Submitted to: Seasonally Frozen Soils Symposium
Publication Type: Abstract Only
Publication Acceptance Date: June 12, 1997
Publication Date: N/A
Technical Abstract: In the deep loess hills along the Missouri River valley of southwestern Iowa, field studies are underway to determine the impact of continuous corn production on both surface water and groundwater quality. The landscape is characterized by gently sloping ridges, steep side slopes, and well-defined alluvial valleys often with incised channels that usually terminate at an active gully head. Surface water quality was evaluated by analyzing runoff for nitrate-N, atrazine and metolachlor. Patterns of movement for both fertilizer and herbicide chemicals are compared for four field-sized watersheds under different tillage practices. Beneath the snow cover of early March 1993, a diurnal freeze-thaw cycle was observed which resulted in displacement of both nitrate-N and parent herbicides in surface runoff generated by melting snowcover. During the five days of repetitive events, the nitrate-N and the herbicide displacement patterns are different for the conventional and ridge-till fields. With daily changes in the frostline depth, biotic and abiotic chemical degradation of the herbicides, together with residual fertilizer and a contribution from the nitrification of organic nitrogen in soil or plant residue, account for differences in the mass of each chemical made available for transport.