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Cover crops can reduce nitrogen (N) loss to subsurface drainage and can be reimagined as bioenergy crops for renewable natural gas production and carbon (C) benefits (fossil fuel substitution and C storage). Little information is available on the large-scale adoption of winter rye for these purposes. To investigate the impacts in the North Central US, we used the Root Zone Water Quality Model (RZWQM) to simulate corn-soybean rotations with and without winter rye across 40 sites. The simulations were interpolated across a five-state area (IA, IL, IN, MN, and OH) with counties in the Mississippi River Basin, which consists of ~8 million ha with potential for rye cover crops on artificially drained corn-soybean fields (more than 63 million ha total). Harvesting fertilized rye cover crops before soybean planting in this area can reduce N loads to the Gulf of Mexico by 27% relative to no cover crops, and provide 18 million Mg yr-1 of biomass–equivalent to 0.21 EJ yr-1 of biogas energy content or 3.5 times the 2022 US cellulosic biofuel production. Capturing the CO2 in biogas from digesting rye in the region and sequestering it in underground geologic reservoirs could mitigate 7.5 million Mg CO2 yr-1. Nine clusters of counties (hotspots) were identified as an example of implementing rye as an energy cover crop on an industrial scale where 400 Gg yr-1 of rye could be sourced within a 121 km radius. Hotspots consisted of roughly 20% of the region's area and could provide ~50% of both the N loss reduction and rye biomass. These results suggest that large-scale energy cover crop adoption would substantially contribute to the goals of reducing N loads to the Gulf of Mexico, increasing bioenergy production, and providing C benefits.

HighlightsVariability of manure N content on the day of application was a major contributor to plot-to-plot N rate variability.Using the average of previous years’ manure samples is a valid strategy to improve the accuracy of P application.Estimated economic losses from missing target manure N rates averaged $34.27 ha-1 year-1 ($13.87 ac-1 year-1).Improving N rate accuracy with real-time N sensing provided an estimated value of $7 to $44 ha-1 ($3 to $18 ac-1).Abstract. Liquid livestock manure application presents both opportunities for replacing commercial fertilizer and challenges to doing so accurately. This study demonstrated the challenges in achieving a target N application rate using liquid swine manure on eighteen 0.4 ha research plots at the Northeast Research and Demonstration Farm (NERF) near Nashua, Iowa. Differences between the nutrient analyses of manure from a pre-application sample and samples taken on the day of application, equipment adjustments, field conditions, and changing manure nutrient content during pit pumping contributed to variability in the actual N rate applied. The coefficient of variability (CV) of manure N during manure pumping ranged from 2.7 to 13.6, with an 8-year average of 6.5. A weighted-average CV for applied manure volume ranged from 1.5 to 4.7, with an 8-year average CV of 3.2, suggesting that plot-to-plot variability in manure volume was less of an issue for achieving the target N rate than was the variability of manure N on the day of application. A separate analysis of manure from six Iowa swine farms showed that using the average of the previous years’ manure samples improved accuracy for phosphorus at Farm 2, whereas using a single sample from the application year improved accuracy for potassium at Farm 5. Averaged across the six farms, using the average of the previous years’ manure samples resulted in less error for phosphorus than using a single sample from the application year. For nitrogen, there was no significant difference between the two approaches within or across farms (p < 0.1). The average economic loss from missing the target N rate in the NERF study was $34.27 ± $32.49 ha-1 year-1 ($13.87 ± $13.15 ac-1 year-1). The estimated economic value from using real-time nutrient sensing to improve N rate accuracy ranged from $7.56 to $32.03 ha-1 ($3.06 to $12.96 ac-1) in a corn-soybean rotation and from $10.38 to $44.41 ha-1 ($4.20 to $17.97 ac-1) in continuous corn. This study illustrates the need for new technologies for real-time manure nutrient sensing and on-the-go rate adjustment. The economic analysis can serve as a guide for manure applicators when evaluating the feasibility of manure nutrient-sensing systems. Keywords: Manure application, Manure management, Manure nutrient content, Manure nutrient sensing, Manure rate calibration.

HighlightsMeeting nutrient reduction goals will be a massive effort with many challenges.No one practice or group of practices will meet the goals; a mix of multiple practices is needed.Edge-of-field practices become increasingly important as implementation level increases.Understanding the scale of the challenge is a necessary step toward meeting the challenge. Keywords: Gulf of Mexico, Hypoxia, Nitrate, Nutrient reduction, Subsurface tile drainage.

HighlightsFilter strip processes for water pollutant reductions were quantified from 74 studies with almost 300 data points.Regression was significant versus width (sediment, N, P), area ratio (sediment, atrazine), and Ks (N, P, atrazine, alachlor).This review discusses ten functional factors affecting FS efficiency as well as FS monitoring recommendations.Cost-effectiveness was assessed and varies considerably by influent load and treatment effectiveness.Abstract. Filter strips (FSs) are edge-of-field conservation practices commonly implemented to reduce flux of sediment, nutrients, and other constituents from agricultural fields. While various aspects of FS effectiveness have been reviewed, this study provides a comprehensive summary of FS efficiency data for sediment, nutrients, pesticides, and pathogens as part of a special collection focused on agricultural conservation practices. This analysis also fills an important gap by assessing performance-based FS costs and cost-effectiveness. Data from 74 U.S. and international studies with 294 different treatments and 3,050 replications were compiled and analyzed. Results showed that runoff reduction tended to increase with increasing FS width up to about 15 m and that sediment reduction was significantly related to the ratio of FS area to drainage area and to FS width, with reduction tending to increase with increasing width up to about 20 m. Total P reduction was significantly related to FS soil saturated hydraulic conductivity, and total N reduction was significantly related to both saturated hydraulic conductivity and width. Total P and total N reductions both tended to increase with increasing FS width up to about 20 m and with increasing FS slope up to about 10%. Annualized FS costs were estimated to range from $314 to $865 ha-1 year-1 for different FS implementations. A major component of the cost is the opportunity cost of taking land out of production. Costs per unit of sediment retained by FS systems ranged from $10.3 to $18.6 Mg-1. A comprehensive assessment of FS cost-effectiveness (cost:benefit) is needed. Monitoring equipment, approaches, and recommendations are discussed, acknowledging the challenges of implementing field-scale FS studies. This information is critical to guide on-farm and programmatic FS decisions and to increase the scientific understanding of this commonly used agricultural conservation practice. Keywords: Best management practice, Buffer strip, Nonpoint-source pollution, Riparian buffer, Vegetated filter strip.

