Mississippi River Valley Alluvial Aquifer Research Articles

Integrated Airborne Geophysical Data for Mapping Saltwater in the Mississippi River Valley alluvial Aquifer, Northeast Louisiana

Salinity in groundwater reduces crop productivity, drinking water quality, and economics. Saltwater plume mapping can provide crucial information for groundwater management. However, delineating saltwater plumes in aquifers is challenging and highly uncertain due to a lack of water quality data from water wells. This study introduces an integrated framework to map saltwater plumes in the agriculturally intensive Mississippi River Valley alluvial aquifer (MRVA) in northeast Louisiana using airborne electromagnetic (AEM) resistivity data. However, AEM resistivity data cannot distinguish saline sands from fine-grained sediments as both exhibit low resistivity values. To overcome this ambiguity, a lithofacies model is first constructed using borehole data through indicator kriging. Then, a 3D resistivity model is constructed for sand facies by fusing AEM resistivity data from two different airborne EM systems through a cokriging method. Finally, chloride concentration distribution in the MRVA is inferred by a resistivity-to-chloride concentration regression formula that is established using nearly collocated wells and AEM data points. The resistivity model shows the stratified pattern with low resistivity at the MRVA base, which resembles saltwater stratification. The salinity model shows that the highest chloride concentration zone coincides with the Jurassic Mississippi Salt Basin, indicating saltwater originates from the deep saline formations. Additionally, saline river water may also contribute salinity to the alluvial aquifer through surface water-groundwater interactions. The delineated saltwater plumes reveal saltwater upconing and proximity to pumping wells, providing unprecedented information to the agriculture sector.

Successive bootstrapping deep learning approach and airborne EM-borehole data fusion to understand salt water in the Mississippi River Valley Alluvial Aquifer

Increasing demands from agriculture and urbanization have decreased groundwater level and increased salinity worldwide. Better aquifer characterization and soil salinity mapping are important for proactive groundwater management. Airborne electromagnetic (AEM) is a powerful tool for aquifer characterization and salinity delineation. However, AEM needs to be interpreted with caution before being used for groundwater quality analysis. This study introduces a framework that utilizes the AEM data for both lithologic modeling and salinity delineation. A resistivity-to-lithology (R2L) model is developed to interpret AEM resistivity to lithology based a depth-dependent multi-resistivity thresholds. Then, a cokriging method is used to integrate AEM data from two different EM systems to predict resistivity at the aquifer. Finally, a resistivity-to-chloride concentration (R2C) model utilizes the resistivity model to estimate chloride concentrations at sand facies. A deep learning artificial neural network (DL-ANN) model is introduced with a successive bootstrapping approach to estimate total dissolved solids first and then use it together with resistivity data to estimate chloride concentration. The methodology was applied to delineating salinity plumes in the Mississippi River Valley alluvial aquifer (MRVA). This study found that the salinity distribution in MRVA is highly correlated with the Jurassic salt basin, salt domes, faulting, seismicity, and river water quality. The result indicates salinity upconing due to excessive pumping.

Cover crops and irrigation impacts on corn production and economic returns

Increases in irrigated crop acreage and frequent droughts during the growing season have caused continual groundwater decline of the Mississippi River Valley Alluvial Aquifer in the Mississippi Delta region. A field experiment was conducted from 2019 to 2021 to determine if combinations of irrigation scheduling thresholds and cover crops (CCs) could improve corn (Zea mays L.) production, water productivity (WP), irrigation water use efficiency (IWUE), and net returns. The irrigation thresholds used for irrigation scheduling were a wet threshold (−40 kPa), a dry threshold (−90 kPa), and no irrigation. The CC treatments were cereal rye (Secale cereale L.), hairy vetch (Vicia villosa R.), wheat (Triticum aestivum L.)-radish (Raphanus sativus L.)-turnip (Brassica rapa L.) mix, and no cover crop. In 2020, CCs reduced corn yield by 9–26% compared to no cover crop. In 2021, wet irrigation threshold treatments had 8% and 9% higher corn yield than no irrigation and dry irrigation threshold treatments, respectively. No irrigation treatments showed higher WP than dry and wet irrigation thresholds, while hairy vetch had higher in WP among CC treatments in year two of this study. Hairy vetch under the dry irrigation threshold had higher IWUE than all other treatments. The no-CC treatments generated $167, $340, and $58 ha−1 more under the wet, dry, and no irrigation treatments, respectively, when averaged over both years. Water conservation was affected by CC selection and irrigation management.

