GREEN MANURE AS A SOIL FERTILITY AND ENVIRONMENTAL OPTION IN SEMIARID AGROSYSTEMS: MINERALIZATION RATE AND N CONTENT

Abstract

Green manures are an adequate alternative for improving the availability of nitrogen and phosphorus for crop nutrition, within a global context of decreasing soil fertility and the urgent need to care for the environment. Mixteca region, covers a wide area of central Mexico, characterized by a semi-arid climate, eroded calcareous soil, and rural poverty. With the aim of proposing technologies for improving soil quality and increasing the availability of nitrogen and phosphorus, an experiment was conducted using green manures: Canavalia ensiformis, Dolichos lablab, Leucaena leucocephala and Avena strigosa and Phaseolus vulgaris, that would ensure a balance between N and P release and the requirements of maize cultivation. The rate of enriched soil mineralization with green manures was determined through incubation, controlled for 15 days with CO₂ emissions using an OxiTop OC110^® kit as an indicator of decomposition. CO₂ emissions were greatest in the soil established with Leucaena leucocephala and least in the soil with no fertilizer, with emissions descending in the following order: Leucaena leucocephala > Canavalia ensiformis > Avena strigosa +Phaseolus vulgaris > Dolichos lablab > soil without green manure. It is assumed that a greater flow of CO₂ is accompanied by greater mineralization and release of nutrients. The N_total in the soil treated with green manures was similar and greater than that of the soil without fertilizer. Soil treated with Avena strigosa+Phaseolus vulgaris contained the highest values of N_mineral (N-ammonium + N-nitrate). P_Olsen content in soils with green manures was double that of the soil without fertilizer. Incubation provided the opportunity of identifying those green manures with higher agronomic potential in the area under study. The biomass comprising Leucaena leucocephala leaves and tender stems constitute an alternative for improving soil by providing OM. However, when considering the availability of N and P, the Avena strigosa+Phaseolus vulgaris combination is a superior alternative for meeting the needs of maize cultivation.