Management Systems Evaluation Area Research Articles

Prediction of nitrate accumulation and leaching beneath groundwater irrigated corn fields in the Upper Platte basin under a future climate scenario

Understanding the impacts of future climate change on soil hydrological processes and solute transport is crucial to develop appropriate strategies to minimize the adverse impacts of agricultural activities on groundwater quality. To evaluate the direct effects of climate change on the transport and accumulation of nitrate-N, we developed an integrated modeling framework combining climatic change, nitrate-N infiltration in the unsaturated zone, and groundwater level fluctuations. The study was based on a center-pivot irrigated corn field at the Nebraska Management Systems Evaluation Area (MSEA) site. Future groundwater recharge (GR) and actual evapotranspiration (ETa) rates were predicted via an inverse vadose zone modeling approach by using climatic data generated by the Weather Research and Forecasting (WRF) climate model under the RCP 8.5 scenario, which was downscaled from the global CCSM4 model to a resolution of 24 km by 24 km. A groundwater flow model was first calibrated on the basis of historical groundwater table measurements and then applied to predict the future groundwater table in 2057–2060. Finally, the predicted future GR rate, ETa rate, and groundwater level, together with future precipitation data from the WRF climate model, were used in a three-dimensional (3D) model to predict nitrate-N concentrations in the subsurface (saturated and unsaturated parts) from 2057 to 2060. The future GR was predicted to decrease in the study area, as compared with the average GR data from the literature. Correspondingly, the groundwater level was predicted to decrease (30 to 60 cm) over the 5 years of simulation in the future. The nitrate-N mass in the simulation domain was predicted to increase but at a slower rate than in the past. Sensitivity analysis indicated that the accumulation of nitrate-N is sensitive to groundwater table elevation changes and irrigation rates.

Three-dimensional modeling of nitrate-N transport in vadose zone: Roles of soil heterogeneity and groundwater flux

Contamination of groundwater from nitrogen fertilizers in agricultural lands is an important environmental and water quality management issue. It is well recognized that in agriculturally intensive areas, fertilizers and pesticides may leach through the vadose zone and eventually reach groundwater. While numerical models are commonly used to simulate fate and transport of agricultural contaminants, few models have considered a controlled field work to investigate the influence of soil heterogeneity and groundwater flow on nitrate-N distribution in both root zone and deep vadose zone.In this work, a numerical model was developed to simulate nitrate-N transport and transformation beneath a center pivot-irrigated corn field on Nebraska Management System Evaluation area over a three-year period. The model was based on a realistic three-dimensional sediment lithology, as well as carefully controlled irrigation and fertilizer application plans. In parallel, a homogeneous soil domain, containing the major sediment type of the site (i.e. sandy loam), was developed to conduct the same water flow and nitrate-N leaching simulations.Simulated nitrate-N concentrations were compared with the monitored nitrate-N concentrations in 10 multi-level sampling wells over a three-year period. Although soil heterogeneity was mainly observed from top soil to 3 m below the surface, heterogeneity controlled the spatial distribution of nitrate-N concentration. Soil heterogeneity, however, has minimal impact on the total mass of nitrate-N in the domain. In the deeper saturated zone, short-term variations of nitrate-N concentration correlated with the groundwater level fluctuations.

Effects of land management practices on water quality in Mississippi Delta oxbow lakes: Biochemical and microbiological aspects

The Mississippi Delta Management Systems Evaluation Area (MSEA) project was designed to assess the effects of land management practices on water quality in three small oxbow lake watersheds; Thighman (1338 ha, 16 ha lake); Beasley (915 ha, 25 ha lake); and Deep Hollow (132 ha, 8 ha lake). Monthly water samples were monitored for enzymatic activity (fluorescein diacetate hydrolysis, alkaline phosphatase, and substrate utilization), chemical and physical analysis (suspended solids, dissolved organic carbon, pH, nitrate, ammonium, orthophosphate, and electrical conductivity), phytoplankton and bacterioplankton populations. All of these parameters were influenced by the intrinsic nature of the watersheds, with some parameters shifting as management changes were imposed on the surrounding agricultural fields. Thighman lake water typically maintained the highest suspended solid levels, dissolved organic carbon, algal and bacterial populations, enzyme activities, and heterotrophic metabolic indexes. Introduction of reduced tillage practices and glyphosate-resistant crops in Beasley watershed resulted in lower levels of suspended sediments, but had minimal impact on overall ranking of biochemical or microbiological properties. Likewise, conversion of Deep Hollow watershed from reduced tillage to conventional tillage had little effect on suspended sediment, and most microbial activity parameters remained intermediate. However, canonical analysis indicated dynamic changes in the microbial community, suggesting that biological parameters of lake water quality were affected by changes in crop and soil management practices.