Extending irrigation reservoir histories for improved groundwater modeling and conjunctive water management in two Arkansas critical groundwater areas

Agricultural land managers in the Mississippi Alluvial Plain rely on the Mississippi River Valley Alluvial Aquifer for the majority of the water used for irrigation in the region. Pumping that outpaces recharge has resulted in significant cones of depression in the region, increasing pumping costs and forcing producers to use more surface water, often in the form of constructing on-farm storage reservoirs. At the same time, efforts are underway to improve groundwater models to run scenarios of conjunctive water management in the region. The improved models require accurate depiction of how the system is being managed including the use of on-farm storage reservoirs. This study extends our knowledge of on-farm storage reservoir construction from those established by a previous study that tracked reservoir construction between 1996 and 2015 backward an additional 20 years to 1976. This was accomplished by using older multi-band satellite and aerial imagery. The study area covers portions of two Critical Groundwater Regions in eastern Arkansas. Reservoir construction was classified into five-year bins starting in 1976 and ending in 2015. Details of how older imagery was processed and analyzed are provided. Previously, nearly 50% of the on-farm storage reservoirs had unknown construction dates, but this research study resolved construction dates for 85% and 72% of the reservoirs in the two study areas. Relationships between time and depth to groundwater, reservoir size, previous land use, and saturated aquifer thickness are described and contrasted in the two study areas across the 40-year study period. Use of the information provided will help guide policy and resource allocation for future reservoir construction activities and help improve conjunctive water management of the region. Specifically, the addition of this historic information will allow modelers to further refine groundwater-surface water models and should improve water resources scenarios that include reservoirs as a tool to reduce groundwater decline.

Opinions on Irrigation Water Management Tools and Alternative Irrigation Sources by Farmers from the Delta Region of Mississippi

AbstractWater withdrawals for irrigation at an unsustainable rate resulted in a decline in the groundwater levels in the Mississippi River Valley Alluvial Aquifer (MRVAA) in the central southern USA. This drawdown of groundwater threatens agricultural production in the Mississippi Delta, an important agricultural region in the state of Mississippi, USA. Effective and efficient use of available resources is important to sustain and enhance agricultural productivity in this area. This study assessed the opinions of farmers on water conservation management practices and technologies that improve irrigation management and save water in the Mississippi Delta region based on data collected in an irrigation survey conducted in 2012. Most landowners believed that water conservation practices were effective in reducing irrigation water use without reducing maximum crop yields and have a positive return on investment. Land forming, tailwater recovery system, on‐farm storage, instream weirs to pond surface water, computerized hole selection for furrow irrigation, short irrigation runs, and irrigation scheduling were considered efficient water conservation technologies by landowners. Perceptions about use of different practices also depend upon the crops produced by the respondents. About 20 to 24% and 14.9 to 86% of survey respondents thought that on‐farm storage and center pivot, respectively, were inefficient water conservation practices for irrigating crops in the Mississippi Delta. The adoption of these practices may be increased if the landowners know the economic returns of implementing them.