HighlightsDenitrifying woodchip bioreactors treat nitrate-N in a variety of applications and geographies.This review focuses on subsurface drainage bioreactors and bed-style designs (including in-ditch).Monitoring and reporting recommendations are provided to advance bioreactor science and engineering.Abstract. Denitrifying bioreactors enhance the natural process of denitrification in a practical way to treat nitrate-nitrogen (N) in a variety of N-laden water matrices. The design and construction of bioreactors for treatment of subsurface drainage in the U.S. is guided by USDA-NRCS Conservation Practice Standard 605. This review consolidates the state of the science for denitrifying bioreactors using case studies from across the globe with an emphasis on full-size bioreactor nitrate-N removal and cost-effectiveness. The focus is on bed-style bioreactors (including in-ditch modifications), although there is mention of denitrifying walls, which broaden the applicability of bioreactor technology in some areas. Subsurface drainage denitrifying bioreactors have been assessed as removing 20% to 40% of annual nitrate-N loss in the Midwest, and an evaluation across the peer-reviewed literature published over the past three years showed that bioreactors around the world have been generally consistent with that (N load reduction median: 46%; mean ±SD: 40% ±26%; n = 15). Reported N removal rates were on the order of 5.1 g N m-3 d-1 (median; mean ±SD: 7.2 ±9.6 g N m-3 d-1; n = 27). Subsurface drainage bioreactor installation costs have ranged from less than $5,000 to $27,000, with estimated cost efficiencies ranging from less than $2.50 kg-1 N year-1 to roughly $20 kg-1 N year-1 (although they can be as high as $48 kg-1 N year-1). A suggested monitoring setup is described primarily for the context of conservation practitioners and watershed groups for assessing annual nitrate-N load removal performance of subsurface drainage denitrifying bioreactors. Recommended minimum reporting measures for assessing and comparing annual N removal performance include: bioreactor dimensions and installation date; fill media size, porosity, and type; nitrate-N concentrations and water temperatures; bioreactor flow treatment details; basic drainage system and bioreactor design characteristics; and N removal rate and efficiency. Keywords: Groundwater, Nitrate, Nonpoint-source pollution, Subsurface drainage, Tile.

HighlightsDrainage water recycling captures and stores agricultural drainage water for reuse as supplemental irrigation.Drainage water recycling can both increase crop production and benefit downstream water quality.Depending on management, drainage water recycling can also provide other complementary benefits.Research needs to advance drainage water recycling are presented and discussed. Keywords: Drainage water quality, Drainage water reuse, Subsurface drainage, Supplemental irrigation, Agricultural resiliency.

Artificial drainage is among the most widespread land improvements for agriculture. Drainage benefits crop production, but also promotes nutrient losses to water resources. Here, we outline how a systems perspective for sustainable intensification of drainage can mitigate nutrient losses, increase fertilizer nitrogen-use efficiency and reduce greenhouse-gas emissions. There is an immediate opportunity to realize these benefits because agricultural intensification and climate change are increasing the extent and intensity of drainage systems. If a systems-based approach to drainage can consistently increase nitrogen-use efficiency, while maintaining or increasing crop production, farmers and the environment will benefit. This Perspective suggests how a systems perspective on artificial drainage can promote sustainable intensification, limiting nutrient losses and greenhouse-gas emissions and increasing nitrogen-use efficiency.

Root distributions determine crop nutrient access and soil carbon input patterns. To date, root distribution data are rare but needed to improve knowledge and prediction of cropping system sustainability. In this study, we sought to (i) quantify variation in maize (Zea mays) and soybean (Glycine max) roots by depth and environment across Iowa, USA and (ii) identify environmental factors explaining the most variation. Over three years we collected soil cores from 0 to 210 cm in 16 maize and 12 soybean field experiments at grain filling. Root mass, length, carbon (C) and nitrogen (N) were determined at 30 cm increments, coupled with crop, soil, management, and weather-related measurements. Percentage of root mass located in the top 30 cm varied from 52 to 94% in maize and 54–84% in soybean. Variation in maize root distributions was strongly associated with depth to water tables, variation in soybean with soil physical attributes. Root C:N ratios were highly variable with no depth-pattern, averaging 20 and 30 for soybean and maize, respectively. In both crops, specific root lengths increased with depth to 60 cm, and thereafter remained constant. Field studies of roots should consider depth to water tables and soil moisture measurements, as they influence vertical root distributions.

Harvesting corn stover removes N from the fields, but its effect on subsurface drainage and other N losses is uncertain. We used the Root Zone Water Quality Model (RZWQM) to examine N losses with 0 (NRR) or 50% (RR) corn residue removal within a corn and soybean rotation over a 10-yr period. In general, all simulations used the same pre-plant or post-emergence N fertilizer rate (200 kg ha−1 yr−1). Simulated annual corn yields averaged 10.7 Mg ha−1 for the post emergence applications (NRRpost and RRpost), and 9.5 and 9.4 Mg ha−1 yr−1 for NRRpre and RRpre. Average total N input during corn years was 19.3 kg N ha−1 greater for NRRpre compared to RRpre due to additional N in surface residues, but drainage N loss was only 1.1 kg N ha−1 yr−1 greater for NRRpre. Post-emergence N application with no residue removal (NRRpost) reduced average drainage N loss by 16.5 kg ha−1 yr−1 compared to pre-plant N fertilization (NRRpre). The farm-gate net energy ratio was greatest for RRpost and lowest for NRRpre (14.1 and 10.4 MJ output per MJ input) while greenhouse gas intensity was lowest for RRpost and highest for NRRpre (11.7 and 17.3 g CO2-eq. MJ−1 output). Similar to published studies, the simulations showed little difference in N2O emissions between scenarios, decreased microbial immobilization for RR compared to NRR, and small soil carbon changes over the 10-yr simulation. In contrast to several previous modeling studies, the crop yield and N lost to drain flow were nearly the same between NRR and RR without supplemental N applied to replace N removed with corn stover. These results are important to optimizing the energy and nitrogen budgets associated with corn stover harvest and for developing a sustainable bioenergy industry.

