Impact of Organic Matter and Method of Addition on Selected Soil Parameters, Growth and Yields of Mungbean Grown in a Minor Season in the Humid Tropics

U. R. Sangakkara 1*, G Pietsch, M. Gollner and B. Freyer Faculty of Agriculture, University of Peradeniya, Peradeniya 20400, Sri Lanka. Institute of Organic Agriculture, University of Natural Resources and Applied Sciences, Gregor Mendel Strasse 33, A-1180, Vienna, Austria. ABSTRACT A field experiment was conducted over a minor (dry) season to ascertain the impact of two organic materials (Gliricidia leaves and rice straw) applied as a surface mulch or incorporated into the root zone, on selected soil parameters, growth, nodulation and yields of mung bean (Vigna radiata L. R. Wilcz). The beneficial effects were compared to soils and the growth of the crop without organic matter. Organic matter, especially Gliricidia leaves, enhanced soil physical properties and plant nutrients (N, P and K) at the time of crop establishment and early growth. Incorporation had a greater beneficial impact, especially on physical properties of soil. While the organic materials increased germination, the method of addition had no significant impact. Growth of shoots, roots and nodulation were enhanced by incorporation of organic matter, again, the greater benefits were derived with Gliricidia leaves. Root growth measured in terms of root length densities was stimulated by organic matter incorporation. In contrast, surface application of the organic matter, especially rice straw, reduced weed growth. The benefits of the organic matter were also evident in seed yields and harvest indices, although incorporation did not increase seed yields to the same magnitude observed in vegetative growth or harvest indices and relative crop yields. The benefits of incorporating organic matter, especially material with low C: N ratios such as Gliricidia leaves in tropical smallholder organic systems are presented.