J. Troiano et C. Garretson, MOVEMENT OF SIMAZINE IN RUNOFF WATER FROM CITRUS ORCHARD ROW MIDDLES AS AFFECTED BY MECHANICAL INCORPORATION, Journal of environmental quality, 27(3), 1998, pp. 488-494
In California, preemergence herbicide residues have been measured in r
unoff water from citrus orchards that resulted from winter rainfall, T
his study measured the effect of rainfall on the redistribution of her
bicides within a citrus orchard and the effect that shallow mechanical
incorporation had on residue movement. Simulated rainfall treatments
were applied to plots within a citrus orchard where simazine was appli
ed only to row middles, Simazine (2-chloro-4, 6-bis [ethylamino]-s-tri
azine) movement in runoff water was compared between middles that were
either undisturbed, the normal orchard practice, or subject to shallo
w mechanical incorporation. In undisturbed middles, simazine concentra
tion in runoff water collected from the first of two simulated rain ev
ents averaged 0.87 mg L-1; simazine concentration in runoff water from
a second event applied 7 d later averaged 0.40 mg L-1. Shallow mechan
ical incorporation of row middies decreased runoff mater volume from t
he first simulated rain event by approximately 50% with simazine conce
ntration decreased to 0.14 mg L-1; runoff water volume was unaffected
at the second rainfall event but simazine concentration remained low a
t 0.07 mg L-1. Total simazine mass removed from both events, which als
o accounts for mass recovered in furrow soil, was estimated at 13.1% o
f the amount applied to row middles in undisturbed plots compared to o
nly 2.1% in mechanically disturbed middies. We conclude that ambient r
ainfall is unreliable for incorporation of preemergence herbicides int
o orchard soil with low infiltration, end that shallow mechanical inco
rporation should be tested under commercial citrus growing conditions.