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Mid‐Missouri experienced up to 2 min 40 s of totality at around solar noon during the total eclipse of 2017. We conducted the Mid‐Missouri Eclipse Meteorology Experiment to examine land‐atmosphere interactions during the eclipse. Here, research examining the eclipse responses in three contrasting ecosystems (forest, prairie, and soybeans) is described. There was variable cloudiness around first and fourth contacts (i.e., the start and end of partial solar obscuration) at the forest and prairie; however, solar irradiance (K↓) signals during the eclipse were relatively clean. Unfortunately, the eclipse forcing at the soybean field was contaminated by convective activity, which decreased K↓ beginning about an hour before first contact and exposed the field to cold outflow ~30 min before second contact. Turbulence was suppressed during the eclipse at all sites; however, there was also an amplified signal at the soybean field during the passage of a gust front. The standard deviations of the horizontal and vertical wind velocities and friction velocities decreased by ~75% at the forest (aerodynamically rough), and ~60% at the prairie (aerodynamically smooth). The eddy fluxes of energy were highly coherent with the solar forcing with the latent and sensible heat fluxes approaching 0 W/m2 and changing in direction, respectively. For the prairie site, we estimated a canopy‐scale time constant for the surface conductance light response of 10 min. Although the eclipse imparted large forcings on surface energy balances, the air temperature response was relatively muted (1.5–2.5 °C decrease) due to the absence of topographic effects and the relatively moist land and atmosphere. Key Points: Micrometeorological observations during the total solar eclipse of 2017 in soybean, prairie, and forest ecosystems were comparedStrong eclipse signals were observed for radiation and energy fluxes, although the soybean field experienced convective activityAlthough the eclipse imparted large forcings on surface energy balances, the air temperature response was relatively muted (≤2.5 °C) [ABSTRACT FROM AUTHOR]

As environmental data are increasingly recognized as important, increased attention is focused on data quality. A critical component of quality assurance and quality control (QA/QC) is implementing tests for problems like missing data, outliers, and changes that might be too abrupt or too slow to be real, and most implementations involve coding the combinational logic of tests in if-then-else constructs to arrive at outcomes or actions depending on the inputs. Herein we propose two alternative implementation methods that avoid if-then-else logic and therefore can be used to perform more complex QA/QC screens on data from stations with one or more sensors. The objectives of this technical note are to describe the methods and to demonstrate their performance using realistic examples with existing data. Both new methods use truth tables to express and implement logic; the first method expands a truth table with N tests to all 2N possible combinations and uses that as a lookup table, while the second method matches test patterns in the truth table using its original unexpanded form. The if-then-else method and the two new methods are illustrated with a simple example of air temperature measurement for scenarios with one, two, or three (redundant) sensors. The relative advantages and disadvantages of each method are discussed. Scalability of the new methods is illustrated using measurements from a local weather station. If provided both the test results and either the expanded truth table (for the lookup method) or the original truth table (for the pattern-match method), the core code was general. The flexibility of these methods should increase the power of QA/QC programs for environmental or other time series data. [ABSTRACT FROM AUTHOR]

Spatial irrigation of agricultural crops using site-specific variable-rate irrigation (VRI) systems is beginning to have widespread acceptance. However, optimizing the management of these VRI systems to conserve natural resources and increase profitability requires an understanding of the spatial crop responses. In this research, we utilize a recently developed spatially explicit analysis model to reanalyze spatial corn yield data. The specific objectives of this research were to (1) calculate a suite of estimates (estimated yield, rainfed yield, maximum yield, and irrigation at maximum yield) and provide credible intervals (measures of uncertainty) around these estimates for comparing with the previous analysis, and (2) examine whether the conclusions from this rigorous re-analysis were different from the prior analysis and if the results would force any modifications to the conclusions obtained with the prior analyses. The spatially explicit analysis was achieved using a mixed model formulation of bivariate penalized smoothing splines and was implemented in a Bayesian framework. This model simultaneously accounted for spatial correlation as well as relationships within the treatments and had the ability to contribute information to nearby neighbors. The model-based yield estimates were in excellent agreement with the observed spatial corn yields and were able to estimate the high and low yields more accurately than the previous analysis. Credible intervals were calculated around the estimates, and the majority encompassed the observed yields. After calculating estimates of yield, we then calculated estimates of other response variables, such as rainfed yield, maximum yield, and irrigation at maximum yield. These estimated response variables were then compared with previous results from a classical statistical analysis. Our conclusions supported the original analysis in identifying significant spatial differences in crop responses across and within soil map units. These spatial differences were great enough to be considered in irrigation system design and management. The major improvement in the 2014 re-analysis is that the model explicitly considered spatial dependence in calculating the estimated yields and other variables and thus should provide improved estimates of the impact of spatial differences for use in irrigation system design and management. [ABSTRACT FROM AUTHOR]

Long-term monitoring data from agricultural watersheds are needed to determine if efforts to reduce nutrient transport from crop and pasture land have been effective. Goodwater Creek Experimental Watershed (GCEW), located in northeastern Missouri, is a high-runoff-potential watershed dominated by claypan soils. The objectives of this study were to: (i) summarize dissolved NH4-N, NO3-N, and PO4-P flow-weighted concentrations (FWC), daily loads, and yields (unit area loads) in GCEW from 1992 to 2010; (ii) assess time trends and relationships between precipitation, land use, and fertilizer inputs and nutrient transport; and (iii) provide context to the GCEW data by comparisons with other Corn Belt watersheds. Significant declines in annual and quarterly FWCs and yields occurred for all three nutrient species during the study, and the decreases were most evident for NO3-N. Substantial decreases in first- and fourth-quarter NO3-N FWCs and daily loads and modest decreases in first-quarter PO4-P daily loads were observed. Declines in NO3-N and PO4-P transport were attributed to decreased winter wheat (Triticumaestivum L) and increased corn (Zeamays L) production that shifted fertilizer application from fall to spring as well as to improved management, such as increased use of incorporation. Regression models and correlation analyses indicated that precipitation, land use, and fertilizer inputs were critical factors controlling transport. Within the Mississippi River Basin, NO3-N yields in GCEW were much lower than in tile-drained areas, but PO4-P yields were among the highest in the basin. Overall, results demonstrated that reductions in fall-applied fertilizer and improved fertilizer management reduced N and P transport in GCEW. [ABSTRACT FROM AUTHOR]

