Showing papers in "Transactions of the ASABE in 2010"

Soil and Water Assessment Tool (SWAT) Model: Current Developments and Applications

Abstract: This article introduces a special collection of 20 research articles that present current developments and applications of the Soil and Water Assessment Tool (SWAT). The first objective is to review and introduce the research addressed within this special collection. The second objective is to summarize and synthesize the model performance statistics and parameters published in these articles to provide a succinct guide to complement a previous SWAT model summary. Recent SWAT developments in landscape representation, stream routing, and soil P dynamics are presented in this collection. Numerous critical applications of the SWAT model were conducted across a variety of landscape scales, climatic and physiographic regions, and pollutant sources. In this article, model performance in terms of coefficient of determination, Nash-Sutcliffe efficiency, and percent bias across all the studies is summarized and found to be satisfactory or better in all cases. These results are then compiled with a previous synthesis of results to generate a comprehensive assessment of SWAT. Model parameters used to calibrate the model for streamflow, sediment, N, and P in numerous studies are also summarized. This collection demonstrates that research in development and application of the SWAT model and associated tools continues to grow internationally in a wide range of settings and applications.

SWAT Ungauged: Hydrological Budget and Crop Yield Predictions in the Upper Mississippi River Basin

Abstract: Physically based, distributed hydrologic models are increasingly used in assessments of water resources, best management practices, and climate and land use changes. Model performance evaluation in ungauged basins is an important research topic. In this study, we propose a framework for developing Soil and Water Assessment Tool (SWAT) input data, including hydrography, terrain, land use, soil, tile, weather, and management practices, for the Upper Mississippi River basin (UMRB). We also present a performance evaluation of SWAT hydrologic budget and crop yield simulations in the UMRB without calibration. The uncalibrated SWAT model ably predicts annual streamflow at 11 USGS gauges and crop yield at a four-digit hydrologic unit code (HUC) scale. For monthly streamflow simulation, the performance of SWAT is marginally poor compared with that of annual flow, which may be due to incomplete information about reservoirs and dams within the UMRB. Further validation shows that SWAT can predict base flow contribution ratio reasonably well. Compared with three calibrated SWAT models developed in previous studies of the entire UMRB, the uncalibrated SWAT model presented here can provide similar results. Overall, the SWAT model can provide satisfactory predictions on hydrologic budget and crop yield in the UMRB without calibration. The results emphasize the importance and prospects of using accurate spatial input data for the physically based SWAT model. This study also examines biofuel-biomass production by simulating all agricultural lands with switchgrass, producing satisfactory results in estimating biomass availability for biofuel production.

Adoption of an unmanned helicopter for low-altitude remote sensing to estimate yield and total biomass of a rice crop.

Abstract: A radio-controlled unmanned helicopter-based low-altitude remote sensing (LARS) platform was used to acquire quality images of high spatial and temporal resolution in order to estimate yield and total biomass of a rice crop (Oriza sativa L.). Fifteen rice field plots with five N treatments (0, 33, 66, 99, and 132 kg ha-1) having three replicates each were arranged in a randomized complete block design for estimating yield and biomass as a function of applied N. Images were obtained by image acquisition sensors mounted on the LARS platform operating at the height of 20 m over experimental plots. The rice yield and total biomass for the five N treatments were found to be significantly different at the 0.05 and 0.1 levels of significance, respectively, and normalized difference vegetation index (NDVI) values at panicle initiation stage were highly correlated with yield and total biomass with regression coefficients (r2) of 0.728 (RMSE = 0.458 ton ha-1) and 0.760 (RMSE = 0.598 ton ha-1), respectively. The study demonstrated the suitability of using LARS images as a substitute for satellite images for estimating leaf chlorophyll content in terms of NDVI values (r2 = 0.897, RMSE = 0.012). The LARS system described has potential to evaluate areas that require additional nutrients at critical growth stages to improve final yield in rice cropping.

Assessment of different representations of spatial variability on SWAT model performance.

Abstract: River basin management requires a spatially distributed representation of basin hydrology and nutrient transport processes. To accomplish this, the Soil and Water Assessment Tool (SWAT) watershed model was enhanced to simulate water flow across discretized landscape units. The model structure more closely reflects the complex controls on infiltration, runoff generation, run-on, and subsurface flow without requiring large computational resources or detailed parameterization. Four landscape delineation methods were compared: lumped, hydrologic response units (HRUs) or hydrotope, catena, and grid. The lumped method using dominant soil and land use and the HRU delineation do not consider landscape position when computing runoff. The catena method routes flow across a representative catena with divide, hillslope, and valley units. The distributed method divides the watershed into cells (1 ha each) for routing. All methods were calibrated and validated for the USDA-ARS Brushy Creek watershed (17.3 km 2 ) near Riesel, Texas. The calibration results indicate that measured flow at the basin outlet is similar (daily N-S around 0.65) for all four models, or conversely, the new models (catena and grid) do as well as the existing models (lumped and HRU based) in predicting daily flow at the basin outlet. The advantage of the catena and grid models is that the impacts of spatial changes in land use and BMPs on the hillslope valley continuum can now be more realistically assessed.

