Corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production dominate Midwestern U.S. agriculture and impact the regional carbon and nitrogen cycles. Sustaining soil carbon is important for corn‐soybean production (CS); however, quantifying soil carbon changes requires long‐term field measurements and/or model simulations. In this study, changes in soil organic (SOC), inorganic (SIC), and total (TC) carbon; pH; total nitrogen (TN); and net ecosystem production (NEP) were measured in a conventional corn‐soybean rotation in central Iowa. Soil samples (n = 42; 0–120 cm depth) were collected from two adjacent fields in 2005 and 2016. Eddy‐flux stations set up in the fields continuously monitored NEP from 2005–2016, and net biome production (NBP) was calculated using yield records. The DayCENT model was used to simulate the effects of conventional management practices on soil carbon and calibrated with field‐measured NEP and SOC. Measured soil TC (0–120 cm) decreased by −14.19 ± 6.25 Mg ha⁻¹, with highest reductions in SOC and SIC (p < 0.05) at 0–15 and 90–120 cm, respectively. Measured TN decreased by −0.7 ± 0.29 Mg ha⁻¹ with N‐accumulation at 60–90 cm (p < 0.05). Eddy‐flux NBP decreased by −13.19 ± 0.05 Mg ha⁻¹. Soil and eddy‐flux records show a carbon reduction by −1.14 ± 0.63 and −1.20 ± 0.06 Mg ha⁻¹ yr⁻¹, respectively. The validated DayCENT model suggests that all SOC pools declined. We postulate that conventional CS production has adverse effects on C and N dynamics in Midwestern United States.

中文翻译：

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美国中西部玉米-大豆轮作的实测和模拟碳动力学

玉米（Zea mays L.）和大豆（Glycine max [L.] Merr。）的产量主导着美国中西部的农业，并影响了该地区的碳和氮循环。维持土壤碳对于玉米-大豆生产（CS）很重要；但是，量化土壤碳变化需要长期的现场测量和/或模型模拟。在这项研究中，土壤有机（SOC），无机（SIC）和总（TC）碳的变化；pH值 总氮（TN）; 在爱荷华州中部的常规玉米-大豆轮作中，对生态系统和净生态系统产量（NEP）进行了测量。土壤样品（n = 42; 在2005年和2016年从两个相邻的田间采集了0-120 cm的深度。2005-2016年在田间建立的涡流站连续监测NEP，并使用产量记录计算净生物群落产量（NBP）。DayCENT模型用于模拟常规管理措施对土壤碳的影响，并通过现场测量的NEP和SOC进行了校准。测得的土壤TC（0-120厘米）减少了-14.19±6.25 Mg ha ^-1，SOC和SIC的减少幅度最大（p  <0.05）分别在0-15和90-120 cm。在60–90 cm处，随着N的累积，测得的TN降低了−0.7±0.29 Mg ha ^-1（p  <0.05）。涡流NBP降低-13.19±0.05 Mg ha ^-1。土壤和涡流记录显示碳减少分别为-1.14±0.63和-1.20±0.06 Mg ha ^-1  yr ^-1。经过验证的DayCENT模型表明，所有SOC池均下降了。我们假设常规的CS生产会对美国中西部的C和N动态产生不利影响。