SOYBEAN CULTIVAR RESPONSE TO COMPETITION WITH A WEED MIMICKING GENOTYPE

Abstract

Crop yield losses due to competition vary according to weed specie(s) involved and tend to be greater as more alike are the competing species, since these would utilize environmental resources from the same ecological niche. The aim of this work was to estimate the response of soybean cultivars “IAS 5” and “Fepagro RS-10”, when submitted to increasing densities of “Cobb” cultivar , mimicking a broadleaf weed species. To accomplish this, it was carried out one field experiment at Eldorado do Sul – RS. The factors and treatments used were: soybean cultivars (IAS 5 and Fepagro RS-10) and densities of the weed mimicker (Cobb), more checks without its presence. Cobb densities varied from 5 to 36 plants m^-2. Data for percent yield losses of the cultivars were adjusted to the non linear retangular hyperbolic regression. The hyperbolic model forecasted at 6,8 and 5,9%, respectively, yield losses suffered by IAS 5 and Fepagro RS-10 cultivars when the weed mimicker genotype aproached zero. It was established that the mutual competition between plants belonging to the same species high, since the presence of a few individuals may greatly reduce soybean grain yield. Soybean cultivar holding low height is affected mostly by competitive stress imposed by concurrent plants presenting high stature.