Material and interaction properties of selected grains and oilseeds for modeling discrete particles

Abstract: Experimental investigations of grain flow can be expensive and time consuming, but computer simulations can reduce the large effort required to evaluate the flow of grain in handling operations. Published data on material and interaction properties of selected grains and oilseeds relevant to discrete element method (DEM) modeling were reviewed. Material properties include grain kernel shape, size, and distribution; Poisson's ratio; shear modulus; and density. Interaction properties consist of coefficients of restitution, static friction, and rolling friction. Soybeans were selected as the test material for DEM simulations to validate the model fundamentals using material and interaction properties. Single- and multi-sphere soybean particle shapes, comprised of one to four overlapping spheres, were compared based on DEM simulations of bulk properties (bulk density and bulk angle of repose) and computation time. A single-sphere particle model best simulated soybean kernels in the bulk property tests. The best particle model had a particle coefficient of restitution of 0.6, particle coefficient of static friction of 0.45 for soybean-soybean contact (0.30 for soybean-steel interaction), particle coefficient of rolling friction of 0.05, normal particle size distribution with standard deviation factor of 0.4, and particle shear modulus of 1.04 MPa.

Modifying Goodness-of-Fit Indicators to Incorporate Both Measurement and Model Uncertainty in Model Calibration and Validation

Abstract: Because of numerous practical implications of uncertainty in measured data and model predictions, improved techniques are needed to analyze and understand uncertainty and incorporate it into hydrologic and water quality evaluations. In the present study, a correction factor was developed to incorporate measurement uncertainty and model uncertainty in evaluations of model goodness-of-fit (predictive ability). The correction factor, which was developed for pairwise comparisons of measured and predicted values, modifies the typical error term calculation to consider both sources of uncertainty. The correction factor was applied with common distributions and levels of uncertainty (represented by coefficients of variation ranging from 0.026 to 0.256) for each measured value and each predicted value from five example data sets. The modifications resulted in inconsequential changes in goodness-of-fit conclusions for example data sets with very good and poor model simulations, which is both logical and appropriate because very good model performance should not improve greatly and poor model performance should not become satisfactory when uncertainty is considered. In contrast, incorporating uncertainty in example data sets with initially moderate goodness-of-fit resulted in important improvements in indicator values and in model performance ratings. A model evaluation matrix was developed to present appropriate model performance conclusions, considering both model accuracy and precision, based on various levels of measurement and model uncertainty. In cases with highly uncertain calibration/validation data, definitive "good" fit conclusions are cautioned against even with "good" indicator values because of the uncertain standard of comparison; however, in these cases, poor model accuracy can be confidently concluded from "unsatisfactory" indicator values. In contrast, model accuracy can be confidently concluded from goodness-of-fit indicator values in cases with low measurement uncertainty. It is hoped that the modified goodness-of-fit indicators and the model evaluation matrix contribute to improved goodness-of-fit conclusions and to more complete assessments of model performance.

Raman Chemical Imaging System for Food Safety and Quality Inspection

Abstract: Raman chemical imaging combines Raman spectroscopy and digital imaging to visualize the composition and structure of a target, and it offers great potential for food safety and quality research In this study, a laboratory-based Raman chemical imaging platform was designed and developed The system utilizes a 785 nm spectrum-stabilized laser as an excitation source to generate Raman scattering The detection module consists of a fiber optic probe, a dispersive Raman imaging spectrometer, and a high-performance spectroscopic CCD camera The imaging system works in a point-scanning mode A Raman spectrum is obtained at a time for individual positions in the scene The specimens are carried by a two-axis motorized positioning table Hyperspectral image data are accumulated as the samples are moved along two spatial dimensions The parameterization and data-transfer interface software was developed using LabVIEW Spectral and spatial calibration procedures are presented The system covers a Raman shift range of 1022 to 25381 cm-1 with a spectral resolution of 37 cm-1, and an area of 127 × 127 mm2 with a spatial resolution as high as 01 mm Performance of the system was demonstrated by an example application on detection of melamine in dry milk Melamine was mixed into dry milk with concentrations (w/w) ranging from 02% to 100% The system was able to create Raman chemical images that can be used to visualize quantity and spatial distribution of melamine particles in the mixtures The developed system is versatile and can be used for safety and quality inspection of food and agricultural products

Nebraska Water and Energy Flux Measurement, Modeling, and Research Network (NEBFLUX)

Abstract: Surface energy and water vapor fluxes play a critical role in understanding the response of agro-ecosystems to changes in environmental and atmospheric parameters. These fluxes play a crucial role in exploring the dynamics of water and energy use efficiencies of these systems. Quantification of the fluxes is also necessary for assessing the impact of land use and management changes on water balances. Accomplishing these goals requires measurement of water vapor and energy exchanges between various vegetation surfaces and microclimates for long-enough periods to understand the behavior and dynamics involved with the flux transfer so that robust models can be developed to predict these processes under different scenarios. Networks of flux towers such as AMERIFLUX, FLUXNET, FLUXNET-CANADA, EUROFLUX, ASIAFLUX, and CAR-BOEUROPE have been collecting data on exchange processes between biosphere and atmosphere for multiple years across the globe to better understand the functioning of terrestrial ecosystems and their role in regional and/or continental and global carbon, water, and energy cycles, providing a unique service to the scientific community. Nonetheless, there is an imperative need for these kinds of networks to increase in number and intensity due to the great diversity among ecosystems and agro-ecosystems in species composition, physiological properties, physical structure, microclimatic and climatic conditions, and management practices. The Nebraska Water and Energy Flux Measurement, Modeling, and Research Network (NEBFLUX) is a comprehensive network that is designed to measure surface energy and water vapor fluxes, microclimatic variables, plant physiological parameters, soil water content, surface characteristics, and their interactions for various vegetation surfaces. The NEBFLUX is a network of micrometeorological tower sites that uses mainly Bowen ratio energy balance systems (BREBS) to measure surface water vapor and energy fluxes between terrestrial agro-ecosystems and microclimate. At present, ten BREBSs and one eddy covariance system are operating on a long-term and continuous basis for vegetation surfaces ranging from tilled and untilled irrigated and rainfed croplands, irrigated and rainfed grasslands, alfalfa, to Phragmites (Phragmites australis)-dominated cottonwood (Populus deltoides var. occidentalis) and willow stand (Willow salix) plant communities. The NEBFLUX project will provide good-quality flux and other extensive supportive data on plant physiology [leaf area index, stomatal resistance, within-canopy radiation parameters, productivity (yield and/or biomass), and plant height], soil characteristics, soil water content, and surface characteristics to the micrometeorology, water resources and agricultural engineering, and science community on broad spectrum of agro-ecosystems. The fundamental premise of the NEBFLUX project is to measure continuous and long-term (at least ten complete annual cycles for each surface) exchange of water vapor and energy fluxes. In addition to the scientific and research objectives, information dissemination to educate the general public and youth is another important objective and output of the network. This article describes the specific goals and objectives, basic principles, and operational characteristics of the NEBFLUX.