Landscapes and watersheds are inherently leaky and some nutrient loss can be expected with productive agricultural systems. Minimizing these losses, without undermining system sustainability is challenging and should involve an open and constructive discussion among all stakeholders as to what nutrient loss is desired, achievable, and how differences between these two endpoints can be reconciled. This is complicated by short- and long-term variations in weather/climate are a major factor influencing nutrient loss from agricultural lands. Nitrogen (N) loss tends to be spatially extensive, with management of the rate and timing of application, along with cropping systems as being important determining factors. Phosphorus (P) loss, on the other hand tends to be a function of critical sources areas, where coincident source (e.g., soil P and rate, timing, method and type of P applied) and transport factors (e.g., runoff and erosion) define losses. Despite this, legacy N and P from prior land management can mask the benefits of current and future conservation practices (CPs) to reduce losses from agricultural systems. Here, the appropriate use of calibrated and validated nonpoint source watershed models to estimate relative contributions of nutrient sources and outcomes of CP implementation can inform future strategies. However, they must be used in conjunction with and cannot replace water quality monitoring programs. Great strides have been made in nutrient use efficiency via nutrient management, crop selection, and CP adoption, which have reduced the risk of nutrient loss to surface and ground waters. Even so, additional research is needed on the areas of nutrient management on drained lands, fluvial legacies, and socio-economic factors influencing the success of conservation strategies.

Controlled drainage (CD), sometimes called drainage water management, is a practice whereby the drainage system outflow is managed during specific periods to retain more water in the field. Although CD has been shown to reduce downstream nitrate-N (NO3--N) load, seasonal patterns have been less consistent which can potentially impact the effectiveness of conservation practices. The main objective of this study was to assess the regional and seasonal impact of conventional free drainage (FD) and CD on drainage flow and nitrate-N load. Using experimental data from ongoing and historical CD experiments across the Corn Belt and in North Carolina, we evaluated subsurface drain flow, nitrate-N load, and performance of CD systems. Across the data set and regions, there was little difference in annual flow from FD conditions. Seasonally, more northern and western sites experienced a greater percentage of the annual flow occurring in the spring. There was no nitrate-N concentration reduction with CD. Flow and nitrate-N load reductions with CD did not vary by plant hardiness zone across the region, but the season with the greatest reduction did shift from winter to spring moving north and west in the study area. Absolute flow reductions (in mm) were similar regardless of precipitation category. Consequently, the percent reduction was lower as the amount of precipitation (category) increased. Overall, this analysis found CD to be an effective practice for reducing drain flow and nitrate-N loading directly delivered by the drains to downstream water bodies across the region.

Increasing nitrogen (N)-use efficiency (NUE) is key to improving crop production while mitigating ecologically-damaging environmental N losses. Traditional approaches to assess NUE are principally focused on evaluating crop responses to N inputs, often consider only what happens during the growing season, and ignore other means to improve system efficiency, such as by tightening the cycling of soil N (e.g. with N scavenging cover crops). As the goals of improving production and environmental quality converge, new metrics that can simultaneously capture multiple aspects of system performance are needed. To fill this gap, we developed a theoretical framework that links both crop- and soil-based approaches to derive a system N-use efficiency (sNUE) index. This easily interpretable metric succinctly characterizes N cycling and facilitates comparison of systems that differ in biophysical controls on N dynamics. We demonstrated the application of this new approach and compared it to traditional NUE metrics using data generated with a process-based model (APSIM), trained and tested with experimental datasets (Iowa, USA). Modeling of maize-soybean rotations indicated that despite their high crop NUE, only 45% of N losses could be attributed to the inefficient use of N inputs, whereas the rest originated from the release of native soil N into the environment, due to the asynchrony between soil mineralization and crop uptake. Additionally, sNUE produced estimates of system efficiency that were more stable across weather years and less correlated to other metrics across distinct crop sequences and N fertilizer input levels. We also showed how sNUE allows for the examination of tradeoffs between N cycling and production performance, and thus has the potential to aid in the design of systems that better balance production and environmental outcomes.

Evapotranspiration (ET) is a vital component of a field water balance. Canopy chambers are a promising method for determining crop ET because they are portable and applicable at a relatively small plot (m2) scale. Although a variety of canopy chamber designs have been proposed, field tests are still necessary to evaluate chamber performance for measuring crop ET. The objectives of this study are (1) to construct and use an improved canopy chamber to measure ET of three crops [corn (Zea mays, L.), soybean (Glycine max), and reconstructed mixed prairie] and (2) to compare the canopy chamber measurements with flux tower results and field water balance measurements (i.e., rainfall, soil water storage, ET and drainage). Three cropping systems including corn/soybean in a corn-soybean rotation, and reconstructed mixed prairie were studied in central Iowa. Canopy chamber daytime measurements were performed on 18 days in 2013 (a relatively dry growing season) and on 15 days in 2014 (a relatively wet growing season). Based on the results, the differences in daily ET and seasonal cumulative ET between canopy chambers and an eddy covariance flux tower over the measurement periods were within 5%, providing evidence that the portable canopy chamber can accurately measured ET. The chamber ET values and field water balance ET values had similar patterns over the 2013 and 2014 measurement periods, and the differences of cumulative results were less than 10%. In conclusion, the canopy chamber was proven to be an effective method for measuring small plot ET.

This article introduces a special collection of fourteen articles accepted from among the 140 technical presentations, posters, and meeting papers presented at the 10th International ASABE Drainage Symposium. The symposium continued in the tradition of previous symposia that began in 1965 as a forum for presenting and assessing the progress of drainage research and implementation throughout the world. The articles in this collection address a wide range of topics grouped into five broad categories: (1) crop response, (2) design and management, (3) hydrology and scale, (4) modeling, and (5) water quality. The collection provides valuable information for scientists, engineers, planners, and others working on crop production, water quality, and water quantity issues affected by agricultural drainage. The collection also provides perspectives on the challenges of increasing agricultural production in a changing climate, with ever-greater attention to water quality and quantity concerns that will require integrated technical, economic, and social solutions. Keywords: ASABE Drainage Symposium, crop response, design and management, hydrology and scale, modeling, water quality.

