Effect of percolation rate on nutrient kinetics and rice yield in tropical rice soils

Abstract

The effect of different percolation rates (0, 15, and 30 mm d−1) and rice straw additions (0, 5, 10, and 20 t ha−1) on the production of organic acids, pH, leaching losses of nutrients, nutrient uptake, and growth and grain yield of rice (Oryza sativa L., var. IR36) were studied in a greenhouse where soil temperature ranged from 21.8 to 30.8°C. Total water soluble organic acids increased with increasing amounts of rice straw, but acid production decreased with percolation. Highest acid concentration (364×10−2 mmol liter−1) was obtained with an addition of 20t rice straw ha−1 and a percolation rate of 15 mm d−1. However, organic acid phytotoxicity was absent in all cases and yield was the same between all treatments. The pH of the soil solution decreased significantly with the addition of rice straw. Different rates of rice straw addition and percolation did not affect soil pH. Leaching losses of NH 4 + −N, Mn, and Fe increased significantly with increasing rice straw and percolation rate. As high as 39 kg NH 4 + −N, 111 kg Mn, and 110 kg Fe ha−1 were lost through leaching in one cropping season. The uptake of NPK by rice was affected more by rice straw addition than by percolation rate. Highest rice grain N and P, and NPK in rice straw were obtained with rice straw addition of 20 t ha−1. Nevertheless, plant growth, grain and straw yield remained unaffected by treatment. In a field trial, rice yield and root length density also remained unaffected by rice straw addition (6 t ha−1) and by percolation rates of 9 and 123 mm d−1.