Environmental quality research in the Beasley Lake watershed, 1995 to 2007: Succession from conventional to conservation practices

The Beasley Lake watershed (BLW), established for the Mississippi Delta Management Systems Evaluation Area project, represents the US Mississippi Delta region in the national Conservation Effects Assessment Project. The 915-ha (2,260-ac) BLW drains into an oxbow lake that has been monitored since 1995 when row crops were grown on 79% of the area, and the remaining area included a 25-ha (62-ac) lake and a 135-ha (330-ac) riparian forest. Currently, row crops account for 66.5% of the area with 12.4% enrolled in the Conservation Reserve Program. Cotton (<i>Gossypium hirsutum</i> L.) acreage has decreased from 63.3% to 8.9%. Historical and current research in BLW focuses on monitoring lake limnology, evaluating conservation practice effects on edge-of-field runoff, quantifying changes associated with the Conservation Reserve Program, and modeling watershed responses. Applying combinations of conservation practices can significantly reduce nonpoint source pollution. For example, converting row crops to reduced tillage and transgenic herbicide-resistant crops in BLW reduced suspended sediment (70% reduction), total phosphorus (41% reduction), and pesticide concentrations in lake water. Corresponding increases in Secchi visibility (97%) and chlorophyll <i>a</i> (a primary productivity indicator) likely contributed to improved fish productivity (e.g., fish weight increase comparing 1998 and 2004: <i>Micropterus salmoides</i> 87%, <i>Lepomis macrochirus</i>, 65%) during this period. Additional studies should quantify effects of individual practices and improve modeling tools for making better management decisions. The utilization of the Annualized Agricultural Non-Point Source (AnnAGNPS) model and the Riparian Ecosystem Management Model (REMM) together provides additional information on the effectiveness of conservation practices within the watershed by combining technology that assesses riparian buffer effectiveness in filtering nutrients at the field scale with the watershed water quality transport capabilities of the AnnAGNPS model.

A Comparison of 18Oδ Composition of Water Extracted from Suction Lysimeters, Centrifugation, and Azeotropic Distillation

The representativeness of soil pore water extracted by suction lysimeters in ground-water monitoring studies is a problem that often confounds interpretation of measured data. Current soil water sampling techniques cannot delineate from which soil volume a pore water sample is extracted, neither macroscopic, microscopic, or preferential flowpath. This research was undertaken to compare δ18O and Br− values of extracted suction lysimeters samples from intact soil cores with samples obtained by the direct extraction methods of centrifugation and azeotropic distillation. Also, the study was concerned with determining what portion of soil pore water is sampled by each method and explaining differences in concentrations of the extracted water from each method to allow a determination of the accuracy and viability of the three methods of extraction. Intact soil cores (30 cm diameter by 40 cm height) were extracted from two different sites. Site 1 was rapid infiltration basin number 50, near Altamonte Springs in Seminole County, Florida. Site 2 was the Missouri Management System Evaluation Area (MSEA) near Centralia in Boone County, Missouri. Isotopically (18Oδ) labeled water and bromide concentrations within water samples taken by suction lysimeters was compared with samples obtained by methods of centrifugation and azeotropic distillation. The 18Oδ water was analyzed by mass spectrometry while bromide concentration, applied in the form of KBr was measured using standard IC procedures. Water collected by centrifugation and azeotropic distillation data were about 0.25‰ more negative than that collected by suction lysimeter values from a sandy soil and about 2–7‰ more negative from a well structured soil. Results indicate that the majority of soil water in well-structured soil is strongly bound to soil grain surfaces and is not easily sampled by suction lysimeters. In cases where a sufficient volume of water has passed through the soil profile and displaced previous pore water, suction lysimeters will collect a representative sample of soil pore water from the sampled depth interval. It is suggested that for stable isotope studies monitoring precipitation and soil water, suction lysimeter be installed at shallow depths (10 cm). Samples should also be coordinated with precipitation events. The data also suggest that each extraction method samples a separate component of soil-pore water. Centrifugation can be used with success, particularly for efficient sampling of large areas. Azeotropic distillation is more appropriate when strict qualitative and quantitative data on sorption desorption, and various types of kinetic studies may be needed.

