Soil C and N stocks as affected by cropping systems and nitrogen fertilisation in a southern Brazil Acrisol managed under no-tillage for 17 years

9 pages, 2 figures, 2 tables.Soil organic matter is an ecosystem component with agronomic and environmental functions and is affected by soil management. The objectives of this study were to evaluate (i) soil organic C and N losses during a period of conventional cultivation (1969–1983) that followed on native grassland and (ii) the potential of four long-term (17 years) no-till cereal- and legume-based cropping systems (bare soil, oat (Avena strigosa Schreb.)/maize (Zea mays L.), lablab (Lablab purpureum L. Sweet) + maize and pigeon pea (Cajanus cajan L. Millsp.)+maize) with different N fertilisation levels (0 and 180 kg N ha−1 year−1) to increase the C and N stocks of a southern Brazilian Acrisol. Samples were taken from 0 to 107.5 cm depth, in 10 soil layers. The C content in the 0–17.5 cm layer of grassland decreased by 22% (8.6 Mg C ha−1) during the period of conventional cultivation. Meanwhile, N decreased by 14% (0.44 Mg N ha−1). Additional C and N losses occurred after the establishment of bare soil and oat/maize (no N). With N fertilisation, the C and N stocks of oat/maize were steady with time. Legume-based cropping systems (lablab + maize and pigeon pea + maize) increased C and N stocks due to the higher residue input. Although the major soil management effects were found in the 0–17.5 cm layer, up to 24% of the overall C losses and up to 63% of the gains of the whole 0–107.5 cm layer occurred below the 17.5 cm depth, reinforcing the importance of subsoil as a C source or sink. The average C sequestration rate of legume-based cropping systems (with N) was 0.83 Mg C ha−1 year−1 in the top 0–17.5 cm layer and 1.42 Mg C ha−1 year−1 in the whole 0–107.5 cm layer, indicating the remarkable potential of legume cover crops and N fertilisation under no-tillage to improve SOM stocks and thus, soil and environmental quality in humid subtropical regions.Peer reviewe