PLANTING DENSITIES AND THE USE OF LOCAL WEEDS AS AN ALTERNATIVE TO ACCELERATE THE INCORPORATION OF GREEN MANURES

Background. Tropical legumes used as green manure require between 2.5 and 4.5 months of growth to be incorporated into the soil, an increase in planting density and the use of weed biomass is expected to help reduce the time required for the incorporation of legumes. Objective. To determine plant survival and dry matter production of five tropical legumes produced in conjunction with local weeds, as a function of planting density and legume age, to identify the most appropriate alternative to accelerate the incorporation of plant biomass in tropical regions. Methodology. The legumes Canavalia ensiformis, Crotalaria juncea, Cajanus cajan, Sesbania sp. and Mucuna aterrima were established in Veracruz, Mexico. Each species was established at five planting densities and biomass was collected at four ages, 30, 60, 90 and 120 days after sowing (DAS). Results. Plant height, leaf/stem ratio, percentage of broadleaf and narrowleaf weeds, as well as dry matter produced by legumes, weeds, and the total of both, changed as a function of plant age. Implications. To use green manures in a crop rotation system under rainfed conditions, it is necessary to know the amount of biomass of local weeds and legumes produced over time. The results of the study will help to define the most appropriate cutting age for each of the green manure species evaluated. Conclusion. It is concluded that, independent of planting density, as the age of the legumes increases, plant survival and the leaf/stem ratio decrease, but the amount of dry matter increases. C. cajan and C. juncea have a greater capacity to compete with local weeds, which is attributed to the height they can reach in the first 30 DAS. Regardless of the species and planting density, the maximum production of total dry matter per hectare is achieved between 30 and 60 DAS, when it is recommended to incorporate the biomass to produce under rainfed conditions.