Poffenbarger Hanna J, Barker Daniel W, Helmers Matthew J, Miguez Fernando E, Olk Daniel C, Sawyer John E, Six Johan, Castellano Michael J
Department of Agronomy, Iowa State University, Ames, Iowa, United States of America.
Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa, United States of America.
PLoS One. 2017 Mar 1;12(3):e0172293. doi: 10.1371/journal.pone.0172293. eCollection 2017.
Nitrogen fertilization is critical to optimize short-term crop yield, but its long-term effect on soil organic C (SOC) is uncertain. Here, we clarify the impact of N fertilization on SOC in typical maize-based (Zea mays L.) Midwest U.S. cropping systems by accounting for site-to-site variability in maize yield response to N fertilization. Within continuous maize and maize-soybean [Glycine max (L.) Merr.] systems at four Iowa locations, we evaluated changes in surface SOC over 14 to 16 years across a range of N fertilizer rates empirically determined to be insufficient, optimum, or excessive for maximum maize yield. Soil organic C balances were negative where no N was applied but neutral (maize-soybean) or positive (continuous maize) at the agronomic optimum N rate (AONR). For continuous maize, the rate of SOC storage increased with increasing N rate, reaching a maximum at the AONR and decreasing above the AONR. Greater SOC storage in the optimally fertilized continuous maize system than in the optimally fertilized maize-soybean system was attributed to greater crop residue production and greater SOC storage efficiency in the continuous maize system. Mean annual crop residue production at the AONR was 22% greater in the continuous maize system than in the maize-soybean system and the rate of SOC storage per unit residue C input was 58% greater in the monocrop system. Our results demonstrate that agronomic optimum N fertilization is critical to maintain or increase SOC of Midwest U.S. cropland.
氮肥施用对于优化短期作物产量至关重要，但其对土壤有机碳（SOC）的长期影响尚不确定。在此，我们通过考虑美国中西部典型玉米种植系统（玉米品种为Zea mays L.）中玉米产量对氮肥施用的地点间差异，来阐明氮肥施用对SOC的影响。在爱荷华州四个地点的连续玉米种植系统和玉米 - 大豆[Glycine max (L.) Merr.]种植系统中，我们评估了在14至16年期间，一系列经实验确定为对最大玉米产量而言不足、最佳或过量的氮肥施用量下，表层SOC的变化情况。在不施氮肥的情况下，土壤有机碳平衡为负，但在农艺最佳施氮量（AONR）时，玉米 - 大豆系统的土壤有机碳平衡为中性，连续玉米系统的土壤有机碳平衡为正。对于连续玉米种植系统，SOC储存速率随氮肥施用量增加而增加，在AONR时达到最大值，高于AONR时则下降。与最佳施肥的玉米 - 大豆系统相比，最佳施肥的连续玉米系统中SOC储存量更大，这归因于连续玉米系统中作物残茬产量更高以及SOC储存效率更高。在AONR时，连续玉米系统的年均作物残茬产量比玉米 - 大豆系统高22%，单作系统中单位残茬碳输入的SOC储存速率比间作系统高58%。我们的研究结果表明，农艺最佳氮肥施用对于维持或增加美国中西部农田的SOC至关重要。