Invited Review Article: The Agricultural Policy/Environmental eXtender (APEX) Model: An Emerging Tool for Landscape and Watershed Environmental Analyses

Abstract: The Agricultural Policy/Environmental eXtender (APEX) model was developed by the Blackland Research and Extension Center in Temple, Texas. APEX is a flexible and dynamic tool that is capable of simulating a wide array of management practices, cropping systems, and other land uses across a broad range of agricultural landscapes, including whole farms and small watersheds. The model can be configured for novel land management strategies, such as filter strip impacts on pollutant losses from upslope crop fields, intensive rotational grazing scenarios depicting movement of cows between paddocks, vegetated grassed waterways in combination with filter strip impacts, and land application of manure removed from livestock feedlots or waste storage ponds. A description of the APEX model is provided, including an overview of all the major components in the model. Applications of the model are then reviewed, starting with livestock manure and other management scenarios performed for the National Pilot Project for Livestock and the Environment (NPP), and then continuing with feedlot, pesticide, forestry, buffer strip, conservation practice, and other management or land use scenarios performed at the plot, field, watershed, or regional scale. The application descriptions include a summary of calibration and/or validation results obtained for the different NPP assessments as well as for other APEX simulation studies. Available APEX GIS-based or Windows-based interfaces are also described, as are forthcoming improvements and additional research needs for the model.

Harvest and storage of two perennial grasses as biomass feedstocks

Abstract: Some perennial grasses, such as reed canarygrass (RCG) and switchgrass (SWG), have prolific yield and low inputs, making them attractive as biomass feedstocks. When harvested as biomass, these grasses are more mature and have much greater yield than when harvested as animal forage. Much is unknown about how harvest equipment performance and storage characteristics are affected by these crop conditions. The objective of this research was to determine the crop yield and drying rate, baling rate, bale density, and bale storage characteristics of these grasses harvested as biomass feedstocks. After the establishment year, the three-year average yield of RCG was 21% less than SWG (7.70 vs. 9.69 Mg DM ha -1 ) using a single-cutting system that occurred in August. When the crops were left standing over winter and harvested in the spring, DM yields were reduced by 17% and 26% for SWG and RCG, respectively. When crop yield was similar, switchgrass tended to dry faster than reed canarygrass. Drying rates of these grasses were faster than typically experienced with forage crops like alfalfa. Bale density averaged 163 kg DM m -3 with no significant differences between crops or type of wrap (twine or net). Dry bales stored outdoors for 9 to 11 months averaged 3.8%, 4.8%, 7.5%, 8.7%, and 14.9% DM loss for bales wrapped with plastic film, breathable film, net wrap, plastic twine, and sisal twine, respectively. Bales stored under cover averaged 3.0% DM loss. The chemical and physical properties of bales stored outdoors were spatially variable. Preservation by ensiling in a tube produced average DM losses of 1.1% at average moisture of 39.9% (w.b.).

Optimal Coverage Path Planning for Arable Farming on 2D Surfaces

Abstract: With the rapid adoption of automatic guidance systems in agriculture, automated path planning has great potential to further optimize field operations. Field operations should be done in a manner that minimizes time and travel over field surfaces and should be coordinated with specific field operation requirements, machine characteristics, and topographical features of arable lands. To reach this goal, an intelligent coverage path planning algorithm is the key. To determine the full coverage pattern of a given field by using boustrophedon paths, it is necessary to know whether to and how to decompose a field into sub-regions and how to determine the travel direction within each sub-region. A geometric model was developed to represent this coverage path planning problem, and a path planning algorithm was developed based on this geometric model. The search mechanism of the algorithm was guided by a customized cost function resulting from the analysis of different headland turning types and implemented with a divide-and-conquer strategy. The complexity of the algorithm was analyzed, and methods for reducing the computational time are discussed. Field examples with complexity ranging from a simple convex shape to an irregular polygonal shape that has multiple obstacles within its interior were tested with this algorithm. The results were compared with other reported approaches or farmers' recorded patterns. These results indicate that the proposed algorithm was effective in producing optimal field decomposition and coverage path direction in each sub-region.

