1. Green manure crops in irrigated and rainfed lowland rice-based cropping systems in south Asia.
In: Proc. of a Symposium on Sustainable Agriculture, IRRI, Philippines,
ISBN 97-104-189-8, 1988, pp. 72-82
Green manuring is the practice of incorporating in situ easily decomposable plant material either from crops grown specifically for organic fertilizer or plant materials brought from outside the field. In situ green manuring is done by turning under the entire plant, usually a leguminous crop. When brought from outside, the green matter may consist of leaves, twigs, and loppings from selected trees or bushes.
Increased food production must come primarily through increased crop productivity and increased cropping intensity. In India, food production has nearly doubled in the last two decades. This has been achieved through the adoption of high-yielding crop varieties, intensive cropping, and improved management practices, including improved fertilizer use.
Nearly one-third of the total N consumed in Indian farming is used for rice. Rice is grown over an area of about 40 million ha. A considerable fraction of the P and K fertilizer used is also for rice. Fertilizer production in India lags behind actual consumption, compelling large imports worth more than US$ 1 billion annually. The increase in fertilizer prices combined with the low purchasing power of farmers is imposing serious limitations on increased crop production and calls for increased efforts to mobilize cheaper and alternative sources of nutrients.
The advent of high-yielding crop varieties in recent years caused organic manure use to decline in favor of mineral fertilizers. There is renewed interest in organic manure, largely because increasing costs of fertilizers, greater incidence of multiple nutrient deficiencies, and deterioration in physical soil properties are resulting in reduced yields.
Farmyard manure, compost, and green manure are the organic materials commonly used. Because the availability of farmyard manure and compost is limited, green manure offers greater potential as a feasible and cheaper substitute for fertilizer N.
Green manuring techniques differ in rice-growing regions. The various techniques are described in this paper.
Research shows almost universal beneficial effects of green manuring on rice yields. Green manure can substitute for up to 60-100 kg fertilizer
N/ha. Many studies have shown it can enhance the availability of native or applied P and of micronutrients. Green manuring hastens the reclamation of alkali soils, largely because increased CO2-production during decomposition of the green manure crop enhances the solubility of lime.
An alternative to growing a crop exclusively for green manure is to grow a short-duration pulse (e.g., mungbean Vigna radiata, cowpea V. sinensis) for a green pod harvest and straw incorporation.
Although the value of green manuring for increasing rice production by supplying nutrients and maintaining soil productivity is well established, the practice has not been widely adopted by rice farmers.
Farmers are unable to appreciate the benefits of green manuring, since the benefits sometimes are not as spectacular as those observed from direct application of inorganic fertilizers.
Green manuring has a large potential to augment nutrient supplies.
Improved experimentation is needed so that crop responses to green manuring can be quantified. The factors responsible for crop responses must be identified to develop sound scientific strategies for green manuring practices.
The patterns of nutrient release during green manure decomposition and the patterns of rice crop utilization need to be better understood. The long-term effects of green manuring on soil properties and crop responses need evaluation. Knowledge of the changes in soil physical properties would be particularly valuable. Organic matter decomposition sets up a chain of physiochemical events which alter the form and availability of several nutrient elements. Green manuring has a special place in problem soils of low fertility and those with alkali problems.
Identification of species or strains that accumulate high N or biomass is another research area of importance.
1091 92 - 4/134
Africa, Nigeria, humid tropics, lowlands, study, field trials, intercropping systems, maize, melon, yam, soil water content, soil temperature, root length, crop performance
GHUMAN, B.S. and R. LAL
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