Long-term tillage systems impacts on soil C dynamics, soil resilience and agronomic productivity of a Brazilian Oxisol

Abstract

No-till (NT) cropping systems have been widely promoted in many regions as an important tool to enhance soil quality and improve agronomic productivity. However, knowledge of their long-term effects on soil organic carbon (SOC) stocks and functional SOC fractions linking soil resilience capacity and crop yield is still limited. The aims of this study were to: (i) assess the long-term (16 years) effects of tillage systems (i.e., conventional - CT, minimum - MT, no-till with chisel - NTch, and continuous no-till cropping systems - CNT) on SOC in bulk soil and functional C fractions isolated by chemical (hot water extractable organic C - HWEOC, permanganate oxidizable C - POXC) and physical methods (light organic C - LOC, particulate organic C - POC, mineral-associated organic C - MAOC) of a subtropical Oxisol to 40cm depth; (ii) evaluate the soil resilience restoration effectiveness of tillage systems, and (iii) assess the relationship between the SOC stock enhancement and crop yield. The crop rotation comprised a 3-year cropping sequence involving two crops per year with soybean (Glycine max, L. Merril) and maize (Zea mays L.) in the summer alternating with winter crops. In 2005, the soil under CNT contained 25.8, 20.9, and 5.3Mgha-1 more SOC (P<0.006) than those under CT, MT, and NTch in 0-40cm layer, representing recovery rates of 1.61, 1.31, and 0.33Mg Cha-1yr-1, respectively. The relative C conversion ratio of 0.398 at CNT was more efficient in converting biomass-C input into sequestered soil C than NTch (0.349), MT (0.136), and CT (0.069). The soil under CNT in 0-10cm depth contained ~1.9 times more HWEOC and POXC than those under CT (P<0.05), and concentrations of LOC and POC physical fractions of SOC were significantly higher throughout the year under CNT. Considering CT as the disturbance baseline, the resilience index (RI) increased in the order of MT (0.10)