Evaluation of on-farm water capture and groundwater decline in the Big Sunflower Watershed, Mississippi River Basin

Study regionBig Sunflower River Watershed (HUC 08030207) of the Lower Mississippi River Basin, United States Mississippi River Valley Alluvial Aquifer Study focusAn on-farm water storage (OFWS) system is a structural best management practice (BMP) that captures irrigation and precipitation runoff from agricultural fields to be reused for irrigation. A geospatial inventory of OFWS systems was conducted in the Big Sunflower River Watershed (BSRW) to quantify surface water used for irrigation. Storage capacity and geographical extent of OFWS systems were compared to aquifer saturation and annual groundwater trends in the underlying Mississippi River Valley Alluvial Aquifer (MRVAA). Changes in surface water storage capacity were measured every two years from 2010 to 2020, and MRVAA trends were evaluated from 2000 to 2020. New hydrological insights for the regionSince 2010, 794.5 ha of surface water storage was added to the BSRW. The lowest aquifer saturation (less than 60%) is in the middle of the watershed, but the area of 60%− 70% saturation is decreasing with the most OFWS systems installed in this area over the entire watershed. MRVAA groundwater levels declined from 2000 to 2015, but drawdowns decreased and water levels rose in observation wells from 2016 to 2020. This paper advances the understanding of how surface water use for irrigation - one of multiple human and natural factors that can affect groundwater levels - impacts MRVAA groundwater resources.

A model of transmissivity and hydraulic conductivity from electrical resistivity distribution derived from airborne electromagnetic surveys of the Mississippi River Valley Alluvial Aquifer, Midwest USA

Groundwater-flow models require the spatial distribution of the hydraulic conductivity parameter. One approach to defining this spatial distribution in groundwater-flow model grids is to map the electrical resistivity distribution by airborne electromagnetic (AEM) survey and establish a petrophysical relation between mean resistivity calculated as a nonlinear function of the resistivity layering and thicknesses of the layers and aquifer transmissivity compiled from historical aquifer tests completed within the AEM survey area. The petrophysical relation is used to transform AEM resistivity to transmissivity and to hydraulic conductivity over areas where the saturated thickness of the aquifer is known. The US Geological Survey applied this approach to a gain better understanding of the aquifer properties of the Mississippi River Valley alluvial aquifer. Alluvial-aquifer transmissivity data, compiled from 160 historical aquifer tests in the Mississippi Alluvial Plain (MAP), were correlated to mean resistivity calculated from 16,816 line-kilometers (km) of inverted resistivity soundings produced from a frequency-domain AEM survey of 95,000 km2 of the MAP. Correlated data were used to define petrophysical relations between transmissivity and mean resistivity by omitting from the correlations the aquifer-test and AEM sounding data that were separated by distances greater than 1 km and manually calibrating the relation coefficients to slug-test data. The petrophysical relation yielding the minimum residual error between simulated and slug-test data was applied to 2,364 line-km of AEM soundings in the 1,000-km2 Shellmound (Mississippi) study area to calculate hydraulic property distributions of the alluvial aquifer for use in future groundwater-flow models.

Row spacing and irrigation management affect soybean yield, water use efficiency and economics

Declining water levels in the Mississippi River Valley Alluvial Aquifer necessitates research on the management practices that can reduce irrigation water use and improve irrigation water use efficiency. A three-year field study from 2019 to 2021 evaluated the effects of row spacing and irrigation management on soybean seed yield and quality, irrigation water use efficiency (IWUE), water productivity (WP), and profitability. Soybean was planted in two row spacings [single- (SR) and twin-row (TR)] and irrigated with three different methods [every row irrigated (ERI), alternate row irrigated (ARI), non-irrigated (NI)]. Soybean yields were increased with application of irrigation either as ERI or ARI as compared to NI in all three years ranging from 20% to 79%. The ERI had 20% increase in yield over ARI in 2021, whereas no significant differences were found between ERI and ARI in 2019 and 2020. Averaged over row spacing, IWUE was 66–91% greater with ARI compared to ERI. Only 2021 showed an increase (34%) in WP with irrigation applied as ARI than NI. Differences in rainfall amount among years and amount of irrigation applied under different treatments affected the soybean yields. Soybean yield showed reduction by 0.37–1.2 kg ha−1 with each unit increase in cumulative stress (kPa-days) for soil moisture potential drier than the −40 kPa on very fine sandy loam soils. Twin-row soybean had higher expected returns in all cases except for the NI and ERI in 2021. The TR soybean produced the greatest average risk-return than other treatments. The ARI with TR had the second highest overall risk-return trade-off. The ARI resulted in an equivalent risk-return production system as ERI for SR soybeans. Alterations in furrow irrigation methods could be more beneficial than row spacing to improve soybean productivity and IWUE.