Goodwater Creek Experimental Watershed (GCEW) has been the focus area of a long-term effort to document the extent of and to understand the factors controlling herbicide transport. We document the dataseis generated in the 20-yr-long research effort to study the transport of herbicides to surface and groundwater in the GCEW. This long-term effort was augmented with a spatially broad effort within the Central Mississippi River Basin encompassing 12 related claypan watersheds in the Salt River Basin, two cave streams on the fringe of the Central Claypan Areas in the Bonne Femme watershed, and 95 streams in northern Missouri and southern Iowa. Details of the analytical methods, periods of record, number of samples, study locations, and means of accessing these data are provided. In addition, a brief overview of significant findings is presented. A key finding was that near-surface restrictive soil layers, such asargillic horizons of smectitic mineralogy, result in greater herbicide transport than soils with high percolation and low clay content. Because of this, streams in the claypan soil watersheds of northeastern Missouri have exceptionally high herbicide concentrations and relative loads compared with other areas of the Corn Belt. [ABSTRACT FROM AUTHOR]

Ten years ago, the USDA Agricultural Research Service (ARS) began a series of watershed assessment studies as part of the Conservation Effects Assessment Project (CEAP). In this overview, a decade of research progress in 14 watersheds dominated by rain-fed croplands is reviewed to introduce a special section of this journal issue containing papers describing multiwatershed syntheses. The papers evaluate impacts of agricultural practices on soil quality, stream sediment sources, and the role of climate variability in watershed studies and conservation assessments at the watershed scale. The cross-watershed comparisons help enhance our understanding of emerging conservation technologies in terms of their readiness and suitability for wide-scale adoption. Research from ARS CEAP watershed assessments published during the past 10 years suggests encouraging (1) wider adoption of minimum disturbance technologies to reduce runoff risks associated with applying manure, nutrients, and agrichemicals; (2) adoption of winter cover crops; and (3) a renewed emphasis on riparian corridors to control loads of sediment, phosphorus (P), and other contaminants originating from within (and near) stream channels. The management of agricultural watersheds requires that watershed-scale data can be interpreted and applied in management at the farm scale, and that farm-scale information, including financial and management constraints, can be used to clarify watershed management opportunities and challenges. Substantial research needs remain, including social engagement of agricultural communities, use of multiple conservation practices to account for environmental tradeoffs, improved models to simulate the dynamics of nutrient retention and movement in watersheds, and understanding ecosystem responses to changes in water quality. Moreover, a long-term commitment to understand land use trends, water quality dynamics, climate impacts, and the real effectiveness of precision conservation approaches for improving water quality will help secure agriculture's capacity to provide food, water, and other ecosystem services vital to society. [ABSTRACT FROM AUTHOR]

Streamflow monitoring typically relies on the establishment of a rating curve that describes the relationship between stage and streamflow. This rating curve is based on direct and indirect measurements of discharge at various stages and application of open-channel hydraulics principles. Potential measurement errors increase with out-of-bank flow conditions because of difficulties in measuring flow velocity and flow depth during increased stages. With increasing frequency of large rain events attributed to climate change, it becomes critical to have an accurate rating curve for flood flows. This article presents techniques that, when used concurrently, can help identify errors and reduce uncertainty in the rating curve. They include commonly used techniques such as comparison of mean annual discharge per unit drainage area with those from nearby watersheds having similar characteristics. In addition, new techniques are proposed based on the hydrologic budget of a storm event and the analysis of the change inflow relative to time and stage. The methodology was tested using flow data from the 72 km2 Goodwater Creek Experimental Watershed in northeast Missouri. Results showed that the original rating curve overestimated flow values by 30% for out-of-bank conditions. A revised rating curve was proposed based on channel conveyance. This revised rating curve satisfied the requirements of water balance and change inflow relative to time and stage. The resulting annual flows were reduced by up to 30%, better matching those of nearby watersheds. These techniques are useful for retrospective analysis of flow data series and for identifying rating curve inconsistencies. [ABSTRACT FROM AUTHOR]

