Soil carbon and nitrogen dynamics as affected by land use change and successive nitrogen fertilization of sugarcane

The land use change (LUC) and application of N fertilizers have potential to affect soil C and N dynamics and long-term C and N stocks. We aimed to evaluate the effects of the LUC from native vegetation (seasonal semideciduous forest) to sugarcane (Saccharum spp.) cultivation under successive annual N fertilizer applications on chemical and microbiological attributes of sugarcane-cropped soils. Two field trials were performed during three (Site 1) or four years (Site 2) in southeastern Brazil. Soil sampling was carried out in the following N treatments applied to the crop: control (N-unfertilized plots), organomineral fertilizer (100 kg ha−1 yr−1 N), and synthetic fertilizer (100 and 200 kg ha−1 yr−1 N). Soil samples from native vegetation located near each site were also taken, to serve as reference for studying LUC. For Site 1, successive application of N fertilizers on sugarcane managed under green cane trash blanketing system maintained the C and N dynamics and stocks in soil to conditions similar to those found before LUC. At Site 2, however, modifications in soil attributes caused by LUC were more impacting than the N fertilization management. Compared to synthetic N fertilizers, successive application of organomineral fertilizer did not improve the soil microbiological attributes as well as organic C and total N stocks. Lastly, successive high N input (200 kg ha−1 yr−1, via synthetic fertilizer) promoted accumulation of mineral N deep in the soil profile, thus increasing potential losses through NO3− leaching.