Abstract

RIZZARDI, Mauro Antônio; FLECK, Nilson Gilberto; RIBOLDI, João  and  AGOSTINETTO, Dirceu. Adjustment of model to quantify the effect of weeds and sowing time on soybean yield . Pesq. agropec. bras. [online]. 2003, vol.38, n.1, pp. 35-43. ISSN 0100-204X.  http://dx.doi.org/10.1590/S0100-204X2003000100005.

The objective of this work was to adjust and validate a mathematical model based beggarticks (Bidens spp.) and arrowleaf sida (Sida rhombifolia L.) densities, integrating the soybean seeding time after plant cover desiccation as a variable in order to quantify the losses in grain yield. Four experiments were conducted in Passo Fundo and Eldorado do Sul, RS, Brazil. Treatments consisted of beggarticks and arrowleaf sida densities, and soybean seeding times in relation to plant cover desiccation date. In the trials performed with beggarticks, soybean seeding was carried 3, 7, and 11 days after desiccation (DAD) of plant cover, in both locations. In the trials that included arrow leaf sida, soybean seeding was performed 3, 7, and 11 DAD in Passo Fundo, and 20, 24, and 28 DAD in Eldorado do Sul. In order to analyse the data, it was used the rectangular hyperbolic model, which incorporates weed density and its emergence time in relation to the crop. Delaying soybean seeding in relation to plant cover desiccation increased the levels of crop grain yield losses due to weed interference, mainly for beggarticks. The rectangular hyperbolic model can be used to predict soybean grain yield losses for both weed species.

Keywords : beggarticks; arrowleaf sida; weed density; crop yield losses; mathematical models; plant cover desiccation.