Quantitative measurements of root traits can improve our understanding of how crops respond to soil and weather conditions, but such data are rare. Our objective was to quantify maximum root depth and root front velocity (RFV) for maize (Zea mays) and soybean (Glycine max) crops across a range of growing conditions in the Midwest USA. Two sets of root measurements were taken every 10–15 days: in the crop row (in-row) and between two crop rows (center-row) across six Iowa sites having different management practices such as planting dates and drainage systems, totaling 20 replicated experimental treatments. Temporal root data were best described by linear segmental functions. Maize RFV was 0.62 ± 0.2 cm d−1 until the 5th leaf stage when it increased to 3.12 ± 0.03 cm d−1 until maximum depth occurred at the 18th leaf stage (860 °Cd after planting). Similar to maize, soybean RFV was 1.19 ± 0.4 cm d−1 until the 3rd node when it increased to 3.31 ± 0.5 cm d−1 until maximum root depth occurred at the 13th node (813.6 °C d after planting). The maximum root depth was similar between crops (P > 0.05) and ranged from 120 to 157 cm across 18 experimental treatments, and 89–90 cm in two experimental treatments. Root depth did not exceed the average water table (two weeks prior to start grain filling) and there was a significant relationship between maximum root depth and water table depth (R2 = 0.61; P = 0.001). Current models of root dynamics rely on temperature as the main control on root growth; our results provide strong support for this relationship (R2 > 0.76; P

Nutrients in drainage waters from the Upper Mississippi River Basin states have been a well-documented contributor to the Gulf of Mexico hypoxic zone for decades, and in response, twelve states have developed strategies to address this issue, with Iowa, Minnesota, and Illinois performing rigorous science assessments which estimated nitrogen and phosphorus reduction effectiveness for numerous agricultural non-point source conservation practices. The practices identified in these strategies were compared to identify areas of consensus and discord on nutrient load reduction potentials. Additionally, each practice was assessed for (1) the suitability to stack or be layered with other practices (stackability), (2) the ability to track implementation within a state or regionally (trackability), and (3) the level of production system change required to implement the practice. Overall, there was general consensus among the state strategies in the nutrient load reduction effectiveness of most practices with the exception of cover crops (10%-31% nitrogen reduction) and bioreactors (13%-43% nitrogen reduction). The most effective water quality-improvement practices (i.e., land-use change practices) required relatively more production system changes to agronomic management and were the most trackable (scores: 5, 1-5 scale), although they were also less stackable with other practices (scores: 1 to 1.8; 1-5 scale) and were the least cost effective on a unit area basis (generally $15 to $964 per ha). The most cost effective practices tended to be highly stackable (e.g., nitrogen management: (-)$49 per ha and stackability of 4.7), which indicated that stacking a variety of practices may be the most cost effective use of conservation dollars. The practices that were most difficult to track had relatively lower nitrogen loss reduction effectiveness, but these practices were less costly to implement and required relatively less production system change to agronomic management, two factors of importance to many producers.

Developing drainage water management (DWM) systems in the Midwest to reduce nitrogen (N) transport to the northern Gulf of Mexico hypoxic zone requires understanding of the long-term performance of these systems. Few studies have evaluated long-term impacts of DWM, and the simulation of controlled drainage (CD) with the Root Zone Water Quality Model (RZWQM) is limited, while shallow drainage (SD) has not been examined. We tested RZWQM using nine years (2007-2015) of field data from southeast Iowa for CD, SD, conventional drainage (DD), and undrained (ND) systems and simulated the long-term (1971-2015) impacts. RZWQM accurately simulated N loss in subsurface drainage, and the simulations agreed with field data that CD and SD substantially reduced N loss to drainage. As indicated by the field data, the SD N concentration was predicted to be greater than DD and CD, likely due to reduced time of travel to shallower drains. The long-term simulations show that CD and SD reduced annual N lost via tile drainage by 26% and 40%, respectively. Annual reductions in N lost via tile drainage ranged from 28% in the driest years to 22% in the wettest years for CD and from 56% in the driest years to 35% in the wettest years for SD. Considering spring N loading for the purpose of addressing hypoxia in the Gulf of Mexico, CD was found to be less effective than SD, and in many years CD exported more N in the spring than DD. Spring N loading (April through June) was indicated by the EPA Science Advisory Board to have the greatest impact on hypoxia in the northern Gulf of Mexico. Therefore, improvement of CD systems within the months of April through June to reduce N loss via drainage across the upper Midwest landscape may be required. Limited research in the upper Midwest has addressed spring N loading under controlled drainage systems (CD). This research will help model developers, model users, and agricultural scientists more clearly understand N transport under different systems, including CD, SD, and ND, which will aid in developing the design and management of drainage systems to reduce N transport from tile-drained agriculture to surface waters. Keywords: Agricultural simulation model, Drainage water management, Nonpoint-source pollution, Northern Gulf of Mexico hypoxic zone, Nutrient reduction, Subsurface drainage.

Vegetative filter strips (VFS) are popular conservation practices installed at the edges of agricultural fields to reduce losses of pollutants from agricultural areas to receiving waterbodies. The recent interest in using VFS areas as multifunctional landscapes necessitates an improved depiction of VFS in simulation models. This study is aimed to enhance the physical representation of VFS in the Soil and Water Assessment Tool (SWAT) to improve the representation of ecohydrologic processes and land management practices in VFS areas. The proposed enhancement enables routing of water, sediment, and nutrients from the source area through the VFS area and makes the infiltrated water and nutrients available for filter crop uptake. The improvements are implemented in SWAT by modifying input files through Matlab scripts and by changing SWAT subroutines to enable routing. The model improvements are tested with three paired watershed studies with and without edge-of-field VFS in central Iowa. The improved model estimated 46% runoff reduction, 91% sediment reduction, 83% total phosphorus reduction, and 54% nitrate reduction with VFS, and these estimates closely matched the measured VFS reductions. The improved model was able to represent increased infiltration, soil moisture, and denitrification in the VFS area, along with accurately capturing crop yields in the source and VFS areas. Overall, the results indicate improved physical representation of VFS in SWAT. Keywords: Conservation measures, Flexible buffer strips, Multifunctional buffers, SWAT model, Vegetative filter strips.

