The Use of the Soil-Plant-Air-Water Model to Predict the Hydraulic Performance of Vegetative Treatment Areas for Controlling Open Feedlot Runoff

Several Iowa beef feedlots have interim, National Pollution Discharge Elimination System (NPDES) permits for vegetative treatment systems (VTS) to control and treat feedlot runoff. In Iowa, performance of these systems is predicted for permitting purposes using either the Iowa State University-Vegetated Treatment Area (ISU-VTA) Model or the Iowa State University -Vegetated Infiltration Basin/Vegetated Treatment Area (ISU-VIB/VTA) Model. For an Iowa NPDES permit, these systems must be shown through modeling to have equal or better performance than a conventional runoff containment basin on the basis of median nutrient mass released over 25 years. Modeling is also a useful design tool for both Concentrated Animal Feeding Operations (CAFOs) and non-CAFO sized operations wishing to utilize VTS systems. Field-scale VTS performance monitoring conducted over the past two years by ISU has shown that the current ISU models do not accurately predict actual hydraulic performance at the monitored VTSs. The ISU models are being revised to improve their performance. Along with improving the ISU-VTS model performance, other modeling alternatives are being investigated. The Soil-Plant-Air-Water (SPAW) model is one possible alternative for modeling the hydraulic performance of a VTA. For this paper, the SPAW predicted performance was compared to monitoring results at four VTAs located in Iowa. Two different methods were used to model the VTA performance, the first method utilized the field module of SPAW; this method was found to have Nash-Sutcliffe modeling efficiencies ranging from 0.16 to 0.57. At all locations, the SPAW model underestimated the amount of release that occurred from the VTAs. The second modeling method utilized the pond module of SPAW, for this method the Nash-Sutcliffe modeling efficiencies ranged from 0.26 to 0.83. Again, the SPAW model underestimated the cumulative volume of effluent released from the VTAs

Impact of Fertilizer Application Timing on Drainage Nitrate Levels

Nitrate loss from drainage systems in Iowa and other upper Midwestern states is a concern relative to local water supplies as well as the hypoxic zone in the Gulf of Mexico. As a result, there is a need to quantify how various nitrogen management practices impact nitrate loss. One practice that is commonly mentioned as a potential strategy to reduce nitrate loss is to vary fertilizer application timing and specifically apply nitrogen as close to when the growing crop needs it as possible. At a site in Gilmore City, Iowa, a number of fertilizer timing and rate schemes within a corn soybean rotation were used to study the impacts on nitrate leaching. Timing schemes include nitrogen application in the fall and an early season sidedress in the spring with each scheme having four replicates for both corn and soybeans. Fertilizer application rates investigated are 84 and 140 kg/ha (75 and 125 lb/ac) in the fall and 84 and 140 kg/ha (75 and 125 lb/ac) in the spring. The timing and rates have been practiced since 2005 with contrasting weather conditions each year. Overall, an annual basis there was not significant differences in nitrate concentrations or loss exiting the drainage system between the application rates or between the fall and spring application. In addition, there was not a yield penalty to the corn crop when fertilizer as applied in the fall versus the spring

Impact of Drainage Water Management on Crop Yield

The objectives of this project were to study nitrate loading in subsurface drainage and corn-soybean yield response under various drainage water management practices. This experiment explores various drainage strategies to reduce nitrate loading to surface waters in southeast Iowa

Role of Directly Connected Macropores on Pathogen Transport to Subsurface Drainage Water

Pathogen contamination of water supplies is now considered one of the top water quality issues in the United States and worldwide. Continual application of livestock manure may contribute to nonpoint source pollution by releasing microbial pathogens including bacteria, virus, and protozoa, through runoff and subsurface drainage water to surface and ground water. Many studies have been conducted in the laboratories and fields to understand the preferential flow through macropores. But no experiments in the field have been conducted to examine the breakthrough curve of pathogen and/or Escherichia coliform (E.coli) with directly connected macropores. The objective of this research is to address the transport of pathogens (specifically the indicator organism E. coli) through soils, and more specifically the role of macropores in the transport of E. coli to subsurface drains. A greater understanding and more theoretical modeling approach is needed to understand the role of directly connected macropores on pathogen transport to subsurface drainage