Roots are the key for soil C restoration: A comparison of land management in the semiarid Argentinean Pampa

FRASIER, ILEANA; BARBERO, FLORENCIA MAGALI; PÉREZ-BRANDAN, CAROLINA; GÓMEZ, MARÍA FLORENCIA; FERNÁNDEZ, ROMINA; QUIROGA, ALBERTO RAUL; POSSE-BEAULIEU, GABRIELA; RESTOVICH, SILVINA; MERILES, JOSÉ; SERRI, DANNAE LILIA; FIGUEROLA, EVA LUCIA MARGARITA; NOELLEMEYER, ELKE; VARGAS-GIL, SILVINA

SOIL & TILLAGE RESEARCH

ELSEVIER SCIENCE BV

Año: 2024 vol. 235

0167-1987

The objective of the study was to elucidate the relationship between soil management and carbon (C) stocks, andto identify the factors that intervene in the processes that favor C sequestration. The study was carried out on afarm in the Argentinean semiarid pampas with four land management practices (2019–2021): natural grassland(NG), crop-pasture rotation (RO), soybean monoculture (S-S) and with cover crop (S-CC). Aerial and rootbiomass were quantified at cover crop termination and soybean flowering. In addition, residues on soil surfacewere determined two times a year. In all cases, C and N contents were quantified. On composite soil samples, soilorganic C (SOC), particulate C (POC), microbial biomass C and N (MBC, MBN), and soluble C and N weredetermined at 0–0.1 m depth. Results showed that NG had the highest and the most stable aboveground (3807.1kg residue-C ha-1) and belowground inputs between years (4965.8 kg root-C ha-1). Similar results were observedin RO treatment during the first year (4221.0 kg root-C ha-1) diminishing by 67% after plowing for the annualcrop in the second year reaching similar root-C values than S-CC and S-S (721.7 kg ha-1). S-S presented the lowestaboveground (49%) and belowground inputs (77%) compared to NG. Cover crops (S-CC) contributed with 31%and 14% of extra residue-C and root-C, respectively, compared to S-S. MBC showed a non-linear response withincreases in root-C, reaching maximum carrying capacity of 110.6 ± 4.3 kg MBC ha-1 with root-C inputs ≥ 2200kg ha-1. Our results showed significant relationships between root-C and POC and SOC, while no relationshipswere found for aboveground residues. Increases in soluble N explained 86% of SOC variability. Both RO and S-CCreached the “4 per Mille” goal with an average annual SOC storage rate (ΔC) of 0.24 and 0.16 Mg ha-1 y-1,respectively, while S-S had SOC losses of 0.04 Mg ha-1yr-1.