Influence of watershed system management on herbicide concentrations in Mississippi Delta oxbow lakes

The Mississippi Delta Management Systems Evaluation Area (MD-MSEA) project was established in 1994 in three small watersheds (202 to 1,497 ha) that drain into oxbow lakes (Beasley, Deep Hollow, and Thighman). The primary research objective was to assess the implications of management practices on water quality. Monthly monitoring of herbicide concentrations in lake water was conducted from 2000 to 2003. Water samples were analyzed for atrazine, cyanazine, fluometuron, metolachlor, and atrazine metabolites. Herbicide concentrations observed in the lake water reflected cropping systems of the watershed, e.g., atrazine and metolachlor concentrations were associated with the level of corn and sorghum production, whereas cyanazine and fluometuron was associated with the level of glyphosate-sensitive cotton production. The dynamics of herbicide appearance and dissipation in lake samples were strongly influenced by herbicide use, lake hydrology, rainfall pattern, and land management practices. The highest maximum concentrations of atrazine (7.1 to 23.4 microg L(-1)) and metolachlor (0.7 to 14.9 microg L(-1)) were observed in Thighman Lake where significant quantities of corn were grown. Introduction of s-metolachlor and use of glyphosate-resistant cotton coincided with reduced concentration of metolachlor in lake water. Cyanazine was observed in two lakes with the highest levels (1.6 to 5.5 microg L(-1)) in 2000 and lower concentrations in 2001 and 2002 (<0.4 microg L(-1)). Reduced concentrations of fluometuron in Beasley Lake were associated with greater use of glyphosate-resistant cotton and correspondingly less need for soil-applied fluometuron herbicide. In contrast, increased levels of fluometuron were observed in lake water after Deep Hollow was converted from conservation tillage to conventional tillage, presumably due to greater runoff associated with conventional tillage. These studies indicate that herbicide concentrations observed in these three watersheds were related to crop and soil management practices.

PHOSPHORUS COMPONENT IN ANNAGNPS

The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) has been developed to aid in evaluation of watershed response to agricultural management practices. Previous studies have demonstrated the capability of the model to simulate runoff and sediment, but not phosphorus (P). The main purpose of this article is to evaluate the performance of AnnAGNPS on P simulation using comparisons with measurements from the Deep Hollow watershed of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project. A sensitivity analysis was performed to identify input parameters whose impact is the greatest on P yields. Sensitivity analysis results indicate that the most sensitive variables of those selected are initial soil P contents, P application rate, and plant P uptake. AnnAGNPS simulations of dissolved P yield do not agree well with observed dissolved P yield (Nash-Sutcliffe coefficient of efficiency of 0.34, R2 of 0.51, and slope of 0.24); however, AnnAGNPS simulations of total P yield agree well with observed total P yield (Nash-Sutcliffe coefficient of efficiency of 0.85, R2 of 0.88, and slope of 0.83). The difference in dissolved P yield may be attributed to limitations in model simulation of P processes. Uncertainties in input parameter selections also affect the model’s performance.

Evaluating toxicity of Asana XL ® (esfenvalerate) amendments in agricultural ditch mesocosms

Agricultural ditches primarily serve to remove and store excess water associated with irrigation and storm events. The ability of these ecosystems to mitigate potential contaminants is not well understood. Five sites along a 650-m agricultural ditch located in the Mississippi Delta Management Systems Evaluation Area (MDMSEA) were used to measure fate and effects of an esfenvalerate (insecticide) exposure. Following a 0.64-cm simulated storm event, samples were collected from water and sediments and analyzed spatially from five sites and temporally from 0.5 h to 56 d. Results of aqueous toxicity bioassays indicated that lethality progressed downstream throughout all sampling intervals, while sediment toxicity bioassays only elicited biological responses at the point of pesticide application to the ditch (0 m). Significant reductions in survival of Ceriodaphnia dubia and Pimephales promelas in water were measured at the 0-, 20-, and 80-m sites following application. Ten-day solid phase sediment testing of Chironomus tentans indicated persistent toxicity only at the point of application (0 m) and throughout 56 d (mean=14.4% survival). No lethality or significant reduction in midge growth was measured for remaining downstream sites. These measurements were used to evaluate the potential of agricultural ditches to reduce potential deleterious effects of contaminants in agricultural drainage systems that precede receiving streams.

