Green manuring 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 manuring 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 manuring 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 manuring and soil improvement
Green manuring will not break down into the soil so quickly, but gradually, add some nutrients to the soil for the next crop. As they decompose rapidly, it is easy to retain the organic matter in the soil. Green manuring improve both physical and chemical properties of the soil. The provide energy to microbes as well as nutrients to the standing crop and also to the next crop.
Addition of green manure crops to the soil, acts as much and prevent soil erosion. Leaching of nutrients in light soils can be prevented by addition of green manure. Cultivating green manure crops can control weeds. Majority of green manure crops being legumes, use of nitrogenous fertilizers can be minimized.
Cowpea is one of the important leguminous green leaf manure crops. As this plant is easily decomposable and very well suited for green manure purpose. June-July months are best suited for sowing of this manure. Even though it is being cultivated in summer months (March to April). Use of effective Rhizobium bacteria increase the fixation of nitrogen up to 40 kg/ha.
Dhaincha is suitable for loamy and clayey soils. It is fairly resistant to drought as well as stagnation of water. It grows well even in alkaline soils and corrects alkalinity if grown repeatedly for 4-5 years. The roots have plenty of nodules. It yields about 10-15 tonnes of green manure per ha and requires a seed rate of 30-40 kg/ha. Use of effective Rhizobium strain with seeds fixes the Nitrogen 1 kg/day.
It is a quick growing green manure crop and gets ready for incorporation in about 45 days after sowing. It does not withstand heavy irrigation leading to flooding. The crop is at times subject to complete damage by leaf eating caterpillars. The crop can produce about 8-12 tonnes of green biomass per ha. The seed requirement is 30 kg/ha.
One of the important features of this green manure is that is addition to the root nodules, it produces nodules in the stem. The stem nodulation is an adaptation for waterlogged situation since flooding limits growth of green manures and may reduce root nodulation.
Under normal condition, both root and stem nodules are effective in N fixation. It has higher N content of 3.56% on dry weight basis. Biomass production is higher during summer (April–June) than in winter (Dec.–Jan.) Season. This green manure can also be produced by raising seedlings (30 days old) and planted in the paddy field along the bunds or as intercrop with rice. Use of Rhizobium bacteria increase the nitrogen fixation about 60-100 kg/ha/year.
This is a slow growing green manure crop and cattle do not prefer to graze it. The green manure is suitable for light textured soils, particularly in single crop wetlands. It establishes itself as a self sown crop and the seeds remain viable till the harvest of rice. On an average about 3-4 tonnes of green manure is obtained in one ha. The seed rate is 30 kg/ha. The seeds have a waxy impermeable seed coat and hence scarification is required to induce germination.
It resembles wild indigo and is along duration crop with more leafy growth. It comes up well in clayey soils with one or two irrigations.
This is a shrubby plant that comes up well in moist situations. Under favorable conditions, it grows well like a tree. It can be easily grown in waste lands, farm road sides, field bunds, etc. the crop can be established by stem cuttings or seedlings planted in the field borders.
It can be pruned for its tender loppings and compound leaves for green leaf manuring at the time of puddling rice. One an average, a well-established plant yields 12-15 kg green matter. About 400 plants on the peripheral bunds yields 5-6 tonnes green manure/ha.
On roadsides and fallow lands, the plant grows wild under different soil and climatic conditions. The leaves are more succulent and a plant can produce about 4-5 kg of green matter. Besides it also helps in controlling soil borne pests like termite.
This article is jointly written by Dr. Muqarrab Ali 1, Muhammad Nazim 1, Dr. Omer Farooq 2 and Qurat-ul-Ain Sadiq 3. The are associated with: 1 Department of Agronomy, Muhammad Nawaz Sharif, University of Agriculture Multan, Pakistan, 2Department of Agronomy, Bahauddin Zakariya University of Multan, Punjab, Pakistan, 3Department of Soil and Environmental Sciences, Muhammad Nawaz Shareef,University of Agriculture Multan, Pakistan