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

Abstract 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 NO 3 − leaching.