Utilização de Flemingia macrophylla como adubo verde na produção orgânica de hortaliças em sistema de aléias

Abstract

The recent increased pressure on natural resources, especially soil and vegetation cover, calls for locally based food production systems. The dependence on external inputs and non-renewable natural resources is then diminished. The practices used in alternative agricultural systems pursue the harmonious combination of all available resources such as nutrient cycling and maximal use of in situ generated inputs. Among various practices available, green manuring, which is defined by the use of legumes or other plant species in rotation or intercropped, deserves attention. Such plants may be incorporated into the soil or mowed and kept on the soil surface, providing improvement on the physical, chemical and biological characteristics of soils. Hence, the objective of this research was to use the legume Flemingia macrophylla under an alley cropping system to grow lettuce, chicory and arugula. The experiments dealt with various agronomic aspects of flemingia to facilitate its inclusion on the crop system proposed. First, the evaluation of flemingia regrowth capacity was studied after cutting at different heights from ground level (0.0 m; 0.3 m; 0.6 m; 1.2 m). The treatments were imposed on one year old plants. This trial lasted for two years, enough time to accomplish eight cuttings. Dry matter and nitrogen content of the shoots of flemingia, as well as biometric variables such as height, stem diameter, and number of branches were determined. The highest cutting height (1.2 m) maximized biomass production, at all cutting dates. This same trend was observed for nitrogen accumulation. Decomposition dynamics and nutrient release from the shoots of flemingia were also studied along with the composition of invertebrates present during the process. Litter bags containing three different flemingia parts were used: leaves, stems and stems + leaves. Bags were set in the field and collected over time to determine moisture and levels of N, P, K, Ca and Mg. Invertebrate composition was determined by placing plant biomass in Berlese funnels installed in a closet set with lamps placed above, collected in jars located below the funnels and sorted under stereoscopic microscope. Subsequently, an alley cropping system was designed to test the production of lettuce, chicory and arugula. The system consisted of a control without flemingia, rows of flemingia cut at 1.2 m followed by mowing and rows of flemingia with no cutting. Nitrogen transfer from flemingia to the vegetables was estimated by isotopic dilution technique of 15. The incidence of spontaneous plants was also assessed. Contribution of N from flelmingia to the vegetables was verified. Generally, yield components in vegetables were superior on the control plots. Cutting flemingia at 1.2 m and deposing its biomass was better for vegetable yields than not cutting flemingia. This trend reflects the limitation of light incidence on the canopy of vegetables. Flemingia formed excellent mulch, which prevented the emergence of unwanted plants on the vegetable crops. The following year, the experiment was repeated at the same area, but replacing the cutting at 1.2 m to 0.6 m, so allowing more light into the canopy. Such adjustment resulted in gains in vegetable production. The data shows that the Flemingia macrophylla as a promising green manure to be included in vegetable organic systems.