Year-to-year dynamics in weather affect both the timing of application and the potential hydrologic transport of pesticides. Further, the most commonly used pesticides dissipate in the environment during the growing season. Interactions among these factors - hydrology, timing of application and dissipation kinetics - hinder the detection of temporal trends in transport. It is increasingly important to be able to discern such trends, to judge effectiveness of management practices or to determine whether observed changes were caused by management or weather. In previous work, a cumulative vulnerability index was developed to account for these three factors. It explained 63% of annual variation in atrazine load in the Goodwater Creek Experimental Watershed (GCEW). The objectives of the current work were (i) to generalize the cumulative vulnerability index to explicitly account for variation in watershed size, area treated with atrazine and average application rate; (ii) to test the overall performance on watersheds showing such variation; and (3) to test whether the generalized index properly accounted for the additional input parameters. The generalized index was tested using data from GCEW (73.7 km2) and seven additional watersheds in the northeast Missouri claypan region that varied in size from 212 to 1180 km2 and from 4% to 23% of watershed area planted to corn or sorghum. Across 32 site-years, the generalized index explained 84% of variation in annual atrazine load. Further, tests of residuals showed no dependence on either watershed area or fraction of area planted to corn and sorghum, indicating that these parameters were properly integrated into the index. The performance of the index supports the conclusion that data obtained from GCEW is representative of the Mark Twain Lake Basin and likely the entire Central Claypan Major Land Resource Area. Published 2012. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Lerch, R.N., E.J. Sadler, K.A. Sudduth, C. Baffaut, and N.R. Kitchen, 2010. Herbicide Transport in Goodwater Creek Experimental Watershed: I. Long-Term Research on Atrazine. Journal of the American Water Resources Association (JAWRA) 1-15. DOI: 10.1111/j.1752-1688.2010.00503.x Atrazine continues to be the herbicide of greatest concern relative to contamination of surface waters in the United States (U.S.). The objectives of this study were to analyze trends in atrazine concentration and load in Goodwater Creek Experimental Watershed (GCEW) from 1992 to 2006, and to conduct a retrospective assessment of the potential aquatic ecosystem impacts caused by atrazine contamination. Located within the Central Claypan Region of northeastern Missouri, GCEW encompasses 72.5 km of predominantly agricultural land uses, with an average of 21% of the watershed in corn and sorghum. Flow-weighted runoff and weekly base-flow grab samples were collected at the outlet to GCEW and analyzed for atrazine. Cumulative frequency diagrams and linear regression analyses generally showed no significant time trends for atrazine concentration or load. Relative annual loads varied from 0.56 to 14% of the applied atrazine, with a median of 5.9%. A cumulative vulnerability index, which takes into account the interactions between herbicide application, surface runoff events, and atrazine dissipation kinetics, explained 63% of the variation in annual atrazine loads. Based on criteria established by the U.S. Environmental Protection Agency, atrazine reached concentrations considered harmful to aquatic ecosystems in 10 of 15 years. Because of its vulnerability, atrazine registrants will be required to work with farmers in GCEW to implement practices that reduce atrazine transport. [ABSTRACT FROM AUTHOR]

Lerch, R.N., E.J. Sadler, C. Baffaut, N.R. Kitchen, and K.A. Sudduth, 2010. Herbicide Transport in Goodwater Creek Experimental Watershed: II. Long-Term Research on Acetochlor, Alachlor, Metolachlor, and Metribuzin. Journal of the American Water Resources Association (JAWRA) 1-15. DOI: 10.1111/j.1752-1688.2010.00504.x Farmers in the Midwestern United States continue to be reliant on soil-applied herbicides for weed control in crop production, and herbicide contamination of streams remains an environmental problem. The main objective of this study was to analyze trends in concentration and load of acetochlor, alachlor, metolachlor, and metribuzin in Goodwater Creek Experimental Watershed (GCEW) from 1992 to 2006. A secondary objective was to document the effects of best management practices (BMPs) implemented within GCEW on herbicide transport trends. Median relative herbicide loads, as a percent of applied, were 3.7% for metolachlor, 1.3% for metribuzin, 0.36% for acetochlor, and 0.18% for alachlor. The major decrease in alachlor use and increase in acetochlor use caused shifts in flow-weighted concentrations that were observed over the entire concentration range. The smaller decrease in metolachlor use led to a consistent decreasing time trend only for the upper end of the concentration distribution. Metribuzin also showed moderate decreases in concentration with time since 1998. Annual loads were generally correlated to second quarter discharge. Despite extensive education efforts in the watershed, conservation BMPs within GCEW were mainly implemented to control erosion, and therefore had no discernable impact on reducing herbicide transport. Overall, changes in herbicide use and second quarter discharge had the greatest effect on trends in flow-weighted concentration and annual load. [ABSTRACT FROM AUTHOR]

Variability in soil landscapes and their associated properties can have significant effects on erosion and deposition processes that affect runoff and transport of pesticides. Simulation models are one way in which the effects of landscapes on these processes can be assessed. This simulation study evaluated the effects of variations in landscape position on runoff and dissolved atrazine utilizing a calibrated farm- and field-scale Agricultural Policy/Environmental eXtender (APEX) model. Twelve agricultural plots (18 m x 189 m) in the Goodwater Creek watershed, a 7250 ha agricultural area in north-central Missouri, were simulated. Plots were treated with three tillage and herbicide management systems for two grain crop rotations. Each plot contained three landscape positions (summit, backslope, and footslope) along with two transition zones. Runoff was measured and samples were collected from 1997 to 2002 during the corn year of the crop rotations. Runoff samples were analyzed for dissolved atrazine. The model was calibrated and validated for each plot with event data from 1997 to 1999 and from 2000 to 2002, respectively. APEX reasonably simulated runoff and dissolved atrazine concentrations, with coefficients of determination (r²) values ranging from 0.52 to 0.98 and from 0.52 to 0.97, and Nash-Sutcliffe efficiency (NSE) values ranging from 0.46 to 0.94 and from 0.45 to 0.86 for calibration and validation, respectively. The calibrated model was then used to simulate variable sequencing of landscape positions and associated soil properties as well as variable lengths of landscape positions. Simulated results indicated that the runoff and the atrazine load at the plot outlet increased when the backslope length increased while keeping the steepness constant. The maximum simulated runoff among different sequences of landscape positions occurred when the backslope position was located adjacent to the outlet. Results from this study will be helpful to managers in placement of conservation practices on sensitive landscapes for improvement in water quality. [ABSTRACT FROM AUTHOR]

