|Lamb, J - UNIVERSITY OF MINNESOTA|
|Anderson, J - UNIVERSITY OF MINNESOTA|
Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 1998
Publication Date: N/A
Interpretive Summary: A reduced non point pollution of surface and ground waters is a national high priority issue. Control on agrichemical escape into the offsite environment can begin with tillage, crop sequence, and method of application to reduce the amount of agrichemical applied, to increase the efficiency of use, and to reduce exposure to soil leaching. For production in a sandy soil under irrigation, the reduced frequency of herbicide application and amount used when combined with cultivation in the ridge till system compared to the non ridge till system - both reduced movement into the groundwater. A special management system for nitrogen prevented nitrate escape into the groundwater - this system involved split time of application, multiple bands each with less N applied per band, and avoidance of application into the depression midway between rows. Yet production was not depressed. This information will be used by producers, NRCS, EPA and others wishing to reduce contamination of ground waters when irrigating sandy soils for production of corn and soybeans.
Technical Abstract: Agrichemical contaminant movement into ground water under irrigated sandy soils can be sensitive to agricultural management systems. Ground water quality in a surficial aquifer under a Zimmerman fine sand was compared as related to two farming systems: ridge tillage (RT) in a corn-soybean (C-S) rotation, and conventional full-width tandem disk tillage in continuous corn (CC). Measured from 1991 to 1995 were: grain yields; atrazine, alachlor, metribuzin, and nitrate-N in soil to a depth of 90 cm; water table concentrations of atrazine, alachlor, metribuzin, and nitrate-N in the surficial aquifer; and changes in ground water quality. Grain yields from corn when rotated with soybeans were greater than with CC. Atrazine, alachlor, and metribuzin concentrations were greatest directly after application and decreased during the growing season to less than 50 ug/kg in the surface 15 cm by the next spring. Herbicides banded over the row in RT were detected only in soil samples taken under the row, while herbicide were detected under the row and between rows when broadcast applied in the CC system. Alachlor and metribuzin were not detected in the ground water, but atrazine and associated breakdown products were detected in the ground water. Deethylatrazine was detected in significant quantities (3 ug/ L) under the CC system but only in small quantities (0.04 ug/ L) with the C-S rotation in the RT system. Nitrate-N concentrations at the water table did not increase under either cropping system, concentrations in soil declined after 1992 because mineralization of organic N from a previous alfalfa history had dissipated. Ridge tillage with the C-S rotation reduced entry of atrazine breakdown products into ground water compared to a full-width tandem disk tillage system with CC.