EVALUATION OF Ann AGNPS NITROGEN LOADING IN AN AGRICULTURAL WATERSHED1

ABSTRACT: Pollutants entering a water system can be very destructive to the health of that system. Best Management Practices (BMPs) are used to reduce these pollutants, but understanding the most effective practices is very difficult. Watershed models are an effective tool to aid in the decision‐making process of selecting the BMPs that are most effective in reducing the pollutant loading and are also the most cost effective. The Annualized Agricultural Nonpoint Source Pollution model (AnnAGNPS 2.0) is a technological tool that can be used to estimate watershed response to agricultural management practices. The main purpose of this paper is to test the performance of AnnAGNPS 2.0 on nitrogen loading using comparisons with measurements from the Deep Hollow watershed of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project. Previous work has demonstrated the capability of the model to simulate runoff and sediment. From sensitivity analyses in this study, initial nitrogen concentration in the soil and crop nitrogen uptake had the most impact on the nitrogen loadings. AnnAGNPS simulations of monthly nitrogen loadings are poor. However, statistical test (t‐test) showed that the predicted nitrogen loading is not significantly different from observed nitrogen loading at the 95 percent level of confidence.

Herbicides in ground water beneath Nebraska's Management Systems Evaluation Area.

Profiles of ground water pesticide concentrations beneath the Nebraska Management Systems Evaluation Area (MSEA) describe the effect of 20 yr of pesticide usage on ground water in the central Platte Valley of Nebraska. During the 6-yr (1991-1996) study, 14 pesticides and their transformation products were detected in 7848 ground water samples from the unconfined water table aquifer. Triazine and acetamide herbicides applied on the site and their transformation products had the highest frequencies of detection. Atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4,-diamine] concentrations decreased with depth and ground water age determined with 3H/3He dating techniques. Assuming equivalent atrazine input during the past 20 yr, the measured average changes in concentration with depth (age) suggest an estimated half-life of >10 yr. Hydrolysis of atrazine and deethylatrazine (DEA; 2-chloro-4-amino-6-isopropylamino-s-triazine) to hydroxyatrazine [6-hydroxy-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] appeared to be the major degradation route. Aqueous hydroxyatrazine concentrations are governed by sorption on the saturated sediments. Atrazine was detected in the confined Ogallala aquifer in ultra-trace concentrations (0.003 microg L(-1)); however, the possibility of introduction during reverse circulation drilling of these deep wells cannot be eliminated. In fall 1997 sampling, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] was detected in 57% of the 230 samples. Metolachlor oxanilic acid [(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl) amino]oxo-acetic acid] was detected in most samples. In ground water profiles, concentrations of metolachlor ethane sulfonic acid [2-[(ethyl-6-methylphenyl)(2-methoxy-1-methylethyl)amino]-2-oxo-ethanesulfonic acid] exceeded those of deethylatrazine. Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] was detected in <1% of the samples; however, alachlor ethane sulfonic acid [2-[(2,6-diethylphenyl)(methoxymethyl)amino]-2-oxoethanesulfonic acid] was present in most samples (63%) and was an indicator of past alachlor use.

Herbicide loading to shallow ground water beneath Nebraska's Management Systems Evaluation Area.

