Abstract
Application of Italian ryegrass (top) to the paddy field remarkably inhibited the growth and nitrogen absorption of rice plants from the transplanting to the rooting stage. The degree of the inhibition was closely correlated to the intensification or rapid reduction of soil due to decomposition of the Italian ryegrass but not to the amount of applied nitrogen fertilizer. From the rooting to the active tillering stage, the rice growth and nitrogen absorption were also inhibited. However, during this period, no correlation was found between the degree of inhibition and the intensification of soil reduction or the amount of nitrogen fertilizer applied. From the active tillering to the maximum tiller number stage, tendency towards restricted nitrogen absorption was no longer observed. However, the number of tillers at the maximum tiller number stage was decreased due to the effect of earlier inhibition. A high nitrogen content in rice plants was maintained after the panicle formation stage, and this induced a reduction in the number of non-productive tillers. But the number of grains, percentage of ripened grains and 1000-grain weight increased.