Managed aquifer recharge using a borrow pit in connection with the Mississippi River Valley alluvial aquifer in northeastern Arkansas

The Mississippi River Valley alluvial aquifer (MRVAA) is one of the overexploited aquifers in the United States. Agriculture in Arkansas relies significantly on the MRVAA for irrigation, due to its accessibility and high yield. Increased irrigation demand since the early 1900s with continued expansion and inequitable recharge contributions resulted in groundwater decline. Overdraft of the MRVAA in Arkansas has resulted in the designation of critical groundwater areas. Managed aquifer recharge (MAR) methods intentionally replenish stressed groundwater resources. A MAR case study was conducted to determine whether infiltration basins, as repurposed borrow pits, could be used to enhance groundwater decline in critical groundwater areas of northeast Arkansas. This rehabilitation would be a practical solution to alleviate groundwater decline as well as economically feasible as land would not need to be taken out of production. In 2015, the Arkansas Department of Transportation contracted sand excavation of fallow land owned by a collaborating producer. This borrow pit would serve as a test case to measure infiltration rates into the MRVAA using nearby surface water as the recharge source. Initial soil core analyses revealed soil properties within the confining clay layer of red-brown clay and silty clay soils (0 to 3.7 m deep) with sand below. Excavation completed to a depth of ~6 m exposed the uppermost-unsaturated section of the alluvial aquifer, consisting of well-sorted medium grain size sand. The borrow pit floor was ~27 m above the existing water table, and it was hypothesized that this exposed unsaturated aquifer section would provide a natural filter and an avenue for increased water storage underground. Sediment samples were collected from the pit floor and sidewall pre- and postexperiment to characterize particle size, textural class, and organic matter. Submersible pressure transducers were installed within the pit and in a nearby irrigation well to monitor water level changes. Meteorological data were collected on-site to measure the water budget components of precipitation and evaporation. Water level declines and infiltration were evident throughout the experiment. An initial infiltration rate of 192 mm d⁻¹ was measured in February of 2016 that decreased until March, with steady state rates of 4.43 to 136 mm d⁻¹ that varied until June. An overall integrated infiltration rate of 36.4 mm d⁻¹ was calculated from the water budget. Total subsurface storage increased by 9.3 ML from February to June of 2016, and a two-dimensional simulation predicted a maximum groundwater mounding of 2.6 m during the experiment. Additionally, 14 borrow pits that had not been repurposed were identified in the area using remote sensing. Results of this study demonstrate that a relatively inexpensive MAR strategy could be implemented using former borrow pits repurposed as infiltration basins to alleviate groundwater decline in a critical groundwater area of northeastern Arkansas.

Leveraging Big Data to Preserve the Mississippi River Valley Alluvial Aquifer: A Blueprint for the National Center for Alluvial Aquifer Research

The challenge of a depleting Mississippi River Valley Alluvial Aquifer (MRVAA) requires reducing groundwater withdrawal for irrigation, increasing aquifer recharge, and protecting water quality for sustainable water use. To meet the challenge, the National Center for Alluvial Aquifer Research (NCAAR) is oriented towards producing scientific work aimed at improving irrigation methods and scheduling, employing alternative water sources, and improving crop management and field practices to increase water use efficiency across the region. Big data is key for NCAAR success. Its scientists use big data for research in the form of various soil, weather, geospatial, and water monitoring and management devices to collect agronomic or hydrogeologic data. They also produce, process, and analyze big data which are converted to scientific publications and farm management recommendations via technology transfer. Similarly, decision tools that would help producers leverage the wealth of data they generate from their operations will also be developed and made available to them. This article outlines some of the many ways big data is intertwined with NCAAR’s mission.

