GREEN MANURING – THE NEED OF THE HOUR

Archita Ojah

(Department of Agronomy, Assam Agricultural University. archita12ojah@gmail.com)

As the global population is beginning to grow rapidly, there is a need for a more sustainable and environment-friendly approach towards food production. Further, the issue of enhancing crop productivity has also to be well thought of. In this case, green manuring can be perfect alternative to the unsustainable ways of farming; which, besides increasing yield, have been also the potential of clearing up the ill-effects of injudicious use of fertilizers. This technique is based on some unique values and has the philosophy of working together with nature.

Green manuring is basically a practice where some specific tender and undecomposed green plants or parts of the plants are ploughed down into the soil. The purpose is to increase the soil fertility (organic matter content, soil nutrient supply) status as well as improving the soil physical condition (viz. soil aggregate stability, porosity, aeration). Green manuring is mostly connected with organic farming and can also be practised as a component of integrated nutrient management. Integrated use of green manure and chemical fertilizer saves 50-70 % fertilizer N in paddy cultivation. Green manures like Sesbania, sunhemp and cowpea have narrow C: N (Carbon – nitrogen) ratio thus helping in easy decomposition. It may be incorporated in paddy field 7-15 days before transplanting. This will supply sufficient quantities of fertilizer nitrogen.

Green Manuring Crops: Different green manuring crops can be grown by the farmers of India. Some of the commonly used green manuring plants are Sunhemp (Crotolariajuncea), Guar (Cyamopsis tetragonoloba), Dhaincha (Sesbania aculeata and Sesbania rostrata), Glyricidia (Glyricidia maculate), Karanj (Pongamia pinnata), Cowpea (Vigna unguiculata), Berseem (Trifolium alexandrium) etc.

Methods of Practising Green Manuring:

1. Green Manuring in Situ: Here, green manuring crops are grown in field up to flowering stage and is over turned in the same field by mouldboard plough. Following are the techniques adopted in this method.

● Sowing of green manuring crop as main crop: Crop like Dhaincha, Guar, Berseem etc., are grown in barren and waste soil and are buried into the soil after completing the period of their growth.

● Sowing of green manuring crop in summer: In between the harvesting of Rabi crop and sowing of Kharif crop, sun hemp, dhaincha etc., are grown in field and buried in soil in the month of June-July.

●▪Sowing of Green Manuring Crop in fallow soil: In fields where vegetables or wheat are grown, dhaincha, guar, sunhemp, cowpea etc., are sown before main crop. After burring the green manuring crop, the field is left fallow for some time and land is prepared for Rabi crop.

● Sowing of green manuring crop as main crop: Here, green manuring crops are grown in lines with the main crop and are buried into the soil after 7-8 weeks. Example – Sunhemp and Cowpea with maize and cotton, dhaincha with paddy etc.

2. Green Leaf Manuring: Here, green manuring crop is grown in one field and is buried in another field. Otherwise, green leaves, branches of plants are collected and buried in the field. This method is used in water deficient zones.

Few benefits of practising green manuring:

Green manuring increases soil organic matter content, improves aeration, supply nutrients to plants and increases the biochemical activity of beneficial soil micro-organisms. It can be used as a cover crop which helps to conserve soil moisture. It prevents the leaching down of soluble nutrients in soil and can bring up crop nutrients from lower profiles of soil. Green manure crops can be grown as inter-crops to suppress weed (unwanted plants in crop fields). They can also be raised in the fallow lands during the non-cropping season, and cut and ploughed down later to ensure soil fertility. Growing of green manure crops also increases crop yield to a great extent. It reduces the dependence on chemical inputs for growing crops to some degrees. Besides nitrogen, it can also supply several micro-nutrients required for growing of crops. This technique is eco-friendly and also reduces soil erosion.

Green manuring crops are supposed to be sown before the main crop season. Inoculation of legume based green manure with appropriate microbial cultures like rhizobium further increases the efficiency of the green manuring crops. The most desirable stage for incorporation of this crop into the soil is when the flowers start to bloom. For in-situ practice, the crops are to be cut close to the ground, then incorporated into the soil and trampled. Special tramplers are now also available for this purpose. Leveling of the soil is a must after every trampling. However, in case of green leaf manure, desirable plant parts must be broadcasted over the entire field and then trampled. These green parts are left for decomposition in the field. If the green manure is young and succulent, paddy can be transplanted immediately. However, we have to wait for a few days if the added manure is woody in nature. Last but not the least; green manuring can be called as the poor farmer's manure.