Nonpoint-source (NPS) pollution is a major cause of surface water quality degradation due to the transport of chemicals, nutrients, and sediments into lakes and streams. Vegetative buffers comprise several effective landscape best management practices (BMPs) that include vegetative filter strips (VFS) and grassed waterways. However, some BMPs are less effective due to concentrated surface flow, improper cropland-to-VFS area ratios, and surface flowpaths that partially or completely bypass vegetative buffers. The overall objective of this study was to quantify the accuracy of simulated flowpaths relative to observed and global positioning system (GPS)-assisted ground-truthed surface flowpaths for improved placement of VFS and other vegetative buffers to effectively intercept surface runoff. This study was conducted on three research sites in Rock Creek watershed in central Iowa. Geographic information system (GIS) software was used for flowpath hydrologic modeling and geospatial map comparison analysis. Digital elevation model (DEM) datasets were used for flowpath simulation and included internet-available USGS 30 m × 30 m grid (typically used to design and site VFS buffers) and light detection and ranging (LiDAR) 5 m × 5 m grid DEMs. Results from this study indicate that the LiDAR 5 m × 5 m DEM generated significantly more accurate simulated flowpaths than the USGS 30 m × 30 m DEM. These results quantitatively underscore the efficacy of using high-resolution LiDAR DEM data to more accurately determine how well surface flowpaths are intercepted by VFS and other vegetative buffers. These results also demonstrate the benefits of coupling high-resolution aerial imagery with quantitative geospatial map comparison data to improve visualization and comparison of field-scale and watershed-scale hydrologic and terrestrial attributes. Ultimately, the results and procedures from this study will be applied to the development of a novel cloud-based, user-interactive, virtual-reality decision support (DS) tool that can be used to remotely assess hydrologic landscape conditions, prescribe improvements to existing BMPs, and determine new sites for enhanced BMP placement and functionality within a high-resolution 3-D imagery environment. Keywords: ArcGIS, Best management practices (BMPs), Decision support (DS) tool, Digital elevation model (DEM), Geospatial analysis, Light detection and ranging (LiDAR), Nonpoint-source (NPS) pollution, Surface runoff, Vegetative filter strip (VFS), Watershed hydrol

The Agricultural Policy Environmental eXtender (APEX) model is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of management practices. The current practice is to fully calibrate the model for each site simulation, a task that requires resources and data not always available. The objective of this study was to compare model performance for flow, sediment, and phosphorus transport under two parameterization schemes: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site-specific soil, weather, event flow, and water quality data. The analysis was conducted using 12 datasets at four locations representing poorly drained soils and row-crop production under different tillage systems. Model performance was based on the Nash-Sutcliffe efficiency (NSE), the coefficient of determination () and the regression slope between simulated and measured annualized loads across all site years. Although the BPJ model performance for flow was acceptable (NSE = 0.7) at the annual time step, calibration improved it (NSE = 0.9). Acceptable simulation of sediment and total phosphorus transport (NSE = 0.5 and 0.9, respectively) was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, uncalibrated use of APEX for planning or management purposes may be misleading. Model calibration with water quality data prior to using APEX for simulating sediment and total phosphorus loss is essential.

Loss of biodiversity and degradation of ecosystem services from agricultural lands remain important challenges in the United States despite decades of spending on natural resource management. To date, conservation investment has emphasized engineering practices or vegetative strategies centered on monocultural plantings of nonnative plants, largely excluding native species from cropland. In a catchment-scale experiment, we quantified the multiple effects of integrating strips of native prairie species amid corn and soybean crops, with prairie strips arranged to arrest run-off on slopes. Replacing 10% of cropland with prairie strips increased biodiversity and ecosystem services with minimal impacts on crop production. Compared with catchments containing only crops, integrating prairie strips into cropland led to greater catchment-level insect taxa richness (2.6-fold), pollinator abundance (3.5-fold), native bird species richness (2.1-fold), and abundance of bird species of greatest conservation need (2.1-fold). Use of prairie strips also reduced total water runoff from catchments by 37%, resulting in retention of 20 times more soil and 4.3 times more phosphorus. Corn and soybean yields for catchments with prairie strips decreased only by the amount of the area taken out of crop production. Social survey results indicated demand among both farming and nonfarming populations for the environmental outcomes produced by prairie strips. If federal and state policies were aligned to promote prairie strips, the practice would be applicable to 3.9 million ha of cropland in Iowa alone.

Understanding the environmental impact of bioenergy crops is needed to inform bioenergy policy development. We determined the effects of five biomass cropping systems—continuous maize (Zea mays), soybean (Glycine max)-triticale (Triticosecale ×)/soybean-maize, maize-switchgrass (Panicum virgatum), triticale/sorghum (Sorghum bicolor), and triticale-aspen (Populus alba × P. grandidentata)—on soil-saturated hydraulic conductivity (K S ) across a toposequence in central Iowa, USA. We compared data from the time of cropping system establishment in 2009 to 4 years post-establishment. Both our 2009 and 2013 data confirmed that cropping system impacts on K S vary by landscape position. We found that differences in cropping system impacts were more likely to occur at lower landscape positions, specifically, within footslope and floodplain positions. Previous research on cropping system impacts suggested that grass and woody systems were associated with a general increase in K S over time, with greater changes likely occurring at landscape positions with a higher erosive potential or lower SOC content. Our results confirmed that the triticale-aspen woody system was associated with a significant increase in K S across all landscape positions. In contrast, we did not observe an increase in K S under maize-switchgrass, which we attributed to the high density of switchgrass roots by the fourth year of study, but expect an increase in K S under switchgrass under longer measurement periods. We also found a significant increase in K S in the annual systems, likely due to the conversion to no-till soil management with cropping system establishment. We expect such differences to become more apparent over longer time scales as cropping systems continue to impact soil hydraulic properties.