Crop residue cover effects on evaporation, soil water content, and yield of deficit-irrigated corn in west-central nebraska

Abstract: Competition for water is becoming more intense in many parts of the U.S., including west-central Nebraska. It is believed that reduced tillage, with more crop residue on the soil surface, conserves water, but the magnitude of water conservation is not clear. A study was initiated on the effect of residue on soil water content and corn yield at North Platte, Nebraska. The experiment was conducted in 2007 and 2008 on plots planted to field corn (Zea mays L.). In 2005 and 2006, soybean was grown on these plots. There were two treatments: residue-covered soil and bare soil. Bare-soil plots were created in April 2007. The residue plots were left untreated. In April 2008, bare-soil plots were recreated on the same plots as in 2007. The experiment consisted of eight plots (two treatments with four replications each). Each plot was 12.2 m × 12.2 m. During the growing season, soil water content was measured several times in each of the plots at six depths, down to a depth of 1.68 m, using a neutron probe. The corn crop was sprinkler-irrigated but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. In 2007, mean corn yield was 12.4 Mg ha-1 in the residue-covered plots, which was significantly (p = 0.0036) greater than the 10.8 Mg ha-1 in the bare-soil plots. Other research has shown that it takes 65 to 100 mm of irrigation water to grow this extra 1.6 Mg ha-1, which may be considered water conservation due to the residue. In 2008, the residue-covered soil held approximately 60 mm more water in the top 1.83 m compared to the bare soil toward the end of the growing season. In addition, mean corn yield was 11.7 Mg ha-1 in the residue-covered plots, which was significantly (p = 0.0165) greater than the 10.6 Mg ha-1 in the bare-soil plots. It would take 30 to 65 mm of irrigation water to produce this additional 1.1 Mg ha-1 of grain yield. Thus, the total amount of water conservation due to the residue was 90 to 125 mm in 2008. Water conservation of such a magnitude will help irrigators to reduce pumping cost. With deficit irrigation, water saved by evaporation is used for transpiration and greater yield, which may have even greater economic benefits. In addition, with these kinds of water conservation, more water would be available for competing needs.

Evaluation of Grape Quality Parameters by a Simple Vis/NIR System

Abstract: Visible/near-infrared (Vis/NIR) spectroscopy is a rapid and nondestructive technique requiring minimal sample processing before analysis, and coupled with chemometrics methods it appears to be one of the most convenient and straightforward analytical tools for studying fruit quality and ripeness. Chemometrics is applied to solve both descriptive and predictive problems in the chemical, pharmaceutical, and food sectors. With this aim, an optical, portable, experimental system (Vis/NIR spectrophotometer) for nondestructive and quick prediction of ripening parameters of fresh berries and homogenized samples of grapes in the wavelength range 450-980 nm was built and tested. A total of 156 grape samples, representing vintage years 2005 and 2006 and harvested in the Valtellina viticultural area of Italy, were evaluated by Vis/NIR spectroscopy for ripeness parameters (soluble solids content, titratable acidity, and pH value) and for phenol ripening parameters (anthocyanins and polyphenols content). Accurate and good calibrations to predict ripeness parameters were obtained for both the 2005 and 2006 vintage years. Calibrations for technological ripening and for anthocyanins had good correlation coefficients (rCV >0.90). These models were extensively validated using independent sample sets. Good statistical parameters were obtained for soluble solids content (r > 0.8, SEP 0.8, SEP < 2.00 g tartaric acid L-1), showing the validity of the Vis/NIR spectrometer. Similarly, anthocyanins could be predicted accurately compared with the reference determination. Finally, for qualitative analysis, spectral data on grapes were divided into two groups on the basis of grapes' soluble content and acidity in order to apply a classification analysis (PLS-DA). Good results were obtained with the Vis/NIR device, with 89% of samples correctly classified for soluble content and 83% of samples correctly classified for acidity. Results indicate that the Vis/NIR portable device could be an interesting and rapid tool for assessing grape ripeness directly in the field or upon receiving grapes in the wine industry.

Uncertainties in assessing annual nitrate loads and concentration indicators: Part 1. Impact of sampling frequency and load estimation algorithms.

Abstract: The objectives of this study are to evaluate the uncertainty in annual nitrate loads and concentrations (such as annual average and median concentrations) as induced by infrequent sampling and by the algorithms used to compute fluxes. A total of 50 watershed-years of hourly to daily flow and concentration data gathered from nine watersheds (5 to 252 km²) in Brittany, France, were analyzed. Original (high frequency) nitrate concentration and flow data were numerically sampled to simulate common sampling frequencies. Annual fluxes and concentration indicators calculated from the simulated samples were compared to the reference values calculated from the high-frequency data. The uncertainties contributed by several algorithms used to calculate annual fluxes were also quantified. In all cases, uncertainty increased as sampling intervals increased. Results showed that all the tested algorithms that do not use continuous flow data to compute nitrate fluxes introduced considerable uncertainty. The flow-weighted average concentration ratio method was found to perform best across the 50 annual datasets. Analysis of the bias values suggests that the 90th and 95th percentiles and the maximum concentration values tend to be systematically underestimated in the long term, but the load estimates (using the chosen algorithm) and the average and median concentrations were relatively unbiased. Great variability in the precision of the load estimation algorithms was observed, both between watersheds of different sizes and between years for a particular watershed. This has prevented definitive uncertainty predictions for nitrate loads and concentrations in this preliminary work, but suggests that hydrologic factors, such as the watershed hydrological reactivity, could be a key factor in predicting uncertainty levels.

Using NEXRAD and rain gauge precipitation data for hydrologic calibration of SWAT in a Northeastern watershed.

