Soil use intensity impact on total and particulate soil organic matter in no-till crop-pasture rotations under direct grazing

Soil organic carbon (SOC) is important for animal production systems sustainability under grazing. We evaluated. soil use intensity effects on SOC and particulate organic carbon (C-POM; 53-2000 mu m) in a 72 ha no-till crop-pasture rotation experiment in Uruguay (Typic Argiudols). Treatments included: 1) continuous cropping (CC) of Lolium multiflorum Lam. or Avena sp. in winter and Sorghum bicolor L. or Setaria italica in summer; 2) short rotation (SR): two years idem CC and two years pasture of Trifolium pretense L. and Lolium multiflorum; 3) long rotation (LR): two years idem CC and four years pasture of Dactylis glomerata L., Trifolium repens L. and Lotus corniculatus L.; 4) permanent pasture (PP): natural pasture overseeded with legumes used in LR. All rotation phases were present each year. After 8 years, LR increased SOC (0-15 cm depth) by 19% compared to CC (31.8 Mg ha(-1)); no SOC differences were found between LR, SR and PP. Plots containing pastures had 14% greater SOC than plots containing crops (33.7 Mg ha(-1)). Crops rotated with pastures (LR, SR) had 5% greater SOC than crops in CC (31.8 Mg ha(-1)). There were no differences on SOC between pastures in LR and PP, but 3-4 years pastures had 33% greater SOC than 1-2 years pastures (34.4 Mg ha-1). The lowest and greatest C-POM was found in CC and in 3-4 years pastures of LR (8.2 and 12.6 Mg C ha(-1), respectively). No till crop-pasture rotation systems including long-term pastures preserved SOC, even in high biomass extractive grazing systems.