Infiltration Rates and Sediment Production Following Herbicide/Fire Brush Treatments

Abstract

Terminal infiltration rates were similar in soils on which a heavy whitebrush (Aloysia lycioides) cover had been aerially treated with 2 kg/ha (active ingredient) of 20% tebuthiuron pellets 4 years previously or on tebuthiuron-treated plots which had been prescribed burned the winter about 9 months prior to infiltration measurements, compared to untreated sites. However, sediment production was greater from plots treated with the herbicide than from areas subjected to the herbicide-fire system or from untreated plots. Only minor variations in infiltration rates occurred among sites originally dominated by running mesquite (Prosopis reptans) which were aerially sprayed with 2,4,5-T + picloram (1:1) at 1.1 kg/ha 3.5 years previously, burned 10 months previously, subjected to the herbicide-fire system or left untreated. However, sediment production on the running mesquite areas which had been sprayed tended to be greater than on untreated plots. Sediment production on areas subjected to the herbicide-prescribed burning system tended to be less than from brush-covered plots. Differences in sediment production in both experiments were generally attributed to slightly reduced mulch loads and mulch covers where the brush was removed as a leaf mulch donor by herbicide treatment. Prescribed burning apparently compensated for loss of brush leaf mulch by promoting grass cover on herbicide-treated areas.