Evaluation of the rationality of nitrogen use efficiency approaches based on long-term fate of nitrogen fertilizer tracing experiments
Nitrogen use efficiency(NUE)is a key indicator for evaluating the crop uptake of nitrogen(N)fertilizer applied to cropland.The principal approaches for quantifying NUE include N difference and 15 N tracer.However,these approaches significantly underestimated the actual efficiency of N fertilizer,as these approaches failed to consider the residual and legacy effects of N fertilizer in soil.Therefore,researchers all over the world have been investigating the more actual NUE.The NUE calculated by improvement methods is analogous to the actual NUE,but higher than the N difference or the 15 N tracer approaches.This can be attributed to the differing forms in which various improvement methods incorporate the legacy effects of N fertilizer,thereby compensating for the underestimation of NUE using the N difference or the 15 N tracer approaches in short-term experiments.In this review,the actual NUE is defined as the percentage of N fertilizer uptake by the crop aboveground to the amount of N fertilizer inputs,while completely consuming the residual N fertilizer in soil.The accumulative N recovery efficiency is 61.3%-65.3%of a 28-year upland cropping system in France,and 38.6%-43.0%of a 17-year paddy-upland rotation system in the Taihu Lake region of China.We obtained the data from the two long-term field experiments using the Digitizer tool of Origin 2021,including the crop 15 N uptake and the residual 15 N in soil.The NUE was calculated based on the N residual in the topsoil(0-20 cm),1 m,and 2 m soil,respectively.We analyzed and evaluated the rationality of the computed results of the soil N balance and N fertilizer efficiency approaches by comparing them to the actual NUE.The soil N balance and N fertilizer efficiency approaches significantly overestimated NUE when calculated by two meters of residual N in the soil.The surface(0-20 cm)soil residual N was found as a calculation parameter for estimating the actual NUE in these two approaches(61%-74%).However,the N fertilizer efficiency(41%-52%)was the only approach that accurately estimated the actual NUE in the Taihu Lake region of China.Therefore,the comparison of NUE across plots or crop systems should be based on a consistently chosen quantification approach to avoid inherent biases introduced by different approaches.In general,the N fertilizer efficiency approach(both crop absorption and soil residual nitrogen are considered to be utilized)achieves near the actual NUE in short-term experiments,demonstrating extensive application value.
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