Abstract: The value of watershed-scale, hydrologic and water quality models to ecosystem management is increasingly evident as more programs adopt these tools to evaluate the effectiveness of different management scenarios and their impact on the environment. Quality of precipitation data is critical for appropriate application of watershed models. In small watersheds, where no dense rain gauge network is available, modelers are faced with a dilemma to choose between different data sets. In this study, we used the German Branch (GB) watershed (~50 km2), which is included in the USDA Conservation Effects Assessment Project (CEAP), to examine the implications of using surface rain gauge and next-generation radar (NEXRAD) precipitation data sets on the performance of the Soil and Water Assessment Tool (SWAT). The GB watershed is located in the Coastal Plain of Maryland on the eastern shore of Chesapeake Bay. Stream flow estimation results using surface rain gauge data seem to indicate the importance of using rain gauges within the same direction as the storm pattern with respect to the watershed. In the absence of a spatially representative network of rain gauges within the watershed, NEXRAD data produced good estimates of stream flow at the outlet of the watershed. Three NEXRAD datasets, including (1) non-corrected (NC), (2) bias-corrected (BC), and (3) inverse distance weighted (IDW) corrected NEXRAD data, were produced. Nash-Sutcliffe efficiency coefficients for daily stream flow simulation using these three NEXRAD data ranged from 0.46 to 0.58 during calibration and from 0.68 to 0.76 during validation. Overall, correcting NEXRAD with rain gauge data is promising to produce better hydrologic modeling results. Given the multiple precipitation datasets and corresponding simulations, we explored the combination of the multiple simulations using Bayesian model averaging. The results show that this Bayesian scheme can produce better deterministic prediction than any single simulation and can provide reasonable uncertainty estimation. The optimal water balance obtained in this study is an essential precursor to acquiring realistic estimates of sediment and nutrient loads in future GB modeling efforts. The results presented in this study are expected to provide insights into selecting precipitation data for watershed modeling in small Coastal Plain catchments.

Differentiating Impacts of Land Use Changes from Pasture Management in a CEAP Watershed Using the SWAT Model

Abstract: Due to intensive farm practices, nonpoint-source (NPS) pollution has become one of the most challenging environmental problems in agricultural and mixed land use watersheds. Usually, various conservation practices are implemented in the watershed to control the NPS pollution problem. However, land use changes can mask the water quality improvements from the conservation practices implemented in the watershed. The objectives of this study were to evaluate the linkage between nutrient input from various pasture management practices and water quality, and to quantify the impacts of land use changes and pasture management on water quality in a pasture-dominated watershed. Land use data from 1992, 1994, 1996, 1999, 2001, and 2004 were evaluated for the land use changes in the watershed, and the corresponding implemented management practices were also incorporated into the Soil and Water Assessment Tool (SWAT) model. The individual impacts of land use change and pasture management were quantified by comparing the SWAT simulation results for different land use change and pasture management scenarios. The results indicated that land use changes resulted in greater total sediment (499 kg ha-1) and nitrogen losses (3.8 kg ha-1) in the Moores Creek subwatershed, whereas pasture management resulted in greater total nitrogen losses (4.3 kg ha-1) in the Beatty Branch subwatershed. Overall, the combined impacts of land use changes and pasture management resulted in greater total sediment (28 to 764 kg ha-1 of cumulative combined impacts between 1992 and 2007) and nitrogen losses (5.1 to 6.1 kg ha-1) and less total phosphorus losses (1.5 to 2.1 kg ha-1) in the Beatty Branch, Upper Moores Creek, and Moores Creek subwatersheds. By quantifying the individual impacts of land use changes and pasture management, we found that an increase in total nitrogen losses in the Beatty Branch subwatershed was mainly due to an increase in nutrient inputs in the pasture areas, and total sediment and nitrogen losses in the Moores Creek subwatershed were mainly due to an increase in urban lands. Therefore, the individual impacts of land use changes and conservation practices should be quantified to get a true picture of the success of CEAP programs in watersheds experiencing significant land use changes.

Determination of Critical Source Areas for Phosphorus Loss: Lake Champlain Basin, Vermont

Abstract: Lake Champlain, located between Vermont, New York, and Quebec, exhibits eutrophication due to continuing phosphorus (P) inputs from upstream nonpoint-source areas To address the effects of this eutrophication and as part of total maximum daily load (TMDL) requirements, state-level P reduction goals have been established by both the Vermont and New York Departments of Environmental Conservation Unfortunately, remedial measures undertaken thus far have been mostly based on voluntary participation by the landowners and have not been guided by a systematic technique to implement remedial measures where they could provide the greatest P loss reduction Consequently, P reduction goals have not been achieved in most segments of Lake Champlain The main objective of this study was to identify and quantify critical source areas (CSAs) of P loss using a model-based approach The Soil and Water Assessment Tool (SWAT) is used for this objective This study focuses on the Rock River watershed, which is one of the highest contributors of P to Lake Champlain Spread over 71 km2, the watershed is dominated by dairy agriculture and has fertile periglacial lacustrine and alluvial soils with an old tile drainage system In this agriculture-dominated watershed, 80% of total P loss occurs from only 24% of the watershed area, signifying the need for focused remedial measures on CSAs of P loss The identification of CSAs for P loss is expected to support the next phase of our project, which involves exploring cost-effective P management strategies with the highest potential for P loss reduction applicable to the study watershed and Lake Champlain basin

Spectral Absorption and Scattering Properties of Normal and Bruised Apple Tissue

Abstract: Knowledge of the spectral absorption and scattering properties of apple tissue, especially bruised tissue, can help us develop an effective inspection method for detecting bruises during postharvest sorting and grading. This research was aimed at determining the optical properties of normal and bruised apple tissue for the wavelength range of 500-1,000 nm and quantifying their changes with time after bruising. Values for the absorption and reduced scattering coefficients were determined for the normal or unbruised tissue of 'Golden Delicious' and 'Red Delicious' apples and then for the bruised tissue, for different time intervals after bruising, using a hyperspectral imaging-based spatially resolved technique. Bruising caused changes to the absorption coefficient, but no consistent pattern of changes was observed for 'Golden Delicious' and 'Red Delicious' apples after they were bruised. The reduced scattering coefficient for normal apples, however, was much higher than that for bruised apples; it decreased consistently with time after bruising. These results suggest that bruising has a greater impact on scattering than on absorption. Hence, an optical system that enhances scattering feature measurement would be better suited for bruise detection.

