Managing runoff of herbicides under rainfall and furrow irrigation with wheel traffic and banded spraying

Herbicide runoff is of concern due to their possible effects on non-target organisms in receiving environments. Band spraying and controlled traffic have potential for managing pesticide runoff in situations where crop residue cover can not be retained. The effectiveness of these two management practices was studied for (simulated) rainfall and the effectiveness of band spraying for furrow irrigation. The site was on a hill-furrow layout, on a heavy cracking clay. Three times after pesticide application treatment (2–42 DAT) were studied. Herbicides with high (pyrithiobac sodium) to moderate solubility (diuron and metolachlor) were studied on simulator plots. Pyrithiobac sodium was studied alone for irrigations. Pyrithiobac sodium was transported >90% in the water phase in rainfall and irrigation runoff, with a sediment-water partition coefficient (Kp) of ∼10 L kg−1 at 2 DAT, increasing to 20–30 L kg−1 after 24 DAT, similar to metolachlor. In contrast, diuron was transported 55% in sediment at 2 DAT (Kp = 43) and ∼85% in sediment at 34 DAT (Kp = 204). Percent in the water phase decreased and Kp increased over time for all herbicides. The 10 and 14 fold greater application rates for diuron and metolachlor than for pyrithiobac sodium led to 120 and 46 times greater herbicide rainfall runoff losses. Rainfall runoff concentrations and losses of herbicides were reduced by >70% at 34 DAT compared with 2 DAT. Non-wheel traffic furrows gave rainfall runoff, soil loss and sediment concentrations 37%, 59% and 33% less than from wheel track furrows. Pesticide runoff concentrations were ∼30% less and losses ∼55% less from non-wheel tracks than from wheel track furrows. This occurred even though conditions were conducive to runoff (moist soil and crusted surface). Band spraying on the hills (∼40% band) reduced rainfall runoff concentrations (cf. blanket) by 41, 32 and 54% and losses by 38, 22 and 50%, for pyrithiobac sodium, metolachlor, diuron, respectively. Band spraying was more effective in reducing rainfall runoff losses for chemicals transported primarily in the sediment phase. Band spraying on the hills (∼40% band) for furrow irrigation reduced concentrations of pyrithiobac sodium by 75% and losses by 88%. Band spraying and non-wheel traffic combined gave greater reductions in pesticide runoff than either practice alone.

► Practices are need for managing pesticide runoff where surface cover is not retained.
► Controlled traffic reduced rainfall runoff losses of three herbicides by 50–58%.
► Band spraying reduced rainfall runoff of three herbicides by 22–50%.
► Band spraying reduced herbicide runoff in furrow irrigations by 88%.
► Herbicide runoff losses declined rapidly with time after spraying.