Use efficiency and residual effect of 15N-labelled ryegrass green manure over a 9-year field micro-plot experiment

A 9-year field micro-plot experiment was conducted to investigate the use efficiency, residual effect, and fate of 15 N-labelled ryegrass green manure in soil-crop system, so as to offer useful information for reasonable application of green manures on meadow burozem. Results showed that high application rate (600g per plot) of 15 N-labelled ryegrass green manure resulted in reduction of percent recovery (PR) 15 N plant and PR 15 N soil by 25.0% and 12.8%, respectively, and elevation of percent loss (PL) 15 N by 31.2%, as compared with low application rate. The 15 N utilization and loss could be divided into three phases, i.e., high uptake and fast loss in the first and second growth seasons, low uptake and slow loss in the following four growth seasons, and little change in the last three growth seasons. This suggested that the green manure N had a long residual effect but its loss was faster at early phase, and thus, rational application of green manure was of considerable importance to reduce its N loss while improve its N use efficiency.