Soil carbon, aggregation and crop residue dynamics under different tillage and nitrogen fertilization strategies in rainfed Mediterranean conditions

n rainfed Mediterranean croplands, the interactive effects of fertilization and tillage types on soil aggregation and soil organic carbon (SOC) have been rarely studied. The objective of this study was to assess the interactive effects of tillage and nitrogen (N) fertilization strategies on different soil and crop properties in a long-term rainfed experiment established in semiarid NE Spain in 2010. During two cropping seasons (2020–2021 and 2021–2022) the following variables were assessed: SOC, particulate organic matter C (POM-C) and mineral-associated organic matter C (Min-C) contents in the 0–5, 5–10 and 10–30 cm depths; soil aggregate stability in the topsoil (0–5 cm); crop yield; and crop residue dynamics (crop residue biomass and the percent residue cover). Two tillage treatments were compared: conventional tillage (CT) and no-tillage (NT), and five N fertilization strategies: unfertilized, medium and high N rates of mineral fertilizer, and medium and high N rates of organic fertilizer. In both cropping seasons, the crop yield, crop residue biomass and percent residue cover were greater in NT compared with CT (2148 and 1319 kg ha −1 crop residue biomass and 72.0 and 49.7 % residue cover for NT and CT, respectively). Regarding N fertilization, crop yields tended to be greater in the organic fertilizer than in the mineral fertilization treatments (1600 vs 1168 kg ha−1, respectively). Differences between N fertilization treatments were more marked in the residue biomass parameter than in the percent residue cover. The SOC, POM-C and Min-C contents decreased in the next order across soil depths: 0–5 > 5–10 > 10–30. The greatest soil C values were observed in the treatments with the greatest N rate of organic fertilizer. The soil aggregate stability in the topsoil (0–5 cm) increased under NT and the application of organic fertilizers. This study has demonstrated that in rainfed semiarid conditions, long-term NT adoption and the use of organic fertilizers are promising strategies for enhancing SOC buildup and the formation of stable aggregates in the topsoil.

The authors would like to thank Carlos Cort\u00E9s, Silvia Mart\u00ED, Victoria Lafuente and Ana Bielsa for laboratory and field assistance This research was supported by the European Union, PRIMA program, Grant Agreement n. 1912; research project \u201CResearch-based participatory approaches for adopting Conservation Agriculture in the Mediterranean Area \u2013 CAMA\u201D and partially by the Spanish State Agency for Research (AEI) (Grant PID2021\u2013126343OB-C31).