Concentração de enxofre nas folhas diagnósticas do capim-marandu após aplicação de fontes nitrogenadas

Abstract

The application of sulfur (S) to pastures established in the Cerrado region, whose soils are poor in this element, increases the forage plant's response to nitrogen (N), improving the efficiency of N-fertilizer use. The objective was to evaluate the concentration of S in the diagnostic leaves of Marandu grass after application of nitrogen sources containing or not other nutrients. The experiment was conducted in the UFMT experimental area, located in the municipality of Barra do Garças-MT, in randomized blocks, with eight treatments: Urea (46N); Ammonium nitrate (34N); Ammonium nitrate (34N) and Potassium sulfate as a source of sulfur (18S); Ammonium nitrate (34N) and Calcium chloride as a source of calcium (24Ca); Ammonium nitrate with calcium and sulfur (27N; 5Ca; 3.7S); Ammonium nitrate with calcium and magnesium (27N; 4Ca; 2Mg); Urea NBPT (32N); Control; with four replications, in plots of 30 m². For all treatments, the N dose applied was 120 kg ha-1 divided into two applications of 60 kg ha-1 . The applications took place on December 4, 2022 and January 14, 2023. After each application, the growth of Marandu grass was monitored weekly and when the average height reached 35 cm, the entire aerial part was collected 20 cm from the ground. Five cuts were made, two cuts after applying the doses and the last three cuts without applying the treatments. After each cut, the aerial part was separated into: FE-expanding leaves; LR-newly expanded leaf blades; LM-mature leaf blades and CB-culm plus sheath. The LR are considered the diagnostic leaves of pastures, therefore, they were placed in a forced air circulation oven at 65ºC until constant weight, subsequently ground and analyzed for S concentrations. The data were subjected to analysis of variance using the F and when they showed a significant difference at 5%, they were evaluated by the Skott knott mean test at 5% probability using the SISVAR statistical program. The application of nitrogen sources, whether or not containing S, led to an increase in the S content in the diagnostic leaves. The sources that presented the best results during the five cuts were: NA + S, NA + S + Ca and Na + Ca. In the first cut, the concentration of S in the LR was 184% higher in the NA + S treatment when compared to the control treatment. In the second and third evaluations, the highest S levels occurred in the NA + S + Ca treatment, being 68% and 46.08% higher when compared to the control, respectively. In the fourth cut, the NA + S treatment presented 1.57 g kg-1 of S with 60.20% more S when compared to the control. In the fifth cut, the NA + S and NA + S + Ca treatments obtained the highest concentrations of S in LR leaves with 1.15 and 1.02 g kg-1 of S, not statistically different from the control. A response to S applied together with N was observed, in concentration of S in diagnostic leaves of Marandu grass.