Nitrogen and Sulfur Fertilization and Dynamics in a Brazilian Entisol under Pasture

Nutrient dynamics in tropical soils sustaining forage grasses are still poorly understood. We conducted a study to evaluate the effect of combined N and S fertilizer rates on the growth of ‘Marandu’ palisade grass [ Brachiaria brizantha (Hochst. ex A. Rich.) Stapf], uptake of these elements from the soil by plants, soil organic matter concentration, soil pH, and the mineral and organic fractions of N and S in an Entisol. Combinations of five N rates (0, 100, 200, 300, and 400 g N m −3 ) with five S rates (0, 10, 20, 30, and 40 g S m −3 ) were evaluated in a partial 5 × 5 factorial in a pot experiment, with and without plants. Nitrogen and S were supplied as NH 4 NO 3 and CaSO 4 ·2H 2 O, respectively. The N addition in excess did not enhance the palisade grass production due to low plant‐available S in the soil. The supply of low rates of S with N greatly improved the overall N uptake efficiency by the forage plant. The contents of total N, NO 3 − –N, and NH 4 + –N in the soil varied with N rate and with N uptake by the plants. The association of palisade grass with S fertilization increased the ester‐bonded S fraction in the soil. The results suggest that soil residual S could be a potential source of S for plants. Proper N and S fertilizer rates promoted increased grass production due to increased uptake of these nutrients and the dynamics of the organic N and S fractions and mineral fractions in this tropical soil.