Managing croplands for increased storage of soil organic matter (SOM) contributes to the development of resilient farming systems in a changing climate. We examined SOM dynamics in a wheat (Triticum durum L.) – maize (Zea mays L.) irrigated bed planting system established near Ciudad Obregón, Sonora, Mexico. Soil samples (0–15 cm) were collected from conventionally tilled raised beds (CTB) with all crop residues incorporated (CTB-I) and permanent raised beds (PB) with crop residues burned (PB-B), removed (PB-R), partly retained (PB-P) or fully retained (PB-K) receiving 0, 150 or 300 kg N ha⁻¹, and analyzed for organic C (OC), total N (TN) and δ¹³C in whole-soil, light fraction (LF) and coarse- (sand) and fine- (silt and clay) mineral-associated organic matter (MAOM). Results indicated that PB-K and PB-B increased soil OC (p <0.05) in whole-soil relative to CTB-I, mainly through increases in sand- and silt-size MAOM, respectively. Similarly, N-fertilization increased soil OC and TN contents in whole-soil, coarse-MAOM and fine-MAOM, but not in the LF pool. Soil δ¹³C was higher (p <0.05) in PB-K (−20.18‰) relative to PB-B (−20.67‰), possibly due to the stabilization of partly decomposed maize-C in silt- and clay-size MAOM. Composition of SOM surveyed by CPMAS ¹³C NMR was not affected by tillage-residue management, and roughly consisted of 35% O-alkyl-C, 31% alkyl-C, 24% aromatic-C and 10% carboxyl-C. Our results indicate that long-term PB-K and PB-B adoption increased surface soil OC contents relative to CTB-I, even though pathways of SOM stabilization differed between systems. Under PB-K, accumulation of fine-MAOM was mostly related to straw-C inputs, whereas in PB-B it was closely associated to black-C precursors. Fine-MAOM appeared responsive to crop residue management, and should be therefore considered when analyzing mechanisms of SOM stabilization in irrigated croplands.

管理农田以增加土壤有机质 (SOM) 的储存量有助于在不断变化的气候中发展有弹性的耕作系统。我们研究了在墨西哥索诺拉州奥雷贡城附近建立的小麦 ( Triticum durum L.) - 玉米 ( Zea mays L.) 灌溉床种植系统中的SOM 动态。土壤样品（0-15 厘米）是从常规耕作的高架床（CTB）收集的，所有作物残留物都包括在内（CTB-I）和永久性高架床（PB）和燃烧的作物残留物（PB-B），移除（PB-R） )、部分保留 (PB-P) 或完全保留 (PB-K) 接受 0、150 或 300 kg N ha ^-1，并分析有机 C (OC)、总 N (TN) 和 δ ¹³全土、轻质部分 (LF) 和粗（砂）和细（粉砂和粘土）矿物相关有机质 (MAOM) 中的 C。结果表明， 与 CTB-I 相比，PB-K 和 PB-B 增加了整个土壤中的土壤有机碳（p <0.05），主要是分别通过增加沙粒和粉粒大小的 MAOM。同样，施氮增加了全土、粗 MAOM 和细 MAOM 中土壤 OC 和 TN 含量，但在 LF 池中没有。土壤 δ ¹³ C 在 PB-K (-20.18‰) 中比 PB-B (-20.67‰)更高 ( p <0.05)，这可能是由于粉砂和粘土尺寸的 MAOM 中部分分解的玉米-C 的稳定性. CPMAS ¹³调查的 SOM 组成C NMR 不受耕作残留管理的影响，大致由 35% 的 O-烷基-C、31% 的烷基-C、24% 的芳族-C 和 10% 的羧基-C 组成。我们的结果表明，相对于 CTB-I，长期采用 PB-K 和 PB-B 增加了表层土壤 OC 含量，即使系统之间 SOM 稳定的途径不同。在PB-K下，细MAOM的积累主要与秸秆-C输入有关，而在PB-B中，它与黑C前体密切相关。Fine-MAOM 似乎对作物残留物管理有反应，因此在分析灌溉农田中 SOM 的稳定机制时应予以考虑。