Application Mode and Alternate Cropping Effects on Atrazine Losses From a Hillside

Abstract

AbstractExternal drainage losses of atrazine (2‐chloro‐4‐[ethylamino]‐6‐[iso‐propylamino]‐s‐triazine) were evaluated at two application rates, applied preemergent, and pre‐plant‐incorporated on a hillside where corn (Zea mays L.) was planted with and without oats (Avena sativa L.) as a strip crop at the slope base. The cropping pattern had the most striking influence on soil, water, and atrazine transport in a growing season where a 100‐y frequency storm occurred during June. Statistical covariance analysis revealed that nearly 100% of the time, total atrazine residue losses in external drainage and soil sediment were most strongly related to the number of days from herbicide application to each erosion event.The small grain strip or buffer zone reduced water and soil losses by 66 and 76%, respectively, compared with nonstripped areas, during 11 erosion events. Atrazine losses of 3.5 and 0.33% of that applied (2.2 kg/ha) were recorded in the absence and presence of an oat strip, which represented a 91% reduction in herbicide loss with strip cropping. At the 4.5 kg/ha application rate, herbicide losses were reduced by 65% in the stripped areas compared with the nonstripped areas. Minimal pre‐plant incorporation of atrazine residues with the soil surface also significantly reduced residue loss with each cropping pattern. Using nonstripped, preemergent treated areas as a reference, pre‐plant incorporation of atrazine with strip cropping reduced total atrazine losses by 91 and 87% at the two respective application rates, and allowed only 7 g/ha of atrazine loss at each rate. Therefore, a conventional tillage‐management system combining a minimal surface‐blending of atrazine residues with strip cropping provided soil, water, and chemical residue retention equivalent to that achieved in reduced‐tillage crop management and controlled weeds effectively.