Effect of Controlled Drainage on Water and Nitrogen Balances in Drained Lands

Abstract: Field studies have shown that subsurface drainage systems can be managed to conserve water and reduce losses of nitrogen (N) to surface waters. The practice, called controlled drainage (CD) or drainage water management (DWM), is a viable alternative for reducing N loads from drained cropland, including millions of acres in the Midwest. This article reviews past studies on the effect of CD on drainage volumes and N losses for a wide range of soils and climatological conditions and uses simulations to examine mechanisms affecting the practice. Results published in the literature show that CD has reduced drainage volumes and N losses in drainage waters by 17% to over 80%, depending on soil properties, crops, drainage intensities, control strategies, and location. This study resulted in the following conclusions. CD reduces subsurface drainage and raises water tables, while increasing ET, seepage, and surface runoff. Seepage, which depends on soil properties and site conditions, is an important factor that often governs the effectiveness of CD. Experiments to determine the effect of CD on drainage volumes and N losses should be conducted on the field or watershed scale so that impacts of seepage are properly represented. Increases in ET in response to CD are important but are rarely greater than 10%. The effect of this increase in water use on drainage water loss is also less than 10% for most locations. CD reduces N losses in drainage water by about the same percentage as its effect on subsurface drainage volume in most cases. The effect of CD on N loss to surface waters depends on denitrification, both in the profile and in reduced zones along seepage paths. For soils that do not develop reduced zones, the effect of CD on N loss may be substantially less than its effect on drainage volume.

Detection of overparameterization and overfitting in an automatic calibration of SWAT.

Abstract: Distributed hydrologic models based on small-scale physical processes tend to have a large number of parameters to represent spatial heterogeneity. This characteristic requires the use of a large number of parameters in model calibration. It is a common view that calibration with a large number parameters produces overparameterization and overfitting. Recent work using prior information, spatial information, and constraints on parameters for regularization of the calibration problem has improved model predictions using a few dozen parameters. We demonstrate that the Soil and Water Assessment Tool (SWAT) and the information associated with a SWAT watershed setup provide a regularized problem with many of recently published regularization techniques already utilized in SWAT. Our hypothesis is that the Soil and Water Assessment Tool (SWAT) regularizes the inverse problem so that a stable solution can be obtained for calibration of SWAT using a very large number of parameters, where very large means up to 10,000 calibration parameters. In this study, a two-objective calibration genetic algorithm based on a non-dominated sorting genetic algorithm (NSGA-II) was used to calibrate the Blue River basin in Oklahoma. We introduce the use of intermediate solutions found by the genetic algorithm to test identification of calibration parameters and diagnose model overfitting. Defining identification as the capability of a model to constrain the estimation of parameters, we introduced a method for statistically testing for changes from the initial uniform distribution of each parameter. We found that all 4,198 parameters used to calculate the Blue River SWAT model were identified. Diagnostic comparisons of goodness-of-fit measures for the calibration and validation periods provided strong evidence that the model was not overfitted.

Effects of agricultural management, land use, and watershed scale on e. coli concentrations in runoff and streamflow

Abstract: Fecal contamination of surface waters is a critical water quality concern with serious human health implications. Many states use Escherichia coli as an indicator organism for fecal contamination and apply watershed models to develop and support bacterial Total Maximum Daily Loads (TMDLs); however, model applicability is greatly restricted due to the sparse availability of E. coli data for validation and calibration at various scales. Similarly, watershed-scale information on the effects of management practices and land use on E. coli fate and transport is limited. Thus, this study was designed to measure E. coli concentrations in edge-of-field runoff and in streams with various agricultural management practices, land uses, and watershed scales. Results showed that application of dairy compost to pasture, cultivated, and mixed land use sites did not significantly affect E. coli concentrations in runoff at the field scale. In contrast, grazed sites had significantly higher runoff E. coli concentrations than cultivated sites, but the increase cannot be attributed solely to grazing cattle. No significant differences in E. coli concentrations were determined for presumably impacted and unimpacted rural streams with differing anthropogenic inputs, which highlights the challenges of managing and regulating bacterial contamination. The results also showed that E. coli concentrations consistently decreased as watershed scale increased from field to small watershed to river basin scale. Results from this study highlight the importance of considering all potential sources (including animal feeding operations, wastewater treatment plants and on-site systems, cultivated and pasture fields, wildlife, and streambed resuspension) to properly assess E. coli contamination in rural watersheds. Results also demonstrated the need for an improved basic scientific understanding of fecal bacteria in the environment to reduce the substantial uncertainty associated with assessing, modeling, managing, and regulating bacterial contamination.

Validating soil phosphorus routines in the SWAT model.