Perceptions of Irrigation Water Management Practices in the Mississippi Delta

The Mississippi River Valley Alluvial Aquifer (MRVAA) is being depleted, and practices that improve water stewardship have been developed to reduce drawdown. This study assesses how Mississippi Delta producers changed their perceptions of these practices over time. The analysis employs data from two surveys carried-out in 2012 and 2014 of all Mississippi permittees who held an agricultural well permit drawing from the MRVAA. Focusing on water-saving practices, this study found that producer perception of the usability of flowmeters improved over time. About 80% and 90% more producers growing corn and soybeans, respectively, felt that computerized hole selection was highly efficient. In 2014, 38% of corn and 35% of soybean producers believed that shortened furrow length was a highly efficient practice—up from 21% in corn and 24% in soybean producers in 2012. Approval of irrigation automation, moisture probes, and other irrigation technology rose from 75% of producers in 2012 to 88% by 2014. Favorability toward water-saving practices increased overall between the survey years.

Mapped Predictions of Manganese and Arsenicin an Alluvial Aquifer Using Boosted Regression Trees.

Manganese (Mn) concentrations and the probability of arsenic (As) exceeding the drinking‐water standard of 10 μg/L were predicted in the Mississippi River Valley alluvial aquifer (MRVA) using boosted regression trees (BRT). BRT, a type of ensemble‐tree machine‐learning model, were created using predictor variables that affect Mn and As distribution in groundwater. These variables included iron (Fe) concentrations and specific conductance predicted from previously developed BRT models, groundwater flux and age estimates from MODFLOW, and hydrologic characteristics. The models also included results from the first airborne geophysical survey conducted in the United States to target an entire aquifer system. Predictions of high Mn and As occurred where Fe was high. Predicted high Mn concentrations were correlated with fraction of young groundwater (less than 65 years) computed from MODFLOW results. High probabilities of As exceedance were predicted where groundwater was relatively old and airborne electromagnetic resistivity was high, typically proximal to streams. Two‐variable partial‐dependence plots and sensitivity analysis were used to provide insight into the factors controlling Mn and As distribution in groundwater. The maps of predicted Mn concentrations and As exceedance probabilities can be used to identify areas where these constituents may be high, and that could be targeted for further study. This paper shows that incorporation of a selected set of process‐informed data, such as MODFLOW results and airborne geophysics, into a machine‐learning model improves model interpretability. Incorporation of process‐rich information into machine‐learning models will likely be useful for addressing a wide range of problems of interest to groundwater hydrologists.

Maximizing soybean productivity and profitability by transitioning from flood to furrow irrigation on clay‐textured soils

AbstractThe type of irrigation delivery system used in the mid‐southern United States can have an effect on crop–water relationships and withdrawal from the Mississippi River Valley Alluvial Aquifer. This study was conducted to determine whether converting from flood irrigation to an optimized furrow irrigation delivery system improves soybean [Glycine max (L.) Merr.] grain yield, net returns, and irrigation water use efficiency (IWUE). The effects of flood and optimized furrow irrigation on soybean grain yield, net returns above specified costs, irrigation water applied, and IWUE were investigated from 2016 to 2018 on 24 paired fields with the same soil type, cultivar, planting date, and management practices in the Delta region of Mississippi. Transitioning from flood irrigation to an optimized furrow irrigation system increased soybean grain yield by 7% and net returns above specified costs by 18% but had no effect on consumptive water use or IWUE. Our data indicate that mid‐southern US soybean producers should convert from flood to optimized furrow irrigation systems to maximize soybean grain yield and net returns; however, switching between irrigation delivery systems will have no effect on aquifer decline

Investigating soybean (Glycine max L.) responses to irrigation on a large-scale farm in the humid climate of the Mississippi Delta region

