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Reducing DCPA Losses in Furrow Irrigation by Herbicide Banding and Straw Mulching

Malheur Exp. Stn., Oregon State Univ., Univ., 595 Onion Ave., Ontario, OR 97914
1 Jefferson Pkwy., #298, Lake Oswego, OR 97035
P.O. Box 2150, Keizer, OR 97307
Dep. of Agric. Chem., Oregon State Univ., Corvallis, OR 97331
Dep. of Cognitive and Neural Systems, Boston University, 677 Beacon St., Rm. 201, Boston, MA 02215
Dep. of Agric. Chem., Oregon State Univ., Corvallis, OR 97331

^* Corresponding author (Clinton.Shock{at}orst.edu).

There are concerns about residues of DCPA (dimethyl 2,3,5,6-tetrachloro-1,4-benzenedicarboxylate) and its two acid metabolites in surface runoff from furrow-irrigated croplands. We studied the effects of mulching irrigation furrows with wheat (Trilicum aestivum L.) straw on DCPA movement in runoff solution, with sediment, and in the soil profile. The study site had a Nyssa silt loam (coarse-silty, mixed, mesic Xerollic Haplodurid) with a 3% slope. The field was planted to onion (Allium cepa L.) and was furrow-irrigated 17 times. Prior to mulching, DCPA was either broadcast at 10 kg a.i. ha^–1 or banded at 3.4 kg a.i. ha^–1 on the top of beds between furrows. DCPA (parent plus metabolites) was measured in the runoff sediment of the first 6 irrigations, and in the runoff solution of the 1st, 3rd, and the 5th irrigation. Regardless of herbicide application method, mulching reduced DCPA losses in sediment of all irrigations and in the runoff solution of the fifth irrigation. Averaged across the 6 irrigations and the 2 herbicide application methods, mulching reduced DCPA transfer in sediment by about 90%. Straw mulch effects on DCPA losses were primarily through reductions in soil loss and runoff volume, whereasDCPA concentration was not affected in runoff solution and was increased in runoff sediment of some irrigations. Mulching increased infiltration of broadcast DCPA but tended to decrease infiltration of banded DCPA. Also, compared with broadcast DCPA, banding the herbicide reduced DCPA losses in sediment of some irrigations. We concluded that the combination of straw mulching and banding DCPA reduces herbicide transfer in surface runoff and movement into thesoil profile.

Received for publication January 6, 1997.