Abstract
A four-year study was conducted to investigate the dry matter yield and nitrogen budget of ratoon-cropped forage rice on farm fields receiving 300kg/a manure, under various combinations of planting densities (18-80 plants/m^2) and chemical fertilizer rates (conventional=1.7 kg N/a, 1.1 or 1.3 kg P_2O_5/a, 1.1 or 1.3kg K_2O/a ; high =2.6 kg N/a, 1.3kg P_2O_5/a, 1.3kg K_2O/a). Rice plants were transplanted using a conventional rice planter (18-27 plants/m^2), a zigzag planter (40 plants/m^2) or a zigzag planter plus manual planting (80 plants/m^2). The annual dry matter yield over two harvests was the highest at a density of 40 plants/m^2, and increased as the chemical fertilizer rate increased, exceeding 200kg/ a when climatic conditions during the cultivation period favored plant growth. This high yield (200kg/a) was achieved by allowing plants to absorb more than 2.4kg N/a, which required application of chemical fertilizer N equivalent to more than 2.9 times that used in conventional cultivation for grain rice, in addition to 300kg/a manure.
