Nitrogen fertilization and desiccation times of palisadegrass pasture driving C and N-cycling traits in an Oxisol under soybean in a crop-livestock system

Abstract

The pasture management and desiccation times before sowing may affect the following grain crop in crop-livestock system. To explore the impacts of N fertilization applied to the palisadegrass (Urochloa brizantha) pasture and the desiccation time before soybean (Glycine max L.) sowing on attributes related to C and N cycling and on soybean yield, we conducted an experiment with palisadegras pasture grazed for 18 months receiving 300 kg ha−1 of N (+N, urea) or without N fertilization (–N), desiccated at 1, 15, 30, 45, or 60 days before soybean sowing. Assessments at the soybean sowing and at R3 stage showed that desiccation times had only minor effects on soil attributes. However, pasture N fertilization (+N) significantly decreased the soil basal respiration (9.6 vs 8.4 μg g−1 day−1 of CO2-C) at soybean sowing; at R3, +N decreased soil organic C (20.8 vs. 19.7 g kg−1), total N (2.1 vs. 2.0 g kg−1), and urease activity (62.6 vs. 42.4 μg g−1 h−1 of NH4+-N). Conversely, +N increased labile C (164 vs. 346 mg kg−1) at R3, and nitrification rate at sowing (6.6 vs. 11.6%) and R3 (2.32 vs. 5.26%). Ammonification rate increased at sowing (0.02 vs. 0.03 μg g−1 day−1 of NH4+-N) due to N fertilization but decreased at R3 (0.06 vs. -0.08 μg g−1 day−1 of NH4+-N). Besides causing negative variations in most of the soil attributes related to C and N cycling, fertilization of palisadegrass pasture with 300 kg ha−1 of N decreased soybean yield (5040 vs. 4770 kg ha−1). Desiccation times of palisadegrass did not affect the soil attributes related to C and N cycling and soybean yield so that short desiccation times before soybean sowing can optimize the forage use in the livestock phase and allow the biomass recovery after grazing for soil mulching in the no-till system of the integrated grain crop.