A web-based, data retrieval application was developed (Sustaining the Earth's Watersheds, Agricultural Research Data System, or STEWARDS) as part of the USDA-ARS Conservation Effects Assessment Project (CEAP) to increase the availability and accessibility of scientific data to the research community. The STEWARDS application is GIS-based and couples temporal and spatial aspects of data collected from each site within a watershed. The STEWARDS database and software design accommodates research data with heterogeneous characteristics and format, and captures rich descriptive information that is important to understand the data from complex, dynamic research programs. The database includes soil, water, climate, land management, and socio-economic data from multiple watersheds across the U.S. and can provide data commonly needed for hydrologic modeling and assessments. The release of STEWARDS marks an advance in the research capacity for the ARS research watershed network by improving access to well-documented and consistently organized data and is becoming the prototype of additional data and software designs for other ARS research projects. [ABSTRACT FROM AUTHOR]

The MarkTwain Lake/Salt River Basin was selected as one of the USDA Agricultural Research Service benchmark watersheds for the Conservation Effects Assessment Project because of documented soil and water quality problems and broad stakeholder interest. The basin is located in northeastern Missouri within the Central Claypan Region, and it is the source of water to Mark Twain Lake, the major public water supply in the region. At the outlet to Mark Twain Lake, the basin drains 6,417 km² (2,478 m²), including 10 major watersheds that range in area from 271 to 1,579 km² (105 to 609 m²). The basin is characterized by flat to gently rolling topography with a predominance of claypan soils that result in high runoff potential. The claypan soils are especially. vulnerable to soil erosion, which has degraded soil and water quality throughout the ,basin, and to surface transport of herbicides. Results from cropping system best management practice studies showed that no-till cropping systems did not reduce surface runoff compared to tilled systems, and no-till led to increased transport of soil-applied herbicides. A major challenge is the need to develop cropping systems that incorporate herbicides yet maintain sufficient crop residue cover to control soil erosion. Results of the Soil and Water Assessment Tool model simulations showed that the model was capable of simulating observed long-term trends in atrazine concentrations and loads and the impact of grass waterways on atrazine concentrations. Current and future research efforts will continue to focus on best management practice studies, development of needed tools to improve watershed management, and refinements in the calibration and validation of the Soil and Water Assessment Tool model. [ABSTRACT FROM AUTHOR]

Information on the effects of landscape and its interaction with management on soil hydraulic properties is scarce. Our objective was to investigate the effects and interactions of landscape position and conservation management systems (e.g., reduced tillage or permanent grass) on soil bulk density, saturated hydraulic conductivity (Ksat), soil water retention, and pore-size distributions for claypan soils in central Missouri. Landscape positions included summit, back- slope, and footslope positions. Management included mulch tillage with a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation (MTCS); no-till with a corn-soybean-wheat (Triticum aestivum L.) rotation (NTCSW) with a red clover (Trifolium pretense L.) cover crop following wheat; a Conservation Reserve Program system (CRP); and a hay crop system (HAY). Intact soil cores (76 by 76 mm) were collected from 0- to 10-, 10- to 20-, and 20- to 30-cm depths. Soil properties were affected by management only in the surface 0 to 10 cm, and were controlled by the depth of the claypan horizon. Management and depth effects on soil properties varied with landscape position. Saturated hydraulic conductivity was highest for CRP and lowest for MTCS (20.2 vs. 4.3 mm h-1), averaged across all landscape positions and depths. The management × landscape position interaction indicated that, at the backslope, Ksat values for CRP and HAY were 16 and 10 times higher, respectively, than values for MTCS. The CRP retained the most water at soil water pressures from saturation to -1 kPa at the 0- to 10-cm depth. The fraction of larger pores was the highest for CRP at the 0- to 10-cm depth. Results suggest that the use of perennial grasses in rotation (or permanently) will benefit soil hydraulic properties, particularly at slope positions most vulnerable to degradation where soil conditions cannot be improved by row-crop conservation systems. [ABSTRACT FROM AUTHOR]

Presents a study on ammonia volatilization from marsh-pond-marsh constructed wetlands treating swine wastewater in Greensboro, North Carolina. Rates of volatilization; Determination of the dominant nitrogen removal mechanism; Preference for continuous marsh systems.

Efficient and environmentally acceptable nutrient management requires an understanding of when and at what rates nutrients are accumulated by plants. For graminaceous species, a mathematical procedure involving compound cubic polynomials was previously demonstrated to be useful for evaluating growth and nutrient accumulation patterns. Our objective for this study was to compare dry matter and nutrient accumulation rates for determinate and indeterminate soybean [Glycine max L. (Merr.)] by reanalyzing the original data from five field experiments. Data from a maximum yield research (MYR) experiment that yielded 6.8 Mg ha‐1 provided information for soybean grown with near‐maximum accumulation rates. The high MYR yield resulted from intensive management practices that included high fertilization, high plant population, complete pest control, and timely irrigations to supplement rainfall. The MYR results were compared with rates determined for four non‐MYR studies that yielded from 2.2 to 5.4 Mg ha‐1 in Iowa, South Carolina, and North Carolina. Contrary to patterns found for corn (Zea mays L.) and wheat (Triticum aestivum L.), no consistent, distinct peaks in accumulation rate were observed for soybean. Instead, trends were masked by short‐term variation caused either by responses to environmental variation or by random sampling errors. In addition, computed maximum growth rates for the 6.8 and 5.4 Mg ha‐1 studies were higher than the hypothesized maximum rate of 360 kg ha‐1 d‐1, suggesting either biased sampling or a need to reexamine the theory. These findings lead us to conclude that further research in intraseasonal accumulation patterns for soybean should concentrate on causes for short‐term variation, such as weather patterns, via mechanistic simulation. Further, the data for extremely high yields should be considered cautiously until supporting data are found. [ABSTRACT FROM PUBLISHER]

Examines the impact of site-specific crop management with a center pivot irrigation system on water conservation, plant stress reduction and fertilizer loss reduction in the American Coastal Plains. Modifications on conventional center pivot systems; Requirements for site-specific management of crop production; Features of the water application and irrigations systems.

