Effect of Rice Straw Incorporation on Rice Plant Growth and Nutrition1

Abstract

AbstractRice (Oryza sativa L.) straw disposal by soil incorporation may have adverse effects on subsequent rice seedling growth from toxic anaerobic decomposition products and temporary immobilization of the soil mineral N. Glasshouse and laboratory studies were conducted to study the problem under conditions of direct sowing of rice.Samples of a typical rice soil, Sacramento clay, which is a very fine, montmorillonitic thermic Vertic Hapiquall, were collected. Rice straw in amounts of 0, 0.25, and 0.5% was added to soils which were incubated aerobically for 0, 15, and 30 days in a glasshouse plant growth experiment, and for 0 and 20 days in preparation for a laboratory soil incubation experiment. Nitrogen was applied at the rate of 50 ppm in the glasshouse experiment and 50, 75, and 100 ppm in the laboratory study. N was added after aerobic incubation and subsequently rice was grown for 21 days to measure seeding growth effects. The glasshouse experiment with rice cultivar ‘Earlirose’ also evaluated the production of acetic, propionic, and butyric acids, while the laboratory soil incubation experiment was for N transformation data.The results clearly indicate that when soil and rice straw were not incubated prior to planting rice seedlings, applied N was immobilized, causing inhibition of plant growth and low N content of plants. When rice straw was incubated in soil for 15 to 30 days before planting seedlings, N immobilization was reduced and plant growth was promoted. Nitrogen immobilization was observed to be the principal cause of inhibition of plant growth from added rice straw. Organic acids (acetic and propionic) were produced in amounts considered to be below the toxic concentration of plants. Butyric acid was not found in the soil extracts.