Neonicotinoids are a widely used class of insecticides that are commonly applied as seed coatings for agricultural crops. Such neonicotinoid use may pose a risk to non-target insects, including pollinators and natural enemies of crop pests, and ecosystems. This study assessed neonicotinoid residues in groundwater, surface runoff water, soil, and native plants adjacent to corn and soybean crop fields with a history of being planted with neonicotinoid-treated seeds from 2008 to 2013. Data from six sites with the same crop management history, three with and three without in-field prairie strips, were collected in 2015–2016, 2–3 years after neonicotinoid (clothianidin and imidacloprid) seed treatments were last used. Three of the six neonicotinoids analyzed were detected in at least one environmental matrix: the two applied as seed coatings on the fields (clothianidin and imidacloprid) and another widely used neonicotinoid (thiamethoxam). Sites with prairie strips generally had lower concentrations of neonicotinoids: groundwater and footslope soil neonicotinoid concentrations were significantly lower in the sites with prairie strips than in those without; mean concentrations for groundwater were 11 and 20 ng/L ( p = 0.048) and p = 0.0004) for soil, respectively. Surface runoff water concentrations were not significantly (p = 0.38) different for control sites (44 ng/L) or sites with prairie strips (140 ng/L). Consistent with the decreased inputs of neonicotinoids, concentrations tended to decrease over the sampling timeframe. Two sites recorded concentration increases, however, potentially due to disturbance of previous applications or influence from nearby fields where use of seed treatments continued. There were no detections (limit of detection: 1 ng/g) of neonicotinoids in the foliage or roots of plants comprising prairie strips, indicating a low likelihood of exposure to pollinators and other insects visiting these plants following the cessation of seed coating use. Offsite transport of neonicotinoids to aquatic systems through the groundwater and surface water were furthermore reduced with prairie strips. This study demonstrates the potential for prairie strips comprising 10% of an agricultural catchment to mitigate the non-target impacts of neonicotinoids.

The effects of intermittent drying of normally saturated organic systems such as peatlands, swamps, or wetlands has not been reported quite as often as those of wetting and drying cycles of normally dry soils. We report here the effects of weekly drying and rewetting events on saturated woodchips used as denitrification bed. We used denitrification rates and gas effluxes as indicators of the response of normally saturated organic substrate to intermittent aerobic conditions. We used replicated eight upflow columns in the lab fed with nitrated water, and undergoing variable duration of intermittent aerobic conditions (none, 2, 8, and 24 hours) over a 400d experiment. We used high-frequency sensors to measure in- and outflow nitrate and DOC concentrations on a 2-hour basis, from which we calculated denitrification rates. We also measured the CO2 and N2O effluxes in the headspace on an hourly basis. The results show a burst of respiration activity during drying events and for several days after rewetting. Isotopic data suggest that respiration was bacterial denitrification. Intermittent aerobic conditions seem to provide the conditions conducive to the generation of more and better quality DOC, which microbes use during subsequent saturated conditions. Our results suggest that intermittent aerobic conditions may have lasting impacts on microbial respiration in wetlands.

Ephemeral gullies (EG) are linear erosion features located in swales where surface and/or subsurface runoff concentrate during or immediately after rainfall events. As its name states, EGs are temporary because they are easily filled by conventional machinery, but when filled they reform if the area is not appropriately managed. Downstream water quality issues and decreased soil productivity are the main environmental impacts. EGs are frequently identified as (the most) relevant sediment sources in agricultural areas but their dimensions and particular contribution to the total erosion under different temporal, spatial, climate and land use condition is still unknown. Therefore, the objective of this study is to obtain ephemeral gully erosion rates and estimate the main morphological characteristics of the ephemeral gullies (width, length and depth) and their evolution both in relation to time and position on the landscape.The studied EGs, B6 with a 0.94 ha watershed and I3 with a 0.95 ha watershed formed in two fields located in the Walnut Creek watershed, Iowa (US). The field-sized watersheds are less than 1.5 Km apart and have similar topography and soils. The cropping system consists of a two-year corn-soybean rotation managed by one farmer using no-till and other standard management practices. EG were measured using close range photogrammetry techniques. In order to achieve a suitable characterization of the EG evolution over time and space, EGs were divided in three sections (bottom, middle and top) of equal length. Photographs were taken at least once in 2013, 2014 and 2018 (a total of five in I3 and three in B6). Cross section profiles along the EG perpendicular to the flow path direction were selected and their width, area and depth were determined from a graphical representation of the cross sections. EG volumes were estimated by the sum of interpolating sequential cross-section areas and multiplying by the distance between them.Average EG erosion rates during 2013-2014 were 3.19 Mg ha-1 year-1 for B6 and 3.63 Mg ha-1 year-1 for I3. Values in agreement with rates estimated by the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) of 0.49 to 5.18 Mg ha-1 year-1 across the USA and other simulated values of 4.00 ± 1.76 Mg ha-1 year-1 for no till systems in the state of Iowa. The current study shows evidences that EG in no till systems may not stabilize after their formation. EG dimensions (depth, width and length, thus volume) varied over time and space during the continuously monitored period. In general, volumes tend to increase in the middle position while depths decrease in the bottom position. When the EG was filled, it reformed again in approximately the same location showing similar dimensions to that which existed prior to filling.

Best management practices (BMPs) are effective in reducing nutrient and sediment export, but further understanding of the benefits of the stacked BMPs is needed. This catchment-scale study was established to evaluate the impact of hydrology and BMPs on phosphorus (P) and sediment losses. Two adjacent catchments, one with a lower level of BMP adoption (Low-BMP #11) and one with a higher level (High-BMP #12), were compared for total P (TP) and total suspended solids (TSS) export. The BMPs include nutrient management plans, reduced tillage, grassed waterways, terraces, and perennial vegetation. The TP event-flow-weighted (EFW) concentration was significantly higher at Low-BMP #11 (0.293 mg L-1) than at High-BMP #12 (0.069 mg L-1). There was no significant difference in TP base-flow-weighted (BFW) concentrations between Low-BMP #11 (0.035 mg L-1) and High-BMP #12 (0.037 mg L-1). The TSS-EFW (148.0 vs. 18.6 mg L-1) and TSS-BFW (13.3 vs. 6.9 mg L-1) concentrations were also higher at Low-BMP #11 than at High-BMP #12. High-BMP #12 had lower TP (0.36 vs. 0.59 kg ha-1 yr-1) and TSS (253 vs. 1,961 kg ha-1 yr-1) loading than Low-BMP #11. The lower TP export at High-BMP #12 was likely attributed to the effectiveness of stacked erosion control BMPs and nutrient management plans. Overall, lower P and sediment loading was observed when a greater areal extent of stacked practices was implemented at the catchment level. This finding provides vital information to encourage wider BMP adoption at the watershed scale.