Better management practices can counter deterioration of ground water quality. From 1991 through 1996 the influence of improved irrigation practices on ground water pesticide contamination was assessed at the Nebraska Management Systems Evaluation Area. Three 13.4-ha corn (Zea mays L.) fields were studied: a conventional furrow-irrigated field, a surge-irrigated field and a center pivot-irrigated field, and a center pivot-irrigated alfalfa (Medicago sativa L.) field. The corn fields received one identical banded application of Bicep (atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4,-diamine] + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamidel) annually; the alfalfa field was untreated. Ground water samples were collected three times annually from 16 depths of 31 multilevel samplers. Six years of sample data indicated that a greater than 50% reduction in irrigation water on the corn management fields lowered average atrazine concentrations in the upper 1.5 m of the aquifer downgradient of the corn fields from approximately 5.5 to <0.5 microg L(-1). Increases in deethylatrazine (DEA; 2-chloro-4-amino-6-isopropylamino-s-triazine) to atrazine molar ratios indicated that reducing water applications enhanced microbial degradation of atrazine in soil zones. The occurrence of peak herbicide loading in ground water was unpredictable but usually was associated with heavy precipitation within days of herbicide application. Focused recharge of storm runoff that ponded in the surge-irrigated field drainage ditch, in the upgradient road ditch, and at the downgradient end of the conventionally irrigated field was a major mechanism for vertical transport. Sprinkler irrigation technology limited areas for focused recharge and promoted significantly more soil microbial degradation of atrazine than furrow irrigation techniques and, thereby, improved ground water quality.

Herbicides in Ground Water beneath Nebraska's Management Systems Evaluation Area

Herbicides in Ground Water beneath Nebraska's Management Systems Evaluation Area

Herbicide Loading to Shallow Ground Water beneath Nebraska's Management Systems Evaluation Area

Better management practices can counter deterioration of ground water quality. From 1991 through 1996 the influence of improved irrigation practices on ground water pesticide contamination was assessed at the Nebraska Management Systems Evaluation Area. Three 13.4-ha corn (Zea mays L.) fields were studied: a conventional furrow-irrigated field, a surge-irrigated field and a center pivot–irrigated field, and a center pivot–irrigated alfalfa (Medicago sativa L.) field. The corn fields received one identical banded application of Bicep (atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4,-diamine] + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]) annually; the alfalfa field was untreated. Ground water samples were collected three times annually from 16 depths of 31 multilevel samplers. Six years of sample data indicated that a greater than 50% reduction in irrigation water on the corn management fields lowered average atrazine concentrations in the upper 1.5 m of the aquifer downgradient of the corn fields from approximately 5.5 to <0.5 μg L−1 Increases in deethylatrazine (DEA; 2-chloro-4-amino-6-isopropylamino-s-triazine) to atrazine molar ratios indicated that reducing water applications enhanced microbial degradation of atrazine in soil zones. The occurrence of peak herbicide loading in ground water was unpredictable but usually was associated with heavy precipitation within days of herbicide application. Focused recharge of storm runoff that ponded in the surge-irrigated field drainage ditch, in the upgradient road ditch, and at the downgradient end of the conventionally irrigated field was a major mechanism for vertical transport. Sprinkler irrigation technology limited areas for focused recharge and promoted significantly more soil microbial degradation of atrazine than furrow irrigation techniques and, thereby, improved ground water quality.

Managing farming systems for nitrate control: a research review from management systems evaluation areas.

The U.S. Department of Agriculture funded the Management Systems Evaluation Area (MSEA) research project in 1990 to evaluate effectiveness of present farming systems in controlling nitrate N in water resources and to develop improved technologies for farming systems. This paper summarizes published research results of a five-year effort. Most research is focused on evaluating the effectiveness of farming system components (fertilizer, tillage, water control, cropping systems, and soil and weather variability). The research results show that current soil nitrate tests reliably predict fertilizer N needed to control environmental and economic risks for crop production. A corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation usually controls risk better than continuous corn, but both may result in unacceptable nitrate leaching. Reduced tillage, especially ridge-till, is better than clean tillage in reducing risk. Tile drainage controls nitrate in ground water, but discharge may increase nitrate in surface waters. Sprinkler irrigation systems provide better water control than furrow irrigation because quantity and spatial variability of applied water is reduced. Present farming systems have two major deficiencies: (i) entire fields are managed uniformly, ignoring inherent soil variability within a field; and (ii) N fertilizer rates and many field practices are selected assuming normal weather for the coming season. Both deficiencies can contribute to nitrate leaching in parts of most fields.