Precision agriculture has mostly emphasized variable-rate nutrients, seeding, and pesticide application, but at several research sites, variable-rate irrigation equipment has been developed to explore the potential for managing irrigation spatially. The modifications to commercial machines are relatively straightforward, but costly; thus economic analyses have not been positive at current grain price: water cost ratios. However, with increased attention to conservation of water during drought, with increased contention for environmental, recreational, municipal, and industry use, or with regulatory constraints, conclusions regarding profitability or desirability of variable-rate irrigation may change. The objectives of this paper are to: 1) define and describe site-specific irrigation, 2) discuss the opportunities for conservation using site-specific irrigation, 3) present case studies from production and research fields that illustrate these opportunities, and 4) discuss critical research needs to fully implement precision irrigation and thus realize these opportunities for conservation. The opportunities for conservation discussed include situations where non-cropped areas exist in a field for which irrigation can be turned completely off, situations where a reduced irrigation amount provides specific benefits, and finally, situations where optimizing irrigation amount to adapt to spatial productivity provides quantitative benefits. Results from the case studies provide estimates of the potential for water conservation using precision irrigation that range from marginal to nearly 50 percent in single years, and average from eight to 20 percent, depending on the previous irrigation management strategy employed. Critical research needs include improved decision support systems and real-time monitoring and feedback to irrigation control. [ABSTRACT FROM AUTHOR]

Analysis and simulation of watershed-scale processes requires spatial characterization of land use, including differentiation among crop types. If this crop type information could be obtained accurately from remote sensing data, the effort required would be significantly reduced, especially for large watersheds. The objective of this study was to compare two methods using multiple satellite remote sensing datasets to differentiate land cover, including crop type, for the Salt River/Mark Twain Lake basin in northeast Missouri. Method I involved unsupervised classification of Landsat visible and near-infrared satellite images obtained at multiple dates in the growing season, followed by traditional, manual class identification. Method 2, developed in this research, employed the same unsupervised classification but also used normalized difference vegetation index (ND VI) maps obtained on a 16-day cycle from MODIS satellite images as ancillary data to derive seasonal NDVI trends for each class in the classification map. Tree analysis was applied to the NDVI trend data to group similar classes into clusters, and crop type for each cluster was determined from ground-truth data. Additional ground-truth data were used to assess the accuracy of the procedure, and crop acreage estimates were compared to county-level statistics. The overall classification accuracy of Method 2 was 3% higher than that of Method 1. Method 2 was also more efficient in terms of analyst time and ground-truth data requirements. Therefore, this method, employing variations in seasonal ND VI trends, is suggested for differentiation of crop type. The 30-m resolution crop type maps developed using this process will be useful as input data to environmental analysis models. [ABSTRACT FROM AUTHOR]

The Conservation Effects Assessment Project was established to quantify the environmental impacts of USDA conservation programs. The Conservation Effects Assessment Project involve multiple watershed assessment studies designed to provide a scientific basis for a national assessment. The USDA Agricultural Research Service established 14 research sites—benchmark watersheds—to measure regionally specific environmental quality effects of conservation practices and to improve and validate models used by the USDA Natural Resources Conservation Service for their national assessment. Within each watershed, data were collected and continue to be collected to provide insight into the effects of specific conservation practices implemented under programs such as the Environmental Quality Incentives Prof ram and the Conservation Reserve Program. A data storage and management system, sustaining the Earth's Watersheds-Agricultural Research -Data System (STEWARDS), was developed to provide easy accessibility to these data for analysis. Models were validated using data from many of the watersheds and were shown to be valuable tools for extrapolating the results in a national assessment. The physical process models were also combined with economic models to optimize tradeoffs among environmental and economic objectives of conservation practices. The benchmark watershed studies have begun to identify the effects of selected conservation practices, although additional data are required to provide definitive results. A prototype of a new modular modeling system has been developed that will provide a more powerful tool for future analyses. The initial Conservation Effects Assessment Project findings and products demonstrate progress toward the overall goals of quantifying conservation practice effects and providing tools to transfer the knowledge to points where they are applied under future conservation policy. [ABSTRACT FROM AUTHOR]