Artificial subsurface drainage is necessary to maintain agricultural production in the soils and climate of north-central Iowa. However, it can result in adverse environmental impacts, because it intercepts and diverts some water and soluble NO3 -N directly to streams. We investigated the impact of no-till and a winter rye cover crop (Secale cereale L.) on seasonal and annual NO3 -N concentration and loading in leachate from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. The eight treatments are chisel plow (CT), chisel plow with winter cereal rye (CTr), no-till (NT), and no-till with winter cereal rye (NTr), with "-C" indicating corn and "-S" indicating soybeans. Plots with artificial subsurface drainage were monitored for water quality from 2011 to 2015. The NT and CTr treatments consistently decreased NO3 -N loss on the seasonal and annual scales compared with CT. Compared with NT, NTr did not reduce NO3 -N loading nor concentration in leachate, probably because of low NO3 leaching potential from NT combined with low rye cover crop biomass throughout the study with NT. The 5-yr average annual NO3 -N concentrations were: 16.9 mg L-1 with CT-S, 16.7 mg L-1 with CT-C, 12.6 mg L-1 with NT-S, 12.0 mg L-1 with CTr-S, 11.8 mg L-1 with CTr-C, 11.4 mg L-1 with NTr-S and NTr-C, and 11.1 mg L-1 with NT-C. Overall, both no-till and a cover crop showed potential for improving N management for water quality.

There is a strong link between nitrate (NO3-N) leaching from fertilized annual crops and the rate of nitrogen (N) fertilizer input. However, this leaching-fertilizer relationship is poorly understood and the degree to which soil type, weather, and cropping system influence it is largely unknown. We calibrated the Agricultural Production Systems sIMulator process-based cropping system model using 56 site-years of data sourced from eight field studies across six states in the U.S. Midwest that monitored NO3-N leaching from artificial subsurface drainage in two cropping systems: continuous maize and two-year rotation of maize followed by unfertilized soybean (maize-soybean rotation). We then ran a factorial simulation experiment and fit statistical models to the leaching-fertilizer response. A bi-linear model provided the best fit to the relationship between N fertilizer rate (kg ha−1) and NO3-N leaching load (kg ha−1) (from one year of continuous maize or summed over the two-year maize-soybean rotation). We found that the cropping system dictated the slopes and breakpoint (the point at which the leaching rate changes) of the model, but the site and year determined the intercept i.e. the magnitude of the leaching. In both cropping systems, the rate of NO3-N leaching increased at an N fertilizer rate higher than the N rate needed to optimize the leaching load per kg grain produced. Above the model breakpoint, the rate of NO3-N leaching per kg N fertilizer input was 300% greater than the rate below the breakpoint in the two-year maize-soybean rotation and 650% greater in continuous maize. Moreover, the model breakpoint occurred at only 16% above the average agronomic optimum N rate (AONR) in continuous maize, but 66% above the AONR in the maize-soybean rotation. Rotating maize with soybean, therefore, allows for a greater environmental buffer than continuous maize with regard to the impact of overfertilization on NO3-N leaching.

This study used a 16-year (1989–2004) field experiment conducted in Iowa to compare the performance of DRAINMOD-N II and Root Zone Water Quality Model2 (RZWQM2) in predicting nitrate-nitrogen (NO3-N) concentration and losses in a subsurface drained field at nine nitrogen application rates (0–252 kg N ha−1). Results showed that the performance of both models can ‘satisfactorily’ predict NO3-N concentration. The Nash–Sutcliffe efficiency (NSE), ratio of the root mean squared error to the standard deviation (RSR), and percent bias (PBIAS) for DRAINMOD-N II were 0.87, 0.36, and −2%, respectively, in simulating NO3-N concentration; and 0.84, 0.39, and −9%, respectively, in simulating NO3-N loss. By contrast, NSE, RSR, and PBIAS for RZWQM2 were 0.76, 0.49, and −3%, respectively, in simulating NO3-N concentration; and 0.64, 0.6, and −16%, respectively, in simulating NO3-N loss. This study indicated that both models can be used to simulate NO3-N loss and concentration in drainage flow at different N application rates. However, DRAINMOD-N II demonstrated slightly better performance than RZWQM2. In terms of the maximum contaminant level, the threshold N rates predicted by RZWQM2 and DRAINMOD-N II did not differ significantly from those in observations and can be used for agricultural production. This study highlights the advantages of DRAINMOD-N II in assessing the effects of nitrogen management practices. Copyright © 2017 John Wiley & Sons, Ltd.

Subsurface drainage improves row crop production but also short circuits nitrate-nitrogen (NO3-N) pathways in the soil with significant losses to surface waters. The objective of this study was to evaluate the effect of shallow, controlled, conventional, and undrained drainage treatments on depth to water table, drainage volume and NO3-N loads, soil water content and storage in the soil profile, and crop yields. This research was conducted at the Iowa State University Southeast Research Farm near Crawfordsville, Iowa, from 2007 to 2015. We report on years five through nine here. The site consisted of eight large field plots with each of the four drainage treatments replicated twice. One-half of each plot was planted with corn (Zea mays L.) and the other half with soybeans (Glycine max [L.] Merr.). The corn and soybean halves were rotated every year in accordance with a typical corn–soybean rotation. The undrained treatment had a shallower water table than the other treatments and had a significantly higher number of days during the growing season when the water table was within 30 cm (12 in) of the ground surface than the other treatments. However, there was no difference in soil water contents in the top 80 cm (31.5 in) of the soil profile during the growing season between drainage treatments. Over the five-year study, controlled and shallow drainage reduced annual subsurface flows by 60% and 58%, respectively, while also reducing NO3-N loads by 61% and 49%, respectively, as compared to the conventional drainage design. Crop yields were similar along the drainage designs but significantly lower in the undrained treatment. This study highlights the effectiveness of shallow and controlled drainage to reduce NO3-N loads.

