Tillage and controlled drainage-subirrigated management effects on soil persistence of atrazine, metolachlor, and metribuzin in corn

The occurrence of herbicides in surface waters necessitates the development of management practices to reduce herbicide loss through tile drainage and surface runoff Four tillage-intercrop systems: moldboard plow (MB), moldbo ard plow with rye grass (Lolium multiflorum Lam.) intercrop (MB+IC), soil s aver (SS), and soil saver with rye grass intercrop (SS+IC), and two water t able management treatments: controlled drainage-subirrigation (CDS) and no control drainage (D) were investigated for their effect on herbicide persis tence. Atrazine [2-chloro-4-ethylamino-6-isopropylamino(1.1 kg ha(-1)), met ribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-o ne] (0.5 kg ha(-1)), and metolachlor [2-chloro-N- (2-ethyl-6-methylphenyl)- N-(2-methoxy-1-methylethyl) acetamide] (1.68 kg ha(-1)) were strip applied in a corn (Zea mays L.) management system to reduce herbicide inputs 50%. T illage-intercrop system had little consistent effect on soil residues of th e herbicides at 0- to 10-cm depth. Control drainage-subirrigation decreased half-life of atrazine and metolachlor in one of two years. Half-life for a trazine ranged from 34 to 56 d, metribuzin 24 to 35 d, and metolachlor 40 t o 79 d, with longer half-life in dry years. Des-ethyl atrazine [2-chloro-4- amino-6-isopropylamino-s-triazine], the major metabolite of atrazine, persi sted along with atrazine and metolachlor to the next planting season. Less than 10% of the original herbicide application was recovered the year follo wing application. It was concluded that environmental factors such as rain affect herbicide residues more than cultural practices.