Abstract
ABSTRACT: The aim of this study was to evaluate the establishment of the pasture of Panicum maximum cv. Aries in an environmentally protected area under levels of interspecific interaction with the weed community. The experiment started after sowing P. maximum, and it was carried out in a randomized block design with four replications and the following factors: 3 light interception levels, 2 nitrogen rates, and 7 weekly sampling dates along pasture establishment (3x2x7). The light interception treatments, determined by photosynthetically active radiation, were given by mowing weeds over the canopy of P. maximum at 40% and 70% light interception, and no mowing (uncontrolled growth of weeds and P. maximum). Topdressing application of nitrogen in the form of urea was performed or not (0 or 200 kg N ha-1). The plant community was evaluated by number of species, dry matter accumulation, and density, and phytosociological indices were determined. The relative importance and dry matter accumulation of P. maximum were greater after nitrogen fertilization, which favored the species against weed competition. In contrast, there was lower weed density without nitrogen fertilization. Mowing weeds at 40% of light interception enabled P. maximum to accumulate more dry matter, while there was no difference between mowing weeds at 70% light interception and growing the forage crop freely with weeds. Reducing weed light interception as well as nitrogen fertilization, and consequently reducing the competitive ability of the weed, favored the establishment of P. maximum in diversified agro-ecosystems.
Highlights
Sustainability is a recurrent and increasingly common theme in the debate on agricultural development in Brazil, and there has been criticism of the excessive use of soil tillage, low biodiversity and degradation of pastures and natural resources (Macedo, 2009)
The levels of interspecific interactions were determined by mowing all weeds found above the canopy of the grass. They were established on the basis of intensity of light interception quantified by photosynthetically active radiation, and topdressing application of N rates was performed to control the presence or absence of limitation of this nutrient for the plants
The third factor consisted of weekly collections of weeds and the forage crop for temporal characterization of the plants, over a period of 42 days as of the 43th day after planting, from February 25, when the forage crop was at the four-leaf stage, to April 8, 2013, which corresponded to 85 days after planting
Summary
Sustainability is a recurrent and increasingly common theme in the debate on agricultural development in Brazil, and there has been criticism of the excessive use of soil tillage, low biodiversity (monoculture) and degradation of pastures and natural resources (Macedo, 2009). Biodiversity-based agriculture seeks to develop different cropping systems to provide ecosystem services and, in turn, drastically reduce the use of anthropogenic inputs (Duru et al, 2015; Gaba et al, 2015, Rollin et al, 2016). Especially when weeds are present in a crop, spatial distribution and stage of development of each specimen and species are very uneven (Colbach et al, 2006; Bourgeois et al, 2012) Because of this temporal and spatial heterogeneity among the species, there is great variability of canopies, which makes competition complex (Munier-Jolain et al, 2013). Freitas et al (2005), in a study that evaluated dry matter of P. maximum under different nitrogen rates, found a greater quantity of dry matter and a greater amount of nitrogen in the plant when the highest nitrogen rates were applied (which ranged from 70 to 280 kg ha-1 yr-1). This is indicative of a great contribution of this nutrient to plants
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