Green Manuring Effect on Yield of Cassava-Sweet Corn Sequential Cropping on Degraded Sandy Soil, Northeast Thailand

Abstract

The green manuring effect on cassava-sweet corn sequential cropping was evaluated in a sandy Typic Plinthustult soil in Thailand. The highest fresh biomass was observed for ruzi grass (18.53 t.ha-1) followed by local weeds (14.08 t.ha-1), sword bean (12.69 t.ha-1) and sun hemp (12.39 t.ha-1). Sword bean tended to contain the highest nitrogen content (2.28%) while ruzi grass had the greatest potassium content (2.32%). The control (local weeds) had the highest phosphorus content (0.15%) but released more nitrogen than did the others with 148.65 mg.kg-1 followed by sword bean, sun hemp and ruzi grass (133.83, 92.77 and 59.5 mg.kg-1, respectively). The release of nitrogen was greatest at 2 wk after the incorporation of these green manures and the amount continuously reduced, while the release from local weeds ended before the others. Sun hemp was found the most suitable green manure in cassava-sweet corn sequential cropping on this soil and gave the highest tuber yield (27.19 t.ha-1) and fresh-peeled sweet corn (4.19 t.ha-1) but it gave the lowest starch content (30.13%) of cassava tuber. The incorporation of sword bean gave the lowest cassava yield (13.56 t.ha-1) whereas the lowest amount of sweet corn yield (2 t.ha-1) was obtained from the incorporation of ruzi grass. The three green manure plants showed almost no effect on soil properties due to the soil still having low residual plant nutrients and weak soil structure but ruzi grass tended to improve the soil physical properties more than did sun hemp and sword bean.