Ecosystems Services and Management Program, International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, Laxenburg, A-2361, Austria.
Glob Chang Biol. 2014 Apr;20(4):1278-88. doi: 10.1111/gcb.12481. Epub 2014 Jan 28.
The impact of soil nutrient depletion on crop production has been known for decades, but robust assessments of the impact of increasingly unbalanced nitrogen (N) and phosphorus (P) application rates on crop production are lacking. Here, we use crop response functions based on 741 FAO maize crop trials and EPIC crop modeling across Africa to examine maize yield deficits resulting from unbalanced N : P applications under low, medium, and high input scenarios, for past (1975), current, and future N : P mass ratios of respectively, 1 : 0.29, 1 : 0.15, and 1 : 0.05. At low N inputs (10 kg ha(-1)), current yield deficits amount to 10% but will increase up to 27% under the assumed future N : P ratio, while at medium N inputs (50 kg N ha(-1)), future yield losses could amount to over 40%. The EPIC crop model was then used to simulate maize yields across Africa. The model results showed relative median future yield reductions at low N inputs of 40%, and 50% at medium and high inputs, albeit with large spatial variability. Dominant low-quality soils such as Ferralsols, which are strongly adsorbing P, and Arenosols with a low nutrient retention capacity, are associated with a strong yield decline, although Arenosols show very variable crop yield losses at low inputs. Optimal N : P ratios, i.e. those where the lowest amount of applied P produces the highest yield (given N input) where calculated with EPIC to be as low as 1 : 0.5. Finally, we estimated the additional P required given current N inputs, and given N inputs that would allow Africa to close yield gaps (ca. 70%). At current N inputs, P consumption would have to increase 2.3-fold to be optimal, and to increase 11.7-fold to close yield gaps. The P demand to overcome these yield deficits would provide a significant additional pressure on current global extraction of P resources.
几十年来，人们已经认识到土壤养分枯竭对作物产量的影响，但缺乏对日益不平衡的氮（N）和磷（P）施用量对作物产量影响的有力评估。在这里，我们使用基于粮农组织 741 个玉米试验和非洲各地 EPIC 作物模型的作物响应函数，研究了在低、中、高投入情景下，由于不平衡的 N：P 施用量导致的玉米产量亏缺，这些情景下过去（1975 年）、当前和未来的 N：P 质量比分别为 1：0.29、1：0.15 和 1：0.05。在低氮投入（10 公斤/公顷）下，当前的产量亏缺达到 10%，但在假设的未来 N：P 比下，这一比例将增加到 27%，而在中氮投入（50 公斤氮/公顷）下，未来的产量损失可能超过 40%。然后，我们使用 EPIC 作物模型模拟了非洲各地的玉米产量。模型结果显示，在低氮投入下，未来的相对中值产量减少 40%，在中氮和高氮投入下减少 50%，尽管存在很大的空间变异性。像 Ferralsols 这样强烈吸附 P 的低质量土壤和养分保持能力低的 Arenosols 等占主导地位的土壤，与产量的大幅下降有关，尽管 Arenosols 在低投入下的作物产量损失非常不稳定。用 EPIC 计算出的最低施用量 P 可产生最高产量（给定 N 投入）的最佳 N：P 比低至 1：0.5。最后，我们估计了在当前 N 投入下，以及在允许非洲缩小产量差距（约 70%）所需的 N 投入下，所需的额外 P。在当前 N 投入下，要达到最佳状态，P 的消耗必须增加 2.3 倍，要缩小产量差距，必须增加 11.7 倍。为弥补这些产量亏缺而对 P 的需求，将对当前全球 P 资源的开采造成重大额外压力。
