Green Manure: Crops, Techniques and Advantages

After reading this article you will learn about:- 1. Important Green Manuring Crops 2. Important Green Leaf Manuring Plants 3. Technique of Green Manuring 4. Advantages and Disadvantages 5. Economics.

Important Green Manuring Crops:

Green manuring crops must grow rapidly on varieties of soil and must decompose quickly enough to release the nutrients they contain in the soluble form, for the growth of crops.

A few most important green manure crops are as follows:

(i) Sunhemp:

Crotalaria juncea is most suitable for loamy soils. It is sown in May or June when the monsoon breaks. It grows very fast and to a height of one to two metres. It can grow even on poor soils and ads about 20 to 25 tons of fresh green plant material per hectare to the soil.

Sunhemp is the most outstanding green manure crop. It is well suited to almost all parts of India and accommodates the growing seasons of sugarcane, potato and garden crop, irrigated wheat in north India and second season paddy crop in South India.

(ii) Dhaincha:

Sesbania bispinosa, it can tolerate waterlogging and salinity and dry conditions if the germination has been good. It grows up to a height of 1.5 to 1.8 metres in water logged paddy fields within a very short period of time. It is best suited for loamy or clayey soils where it adds about 10 to 20 tons of green material per hectare. It is mainly grown as a green manure crop in Assam, Bihar, West Bengal, Orissa and Tamil Nadu.

(iii) Sesbania Speciosa:

It can also tolerate waterlogging and dry periods. It is suitable for loamy or clayey soils. It grows very slowly during the earlier stages. It is also suitable for paddy field and adds about 25 to 20 tonnes /hectare of green plant materials.

(iv) Mung (Phaseolus Ausreus) is a Pulse Crop:

The variety Mung Type 1 which is sown in the first week of July matures and yields about 3 to 4 quintals of seed per hectare by the first week of September. After picking the pods, the crop is ploughed down as green manure and wheat may be sown in the first week of November.

(v) Pillipesara, (Phaeolus trilobus):

It is a minor pulse crop. It is mainly suitable for clayey soil where it grows very fast, completely covers the surface and is quickly decomposed. About 30 kg of seed is sown in a hectare field where 10 kg of nitrogen and 30 kg of phosphorus (P₂O₅) has been applied. It adds about 8 to 10 tonnes of green material per hectare.

(vi) Gaur (Cyamopsis tetragonoloba):

It is a good fooder cum green manuring crop in the dry regions of north-western India where it grows even on poor soils.

(vii) Other pulse crops like horse gram, cowpea etc. can also be grown as green manure crops.

Important Green Leaf Manuring Plants:

Some plants are grown on field bunds and waste land. Their green foliage is added to the soil. Therefore organic matter and plant nutrients are added to the soil from outside sources.

A few most common plants are:

(i) Gliricida maculata grows on most soils to a height of about four and half metres. One cutting should be taken in June when the monsoon breaks, and another one in December. Each plant supplied about 22 to 23 kg of green material containing about 0.48 per cent nitrogen.

(ii) Pongamia glabra. Each plant supplies about 130kgs of fresh green material containing about 0.56 per cent nitrogen.

(iii) Sesbania Speciosa is grown around the borders of paddy fields and irrigation channels. Sesbania Speciosa seedlings planted on the field bunds four inches apart around the paddy field of hectare, produces about 3000kgs of green leaves per hectare.

Technique of Green Manuring:

Usually the field in ploughed, a little fertilizer i.e. 10kgs of nitrogen and about 30kgs of phosphorus (P₂O₅) per hectare is added to the soil.

The fields are again ploughed and about 50 to 60kgs sunhemp or Dhaincha seeds are sown in June when the monsoon breaks. These grow rapidly and are ploughed after 5 to 6 weeks, just before the flowering stage when they are the most succulent.

The main crop is sown after another two months when the green plant materials have been thoroughly decomposed. Dhaincha and sunhemp add about 75kgs of nitrogen per hectare to the soil.

Advantages and Disadvantages of Green Manuring:

Advantages:

(i) Leguminous green manure crops add nitrogen to the soil.

(ii) Green Manure Crops Usually Deep Rooted:

They take nutrients from the deeper layers and leave them on the surface in the form of decaying organic matter. In green leaf manuring, nutrients are brought from elsewhere and added to the field.

(iii) Green manure, while it decomposes, improves the soil structure.

Disadvantages:

(i) It is difficult to practice green manuring under rainfed condition.

(ii) It is not convenient to include a green manure crop in crop rotation in areas where intensive farming is practiced.

Economics of Green Manuring:

Wheat, paddy and sugarcane have response to green manuring under irrigated conditions in India. The results of experiments conducted in different parts of India have shown that it is more remunerative to grow legumes for grain and/or fodder and to apply moderate amounts of fertilizers to the succeeding crops, then to grow them for green manuring only.

Nowadays, agricultural research has advanced enough to produce a large number of short duration high yielding cereal crops like paddy (‘TN.1’, ‘TN.3,’T.65’) wheat (‘Sonara 64’, ‘Lerma Roja’,’S. 227’), many hybrids of maize (‘Ganga 2’, ‘Ganga 3’) and Sorghum (‘CSH. 1, CSH. 2’).

Prices are also increasing steeply. So farmers are trying to grow as many crops as possible every year if irrigation water is available.

Green manure Crops cannot be accommodated in these multiple cropping rotation systems, the opportunity cost of green manure in wheat rotation has been assessed to be equivalent to 40 to 50 quintals per hectare of paddy, maize or pearl millet.

Green manuring may be practiced under special circumstances e.g. to reclaim alkali soils. Actually it is a very costly source of nitrogen and therefore cannot complete with relatively cheap nitrogenous fertilizer which, when applied with crop residues, will increase the yields of crops and sustain the fertility of the soil.