The aim of this study was to evaluate the impact of 21 years of tillage and N fertilization and the conversion from a rainfed to an irrigated cropping system on soil organic C (SOC). The study was carried out in northeastern Spain in a long‐term tillage and N rate field experiment established in 1996 under barley rainfed conditions, which in 2015 was converted into irrigation with corn. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no‐tillage, NT) and three mineral N fertilization rates (0, 60, and 120 kg N ha⁻¹ under barley, and 0, 200, and 400 kg N ha⁻¹ under corn) were compared. Annual C‐inputs as aboveground crop residues and annual SOC sequestration rate (∆SOC_rate) (0–40 cm depth) were calculated in three different periods (P1, P2 and P3) under rainfed (‐R) and irrigated (‐I) conditions (P1‐R, from 1996 to 2009; P2‐R, from 2009 to 2015; P3‐I, from 2015 to 2017). At the end of P3‐I, particulate organic C (POC) was measured from the 0–5, 5–10, 10–20, 20–30, and 30–40 cm depths. Averaged over all treatments, ∆SOC_rate was 492, 222, and 969 kg C ha⁻¹ yr⁻¹ for P1‐R, P2‐R, and P3‐I, respectively. In P1‐R and P3‐I, C‐input explained 70% of the variability of ∆SOC_rate. In P1‐R, ∆SOC_rate followed the order NT > RT > CT, while for N rate, order was high > medium > 0. In P3‐I at the highest N rate, ∆SOC_rate followed the order NT > RT > CT. In P2‐R, ∆SOC_rate did not show differences between tillage and/or N rate treatments. The increase in SOC after conversion from a rainfed to an irrigation system was mainly explained by POC, which was increased by 75% compared to the previous rainfed period. The modification of the cropping system through the introduction of irrigation and adequate crop management practices under no‐tillage and adjusted N fertilizer rates can contribute to the sequestration of large amounts of atmospheric CO₂.

中文翻译：

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在不同耕作制度和不同氮肥用量下，将雨养作物系统转换为灌溉玉米时的土壤有机碳固存

这项研究的目的是评估21年耕作和氮肥的施肥以及雨养向灌溉耕作系统对土壤有机碳（SOC）的影响。该研究是在西班牙东北部进行的一项长期耕作和氮肥田间试验，该试验于1996年在大麦降雨条件下进行，并于2015年转化为玉米灌溉。三种耕作类型（常规耕作，CT；减少耕作，RT；免耕，NT）和三种矿质氮的施肥率（大麦下分别为0、60和120 kg N ha ^-1，分别为0、200和400 kg比较玉米下的N ha ^-1）。年度C投入为地上作物残留量和年度SOC固存率（∆SOC_率）（0–40 cm深度）在雨养（‐R）和灌溉（‐I）条件下（P1-R，从1996年至2009年; P2-R，从2009年开始）在三个不同的时期（P1，P2和P3）中计算到2015年； P3-I，从2015年到2017年）。在P3-1的末尾，从0-5、5-10、10-20、20-30和30-40厘米深度测量了颗粒有机碳（POC）。平均超过所有处理，ΔSOC_率是492，222，969千克碳公顷^-1年^-1为P1-R，P2-R，和P3-I，分别。在P1-R和P3-I中，C输入解释了∆SOC_速率变化的70％。在P1-R中，∆SOC_速率遵循NT> RT> CT的顺序，而在N速率中，SOC顺序高>中>0。在P3–I中，N速率最高的∆SOC_速率遵循NT> RT>阶。 CT。在P2-R中，∆SOC_率并没有表现出耕作和/或N量处理之间的差异。从雨养转变为灌溉系统后，SOC的增加主要由POC解释，与前一雨育期相比，增加了75％。在免耕和调整氮肥用量的情况下，通过引入灌溉和适当的作物管理措施来改变种植系统，可以促进隔离大量的大气CO ₂。