Comparison of organic fertilizer nitrogen use efficiency calculated by several typical methods

Objectives Many methods are used for the calculation of nitrogen efficiency. The precision and stability of the results may impact the outcome of nitrogen nutrient management. We compared and discussed the precision and availability of the mostly used calculation methods from the subtraction and meaning of the parameters in the formula.

Methods The study was based on 2 years of long-term experiment under winter wheat-summer maize cropping system, in which the organic fertilizer nitrogen treatments were composed of N 0, 120, 240, 360, 600 kg/hm². Subtraction method, accumulation method, ratio method, nitrogen balance method and the international general nitrogen use efficiency (NUE) method were used to calculate the nitrogen utilization efficiencies of organic fertilizer. The variation of the results of the five methods with fertilizer application years and rates were compared.

Results The value calculated by subtraction method and accumulation method was relatively low, because the crops in blank control might be able to absorb nitrogen from the fertilization treatment through latent diffusion. The value had no significant difference between subtraction method and accumulation method. The results calculated by the ratio method and the international general nitrogen use efficiency method were very close. If the latent diffusion of N to blank control could be prevented, the results would be closer. The nitrogen balance method considered the effect of fertilization on soil nitrogen pool, so the value calculated by NUE method should be the closest to the actual value. Balance mehod was better than the international general NUE method, and NUE method was better than ratio method.

Conclusions The variation of soil nitrogen pool influences the accuracy of ratio method. In the long-term experiment, the soil nitrogen pool is relatively stable, so the efficiency of organic nitrogen fertilizer calculated by the ratio method, the nitrogen utilization rate method and the nitrogen balance method are close with each other. Under condition of gradual increase or decrease of nitrogen pool in the long-term fertilization, the nitrogen use efficiency calculated by the nitrogen balance method is the most reasonable.