Conventional cultivation of claypan soils leads to soil and water quality degradation because of high runoff and associated soil erosion. The Goodwater Creek Experimental Watershed, which is part of the USDA Agricultural Research Service Benchmark Conservation Effects Assessment Project, Watershed Assessment Studies, was established to address these issues. Plot studies have highlighted trade-offs between erosion control and herbicide or nutrient runoff. There is a need for long-term field-scale evaluation of combined practices that reduce sediment, nutrient, and herbicide losses by runoff. A 36 ha field located in Missouri was under a conventional corn (Zea mays L.)-soybean (Glycine max L.) system from 1993 to 2003 with fertilizer application and tillage prior to planting in the spring. A precision agriculture system defined by two main management zones was implemented from 2004 to 2014: wheat (Triticum aestivum L.) and soybean in 60% of the field, and corn and soybean in the remaining 40%. The system included no-till, cover crops, atrazine split-applications based on weed pressure, variable rates of nitrogen (N), and variable rates of fall-applied phosphorus (P). The objective of this study was to compare runoff water quality from the two management systems, based on flow and load duration curves, cumulative distribution functions, and conclusions from replicated plot studies. The precision agriculture system did not affect annual runoff, but it did increase the frequency of low flows. Sediment losses were reduced by 87% as a result of no-till and cover crops. Atrazine and P losses were lower than expected, despite the lack of incorporation into the soil. Atrazine losses were possibly lower because of the wheat area acting as a buffer, greater atrazine adsorption and retention in the field, and faster decay. Dissolved P losses as a fraction of applied remained the same, likely because of greater adsorption and lower runoff risk when applying P. Finally, nitrate-N (NO3-N) losses decreased and resulted in an overall decrease of N losses despite a slight increase of ammonium-N (NH4-N) losses. Explanations included a greater soil water content, a different timing of N applications, and N uptake by cover crops. Building on these successes, an aspirational management system is proposed to further improve on the performance and practicality of the precision agriculture system. [ABSTRACT FROM AUTHOR]

The Soil Vulnerability Index (SVI) was developed by the USDA Natural Resources Conservation Service (NRCS) to identify inherent vulnerability of cropland to runoff and leaching. It is a simple index that relies on the SSURGO database and can be used with basic knowledge of ArcGIS. The goal of this study was to investigate a relationship between constituent (sediment and nutrient) loadings and fraction of the watershed in each SVI class. The SVI maps were developed for each of the seven subwatersheds of the Mark Twain Lake watershed in Missouri, which were similar in soil conditions and climatic variability. The SVI assessment was performed by investigating if the distribution of the SVI for cropland in each subwatershed could help explain measured 2006 to 2010 sediment and nutrient loads better than crop distribution alone. Regression analyses were performed between annual loads of sediment and nutrients exported from the watersheds and a composite number that included either cropland distribution alone, or cropland distribution combined with the SVI. Coefficients of determination and p-values were compared to assess the ability of land use and SVI distributions to explain stream loads. Integrating the SVI in the land cover variable improved the ability to explain constituent loads in the watersheds for sediment, total nutrients, and dissolved nitrogen (N). Regression results with and without the SVI were identical for dissolved phosphorus (P), potentially indicating that SVI was not indicative of dissolved P transport at the current site. Overall, the application of the SVI at watershed scale was not perfect, but acceptable at correctly identifying cropland of greatest vulnerability and linking with transported constituent loads. [ABSTRACT FROM AUTHOR]

Selected watershed studies of the Conservation Effects Assessment Project (CEAP) are reviewed and findings are interpreted from the perspective of potential conservation outcomes due to climate change scenarios. Primary foci are runoff, soil erosion, sediment transport, and watershed sediment yield. Highlights, successes, and challenges with regards to climate change impacts on soil erosion, runoff, and watershed sediment yield are presented. The covered information adds to the existing knowledge base of climate change impacts and provides another piece of information that may be useful in the planning and management of agricultural watersheds; assessment of conservation needs; and development, funding, and implementation of conservation programs. The selected conservation assessment studies include, among others, a thought experiment on the sensitivity of soil erosion, runoff, and sediment yield to changes in rainfall; a computer-based investigation of potential climate change effects on runoff and soil erosion in a southeastern Arizona rangeland; the complex response of northern Mississippi watersheds to runoff variations and channel stabilization measures; the impact of conservation practices and a persistent pluvial period on watershed runoff and sediment yield in Oklahoma; and stream bank erosion during major flooding in Iowa and river corridor management. A study of rainfall-runoff in an north-central Missouri watershed and a curve number analysis in a northern Appalachian experimental watershed are included herein. Findings showed that climate change scenarios of increased precipitation intensity lead to an exponential increase in soil erosion, runoff, and watershed sediment yield, thereby stressing current conservation practices or future practices designed with present day practice standards. This diminishes conservation practice effectiveness and increases sediment supply to the stream network. The sensitive response of the watershed hydrologic system may lead to renewed soil erosion that is large enough to offset the reduction in soil loss achieved by current conservation practices. However, in alluvial-floodplain environments with noncohesive bed and bank material, watershed sediment yield is controlled by channel discharge and energy slope, neither of which is influenced by traditional in-field conservation practices or channel bank stabilization structures. Thus, control of sediment yield will gradually shift in the downstream direction from sediment supply to sediment transport capacity and blur any existing relation between a climate change signal, in-field conservation outcomes, and sediment yield at watershed outlets. Targeting conservation practices to erosion prone areas, expanding conservation coverage, and adapting agronomic practices may be necessary to prevent excessive soil erosion and downstream sedimentation under climate change scenarios that include intensified precipitation. [ABSTRACT FROM AUTHOR]

Targetin g critical management areas (CMAs) within cropped fields is essential to maximize production while implementing alternative management practices that will minimize impacts on water quality. The obj ective of this study was to develop physically based indi ces to identify CMAs in a 35 ha (88 ac) fi eld characterized by a restrictive clay layer occurring within the upper 15 to 100 em (6 to 40 in) and under a corn (Z ea mays L.)-soybean (Glycine max L.) crop rotation since 1991. Thirty-five subareas were defin ed based on slope, depth to claypan (CD), and soil mapping units. The Agricultural Policy/ Environmental eXtender (APEX) model was calibrated and validated from 1993 to 2002 using measured runoff, sediment, and atrazine loads, and crop yields. CMAs were delineated based on simulated subarea runoff, sediment, and atrazine loads. Correlation analysis was performed between simulated output by subarea and physical parameters, including CD, surface satu ra ted hydraulic conductivity (Ksat), and subarea slope (SL). Two indices were developed, the Conductivity Claypan Index (CCI; CD XKsat -7-SL) and th e Claypan Index (CPI; CD -7- SL), to correlate with simulated crop yields, runoff, atrazine, and sediment loads. Together, these indices captured 100% of CMAs for simulated runoff and sediment yield and 60% of CMAs for simulated atrazine in surface runoff, as predicted by APEX. These critical areas also matched lower corn productivity areas . Management scenarios were simulated that differentiated the management of the CMAs from the rest of the field. Indices, such as these, for identifying areas of higher environmental risk and lower productivity could provide obj ective criteria for effective targeting of best management practi ces. [ABSTRACT FROM AUTHOR]