Abstract: Phosphorus transfer from agricultural soils to surface waters is an important environmental issue. Commonly used models like SWAT have not always been updated to reflect current understanding of soil P transformations and transfer to runoff. The objective of this study was to validate the ability of routines in both SWAT2000 and SWAT2005 to initialize the quantity of P in different soil P pools (and thus soil total P) and simulate changes in the simulated solution P pool. Based on data from 40 published studies, results show that currently published equations to estimate the soil PSP parameter and SWAT's method of summing four soil P pools underpredict soil total P. An underprediction of soil total could result in underprediction of P loss in runoff with eroded sediment. Conversely, the proposed alternative for estimating soil total P, which includes a new equation to estimate the soil PSP parameter and includes the solution P pool when summing soil P pools, resulted in accurate predictions of soil total P for 484 topsoil samples from 35 published studies. Results also show that both the SWAT routines and the routines proposed by a previous study for simulating changes in soil P were able to accurately predict long-term changes in soil solution P. However, routines in both SWAT2000 and SWAT2005 may underpredict solution P for several weeks after P is added to soils. This could result in underprediction of dissolved inorganic P loss in runoff soon after a P application to soils. The routines proposed by the previous study would not result in similar underpredictions.

Water desorption and thermodynamic properties of okra seeds.

Abstract: The objective of the present work was to determine desorption isotherms of okra seeds for diverse conditions of temperature (10°C to 50°C) and relative humidity (0.11 to 0.96) of the air, as well as determine the values of isosteric heat of desorption, differential entropy, and Gibbs free energy. To obtain the equilibrium moisture content, a static method was used. Experimental data were adjusted to frequently used mathematical models for representation of hygroscopicity of agricultural products. Calculation of the net isosteric heat of desorption was performed based on the Clausius-Clapeyron thermodynamic relation. From the obtained results, it was concluded that equilibrium moisture content of the okra seeds decreased with an increase in temperature at the same relative humidity, as is the case of the majority of agricultural products. Based on statistical parameters, the Chung-Pfost model best represented the hygroscopicity of the okra seeds. Values of the integral isosteric heat of desorption as well as the differential entropy and Gibbs free energy for the okra seeds decreased with an increase in moisture content.

Parameter Sensitivity and Uncertainty in SWAT: A Comparison Across Five USDA-ARS Watersheds

Abstract: The USDA-ARS Conservation Effects Assessment Project (CEAP) calls for improved understanding of the strengths and weaknesses of watershed-scale water quality models under a range of climatic, soil, topographic, and land use conditions. Assessing simulation model parameter sensitivity helps establish feasible parameter ranges, distinguish among parameters having regional versus universal interactions, and ensure that one model process does not compensate for another due to poor parameter settings. The Soil and Water Assessment Tool (SWAT) parameter sensitivity and autocalibration module was tested on two northern and three southern USDA-ARS experimental watersheds. These previously calibrated watersheds represent a range of climatic, physiographic, and land use conditions present in the U.S. Sixteen parameters that govern basin, snow accumulation/melt, surface, and subsurface response in the model were evaluated. Parameters governing surface runoff due to rainfall were found most sensitive overall, while parameters governing groundwater were the least sensitive. Surface runoff parameters were found most sensitive for areas with high evaporation rates and localized thunderstorms. Parameters from all categories were important in areas where precipitation includes both rainfall and snowfall. Differences in model performance were noticeable on a climatic basis; SWAT generally predicted streamflow with less uncertainty in humid climates than in arid or semi-arid climates. Study findings can be used to determine appropriate parameter ranges for ungauged watersheds of similar characteristics.

Apex model assessment of variable landscapes on runoff and dissolved herbicides

Abstract: 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 × 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.

Evaluation of the CSM-CROPSIM-CERES-Wheat Model as a Tool for Crop Water Management

Abstract: Development and implementation of improved methodologies for crop water management will conserve valuable water resources in agricultural regions that depend on irrigation. To address this problem for conditions in central Arizona, we have evaluated the CSM-CROPSIM-CERES-Wheat model using measured wheat growth and soil water data from plot-level irrigation scheduling experiments conducted during the winters of 2003-2004 and 2004-2005. During each season, wheat plots were managed using two FAO-56-based irrigation scheduling approaches at three planting densities (~75, ~150, and ~300 plant m-2) and at two nitrogen application rates (~80 and ~215 kg ha-1 year-1). For these treatments, the calibrated model simulated wheat yield with relative root mean squared errors (RRMSE) of 7.4% and 1.7% for the 2003-2004 and 2004-2005 seasons, respectively. Time series plots of measured and simulated Zadoks number, leaf number, leaf mass, stem mass, spike mass, and green leaf area index demonstrated favorable wheat development and growth responses to experimental treatments and seasonal weather and management variability. The model was able to quantify average soil water contents in eight soil layers to a depth of 210 cm with RRMSEs ranging from 3.3% to 18.9% for the 2003-2004 season and from 2.7% to 11.3% for the 2004-2005 season. Evapotranspiration was simulated with RRMSEs of 2.4% and 3.2% for the 2003-2004 and 2004-2005 seasons, respectively. Deficiencies were demonstrated in the ability of the model's automatic irrigation routines to reproduce the FAO-56 irrigation schedules devised during field experimentation. With further development, the CSM-CROPSIM-CERES-Wheat model could become a valuable central component for decision tools designed to evaluate alternative water management scenarios and improve water management for irrigated agricultural systems.

Progress toward evaluating the sustainability of switchgrass as a bioenergy crop using the SWAT model.

