Soil acidity amelioration improves N and C cycles in the short term in a system with soybean followed by maize-guinea grass intercropping

• In a N poor environment, lime + gypsum increases C balance in the soil–plant system. • C-CO 2 emission from the soil is not affected by lime, gypsum and N fertilizer in short term. • N exported in grains controls the negative N balance in the system. • Biological nitrogen fixation and cover crops help to improve the soil N stock. • Appropriate N fertilizer management results in positive C and N balances in the soil. Lime application has been associated with N and C losses from agricultural systems through NO 3 – leaching, N 2 O and CO 2 emissions. However, we hypothesized that in an intensive crop system where soybean is grown in rotation with maize intercropped with a forage grass, liming associated with the application of gypsum to ameliorate the subsoil, and N fertilization increase soil N and C by improving root and crop growth. To evaluate the interaction of lime, gypsum and N fertilizer on soil and N and C partial balances, an experiment was carried out under no-till, where soybean was grown in rotation with maize intercropped with Guinea grass ( Megathyrsus maximus cv Tanzânia) as relay crop. Lime and gypsum were applied before soybean planting in October 2016 and October 2017. Two N rates (0 and 160 kg ha −1 yr −1 of N as ammonium sulphate) were applied to maize annually. Outputs through N-NO 3 – leaching, N-N 2 O emission and N-NH 3 volatilization did not exceed 30 kg ha −1 of N in two years. The N exported in grains consisted in 96% of the N output and was greater with fertilizer and lime. Soil acidity amelioration and N-fertilization favoured soil C fixation with high plant biomass production (C in plant residue, roots, and grains), while soil C-CO 2 emission was not affected, and soil C increased. Although the partial N balance was negative, there was an increase in soil N, probably due to biological N fixation by soybean, which was not considered in the partial balance. We concluded that lime and gypsum application, along with an adequate N fertilization, to a tropical highly-weathered soil with soybean cropped in rotation with maize-guinea grass intercropping benefit N and C cycles and the environment in the short-term, increasing soil N and C stocks and reducing GHG emitted to the atmosphere.