Various land management decisions are based on local soil properties. These soil properties. include average values from soil characterization for each soil series. In reality, these properties might be variable due to substantially different management, even for similar soil series. This study was conducted to test the hypothesis that for claypan soils, hydraulic properties can be significantly affected by long-term soil and crop management. Sampling was conducted during the summer of 2008 from two fields with Mexico silt loam (Vertic Epiaqualfs). One field has been under continuous row crop cultivation for over 100 years (Field), while the other field is a native prairie that has never been tilled (Tucker Prairie). Soil cores (76 × 76 mm [3.0 × 3.0 in]) from six replicate locations from each field were sampled to a 60 cm (24 in) depth at 10 cm (3.9 in) intervals. Samples were analyzed for bulk density, saturated hydraulic conductivity (Ksat), soil water retention, and pore-size distributions. Values of coarse (60 to 1,000 μm [0.0024 to 0.039 in] effective diameter) and fine mesoporosity (10 to 60 μm [0.00039 to 0.0024 in] effective diameter) for the Field site (0.044 and 0.053 m3 m-3 [0.044 and 0.053 in3 in-3]) were almost half those values from the Tucker Prairie site (0.081 and 0.086 m3 m-3 [0.081 and 0.086 in3 in-3]).The geometric mean value of Ksat was 57 times higher in the native prairie site (316 mm h-1 [12.4 in hr-1]) than in the cropped field (5.55 mm h-1 [0.219 in hr-1]) for the first 10 cm (3.9 in) interval. Differences in Ksat values were partly explained by the significant differences in pore-size distributions. The bulk density of the surface layer at the Tucker Prairie site (0.81 g cm-3 [50.6 lb fr-3]) was two-thirds of the value at the Field site (1 .44 g cm-3 [89.9 lb ft-3]), and was significantly different throughout the soil profile, except for the 20 to 30 cm (7.9 to 12 in) depth. These results show that row crop management and its effect on soil loss have significantly altered the hydraulic properties for this soil. Results from this study increase our understanding of the effects of long-term soil management on soil hydraulic properties. [ABSTRACT FROM AUTHOR]

Streams and drinking water reservoirs throughout the claypan soil region of Missouri and Illinois are particularly vulnerable to herbicide contamination from surface runoff during spring. This study follows a plot-scale study conducted on claypan soils to quantify and compare edge-of-field herbicide losses from a corn-soybean rotation under mulch tillage and no-tillage systems. The objectives of the present study were to confirm at field scale (34.4 ha [85 ac] and 7.8 ha [19.3 ad) the plot-scale findings (0.37 ha [0.92 ad) on the effects of tillage and herbicide incorporation on herbicide transport and to evaluate the applicability of plot-scale exponential models in calculating atrazine and metolachlor concentrations as a function of application rate, runoff volume, and days after application at the field scale. Herbicide transport to surface runoff was studied (1997 to 2001) from two fields with cropping systems similar to those on the plots. Field 1 (F1) was a mulch tillage corn-soybean rotation system with surface-applied herbicides, which are then incorporated. Field 2 (F2) was a no-tillage corn-soybean rotation system with surface-applied herbicides that were not incorporated. During each event, runoff volumes were measured, and water samples were collected and analyzed for atrazine and metolachlor concentrations. The percentages of applied atrazine and metolachlor transported to surface runoff from no-tillage (P2) were 3.2 and 2.0 times those from mulch tifiage (F1), respectively. Throughout the study period, 1.0% and 3.2°/ of total atrazine and 1.0°/ and 2.0% of total metolachlor applied to F1 and F2 were lost to surface runoff, respectively. Similar to the results from the plot study, the model performed well iii calculating field atrazme concentrations from both mulch and no-tillage systems with coefficient of determination ⩾ 0.70 and Nash and Sutciffe efficiency ⩾ 0.64. However; model performance in calculating metolachlor concentrations was poor for both tillage systems (Nash and Sutcliffe efficiency < 0.35). When the model was modified to include cumulative temperature instead of days after application, performance in calculating atrazine and metolachlor concentrations was improved, particularly metolachlor concentrations at the field scale. The coefficient of determination and Nash and Sutciffe efficiency values for metolachlor relative to cumulative temperature and days after application were 0.62 and 0.61 versus 0.41 and -0.13 for F1, and 0.73 and 0.55 versus 0.53 and 0.34 for F2, respectively. Overall, the study confirmed plot-scale results that atrazine concentrations and losses were greater for a no-tillage system than for a mulch-tillage system, in which the herbicide was incorporated. The study also showed that the model developed using plot-scale data was applicable in calculating concentrations at the field scale, particularly for atrazine. [ABSTRACT FROM AUTHOR]

