Evaluation of the method for determining organic fertilizer efficiency by indirect labelling of 15N

By using the A-value method, direct method and differential method respectively, the absorption and utilization of organic fertilizer-N by rice were studied. The results are as follows. The utilization efficiency of organic fertilizer-N was 25.48%∼50.5% by the differential method, 19.70%∼27.17% by the A-value method, and 18.49%∼24.80% by the direct method. The data by the differential method was higher than those by the other two methods, and there was no significant difference between the direct method and the A-value method. Meanwhile, when the ratio of inorganic fertilizer-N to organic fertilizer-N was 1:0.48, the results from above two methods were similar. The nitrogen efficiency of 1,5 x 104 kg fresh Astragalus sinicus L. was equivalent to 53.43 kg urea for early rice, and 39.15 kg urea for late rice