Abstract: Adding bioenergy to the U.S. energy portfolio requires long-term profitability for bioenergy producers and long-term protection of affected ecosystems. In this study, we present steps along the path toward evaluating both sides of the sustainability equation (production and environmental) for switchgrass (Panicum virgatum) using the Soil and Water Assessment Tool (SWAT). We modeled production of switchgrass and river flow using SWAT for current landscapes at a regional scale. To quantify feedstock production, we compared lowland switchgrass yields simulated by SWAT with estimates from a model based on empirical data for the eastern U.S. The two produced similar geographic patterns. Average yields reported in field trials tended to be higher than average SWAT-predicted yields, which may nevertheless be more representative of production-scale yields. As a preliminary step toward quantifying bioenergy-related changes in water quality, we evaluated flow predictions by the SWAT model for the Arkansas-White-Red river basin. We compared monthly SWAT flow predictions to USGS measurements from 86 subbasins across the region. Although agreement was good, we conducted an analysis of residuals (functional validation) seeking patterns to guide future model improvements. The analysis indicated that differences between SWAT flow predictions and field data increased in downstream subbasins and in subbasins with higher percentage of water. Together, these analyses have moved us closer to our ultimate goal of identifying areas with high economic and environmental potential for sustainable feedstock production.

Influence of Water and Air Flow on the Performance of Cellulose Evaporative Cooling Pads Used in Mediterranean Greenhouses

Abstract: Evaporative cooling systems are a widely used technique in Mediterranean greenhouses. In this study, the cellulose evaporative cooling pads most commonly used in this region were tested in the laboratory using a new methodology in a wind tunnel to determine the water flow on the pad and air flow through it, as well as the water consumption and pressure drop caused by each pad as a function of air speed. Greater water flow increased the pressure drop, but the main effect on performance was caused by modifying the air flow through the pad. We recommend a range of air speeds through the pad of 1 to 1.5 m s-1, at which the pressure drop was between 3.9 and 11.25 Pa, depending on the type of pad and the water flow applied. On the other hand, saturation efficiency ranged between 64% and 70%, while the amount of evaporated water varied between 1.8 and 2.62 kg h-1 K-1 per square meter of pad area.

Adjuvant effects on evaporation time and wetted area of droplets on waxy leaves.

Abstract: The use of an appropriate adjuvant for pesticide applications is a critical process to improve spray deposit characteristics on waxy leaves and to reduce off-target losses. After deposition and evaporation, residue patterns of 500 ° m sessile droplets that incorporated four classes of adjuvants on five different waxy plants were investigated. Droplets were generated with a single-droplet generator and deposited on target leaves placed in an environmentally controlled chamber at 60% relative humidity and 25°C ambient temperature. Adjuvants tested were two oil-based types (crop oil concentrate, or COC; and modified seed oil, or MSO), a nonionic surfactant (NIS), and a mixture (oil surfactant blend, or OSB). Water-only droplets were also tested for comparative purposes. The five waxy plants were difficult to wet and had a water contact angle greater than 90°. The water-only droplets did not spread at all and formed extremely small wetted areas on the leaf surface. The addition of an adjuvant to the spray solution significantly reduced the contact angle and increased the wetted area, but the change or improvements varied with the plant species and adjuvant class. In general, MSO and NIS enhanced the droplet spread and maintained the droplet evaporation time on the waxy leaf surfaces. After evaporation, the residues formed patterns of "coffee rings". Droplets with oil-based adjuvants had more uniform residual distribution in the deposition patterns than droplets with the surfactant adjuvant. Results of this study demonstrated that selection of the appropriate class of adjuvants significantly improved deposit formation on waxy leaves, leading to more effectiveness of pesticides.

Preferential Flow Effects on Subsurface Contaminant Transport in Alluvial Floodplains

Abstract: For sorbing contaminants, transport from upland areas to surface water systems is typically considered to be due to surface runoff, with negligible input from subsurface transport assumed. However, certain conditions can lead to an environment where subsurface transport to streams may be significant. The Ozark region, including parts of Oklahoma, Arkansas, and Missouri, is one such environment, characterized by cherty, gravelly soils and gravel bed streams. Previous research identified a preferential flow path (PFP) at an Ozark floodplain along the Barren Fork Creek in northeastern Oklahoma and demonstrated that even a sorbing contaminant, i.e., phosphorus, can be transported in significant quantities through the subsurface. The objective of this research was to investigate the connectivity and floodplain-scale impact of subsurface physical heterogeneity (i.e., PFPs) on contaminant transport in alluvial floodplains in the Ozarks. This research also evaluated a hypothesis that alluvial groundwater acts as a transient storage zone, providing a contaminant sink during high stream flow and a contaminant source during stream baseflow. The floodplain and PFP were mapped with two electrical resistivity imaging techniques. Low-resistivity features (i.e., less than 200 O-m) corresponded to topographical depressions on the floodplain surface, which were hypothesized to be relict stream channels with fine sediment (i.e., sand, silt, and clay) and gravel deposits. The mapped PFP, approximately 2 m in depth and 5 to 10 m wide, was a buried gravel bar with electrical resistivity in the range of 1000 to 5000 O-m. To investigate the PFP, stream, and groundwater dynamics, a constant-head trench test was installed with a conservative tracer (Rhodamine WT) injected into the PFP at approximately 85 mg/L for 1.5 h. Observation wells were installed along the PFP and throughout the floodplain. Water table elevations were recorded real-time using water level loggers, and water samples were collected throughout the experiment. Results of the experiment demonstrated that stream/aquifer interaction was spatially non-uniform due to floodplain-scale heterogeneity. Transport mechanisms included preferential movement of Rhodamine WT along the PFP, infiltration of Rhodamine WT into the alluvial groundwater system, and then transport in the alluvial system as influenced by the floodplain-scale stream/aquifer dynamics. The electrical resistivity data assisted in predicting the movement of the tracer in the direction of the mapped preferential flow pathway. Spatially variable PFPs, even in the coarse gravel subsoils, affected water level gradients and the distribution of tracer into the shallow groundwater system.