Dormência, competitividade com soja e qualidade de sementes de plantas daninhas em solo de terras baixas

Abstract

Soybean in lowland regions has expanded as a rotation alternative to rice. However, with the introduction of soybean in these new areas, there is a possibility that weeds that are associated with soybean in the traditional production regions of this crop could be adapted to lowland conditions. Thus, the objectives of this research were: to evaluate the breaking of the dormancy in seeds of soybean weeds; to determine the competitive ability of soybean when associated to different weeds; to study the physiological, metabolic and reproductive responses of weeds subjected to different irrigation management, and to evaluate the longevity and persistence of the weed soybean seed bank. Sourgrass (Digitaria insularis) and johnsongrass (Sorghum halepense) as weed grass species; and slender amaranth (Amaranthus viridis) and wild poinsettia (Euphorbia heterophylla) as broadleaf weed species were studied in lowland soil. For this, pre-germination treatments were tested to break seed dormancy, competition of individual soybean replacement series with each competitor were established, variables related to gas exchange, oxidative stress and seed quality of weeds under different kinds of irrigation were quantified; and the longevity of the weed seed bank was determined by buried the weed seeds in lowland soil. In general, soybean shows greater competitive ability than the sourgrass and wild poinsettia, which the intraspecific competition is more harmful to the crop; while, the competitive capacity was similar to johnsongrass, being more important the interspecific competition. In addition, johnsongrass has tolerance to flooding, sourgrass and wild poinsettia shows moderate tolerance, and slender amaranth is sensitive to flooding. Sourgrass and wild poinsettia shows a transient seed bank, and johnsongrass and slender amaranth have a persistent seed bank on lowland soil.