Carl H. Pederson

Nitrate-Nitrogen Losses through Subsurface Drainage under Various Agricultural Land Covers

Nitrate-nitrogen (NO₃-N) loading to surface water bodies from subsurface drainage is an environmental concern in the midwestern United States. The objective of this study was to investigate the effect of various land covers on NO₃-N loss through subsurface drainage. Land-cover treatments included (i) conventional corn ( L.) (C) and soybean [ (L.) Merr.] (S); (ii) winter rye ( L.) cover crop before corn (rC) and before soybean (rS); (iii) kura clover ( M. Bieb.) as a living mulch for corn (kC); and (iv) perennial forage of orchardgrass ( L.) mixed with clovers (PF). In spring, total N uptake by aboveground biomass of rye in rC, rye in rS, kura clover in kC, and grasses in PF were 14.2, 31.8, 87.0, and 46.3 kg N ha, respectively. Effect of land covers on subsurface drainage was not significant. The NO₃-N loss was significantly lower for kC and PF than C and S treatments (p < 0.05); rye cover crop did not reduce NO₃-N loss, but NO₃-N concentration was significantly reduced in rC during March to June and in rS during July to November (p < 0.05). Moreover, the increase of soil NO₃-N from early to late spring in rS was significantly lower than the S treatment (p < 0.05). This study suggests that kC and PF are effective in reducing NO₃-N loss, but these systems could lead to concerns relative to grain yield loss and change in farming practices. Management strategies for kC need further study to achieve reasonable corn yield. The effectiveness of rye cover crop on NO-N loss reduction needs further investigation under conditions of different N rates, wider weather patterns, and fall tillage.

Water table, drainage, and yield response to drainage water management in southeast Iowa

Subsurface drainage is an important practice for optimizing crop production, but it accelerates nitrate-nitrogen (NO3-N) loss to downstream water bodies. As a result, there is a need for practices that can maintain crop production while decreasing subsurface drainage volume and NO3-N export. The objectives of this work were to evaluate the impact of drainage water management through controlled drainage, shallow drainage, conventional drainage, and no drainage on subsurface drainage volumes, water table depths, crop yields, and NO3-N export. This research was conducted at the Iowa State University Southeast Research Farm and consisted of four management schemes with two replicates for a total of eight plots. Plots consisted of a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation with half of the plot planted in corn and half planted in soybeans each year. Findings from four years show that undrained plots had a high occurrence of elevated water tables. Controlled and shallow plots had elevated water tables in the early spring and early fall in accordance with the rainfall and management protocols for controlled drainage. Water table response was quick, with drawdown to tile depth within one to two days after significant rain events. During the period of the study, drainage water management through controlled drainage or shallow drainage reduced overall drainage volume by 37% and 46%, respectively. Average annual NO3-N loss for the study period was reduced by 36% and 29% for controlled drainage and shallow drainage, respectively. Over the four-year period, corn yields in the controlled plots were significantly lower than conventional drainage; however, yields were not statistically different from shallow drained plots. There was no statistically significant difference between drained plots in terms of soybean yield for the study period. Undrained plots, however, had significantly lower yields for corn when compared with shallow and conventional treatments and for soybeans when compared to all treatments. This study highlighted the potential for use of drainage water management practices in reducing subsurface drainage volume and downstream NO3-N loss. In addition, the study highlighted the overall importance of drainage on maintaining crop yields.

Vegetative Treatment Systems for Open Feedlot Runoff: Project Design and Monitoring Methods for Five Commercial Beef Feedlots

A project to demonstrate, implement, and model non-basin technologies for open beef feedlot runoff at five commercial locations is in progress. The investigation will evaluate through field monitoring the performance of these technologies. This information will be used to address whether the systems are feasible alternatives to traditional basin technologies and used to assess non-basin computer models for planning and design of future systems. The non-basin technologies demonstrated in the study include either a vegetated treatment area (VTA) or a vegetated infiltration basin (VIB) in combination with a VTA. The paper will cover the experimental design, monitoring equipment, and methodologies established to meet the project’s objectives. The objectives of the experimental design will be to quantify contaminant concentrations and annual mass flow of nutrients from treatment areas receiving settled feedlot runoff. Results will be compared to potential annual control attainable with traditional containment systems. Monitoring equipment and methodologies discussed in the paper will cover the following: 1) measurement of the quantity and quality of effluent leaving the solids settling basin (entering the treatment area), 2) measurement of the quantity and quality of runoff leaving the receiving treatment area below the settling basin, 3) measurement of the groundwater quality beneath the receiving treatment area, and 4) if applicable, measurement of receiving stream water quality upstream and downstream of the site.

