Plant Growth and Fate of Nitrogen in Mixed Cropping, Intercropping and Crop Rotation : VI. Nitrogen uptake in rice plants from the applied Italian ryegrass, fertilizer and soil

Abstract

The process of nitrogen uptake in rice plants from applied Italian ryegrass (top), fertilizer, and soil was investigated using ¹⁵N as a tracer in a paddy field. At the rooting stage, rice plants absorbed an extremely small amount of nitrogen, and the recovery rate of nitrogen from the fertilizer was below 1%. The fertilizer-nitrogen had a very minor effect on the growth of rice plants at this stage. Due to decomposition of the Italian ryegrass, fertilizer-nitrogen was preferentially consumed after the rooting stage, therefore the ratio of the absorption of fertilizer-nitrogen to that of total nitrogen by rice plants was reduced. It was found that nitrogen from the decomposed Italian ryegrass was simultaneously absorbed by rice plants from this early stage. At the most active tillering atage, the applied Italian ryegrass maximized the inhibitory effect on fertilizer-nitrogen absorption. But the contribution ratio of nitrogen originated from the Italian ryegrass increased to the maximum amount at this stage. The nitrogen content in rice plants after heading was maintained at a high level by the combination of the late-effect of soil- and fertilizer-nitrogen and the additive effect of nitrogen from the decomposed Italian ryegrass. The maintenance of nitrogen content at a high level remarkably contributed to the active growth of rice plants at the ripening stage.