Can no-till grain production restore soil organic carbon to levels natural grass in a subtropical Oxisol?

The conversion of native vegetation (NV) to agricultural systems, especially with intensive tillage and low carbon (C) input, decreases soil organic carbon (SOC) stocks. However the adoption of conservation agriculture (CA) may partially restore SOC stocks. However, the magnitude of this restoration is dependent on the cropping system, quality and quantity of C input, soil, and climate. In this study, we assessed the redistribution and recovery of SOC stocks in six no-till (NT) fields (> 20 years) in the small grain production area of southern Brazil. The adoption of NT in the fields investigated started between 1978 and 1990 and represent a range of textural and mineralogical characteristics. Soil samples were collected in paired fields (NV vs. long-term NT) to a depth of 1 m. The pioneer NT areas of Rio Grande do Sul State investigated in this study were managed according to the principles of CA (minimum soil disturbance, permanent soil cover and diverse crop rotation). The sites had recovered to 92-100% of the original SOC stocks. The sites which represented medium cropping intensity recovered 79.5 and 85.4%, of NV SOC stocks. The sites representative of high cropping intensity had recovered 84.9-116.5% of NV SOC stocks. The lowest recovery of SOC stock (60.6%) had higher frequency of soybean (Glycine max L. Merril) in the crop rotation. Therefore, NT following the principles of CA was an efficient system to restore SOC stock lost due to land-use change, performing a crucial role in the system productivity and soil quality.