The shallow Lower Mississippi River Valley Alluvial Aquifer, which supports irrigated agriculture in the Lower Mississippi Delta (LMD) region, is fast depleting from unsustainable water extractions for irrigations. The survival of irrigated agriculture in the region today hinges on enhancing the irrigation use efficiencies of the water pumped out. Furrow irrigation practices (surface or flood irrigation) dominate the LMD region's irrigated agriculture scenario. We investigated soybean productivity in response to irrigations applied through every furrow (FI), applied through alternate furrow (AFI), and rainfed (RF, no irrigation). Approximately half the volume of water applied in FI was applied in the AFI. The experiments were conducted in 2016, 2018, and 2020, which constituted the soybean phases of a corn-soybean rotation trial conducted on a clay soil in farm-scale plots (15 ha). The plots were equipped with eddy covariance systems for quantifying crop water use (ET, evapotranspiration). There was no appreciable difference in soybean grain yield between FI and AFI, but RF yielded significantly lower than FI and AFI. Leaf area index was also significantly lower in RF compared to FI and AFI. Across the three years, the average reduction in soybean yield was only 2% in AFI, while it was 24% in RF compared to FI. Average grain yields were 4507, 4413, and 3422 kg ha−1; seasonal ET were 549, 562, and 527 mm; and water use efficiencies (WUE) were 8, 8, and 7 kg ha−1 mm−1 in FI, AFI, and RF, respectively. This large farm-scale study demonstrated that grain yields from irrigating soybean through alternate furrows were comparable to irrigating through every furrow, thus saving about half the water pumped out of the aquifer. This unique study was conducted in farm-scale fields; as such, the results obtained directly apply to a farm environment, so they are ready for recommendation to soybean farmers for adoption without further field trials.

The Influence of a Climate Change Narrative on the Stated Preferences for Long-term Groundwater Management.

The literature identifies cultural values and beliefs as key drivers of climate change risk perception, but evidence is lacking about how media narratives and cultural values influence preferences for adapting to environmental consequences of climate change, including groundwater shortage. We elicited groundwater preferences using a choice experiment survey involving outcomes of the Mississippi River Valley Alluvial Aquifer. We randomly assigned respondents to an individualistic cultural narrative about climate change to test for framing effects predicted by culturally congruent and incongruent messaging. Results suggest that culturally incongruent messaging (i.e., to non-individualists) emboldens opposition and makes promoted groundwater policies less tractable. This is instructive to policy makers that identifying different stakeholders and avoiding incongruent messages about climate change could improve the effectiveness of collaborative water governance.

Groundwater trends during 1985 to 2019 in a critical groundwater area of northeastern Arkansas

The Mississippi River Valley alluvial aquifer provides over 90% of irrigation water for agriculture in the Lower Mississippi River Basin. Overexploitation of the alluvial aquifer in the Cache River Critical Groundwater Area (CRCGA) in Arkansas started impacting crop production in the 2000s with previous historical data identifying sustained groundwater declines. Groundwater depletion resulted in many producers investing in on-farm reservoir-tailwater recovery systems to provide a more secure irrigation source. More focused and consistent water level measurements were necessary to identify any groundwater level changes. Groundwater trends focused on the CRCGA cone of depression were compared from two-time groupings: 1985 to 2012 and 2012 to 2019. On-farm reservoirs in the CRCGA were inventoried in 2015, and 90% of those inventoried were constructed by 2012. More frequent groundwater level data collection in the CRCGA started in 2012 as well. Groundwater levels during 1985 to 2012 had consistent decline rates of –0.17 to –0.44 m y^–1. Groundwater levels during 2012 to 2019 varied with decline rates of ≤–0.10 to ≤–0.50 m y^–1, but also areas of no significant change and recovery at rates of ≤0 to ≤0.25 m y^–1. Trend differences between the two periods showed improved water level trends for most of the study area, with rates ranging ≤–0.30 to ≤0.50 m y^–1. The measured improvements were attributed to less pumping due to greater precipitation and the use of surface water irrigation from 60 on-farm reservoir-tailwater recovery systems. Detection of these improvements is crucial to understanding the response and status of the alluvial aquifer within the agricultural area of the CRCGA. It is recommended that adding continuous groundwater monitoring stations in west Craighead and Poinsett counties would be beneficial to inform the status of the cone of depression, considering the importance of protecting the main agricultural irrigation supply for the state. If warmer temperatures occur in the future, higher temporal and spatial groundwater level data in the CRCGA will allow policymakers and water resource managers to make timely groundwater management decisions to ensure its supply for future generations.

