Acúmulo de nitrogênio nas folhas diagnósticas do capim-marandu após aplicação de ureia

Abstract

Nitrogen (N) is one of the most limiting nutrients for the development and maintenance of forage grasses due to the large amount required by the plant. The supply of N is directly associated with greater dry matter mass production, as well as an increase in forage quality, helping to maintain the productive capacity of the pasture, making the system more sustainable. The aim was to evaluate the accumulation of N in the diagnostic leaves of Brachiaria brizantha cultivar Marandu after the application of doses of urea. The experiment was conducted in the experimental area of the Federal University of Mato Grosso, located in the municipality of Barra do Garças -MT, in randomized blocks with four replications. The plots were 30 m² in size and had a useful area of 0.5 m2. The treatments were five doses of N (0, 60, 120, 180, 240 and 300 kg ha-1 and N) using urea as the source, with four replications. The experimental plots were 6 m x 5 m and had a useful area of 0.5 m2. The applications were made in five stages of 60 kg ha-1 of N at a time. After each application, the development of the Marandu grass was monitored and when it reached a height of 35 cm, the aerial part was cut at a height of 20 cm from the ground. The entire aerial part collected was weighed to obtain the mass of green matter in 0.5 m2. Around 500g of this material was removed and separated into the following parts: FE, LR, LM and CB. These parts were weighed, then placed in a forced-air oven at 65oC until constant weight, then weighed to obtain the dry matter mass and the data transformed into kg ha-1. The LRs are the diagnostic leaves of forage grasses because they are the part that best represents the nutritional state of the forage and were therefore analyzed for N concentration. Using the dry matter mass data of the LRs and the N concentration in these parts, it was possible to obtain the accumulation of N in the LRs. The data was analyzed using the F test and, when significant at 5%, the regression test at 5% was performed using the SISVAR 4.6 statistical program. The N accumulated in the LR in all cuts, i.e. after the application of 60 kg ha-1 up to a total of 300 kg ha-1 of Urea, there was a significant difference in N accumulation, where the percentage of N accumulated in relation to the control dose was over 40% for all cuts. The accumulation of N increased in the diagnostic leaves of the Marandu grass as a function of the doses of urea applied, with variations ranging from 42% to 83% in relation to the control treatment. The accumulation between doses did not increase linearly, but it did in relation to the control. Regardless of the factors, the application of urea was positive for the increase in nitrogen accumulation in all cuts and applications.