manures improve the nutrient balance.

Bulky organic manures can be supplied through farmyard manure, farm compost, town compost, night soil, sludge, green manure, etc. Out of these sources only farmyard manure and green manure are widely used. Farmyard manure is prepared from dung, yet about 60 to 70 per cent of dung is used as fuel in rural areas. Also, the dung is not managed properly and the quality of manure is not good.

•      Thus one practical way left for supplying organic matter is green-manuring.

Green-manuring is ploughing into soil live plant material for improving the physical structure as well as fertility of the soil. This practice is feasible in the rice-wheat cropping system, because a green manure crop requires large quantities of water for decomposition.

Green-manuring can be done in two ways depending on the situation. (1) Green-manuring in situ: this is the growing and burying of a green manure crop in the same field as the one to be manured. (2) Green-leaf manuring: this is turning into soil green material like leaves and twigs collected from shrubs and trees grown on bundhs, wastelands or nearby forest areas. Depending on the conditions, farmers can follow either of the two methods.

This practice adds organic matter to the soil, improves the physical properties of soil in terms of aeration, porosity, water-holding capacity, and facilitates penetration of rainwater. Green-manure crops hold plant nutrients that would otherwise be lost by leaching. Leguminous green-manure crops add nitrogen to the soil. This practice increases the availability of nutrients like phosphorus, calcium, potassium, magnesium and iron. In the rice-wheat cropping system the use of chemical fertilisers can be reduced by one-third if green-manuring is done before the rice crop.

Researchers have documented that there is no need of applying phosphate fertilisers in the rice crop if the same dose is applied in the green-manure crop. This enhances the growth of the green-manure crop, thereby giving more quantity of organic matter.

While green-manuring one has to keep in consideration that there should be sufficient water available for decomposition of the green-manure crop. The practice is economical if the green-manure crop is taken between two consecutive crops.

In Punjab and Haryana, wheat is harvested in April and rice is transplanted in June. The fields thus remain vacant for about two months, which can be utilised for green-manuring. Scientists have developed a package of practices for this.

The green manure crop dhaincha (Sesbaina aculeata) should be sown in the second half of April using 10 kg of seed per acre. The dose of phosphate fertilisers meant for the rice crop should be applied in dhaincha at the time of sowing. This green-manure crop should be ploughed into the field at 6-7 weeks of age. The transplanting of rice seedlings can be done easily after a week.

  Source : The Tribune Dated 30th June 2003