Subsurface Drainage Nitrate and Total Reactive Phosphorus Losses in Bioenergy-Based Prairies and Corn Systems

We compare subsurface-drainage NO-N and total reactive phosphorus (TRP) concentrations and yields of select bioenergy cropping systems and their rotational phases. Cropping systems evaluated were grain-harvested corn-soybean rotations, grain- and stover-harvested continuous corn systems with and without a cover crop, and annually harvested reconstructed prairies with and without the addition of N fertilizer in an Iowa field. Drainage was monitored when soils were unfrozen during 2010 through 2013. The corn-soybean rotations without residue removal and continuous corn with residue removal produced similar mean annual flow-weighted NO-N concentrations, ranging from 6 to 18.5 mg N L during the 4-yr study. In contrast, continuous corn with residue removal and with a cover crop had significantly lower NO-N concentrations of 5.6 mg N L when mean annual flow-weighted values were averaged across the 4 yr. Prairies systems with or without N fertilization produced significantly lower concentrations below <1 mg NO-N L than all the row crop systems throughout the study. Mean annual flow-weighted TRP concentrations and annual yields were generally low, with values <0.04 mg TRP L and <0.14 kg TRP ha, and were not significantly affected by any cropping systems or their rotational phases. Bioenergy-based prairies with or without N fertilization and continuous corn with stover removal and a cover crop have the potential to supply bioenergy feedstocks while minimizing NO-N losses to drainage waters. However, subsurface drainage TRP concentrations and yields in bioenergy systems will need further evaluation in areas prone to higher levels of P losses.

COLLECTION AND MONITORING OF ONE-METER CUBIC SOIL MONOLITHS FOR LEACHING STUDIES

This report presents methodology for excavating one-meter cubic undisturbed soil monoliths for detailed laboratory investigations of solute transport through the soil profile. Eight soil monoliths were collected in 1992 from three field areas that had been under consistent tillage systems since 1978. The soil was predominantly a Kenyon silt loam (Typic Hapludoll) with the water table maintained by subsurface drainage. Each monolith was instrumented with time-domain reflectometer (TDR) waveguides, and mini-tensiometers to monitor changes in soil water content and soil matric potential on three sides. A rainfall simulator was constructed to apply water at a rainfall intensity of 33 mm-h–1 to a 0.8 m × 0.8 m surface area of the monolith. A conservative tracer (KBr) was applied to the soil surface and leachate samples were collected from 36 locations at the bottom of each monolith using fiberglass wick extractors attached to 810 mm2 areas in a 6 ×6 grid arrangement. Water application, soil water content and leachate were monitored to determine how surface tillage affected preferential flow. Results suggest that the soil monolith collection and transportation procedures maintained the integrity of the soil profile. Anion tracers provided an inexpensive means of simulating different nitrogen application methods. Grid cell samplers using fiberglass wicks allowed analysis of the spatial variation in leaching losses. Leachate samples provided information about the potential impact of nitrogen application method on leaching losses. When coupled with time domain reflectometry and mini-tensiometers, electronic data logging equipment can be used to monitor changes in soil volumetric water content and matric potential.

Impact of system management on vegetative treatment system effluent concentrations

Beef feedlots of all sizes are looking for more cost-effective solutions for managing feedlot runoff. Vegetative treatment systems are one potential option, but require performance evaluation for use on concentrated animal feeding operations. The performance of six vegetative treatment systems on open beef feedlots throughout Iowa was monitored from 2006 through 2009. These feedlots had interim, National Pollution Discharge Elimination System permits that allowed the use of vegetative treatment systems to control and treat runoff from the open feedlots. This manuscript focuses on making within site comparisons, i.e., from year-to-year and component-to-component within a site, to evaluate how management changes and system modifications altered performance. The effectiveness, in terms of effluent concentration reductions, of each system was evaluated; nutrient concentration reductions typically ranged from 60 to 99% during treatment in the vegetative components of the vegetative treatment systems. Monitoring results showed a consistent improvement in system performance during the four years of study. Much of this improvement can be attributed to improved management techniques and system modifications that addressed key performance issues. Specifically, active control of the solid settling basin outlet improved solids retention and allowed the producers to match effluent application rates to the infiltration rate of the vegetative treatment area, reducing the occurrence of effluent release. Additional improvements resulted from system maturation, increased operator experience, and the addition of earthen flow spreaders within the vegetative treatment area to slow flow and provide increased effluent storage within the treatment area, and switching to active management of settling basin effluent release.

