One of the expected benefits of no-tillage systems is a higher rate of soil C sequestration. However, higher C retention in soil is not always apparent when notillage is applied, due e.g., to substantial differences in soil type and initial C content.
The main purpose of this study was to evaluate the potential of no-tillage management to increase the stock of total organic C in soils of the Pampas region in Argentina. Forty crop fields under no-tillage and conventional tillage systems and seven undisturbed soils were sampled. Total organic C, total N, their fractions and stratification ratios and the C storage capacity of the soils under different managements were assessed in samples to a depth of 30 cm, in three layers (0?5, 5? 15 and 15?30 cm). The differences between the C pools of the undisturbed and cultivated soils were significant (p < 0.05) and most pronounced in the top (0? 5 cm) soil layer, with more active C near the soil surface (undisturbed > no-tillage > conventional tillage). Based on the stratification ratio of the labile C pool(0?5/5? 15 cm), the untilled were separated from conventionally tilled areas. Much of the variation in potentially mineralizable C was explained by this active C fraction (R2 = 0.61) and by total organic C (R2 = 0.67). No-till soils did not accumulate more organic C than conventionally tilled soils in the 0?30 cm layer, but there was substantial stratification of total and active C pools at no till sites. If the C stratification ratio is really an indicator of soil quality, then the C storage potential of no-tillage would be greater than in conventional tillage, at least in the surface
layers. Particulate organic C and potentially mineralizable C may be useful to evaluate variations in topsoil organic matter.
