Soil organic matter dynamics after 27 years of different tillage-residue management in northern Mexico

We examined soil organic matter (OM) dynamics in a wheat (Triticum durum L.) – maize (Zea mays L.) irrigated bed planting system established in 1992 at the Campo Experimental Norman E. Borlaug (CENEB) near Ciudad Obregón, Sonora, Mexico (27°33’N, 109°09’W; elevation 38 m). The location has an arid subtropical climate with a mean annual temperature of 23.7 °C and average precipitation of 311 mm. Treatments included conventionally tilled raised beds (CTB) with residue incorporated (CTB-I) and permanent raised beds (PB) with residue burned (PB-B), removed (PB-R), partly retained (PB-P) or fully retained (PB-K) receiving 0, 150, or 300 kg N/ha. We sampled surface soil (0-15 cm) in 2019 and compared soil organic C (OC), total N (TN), and δ13C distribution in the whole-soil as well as within light- (LF) and mineral-associated OM (MAOM) fractions. Additionally, solid-state 13C NMR spectroscopy was used to characterize whole-soil OM composition.