Plant water and nutrient use for claypan soils are restricted by an argillic horizon (clay content > 500 g kg-1) that typically occurs 20 to 40 cm (8 to 16 in) below the soil surface. Identifying water infiltration characteristics for claypan soils under different management provides crucial information needed to optimize crop management and estimate watershed hydrology. The objectives of the study were: 1) to evaluate the influence of long-term annual cropping system (ACS) and perennial cropping system management (PCS) [such as Conservation Reservation Program (CRP) and hay crop] on water infiltration, and 2) to examine relationships between apparent soil electrical conductivity (ECa) and other claypan soil properties with water infiltration parameters. The effects of the ACS and PCS management on water infiltration parameters were evaluated using ponded water infiltration measurements in the field. Water infiltration parameters were estimated using the Green-Ampt infiltration equation. Apparent profile soil electrical conductivity was obtained using an EM38 sensor. Analysis of variance and orthogonal contrasts were used to determine effects of management treatments on water infiltration parameters and associated soil properties. Soil organic carbon and aggregate stability were significantly (P < 0.05) improved after 12 years of CRP management compared to 12 years of ACS management. Antecedent soil water content and ECa were lower and water infiltration was greater for PCS than for the ACS. For a hay crop treatment (PCS), water infiltration was greatly improved when compared to any ACS or other PCS management treatments. Antecedent soil water content and soil organic carbon were significantly correlated with the water infiltration parameters. Soil ECa was significantly correlated with infiltration-estimated saturated hydraulic conductivity (Ks). This relationship may be useful for mapping spatially-variable water infiltration within fields. In summary, PCS contributed to improved water infiltration as well as to increased soil organic carbon and soil aggregate stability. Soil ECa may be useful for characterizing management influence on water infiltration without labor intensive sampling. [ABSTRACT FROM AUTHOR]

From site-specific crop and soil information collected from a Missouri claypan soil field for over a decade (1993 to 2003), we implemented a precision agriculture system in 2004 with a goal of using site-specific management practices to improve farming profitability and conserve soil and water resources. The objectives of this study were to: 1) show how precision crop and soil information was used to assess productivity, and 2) document the development of the precision agriculture system plan for implementation on the field, relying on this productivity assessment and conservation opportunities. The study field was uniformly managed from 1991-2003, during which time variability in soil and landscape parameters and yield were measured, and causes of yield variation were determined. Profitability maps were created from yield maps and production records. Because erosion has degraded the topsoil on shoulder and side slope positions of major portions of this field, corn-soybean management practices have rarely been profitable in these shallow topsoil areas. We prioritized these and other results, and developed the precision agriculture system plan. The plan, described in detail, is aimed at increasing profitability while improving water and soil quality. [ABSTRACT FROM AUTHOR]

A comprehensive approach to achieving sustained crop productivity and profitability requires implementation of conservation systems that simultaneously consider soil and water quality. The objectives of this study were to: 1) assess long-term surface and groundwater quality in a conventionally managed field; 2) assess long-term changes in soil quality under a conventional management field; and 3) use this assessment to support development of the precision agriculture system presented in the companion paper. The study site was a 36-ha (89 ac) field in the Central Claypan Area of northeastern Missouri. The field was managed in a corn-soybean rotation using mulch tillage and soil incorporated fertilizer and pre-emergence herbicide inputs for 13 years (1991 to 2003). In general, agrichemical leaching to groundwater was minimal, but the existing management system negatively impacted the quality of surface runoff in five of the nine years reported. Preliminary spatial assessment indicated that the northern half of the field has been the main source of herbicides, nutrients, and sediment transported in surface runoff from this field. Topsoil loss and, therefore, decreased depth to the claypan from historic erosion of the field was a key soil quality indicator related to limitations in crop productivity. Spatial variability in soil loss over the last 150 to 200 years controls the soil quality, water quality, and crop productivity patterns currently observed within this field. Therefore, spatial variability in soil erosion, or a surrogate measure such as depth to claypan, serves as a useful basis for the development of a comprehensive precision agriculture system. [ABSTRACT FROM AUTHOR]

Soils that naturally have a significant runoff component because of low permeability, such as claypans or steep slopes, are especially susceptible to herbicide losses in runoff. For these soils, seasonal losses as impacted by management practices are not well quantified. The objectives of this study were to evaluate the effect of three cropping systems on herbicide loss in surface runoff and develop a model that calculates herbicide concentration. Cropping System 1 (CS1) was a mulch tillage corn-soybean rotation system with herbicides surface applied then incorporated. Cropping System 2 (CS2) was a no-till corn-soybean rotation system with herbicides surface applied and not incorporated. Cropping System 5 (CS5) was a no-till corn-soybean-wheat rotation system with split herbicide application in 1997 and 1999 and no incorporation. The study was conducted on 0.37 ha (0.92 ac) plots equipped with flumes and automated samplers. During each runoff event, runoff volumes were measured, and water samples were collected at equal flow increments and analyzed for atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethy/acetamide]. Averaged over years, atrazine and metolachlor losses from CS2 were 2.2 and 1.6 times those from CS1, respectively. Atrazine loss to surface runoff from CS1, CS2, and CS5 accounted for 1.6, 2.5, and 5.7% of the total atrazine applied, respectively. Metolachlor loss to surface runoff accounted for 1.8, 2.0, and 2.0% of the total applied for the three cropping systems. Herbicide concentrations were extremely high in the first runoff event measured after application, particularly when it occurred within a few days after application. A generalized model was developed to account for the effects of time after application, runoff volume, and application rate on herbicide concentration in runoff. Overall, the study showed that accounting for incorporation, split application, runoff volume, and timing of runoff events relative to the day of application can increase the confidence in calculations of the amount of herbicide transported to surface runoff. [ABSTRACT FROM AUTHOR]