Loss of pendimethalin in runoff and leaching from turfgrass land under simulated rainfall

A field study was undertaken to investigate runoff and leaching loss of the herbicide pendimethalin in turfgrass land of loamy sand soil. A series of plots constructed in a golf course fairway were surface-applied with pendim ethalin SC formulation at the rate of 2.25 or 4.50 kg a.i./ha and subjected to simulated rainfall at 2.0 cm/day for 10 consecutive days. Runoff losses of pendimethalin were the highest at the first rainfall and then gradually decreased with time. The first runoff event contained pendimethalin in its highest concentration, and in subsequent runoff samples the concentration decreased exponentially. The ranges of pendimethalin concentration were 80. 9-18.2 and 177.4-48.6 mug/L in the standard and double doses, respectively. Total losses by 20 cm of rainfall for 10 days reached 0.81 and 1.22% of th e initial, deposits at 2.25 and 4.50 kg a.i./ha, respectively. Pendimethali n concentration in the leachate collected at 30-cm soil depth was quite low er than that in the runoff, and the concentration rapidly decreased from 4. 3-4.7 to 0.2-0.4 mug/L during the 10 days of rainfall treatment. Soil resid ue analysis at 45 and 90 days after pendimethalin treatment showed that mor e than 90% of the residue remained at the top 10 cm of soil depth. Low runo ff and leaching confirmed that lateral and downward movement of the herbici de should be limited in turf soil. The half-life of pendimethalin under fie ld conditions was 23-30 days and was not affected by application dose and r ainfall treatment, but longer persistence was observed under laboratory con ditions. Considering low runoff and leaching, as well as relatively short p ersistence in soil, it is concluded that little environmental carryover of pendimethalin would be expected in turfgrass land.