Plastocrono, eficiência de conversão e estimativa de duração das fases fenológicas na cultura da soja

Abstract

This study aimed to evaluate the growth and development of soybean cultivars submitted in different spatial arrangements associated with weather temperature elements and solar radiation, and also the contribution of temperature elements, solar radiation, precipitation and the thermal time the duration of the development phases. The cultivars used were BMX Ativa RR, BMX Turbo RR e BMX Potência RR and the spatial arrangements were 45, crossed, 20, 20x40, 20x60 and 20x80 cm. Two field experiments were conducted in the experimental area of Agroclimatology Laboratory of the Federal University of Santa Maria, campus Frederico Westphalen/RS in the growing seasons of 2012/2013 and 2013/2014. During the crop cycle asked the following ratings: weekly count of the number of nodes; growth analysis; and monitoring of phenological scale. From these data, there was obtained plastochron, the conversion efficiency and regression models for the phenological stages. In the growing seasons 2012/2013 the plastochron cultivar BMX Turbo RR in spatial arrangement of 20 cm and the lowest BMX Potência RR, in the arrangement of 20x80 cm. In the growing seasons 2013/2014 the plastochron cultivar BMX Ativa RR in the cross arrangement and the lowest this cultivar in the arrangement of 20x40 cm. For all cultivars the only spatial arrangement which differed in both years, was to 20x40 cm which had lower plastochron values in the second year. The arrangement of 20x40 cm is favored by the approach of the internal lines of 20 cm, the best use of solar radiation by the rapid closure of these lines. The external lines of 40 cm favor the development, and facilitate the application of phytosanitary treatments. Higher conversion efficiencies of cultivars are obtained in paired arrangements. Paired arrangements and 20 cm, for having the highest leaf area index and possibly increased interception of diffuse radiation increase the conversion efficiency and productivity of the cultivars BMX Ativa RR and BMX Turbo RR. The thermal time in different phenological stages of soybean cultivars varies according to the growing seasons, and is determining the duration and follow-up phases. It is the factor that most influenced at all stages of development of cultivars, contributing over 95% in the regression models. Meteorological data associated with phenology identify the different weather conditions which culture is exposed and demonstrate the plasticity that this species has.