Transport and fate of atrazine and lambda-cyhalothrin in an agricultural drainage ditch in the Mississippi Delta, USA

Drainage ditches are integral components of agricultural production landscape, yet their contaminant mitigation capacity has been scarcely examined. If ditches are indeed capable of contaminant mitigation, then their use may serve as an alternative agricultural best management practice (BMP). A 50 m portion of an agricultural drainage ditch, located in the Mississippi Delta Management Systems Evaluation Area (MDMSEA), USA, was amended with a mixture of water, atrazine (2-chloro-4-ethylamino-6-isopropylamino- s-triazine) (herbicide) and lambda-cyhalothrin (λ-cyano-3-phenoxybenzyl-3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethyl cyclopropanecarboxylate) (insecticide), simulating a storm runoff event. Pesticide amendment was achieved using a diffuser to disperse the mixture at an inflow point along the ditch (designated as “0 m”). Pesticide concentrations in water, sediment, and plants were monitored for 28 days. One hour following initiation of simulated runoff, mean percentages of atrazine concentrations measured in water and sediment were 37 and 2%, respectively, while mean percentages of lambda-cyhalothrin concentrations in water and sediment were 12 and 1%, respectively. Atrazine and lambda-cyhalothrin mean percentage concentrations in plants ( Polygonum (water smartweed), Leersia (cutgrass), and Sporobolus (smutgrass)) were 61 and 87%, respectively. Therefore, plants serve as an important site for pesticide sorption during runoff events. Aqueous concentrations of both pesticides decreased to levels which would not elicit non-target toxicological effects by the end of the 50 m portion of the drainage ditch. This research provides fundamental answers concerning the capability of vegetated agricultural drainage ditches to mitigate pesticide-associated storm water runoff.

Spatial Variability of Soil Properties and Weed Populations in the Mississippi Delta

Simulation models and precision agriculture practices may require more detail and certainty about soil spatial variability than provided by soil surveys. This study described soil and weed spatial variability in 50‐ha subareas of two sites included in the Mississippi Delta Management Systems Evaluation Areas project. Objectives were (i) to describe the spatial variability of soil properties and (ii) to determine relationships between spatially variable weed populations and soil properties. Surface soil samples were collected at nodes of 60‐m square grids prior to planting cotton (Gossypium hirsutum L.) in 1996. Field‐moist soil was analyzed for microbial activity. Air‐dried soil was used to determine soil organic C, pH, and texture. Fluometuron and either clomazone, metolachlor, or norflurazon were banded over the crop row at planting. Weed counts were taken 6 wk after herbicide application. The spatial variability of soil properties and weed populations was described using geostatistics. Soil microbiological activity exhibited limited spatial dependence, but pH, organic C, and texture semivariograms were well‐described with spherical models. Although short‐range (&lt;60 m) variability was often high, the range of spatial dependence typically exceeded 120 m. Total weeds were spatially dependent both years; however, weeds susceptible to control by herbicide were not. Weed densities were significantly greater (P &lt; 0.05) in areas that had higher organic C and finer texture. Areas of low organic C and coarse soil often had no weeds. Thus, more uniform weed control might be achieved by varying preemergence herbicide application rate. Acceptable weed control might be achieved with lower herbicide application rates in certain areas.

EVALUATION OF ANNAGNPS ON MISSISSIPPI DELTA MSEA WATERSHEDS

Sediment and its associated pollutants entering a water body can be very destructive to the health of that system.Best Management Practices (BMPs) can be used to reduce these pollutants, but understanding the most effective practicesis very difficult. Watershed models are the most costeffective tools to aid in the decisionmaking process of selecting the BMPthat is most effective in reducing the pollutant loadings. The Annualized Agricultural NonPoint Source Pollutant Loadingmodel (AnnAGNPS) is one such tool. The objectives of this study were to assemble all necessary data from the MississippiDelta Management System Evaluation Area (MDMSEA) Deep Hollow watershed to validate AnnAGNPS, and to use thevalidated AnnAGNPS to evaluate the effectiveness of BMPs for sediment reduction.In this study, AnnAGNPS predictions were compared with three years of field observations from the MDMSEA DeepHollow watershed. Using no calibrated parameters, AnnAGNPS underestimated observed runoff for extreme events, but therelationship between simulated and observed runoff on an event basis was significant (R2 = 0.9). In contrast, the lower R2of 0.5 for event comparison of predicted and observed sediment yields demonstrated that the model was not best suited forshortterm individual event sediment prediction. This may be due to the use of Revised Universal Soil Loss Equation (RUSLE)within AnnAGNPS, and parameters associated with determining soil loss were derived from longterm average annual soilloss estimates. The agreement between monthly average predicted sediment yield and monthly average observed sedimentyield had an R2 of 0.7. Threeyear predicted total runoff was 89% of observed total runoff, and threeyear predicted totalsediment yield was 104% of observed total sediment yield. Alternative scenario simulations showed that winter cover cropsand impoundments are promising BMPs for sediment reduction.

