S-METOLACHLOR + ATRAZINE EM SUBSTRATOS COM DIFERENTES TEORES DE MATÉRIA ORGÂNICA AFETAM A EMERGÊNCIA E CRESCIMENTO DE PLÂNTULAS DE MILHO

Abstract

In the chemical management of weeds, it is essential to understand how pre-emergent herbicides behave in soils with varying levels of organic matter. The objective of this research was to understand the effect of the pre-emergent herbicide s-metolachlor + atrazine on phytotoxicity in maize crops across soils with different organic matter contents, focusing specifically on the seedling emergence and growth phases. Different organic matter levels (1.3%, 3.1%, and 4.45%) were simulated in a prepared substrate where maize seeds were sown. Herbicide doses ranging from 0% to 50% concentration were applied after sowing using a CO2-pressurized backpack sprayer. Maize seedling emergence variables were evaluated using both traditional methods and digital image processing, which demonstrated high efficiency starting from the fifth day when seedlings began to show higher green pigment content. The s-metolachlor + atrazine herbicide affected emergence in a manner directly proportional to the dose. Lower concentrations (2% to 10%) allowed for 50% to 70% emergence and a normal growth rate over time, while higher doses (20% and 50%) resulted in a sharp drop in emergence, delayed development, and, in some cases, total inhibition of emergence. The emergence process occurred slowly during the first three days, accelerating significantly from the fourth to the sixth day. At higher doses, emergence remained low with little progression over time. Soil organic matter did not mitigate the phytotoxic effects of the herbicide at the tested concentrations, with emergence being only slightly higher at doses up to 10%, suggesting minimal adsorption. The application of the Excess Green (ExG) spectral index associated with seedling segmentation was effective in automating the maize emergence counting process for evaluations conducted between the third and tenth day after sowing.