COMPOSIÇÃO QUÍMICA DO CAPIM BRAQUIÁRIA NAS DISTINTAS POSIÇÕES DO RELEVO DE UM ARGISSOLO VERMELHO AMARELO

Abstract

Productivity and forage quality in the pastures of Agreste Paraibano are low due to region’s edaphoclimatic conditions. With this work we aimed to analyze Nitrogen, Phosphorus, Potassium and Sodium levels during a rainy season in Urochloa decumbens pasture grown for 20 years on three relief conditions (shoulder, half slope and pediment) of a Yellow Red Argisol slope. Experiment was conducted in the Vaca Brava hydrographic basin located in Brejo Paraibano. The slope has a concave shape, inserted in a 13 ha area, with pasture covering more than 85% of the area, consisting of Urochloa decumbens, established 20 years ago, after scarification to decompress the soil and plow for soil planning, where sowing was done with no new seeds, but only by germination of the seeds present in pasture. It is important to emphasize there was no practice of nutrient replacement in area of pasture during the years of pasture consumption by the animals, which feed according to the availability of forage over the years. We did observational type evaluation, in a 5x3 factorial arrangement, with five sample dates and three relief positions. We analyzed forage production and nutrients content as a function of the total mass produced in the cages. In addition, we determined amount of nutrients exported by pasture consumption in the total evaluation period (150 days). Data were separately analyzed, comparing each sample date (5 sample dates), being each sample period a separated for 30 days, and comparing the accumulated data (120 evaluation days). Data of analyzed variables [forage production, extraction (or export) of nutrients, contents and contents of N, P, K and Na] were submitted to analysis of variance and means comparisons was realizeds by Tukey test (p≤0.05). We verified that the dry mass production was higher in the first cut done at 30 days during the rainy season; position of slope, intervals between cuts and plant age are factors that favor the vegetative development; highest nutrient content were found in pediment position, reinforcing the thesis that position is an important factor to be considered in the management of the landscape; extraction of N, P, K and Na elements was higher in pediment position, followed by shoulder position, confirming that the dynamics of extraction, absorption and export of nutrients by the plant also happen as a function of slope.