In Iowa, producers achieve an adequate growing season for high yielding corn (Zea mays L.) by beginning field activities in a timely fashion. Subsurface drainage allows for early field activities by improving trafficability and decreasing excess water stress to crops on poorly drained soils. Drainage water management practices reduce drainage volumes and nitrate (NO3) loss by maintaining the water table closer to the ground surface when compared to conventional drainage systems. The objective of this study was to determine the effect of shallow, controlled, conventional, and no drainage on depth to water table, volumetric water content, and soil temperature during a 51-day period, from mid-April through May, to evaluate if drainage water management practices delay planting. At the Iowa State University Southeast Research Farm near Crawfordsville, Iowa, we evaluated eight large-scale research plots with two replicates for each of the four drainage treatments over the 51-day planting period during 2012 to 2015. Each plot was planted half to soybeans (Glycine max [L.] Merr.) and the other half to corn, and the halves rotated every year in accordance with a typical corn–soybean rotation. Conventional and controlled drainage significantly lowered (p

Subsurface tile drainage is a commonly used agricultural practice in Iowa croplands. Little is known about the effect of drainage on soybean (Glycine max) disease. Field and greenhouse studies were conducted to study the effect of drainage on seedling health. A field experiment was conducted at the Iowa State University research farm near Crawfordsville, Iowa, in 2012 and 2013. Four treatments were compared: conventional drainage (CvD, subsurface drains installed 1.2 m [3.9 ft] deep with 18 m [59 ft] spacing), shallow drainage (SD, 0.76 m [2.5 ft] deep with 12.2 m [40 ft] spacing), controlled drainage (CtD, 1.2 m [3.9 ft] deep and 18 m [59 ft] spacing with a water table control structure located at the outlet), and no drainage (ND, no artificial drainage). A greenhouse experiment was conducted three times to compare two soil sources (ND and CvD soil from the field experiment), two soybean cultivars (Ripley and Williams 82), and three watering intensities (low, moderate, and saturated). Plants were sampled at the second trifoliate stage to assess root rot severity, root dry weight, root size, and Fusarium spp. incidence in roots. In the field, root rot severity was significantly (p

Inclusion of a rye cover crop into maize-based systems can offer environmental benefits, but adoption of the practice in the US Midwest is still low. This is related to the possible risk of reduced maize yields following rye. We hypothesized that the magnitude of rye effects on maize yields and drainage water and nitrate (NO3)-N losses would be proportionally related to rye biomass. We tested this hypothesis by analyzing data from continuous maize treatments (with and without cover crop) in Iowa, US, that were fertilized following recommendations from late spring nitrate tests. Dataset included measurements (2009–2014) of soil water and temperature, drainage water and NO3-N losses, soil NO3, rye shoot and root biomass and C:N, and maize yields. We supplemented our analysis with a literature review and the use of a cropping systems model (APSIM) to calculate trade-offs in system performance characteristics. Experimentally, rye cover crop reduced drainage by 12% and NO3-N losses by 20% (or 31% per unit of N applied), and maize yields by 6%. We also found minimal effects on soil temperature, water deficits that reduced yields only during drought years (2012 and 2013), and lower NO3-N losses that were related to reduced NO3-N concentrations in drainage. Results also revealed a linear relationship between drainage and precipitation (r2 = 0.96), and rye transpiration and shoot biomass (r2 = 0.84). Model scenario analysis (4 termination dates × 30 years) indicated that rye cover crop decreases NO3-N losses (-25.5 ± 26%) but does not always reduce drainage water (-3.9 ± 13%) or grain yields (-1.84 ± 6%), which is consistent with experimental and literature results. However, analysis of the synthesized measured and simulated dataset do not support a strong relationship between these variables and rye biomass. These results are valuable for decision-making and add new fundamental knowledge on rye water and nitrogen use.

Artificial drainage (AD) in producer fields can help avoid excess water and improve workability and timely fieldwork in comparison with soils that rely on natural drainage (ND). To date, most studies examining the effect of AD on crop yield were conducted at research stations and limited to a few sites and years. Here, we explored the influence of AD on soybean yield across the North Central US region (NC-US), which accounts for a third of global soybean production and where AD is widely used to prevent excess water early in the crop season. We used two sources of data: (i) records from 2805 soybean producer fields collected via a multi-year, multi-state survey of soybean producers in the NC-US region; and (ii) information from 47 site-year experiments that included paired AD-ND treatment comparisons. In all cases, AD corresponded to subsurface drainage, except for producer fields in North Dakota where AD corresponded to surface drainage. Producer fields were grouped into technology extrapolation domains (TEDs) delineating regions with similar climate and soils to allow comparison of yields in AD versus ND fields. In the case of subsurface drainage, average yield in AD versus ND was 8% higher (+275 kg ha−1) and 4% higher (+157 kg ha−1) based on analysis of experimental and producer data, respectively. Our analysis indicated that part of the AD-ND yield difference in producer fields can be attributed to a shift towards earlier sowing after AD adoption. Findings from this study explain the wide adoption of AD across the central and eastern areas of the NC-US region and provide a basis to determine the productivity and economic impact of AD installation at field and regional level.

Woodchip bioreactors are a practical, low-cost technology for reducing nitrate (NO3) loads discharged from agriculture. Traditional methods of quantifying their performance in the field mostly rely on low-frequency, time-based (weekly to monthly sampling interval) or flow-weighted sample collection at the inlet and outlet, creating uncertainty in their performance and design by providing incomplete information on flow and water chemistry. To address this uncertainty, two field bioreactors were monitored in the US and New Zealand using high-frequency, multipoint sampling for in situ monitoring of NO3–N concentrations. High-frequency monitoring (sub hourly interval) at the inlet and outlet of both bioreactors revealed significant variability in volumetric removal rates and percent reduction, with percent reduction varying by up to 25 percentage points within a single flow event. Time series of inlet and outlet NO3 showed significant lag in peak concentrations of 1–3 days due to high hydraulic residence time, where calculations from instantaneous measurements produced erroneous estimates of performance and misleading relationships between residence time and removal. Internal porewater sampling wells showed differences in NO3 concentration between shallow and deep zones, and “hot spot” zones where peak NO3 removal co-occurred with dissolved oxygen depletion and dissolved organic carbon production. Tracking NO3 movement through the profile showed preferential flow occurring with slower flow in deeper woodchips, and slower flow further from the most direct flowpath from inlet to outlet. High-frequency, in situ data on inlet and outlet time series and internal porewater solute profiles of this initial work highlight several key areas for future research.