Soybean growth and production under straw of maize, Urochloa brizantha, Conyza spp. and Digitaria insularis

Weeds can cause serious damage during soybean development, due to allelopathy, competition for water, light and nutrients. It is necessary to investigate the influence of straw, of weeds Conyza spp. and Digitaria insularis, in soybean growth, production and composition and grains. If there is influence of allelopathic compounds at the crop. The aim of this study was to evaluate the influence of straw of maize and Urochloa brizantha (A.Rich.) R.D.Webster crops and Conyza spp., D. insularis, on growth, production and composition of grains produced by soybean. Treatments consisted of the control (absence of straw), maize straw, Urochloa brizantha straw, Conyza spp. straw (500, 1000, 1500 or 2000 kg ha-1) and D. insularis straw (500, 1000, 1500 or 2000 kg ha-1). The chlorophyll index, height of plants and insertion of the first pod, stem diameter at the collar and at 5 cm from the collar, root dry mass, number of pods and grains, weight of total grains, weight of 100 grains, protein and nitrogen (N), catalase and peroxidase contents in grains were evaluated. There was no difference between treatments for plant height, first pod height and chlorophyll index, as well as for total pods and 100 grain weight and protein content, N content and peroxidase and carboxylase enzymatic activity of the grains produced. For stem diameter, a higher value was found for the treatment with maize straw compared to the control (no straw). For dry root matter, treatments without straw and with Conyza spp. straw up to 1500 kg ha-1, differed from the treatment with maize straw. Even in some respects they provided beneficial effects compared to the absence of straw, which indicates the importance of crop residues. No allelopathic effects of weeds were observed on the growth and development of soybean. Conyza spp., D. insularis, maize or U. brizantha straws do not negatively affect soybean growth, production and grain composition