Browsing by Author "Shukla, S."
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- Impact of agrichemical facility best management practices on runoff water qualityShukla, S.; Mostaghimi, Saied; Lovern, S. B.; McClellan, P. W. (American Society of Agricultural and Biological Engineers, 2001)Water quality effects of structural and managerial BMPs implemented at an agrichemical mixing and handling facility, located in an agricultural watershed in Virginia, were investigated in this study. The measured water quality parameters include two commonly used pesticides (atrazine and metolachlor), nitrogen (N), and phosphorus (P). BMPs implemented include: pesticide mixing and loading concrete pad with a sump and pump fitting; a variety of runoff diversion structures to divert the rooftop runoff away from the critical areas; structures to contain transport of chemicals to the drainage leaving the facility; and recycling of rinsate by applying it on the agricultural land. Concentration of pesticides and nutrients were measured at the facility outlet as well as the outlet of the main watershed in which the facility was located. Implementation of BMPs resulted in drastic reduction in mean concentrations of the two pesticides in the stream leaving the facility as well as in the main watershed stream. Maximum atrazine concentrations in the drainage leaving the facility reduced from 17,389 mug/l during the pre-BMP period (1986-1988) to 1,452 mug/l during the post-BMP period (1989-1996). The post-BMP mean concentrations of atrazine and metolachlor at the facility outlet were reduced by 94% (2690 mug/l to 166 mug/l) and 91% (4579 mug/l to 402 mug/l), respectively. The corresponding post-BMP reductions in concentration at the main watershed outlet were 52% and 78% for atrazine and metolachlor, respectively. Nonparametric trend tests results indicated statistically significant downward trend and reduced post-BMP concentrations of the two pesticides at the facility as well as the watershed outlets. Impact of BMPs on the nutrient concentrations were not clear due to large nutrient contributions from animal production activities in upland areas of the watershed Results from this study will provide needed impetus for implementation of BMPs at other agrichemical mixing and handling facilities in Virginia as well as other states to drastically reduce the transport of pesticides and nutrients to surface water bodies.
- Laboratory measurements and modeling N mineralization potential in Virginia Coastal Plain agricultural, fallow, and forest soilsShukla, S.; Mostaghimi, Saied; Burger, James A. (American Society of Agricultural and Biological Engineers, 2000)A long-term aerobic incubation and leaching technique was used to measure N mineralization of surface and subsurface soils (sandy loam) from agricultural,forest, and fallow sites in a Virginia Coastal Plain watershed. N mineralization potential was measured to refine models used to describe this process in a watershed-scale nutrient export assessment. Potentially mineralizable N (N-0) and reaction rate constants (k) were estimated using a first-order model and a nonlinear regression procedure. Large variations in cumulative N mineralized, N-0, and k, were found for the surface soils from agricultural areas. Forest soils had much higher potentially mineralizable N than agricultural soils. For subsurface soils, the differences among land uses were less variable than those observed for the surface soils. The first order model (single-pool approach) was adequate for predicting N mineralization in surface soils from agricultural and fallow areas, but less suitable for forest surface soils. Consideration of a double exponential (two-pool approach) model did not improve the performance of N mineralization prediction for forested or agricultural soils. Large variations occurred in the field-predicted values of mineralized N due to temperature and moisture ranges commonly occurring throughout the season. Variability in the N mineralization potential of soils in the watershed suggests that individual k and N-0 should be derived for soils with similar properties to obtain better predictions of N mineralization and thus N movement to groundwater.