A large fraction of many applied pesticides are lost to the air and dissipated. Microclimatological methods were used to determine the diurnal loss rates by volatilization of trifluralin applied and incorporated into the soil of a 1.26‐ha upper Piedmont plateau watershed. Trifluralin flux decreased to very low levels during daytime when surface soil water content was low even though turbulence, soil temperature, and evaporative demand were high. During nighttime, when evaporative demand subsided and the surface soil water content increased, the trifluralin flux increased as the surface soil water content increased. Trifluralin and lindane flux on a limited plot‐size study were compared and both pesticides reacted similarly to environmental conditions, except lindane volatilized more rapidly.When the soil surface was not wet, trifluralin and lindane fluxes appeared to be controlled by surface soil water content and the water content's effect on pesticide adsorption to the soil particle. Apparently, adsorption to the soil particle upon soil drying is a reversible process since efflux of the pesticides was rapid when soil was rewetted by dew or rainfall to above the equivalent of three molecular layers of adsorbed soil water. Under controlled soil‐water conditions, where the soil surface remained wetter than three molecular layers of adsorbed water, the pesticide fluxes responded to increased soil temperature and turbulence, and atmospheric stability conditions.
Consolidation and changes in surface horizon properties induced by no‐tillage may reduce soil loss to levels beyond those attributable to surface residue alone. To evaluate effects of consolidation and surface horizon modification induced by long‐term no‐tillage on rill erodibility (Kr) and critical hydraulic shear (τc), simulated rainfall and inflow were applied to plots managed under conventionally tilled monocropped soybean [Glycine max (L.) Merr.], conventionally tilled monocropped grain sorghum [Sorghum bicolor (L.) Moench], and no till double cropped crimson clover (Trifolium incarnatum L.) and grain sorghum at three sites with differing surface horizon clay contents. All surface residue was removed prior to rainfall simulation, and conventionally tilled cropping systems were evaluated in both consolidated and freshly tilled conditions. Increases in organic C from 9.3 to 12.9 g kg−1 and water‐stable aggregates from 50 to 76% induced by no‐tillage resulted in a 60 to 70% decrease in Kr for the no‐till system, compared with conventionally tilled systems. No differences in Kr were observed for the two conventionally tilled systems. No differences in τc were observed among the tillage systems. Consolidation within the conventionally tilled treatments reduced Kr by ≈60% from that observed for freshly tilled soil. The reduction was attributed to greater resistance to detachment by flow associated with soil strength increases due to consolidation. Differences in Kr and τc among the sites were small and were not readily explained by any of the soil properties evaluated. These results indicate that consolidation and modification of surface soil properties under no‐till cropping systems are important factors that contribute to reduced rill soil loss observed under no‐tillage.
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