Controlling Nitrate Leaching in Irrigated Agriculture

The impact of improved irrigation and nutrient practices on ground water quality was assessed at the Nebraska Management System Evaluation Area using ground water quality data collected from 16 depths at 31 strategically located multilevel samplers three times annually from 1991 to 1996. The site was sectioned into four 13.4-ha management fields: (i) a conventional furrow-irrigated corn (Zea mays L.) field; (ii) a surge-irrigated corn field, which received 60% less water and 31% less N fertilizer than the conventional field; (iii) a center pivot-irrigated corn field, which received 66% less water and 37% less N fertilizer than the conventional field; and (iv) a center pivot-irrigated alfalfa (Medicago sativa L.) field. Dating (3H/3He) indicated that the uppermost ground water was <1 to 2 yr old and that the aquifer water was stratified with the deepest water approximately 20 yr old. Recharge during the wet growing season in 1993 reduced the average NO3-N concentration in the top 3 m 20 mg L(-1), effectively diluting and replacing the NO3-contaminated water. Nitrate concentrations in the shallow zone of the aquifer increased with depth to water. Beneath the conventional and surge-irrigated fields, shallow ground water concentrations returned to the initial 30 mg NO3-N L(-1) level by fall 1995; however, beneath the center pivot-irrigated corn field, concentrations remained at approximately 13 mg NO3-N L(-1) until fall 1996. A combination of sprinkler irrigation and N fertigation significantly reduced N leaching with only minor reductions (6%) in crop yield.

Managing Nitrogen for Water Quality—Lessons from Management Systems Evaluation Area

AbstractThe Management Systems Evaluation Area (MSEA) project was initiated in 1990 to evaluate existing and develop new N management technologies to reduce the potential adverse impacts of agricultural practices on surface and ground water quality. Field research sites were established in nine Midwestern states. Results from MSEA research showed that nitrate leaching was greatly reduced by changing from furrow to sprinkler irrigation. At least 95% of the nitrate N percolating through tiled soils was intercepted and discharged into surface waters. Computer models indicated that routing tile discharge through wetlands would greatly reduce the nitrate load. Nitrate losses also were reduced by establishing controlled water tables using drainage lines for subirrigation. Preplant and presidedress soil nitrate tests were effective in determining proper N fertilizer rates and reducing nitrate losses. Banding ammoniated fertilizers slowed nitrification rates and nitrate leaching, especially if soil over the bands was packed. A major new technology was proof that crop greenness can be used to monitor crop N sufficiency, and that N deficiencies after the V8 stage can be corrected by sidedressing or fertigation (reactive N management). Inexpensive sensors or aerial photographs can be used to assess crop greenness. Using Global Positioning Systems (GPS), N‐deficient areas of the field can be managed differently from the remainder of the field. These results point to the need to develop site‐specific or precision farming systems to control nitrate losses to water resources and reduce the impact of natural variability in both soils and weather.

The relations between spectral data and water in a crop production environment

The results of a correlation study between high spatial resolution (1m) Multi-Spectral Scanner (MSS) data and reference data with particular emphasis to soil-plant water parameters are presented. Digital images of the Management Systems Evaluation Area (MSEA) research site in south central Ohio were acquired using MSS mounted on an aircraft. Gravimetric soil water, plant water, and plant residue information relating to MSS data were collected in April, July, August, and September, 1994. It was found that the correlation between MSS data and soil water was changed by the presence of crop residue versus bare soil. The combined water estimates from the soil and plant enhanced the correlation structure between MSS parameters and soil-plant water variables. It was also shown that when using soil water content data below the 0.5-2.0 cm soil depth, the correlation with MSS parameters decreased.