Rethinking discrepancies between difference and 15 N methods for estimating fertilizer nitrogen recovery

• Published in: Biology and fertility of soils 2022-11, Vol.58 (8), p.855-869
• Main Authors: Sun, Zhaoan, Zhu, Biao
• Format: Article
• Language: English
• Subjects: Agriculture; Biological fertilization; Biomedical and Life Sciences; Cereal crops; Corn; Crops; Fertilization; Fertilizer application; Fertilizers; Life Sciences; Methods; Nitrogen; Original Paper; Priming; Recovery; Rhizosphere; Rice; Soil; Soil Science & Conservation; Soils; Tracers; Uptake; Wheat
• ISSN: 0178-2762; 1432-0789
• DOI: 10.1007/s00374-022-01672-7

Because of the effect of nitrogen (N) fertilization on soil-derived N uptake, N difference (FNR Diff ) and 15  N tracer (FNR 15N ) methods may give significantly different estimates of the fertilizer N recovery (FNR) in crops. To better understand quantitative differences in FNR (∆FNR) between the two methods, we evaluated the effect of fertilizer N input rates on ∆FNR and soil-derived N uptake by considering data from field 15  N tracer experiments of cereal crops across China, including N-unfertilized treatments. The FNR Diff was significantly higher than the corresponding FNR 15N in wheat (38% vs. 36%), maize (38% vs. 31%), and rice (40% vs. 31%) under fertilizer applications of 40–500 kg N ha −1 . Except in wheat at 250–500 kg N ha −1 , FNR Diff was higher than FNR 15N at various N input rates in the three crops, and ∆FNR decreased with increasing rates of applied N. The ∆FNR apparently occurred because added-N interaction (ANI) increased soil-derived N uptake (by 5% for wheat, 11% for maize, and 24% for rice). For wheat in particular, ANI values decreased significantly as N input rates increased, with a switch from positive to negative above 252 kg N ha −1 . This result suggests that the decrease in soil-derived N uptake is mainly caused by the negative rhizosphere N priming and the law of diminishing returns (current-season non-fertilizer N input or previous-season residual fertilizer N) under high N input, but not by the N pool substitution. Finally, we propose a new method for accurately distinguishing direct and indirect pathway contributions to ∆FNR. This study helps to improve understanding of the underlying mechanisms of discrepancies between the N difference method and the 15  N tracer method for estimating the fertilizer N recovery in crops.