Adubação com fontes nitrogenadas e enxofre elementar: resposta agronômica do capim BRS Paiaguás e acidificação de solo alcalino

Abstract

Irrigation with limestone water coming from tubular wells is one of the main causes of alkalization of cultivated soils. The high pH of some of these soils can impair absorption and lead to losses of nutrients such as nitrogen (N). However, nitrogen and sulfur (S) fertilization itself are alternatives to reduce soil pH and improve the efficiency of N fertilization. The aim of this study was to evaluate the effect of nitrogen sources and elemental S on the agronomic response of BRS Paiaguás grass (Urochloa brizantha) and acidification of soils irrigated with limestone water in different cuts. The experiment was conducted in a randomized block design with split plots in time, containing five treatments and four replicates. The treatments were: control without nitrogen (SN), urea (UR), urea with elemental sulfur (URS), ammonium nitrate (NA) and ammonium sulfate (SA). All N treatments received 250 kg ha-1 of N and the S treatment received 60 kg ha-1 of elemental S. The plots were subjected to three standardization cuts and, after the second standardization cut, they were applied treatments with four doses of 62.5 kg ha-1 of N and, for the treatments containing S, three doses of 20 kg ha-1 of elemental S. The evaluations took place in four 30-day periods of forage growth. They were evaluated aspects of the production, structure, chlorophyll and morphological composition of the plant. In addition to these, they were evaluated pH, total soil N and nutrient concentration in the soil and plant. Fertilization with SA (55.5 cm) and UR (55.1 cm) resulted in greater height than the control (43.5 cm). The number of tillers was greater in fertilized plants than in the control, regardless of the type of fertilization. The same response was observed for forage dry mass, which was 85.77; 63.41; 56.32; and 51.13% higher than the control in the treatments with NA, UR, URS and SA, respectively. No treatment reached 95% of IL in the study and the fertilized plots intercepted more light than the control. There was an interaction between fertilization type and cutting for total chlorophyll content. In this sense, only in the third cut did the UR treatment (42.15) differ from the control (32.52). There was an effect of the type of fertilization and cutting on the soil pH. Thus, the pH of the plants fertilized with NA (7.25) was higher than the pH of SA (6.81). Regarding the times, the pH increased, being higher in cuts 2 and 3 compared to cut 1. Fertilization with N, regardless of the source used, increases forage production, number of tillers and light interception of BRS Paiaguás grass. The advancement of the times provides an increase in production and light interception. Only fertilization with SA was able to reduce the pH compared to the NA treatment. The advancement of the times provides an increase in production and light interception. Only fertilization with SA was able to reduce the pH compared to the NA treatment.