Produção de matéria seca e ciclagem de nutrientes por adubos verdes cultivados em Rio Largo – AL

Abstract

Green manure consists of the cultivation of plants that, after reaching their full vegetative development, will be cut or layered, leaving them on the surface or incorporated into the soil, to maintain or increase the organic matter of the land, in order to improve its physical, chemical conditions. and biological. The objective of this course conclusion work was to evaluate, in the edaphoclimatic environment of Rio Largo - AL, the accumulation of dry matter and the nutrient cycling of green manures: crotalária juncea, crotalária spectabilis, feijão-de-porco, mucuna preta and a fallow treatment with spontaneous vegetation. The study wasconducted at the Campus of Engineering and Agricultural Sciences of the Federal University of Alagoas (CECA/UFAL). Soil samples were initially collected from layers 0 to 20 and 20 to 40 cm, and with the results, 5,0 t of dolomitic limestone and 1,5 t of gypsum were applied, aiming to raise the base saturation to 60 % and decrease aluminum saturation. The soil was plowed, harrowed and furrowed at a spacing of 0,5 m. The experimental design was randomized blocks, with five replications, and the plots consisted of five five-meter-long furrows. In the full flowering phase of each treatment, the plants were cut close to the ground and weighed. A subsample from each plot was chopped, dried in a forced ventilation oven at 65°C until constant weight, passed through a stainless steel mill and determined for nitrogen, phosphorus, potassium, calcium, magnesium and sulfur contents. From the values sampled and the chemical analysis, the accumulation of dry matter and nutrients in the aerial biomass of the treatments was determined. The results of nutrient concentration in shoots and dry matter accumulation were submitted to analysis of variance and the means were compared by the Scott-Knott test at 5% probability. A lower concentration of nitrogen was observed in the vegetation of the fallow area and a higher concentration in crotalaria spectabilis ranging from 12.3 to 34.0 g kg-1 and crotalária juncea, feijão-de-porco and mucuna preta had statistically equal concentrations, with mean value of 30.25 g kg-1. For phosphorus concentration, green manures were classified into two groups. The first group consisted of feijão-de-porco, fallow area vegetation and mucuna preta, with an average value of 2.00 g kg-1, in the second crotalaria juncea and crotalária spectabilis, with an average value of 2.50 g kg-1. For potassium concentration, there were three groups: the first included feijão-de-porco and mucuna preta, with an average concentration of 11.60 g kg-1. In the second group were the vegetation of the fallow area and crotalaria juncea. In the third group, crotalária spectabilis with an average concentration of 16.82 g kg-1. The lowest accumulation of dry matter was observed in the vegetation of the fallow area: 3.83 t ha-1 and the highest in mucuna preta and feijão-de-porco, with an average of 8.18 t ha-. With the highest accumulation of dry matter, mucuna preta and feijão-de-porco were the plants that most accumulated N, P and K, with mean values: 245, 16, 95 kg ha-1, respectively. Keywords: Sustainability, biological nitrogen fixation, production system, mineral nutrition.