Abstract
ABSTRACT: Weed species is one of the factors contributing to grain yield losses due to crop-weed competition. Two of the most common weeds of soybean fields in Brazil are from the Rubiaceae family: Borreria latifolia and Richardia brasiliensis. This study aimed to evaluate the effects of B. latifolia and R. brasiliensis on plant development, yield components, and soybean productivity. Two assays were conducted in a randomized block design with four replications, using a two-level factorial design, in which the first factor consisted of the species B. latifolia and R. brasiliensis and the second factor consisted of the densities 0, 2, 4, 6, 8, 10, and 12 plants m-2. Plant height, leaf area and total chlorophyll in the V6 and R5 stages, number of pods per plant, number of grains per pod, 1000-grain weight, and grain yield loss were evaluated in both cultivars. Grain yield of both soybean cultivars was negatively affected by the interference with B. latifolia and R. brasiliensis. The species B. latifolia was more competitive with soybean when compared to R. brasiliensis, causing higher reductions for all variables. Each B. latifolia plant per square meter is able to reduce the yield of soybean by 3 a 4.4%, while each R.brasiliensis plant reduces yield by 2 a 2.6%. For both species, the reduction in soybean yield due to competition was caused by a decrease in the number of pods per plant, number of grains per pod, and 1000-grain weight.
Highlights
The presence of weeds in farming areas has been pointed out as one of the most important factors since it contributes significantly to reduce crop productivity, presenting a great threat to sustainable food production
The three- and four-parameter logistic models had a good fit between densities of B. latifolia and R. brasiliensis and response variables, with coefficients of determination varying from 0.85 to 0.99 (Tables 2 and 3)
The variables plant height and total chlorophyll of soybean plants in the V6 stage were not affected by the variation in plant density of R. brasiliensis (Figure 2A, C)
Summary
The presence of weeds in farming areas has been pointed out as one of the most important factors since it contributes significantly to reduce crop productivity, presenting a great threat to sustainable food production. Soybean grain yield losses due to the presence of weeds in the absence of control (potential) measures are estimated at 37% and losses due to the adoption of control measures are estimated at 7.5%, which means a high degree of effectiveness when compared to measures to control pests and pathogens (Oerke, 2006). Among them is the process of selection of more tolerant and resistant plants resulting from the high selection pressure exerted by herbicides, the reduced number of new active ingredients of herbicides released in recent years, and the low diversification of weed management methods used by farmers (Christoffoleti and López-Ovejero, 2003)
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