Herbicide Leaching under Tilled and No-Tillage Fields

The effect of no-tillage practices on water quality exiting the root zone of deep, well-drained fields is largely unknown. This project was initiated to determine herbicide leaching characteristics as influenced by tillage practice and herbicide formulation. The research site consisted of four adjacent (0.25-ha) fields, two fields each dedicated to either tilled or no-tillage management. One field in each tillage regime received a controlled-release formulation of atrazine [6-chloro-N-ethyl- N\u27-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and alachlor [2-chloro- N-(2,6-diethylphenyl)-N-(methoxymethyl)-acetamide, starch encapsulated], while the others received standard herbicide formulations of atrazine and alachlor. Both herbicide formulations were annually applied at the same rate: 1.7 kg ha‒1 for atrazine and 2.8 kg ha‒1 for alachlor. Atrazine, deethylatrazine [DEAT; 6-chloro-N-(l-methylethyl)- 1,3,5-triazine-2,4-diamine], alachlor, and Br ‒ concentrations were monitored with 12 suction lysimeters (six each at 1.5- and 1.8-m depths) in each field. Alachlor was detected in \u3c3% of all samples collected, regardless of tillage practice or herbicide formulation, while atrazine was detected in \u3e41% of the samples. Under no-tillage, atrazine was detected in \u3c28% of the samples with \u3c13% exceeding the U.S. Environmental Protection Agency Health Advisory level of 3 μg L‒1 atrazine. Under tilled conditions, 53% of the samples contained atrazine, with 35% exceeding 3 μg L‒1 atrazine. Averaged atrazine metabolite concentration of DEAT under no-tillage was 0.52 μg L‒1 vs. 0.39 μg L‒1 for tilled fields. Similar Br ‒ transport between tillage practices and reduced atrazine levels under no-tillage fields suggest that no-tillage management, on deep well-drained soils, can have a positive impact on groundwater quality