Caracterização agronômica de espécies de Crotalaria L. em diferentes condições edafoclimáticas e contribuição da adubação verde com C. juncea no cultivo orgânico de brássicas em sistema plantio direto

Abstract

The objective of this work was to evaluate growth of Crotalaria species in different soil and climate conditions and to investigate the contribution of Crotalaria juncea, as a cover crop, on organic cultivation of cabbage and cauliflower, under no-tillage system. Five experiments were conducted. Three of them referred to the performance of Crotalaria species, evaluated in the spring/summer and fall/winter periods, on the experimental field at Embrapa Agrobiologia, in Seropedica, Rio de Janeiro State, and in the spring/summer period, on the experimental field at Pesagro-Rio, in Paty do Alferes, Rio de Janeiro State. Treatments consisted of the species Crotalaria juncea, C. mucronata, C. spectabilis, C. ochroleuca and C. breviflora arranged in a randomized blocks design. The aboveground biomass production was determined throughout the flowering period and the biological nitrogen fixation (BNF) was measured by the 15N natural abundance technique. Functional analysis of growth and soil cover rates were also determined in the first experiment. The fourth experiment evaluated green manuring with sunnhemp (C. juncea) on yield, productivity and nutrient accumulation of cabbage heads, on the experimental field at Pesagro-Rio, in Paty do Alferes, Rio de Janeiro State. A complete randomized block design was used and treatments were arranged in a 2x2x2 factorial split-plot: pre-cropped sunnhemp and fallow with spontaneous weeds, conventional tillage and no-tillage planting systems and 0 and 200 kg ha-1of N in a poultry manure. The fifth experiment was carried out on the experimental field at Pesagro-Rio, in Nova Friburgo, Rio de Janeiro State. The effect of green manures sunnhemp, millet, sunnhemp + millet and fallow with spontaneous vegetation, arranged in a complete randomized block design, was evaluated on weight and productivity of cauliflower cropped in no-tillage system. The contribution of sunnhemp mulch to nitrogen nutrition of cauliflower was assessed by isotopic dilution of 15N. Results from the first experiment showed that Crotalaria juncea presented the highest scores of growth rate and biomass production and reached 50% soil coverage at 15 days after seeding. Dry matter production, nitrogen accumulation and nitrogen coming from BNF reached superior rates in C. juncea, in the first and in the third experiments, and in C. ochroleuca in the second experiment. Trials number four and five showed why green manure can be considered a promising method to cultivate organic vegetables. No-tillage cabbage cropping under sunnhemp mulch discarded additional organic manure as head productivity reached 56 Mg ha-1. In the fifth experiment, 39% of cauliflower nitrogen content was originated from sunnhemp and productivity increased 42% in relation to spontaneous vegetation.