Influência da densidade de semeadura do feijoeiro comum na incidência de plantas espontâneas em sistema orgânico de produção

Abstract

Organic production is an alternative for family farmers where practices to reduce costs and to preserve natural resources can add value to the product and improve quality of life. The weeds can cause losses in crops, by reduction of income, increase in pests and diseases, non uniformity in maturity and difficulties for harvesting. The objective of this study was to evaluate the performance of common bean cultivars (Phaseolus vulgaris) at different sowing densities regarding the incidence of weeds in organic production system. Two field experiments were conducted in the Agroecological Production Integrated System of 47 km in Seropédica-RJ, in the years 2013 and 2014, in a randomized block design with four replications. In 2013 a 4x3 factorial was used, combining four cultivars (Ouro Negro, Manteigão, Radiante and Aporé) and three densities (8, 13 and 18 plants m-1 linear). In 2014 a 2x3 factorial was used, between two cultivars (Manteigão and Ouro Negro) and three treatments (13 plants m-1 with manual cleaning of weeds, 13 and 18 plants m-1 without cleaning). To obtain the desired plant population, 50% more seeds were sown in each treatment and plants were thinned 15 days after. Sampling was carried out at the flowering stage to assess biomass and nodulation of bean and biomass of weeds, and at physiological maturity to evaluate grain yield. In 2013, the largest shoot and root dry mass and number of nodules per plant occurred in the density of 8 plant m-1. Increased planting density reduced the number of pods per plant, with no effect of density on grain yield. The lower biomass of weeds was observed at densities of 13 and 18 plant m-1, and also for cutivars Manteigão and Ouro Negro. In 2014, treatment with 13 plants m-1 with cleaning showed greater dry mass of shoots and roots per plant. At flowering, treatment with 13 plants m-1 showed higher dry matter and number of weeds. The cultivar Ouro Negro showed higher grain yield at density of 13 plants m-1 with cleaning, followed by 18 plants m-1, with no differences between treatments for cultivar Manteigão. The treatment with 18 plants m-1 showed lower mass of weeds at bean flowering, similar to the treatment with 13 plants m-1 with cleaning. Plots with cultivar Manteigão had the highest dry matter of weeds in the three density treatments. Grain yield did not differ significantly among cultivars, ranging in 2013 from 1310 kg ha-1 for Aporé and 1409 kg ha-1 for Manteigão, and in 2014 of 1298 and 1419 kg ha-1 for Manteigão and Ouro Negro. It is concluded that increasing plant density reduced the incidence of weeds and did not affect grain yield. It was also carried out a field trial in 2013 in family agricultural establishment in the city of Teresopolis-RJ, in order to encourage the cultivation of special beans and to experience economic and social strategies of reproduction. The experiment had a 4x2 factorial with four replications, using four cultivars (Aporé, Manteigão, Radiante and Valente) and two treatments (with and without commercial inoculant with rhizobia). Grain yield of the four cultivars did not differ between the treatments in the absence and presence of seed inoculation with rhizobia