Settling Basin Design and Performance for Runoff Control from Beef Feedlots

Regulatory requirements and environmental awareness have increased the need for controlling runoff from beef feedlots. Vegetated treatment systems (VTS) that contain solids settling basins are currently being tested and monitored in Iowa for use as an approved Alternative Technology. The purpose of the solids settling basins in these systems is to settle solids and attenuate the flow from the open lot prior to discharging into the VTS. As part of an intensive study, VTSs have been built at four Iowa beef feedlots capable of maintaining 1000 to 5000 head of cattle. The solids settling basins were designed by an engineering firm according to the NRCS Conservation Practice Standard, 350 Solid Sedimentation Basins. Because of site location characteristic differences, each design was different. The objectives of this study were to 1) define the settling basins implemented at each of the four beef feedlots in Iowa in the VTS study, and 2) evaluate the settling basin effluent data collected at each of the sites during monitoring of the study. Multiple discharge sample characteristics were analyzed, but the primary parameter evaluated was total solids. No correlation was observed between total solids concentration and rainfall depth, duration, intensity, or last rainfall date. However, the mass of solids discharged from the basin did increase with rainfall depth and duration. Also, no correlation was found between total solids concentration and the number of days since the lot was last scraped. The computer model used for the design of these vegetated systems assumess discharge pollutant concentrations that are, in general, significantly lower than the values measured in this study. This study provides valuable settling basin data and suggests the need for further study of settling basins used with vegetated treatment systems.

The Impact of Poultry Manure on Water Quality Using Tile Drained Field Plots and Lysimeters

A six-year study was conducted to determine the effects of four experimental treatments [168 kg N/ha from poultry manure (PM), 168 kg N/ha from urea-ammonium nitrate (UAN), 336 kg N/ha from poultry manure (PM2), and 0 kg N/ha (control treatment)] on corn and soybean yields, grain quality, corn stalk N, soil NO3-N, soil PO4-P, subsurface tile drain water quality, runoff water quality, and bacteria concentrations in subsurface drain and runoff waters. Eleven field plots were planted to a corn-soybean rotation, while six lysimeters were planted to continuous corn. Conclusions indicate that the PM treatment is the better choice in applying nutrients to fields because of high yields, which were significantly higher than the UAN treatment and similar to the higher rate PM2 treatment. In addition, the PM treatment resulted in reduced levels of soil NO3-N levels compared to UAN treatment and lower soil PO4-P trends compared to the PM2 treatment. Also, the PM treatment resulted in reduced NO3-N losses in subsurface drain water as compared to the UAN and PM2 treatments. Bacteria concentrations in subsurface drain and runoff waters from the PM2 treatment were higher in comparison with the UAN and PM treatments. Additionally, the bacteria concentrations from the PM2 treatment were double the concentrations of the PM treatment. Thus, as long as the poultry manure is applied at reasonable nitrogen rates (of 168 kg N/ha), it makes a good soil amendment, gives better crop yields, and reduced NO3-N concentrations in subsurface drain water compared to 168 kg N/ha from UAN and 336 kg N/ha from poultry manure.

Corn stover harvest increases herbicide movement to subsurface drains - Root Zone Water Quality Model simulations

BACKGROUND Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor and metolachlor oxanilic acid (OXA). RESULTS The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4-5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal. CONCLUSION The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase owing to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease as a result of the more rapid movement of the parent compound into the soil. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Poultry Manure and Landscape Slope Effect on E. coli Transport with Surface Runoff

Interaction between rainfall and natural landscape conditions can significantly affect the transport of nutrients and pathogens with surface runoff from manure applied fields. When rainfall occurs immediately after the application of manure, the concentration of pathogen in the runoff water could increase and affect the quality of surface water. The objective of this study was to investigate the effects of different poultry manure application rates and different field slopes on the transport of Escherichia coli (E. coli) with surface runoff. This laboratory study was conducted using a rainfall simulator and set of soil trays in the Porous Media Laboratory at Iowa State University. This experiment consisted of nine different treatments consisting of three different poultry manure application rates (0, 168 and 336 ton. ha-1) and three artificial slopes of 2, 4 and 9 %. Nine rectangular-steel trays were used for each of the four replications for each treatment, under the rainfall simulator, applying rainfall for a total period of 2.5 hours at an intensity of 25 mm. h-1. The experimental treatments used in this study reflected the real cultural practices used by farmers, within the natural landscape of central Iowa. Results of this study showed that the estimated total amount of E. coli transport with runoff water was different from slope to slope for the three slopes studied in this experiment; but the total amount of E-Coli transport was significantly higher at 9% slope in comparison to other twp slopes. An increase of 25 % of the total estimates E. coli FCU took place when manure application rate varied from 168 kg ha-1 to 336 kg ha-1.