Erratum: Evidência geoquímica e isotópica de fluxo ascendente de fluido salino para o aquífero aluvial do Vale do Rio Mississippi, sudeste do Arkansas, EUA

Erratum: Evidência geoquímica e isotópica de fluxo ascendente de fluido salino para o aquífero aluvial do Vale do Rio Mississippi, sudeste do Arkansas, EUA

Optimum Irrigation Termination Timing in Furrow Irrigated Cotton

Properly terminating furrow irrigation in mid-southern United States (U.S.) crops could reduce irrigation costs, the likelihood of adverse harvest conditions, and agricultural withdrawal from the Mississippi River Valley Alluvial Aquifer (MRVAA). This research was conducted to determine an optimum termination window for furrow-irrigated cotton (Gossypium hirsutum L.) in the mid-southern U.S. The effects of irrigation termination timing on cotton lint yield, net returns, and irrigation water use efficiency (IWUE) were evaluated on a Leeper silty clay loam (fine, smectitic, nonacid, thermic Vertic Epiaquepts) and on a Dundee silty clay (fine-silty, mixed, active, Typic Endoaqualfs). Neither terminating nor continuing to irrigate cotton from cutout (NAWF = 5) up to three weeks past first cracked boll had an effect on lint yield or fiber quality (p ≥ 0.6107). Irrigation water use efficiency declined when water was applied past cutout (p < 0.0001). Results indicate that irrigation in cotton can be terminated at cutout without adversely effecting lint yield and fiber quality if soil water potential does not exceed -130 kPa prior to first cracked boll. Terminating irrigation in cotton at cutout could reduce late season irrigation cost and reduce water withdrawal from the MRVAA thus improving it sustainability.

Non-radial technical efficiency measurement of irrigation water relative to other inputs used in Arkansas rice production

Groundwater from the Mississippi River Valley alluvial aquifer is an essential resource for agricultural irrigation in Arkansas, but groundwater from this valuable resource is being withdrawn more rapidly than aquifer recharge in many parts of the state. Rice accounts for a significant portion of groundwater withdrawn from the aquifer. Rice is also a high-cost crop relative to other field crops. This study uses data envelopment analysis and non-radial technical efficiency to evaluate irrigation water efficiency along with the efficiency of other key rice production inputs using data from 142 rice fields enrolled in the University of Arkansas Rice Research Verification Program (RRVP). The study also evaluates the impacts of management practices on input use efficiency using fractional regression. This study differs from most other studies that focus specifically on irrigation water efficiency in that efficiencies of other related rice inputs are also evaluated. We found irrigation water was overused on average by 37.3 % across the 142 fields, with 60 fields (42.3 % of all fields evaluated) over-applying irrigation water by over 50 %. Other rice inputs identified as highly inefficient included herbicides, diesel, and labor, which were overused on average by 46.4 %, 54.6 %, and 58.9 %, respectively, across the 142 fields. Results of the fractional regression analysis revealed management practices significantly improving irrigation water efficiency also significantly improved diesel and labor efficiency as well as overall field efficiency.

Methods to quality assure, plot, summarize, interpolate, and extend groundwater-level information—examples for the Mississippi River Valley alluvial aquifer

Large-scale computational investigations of groundwater levels are proposed to accelerate science delivery through a workflow spanning database assembly, statistics, and information synthesis and packaging. A water-availability study of the Mississippi River alluvial plain, and particularly the Mississippi River Valley alluvial aquifer (MRVA), is ongoing. Software (visGWDBmrva) has been released as part of the study that demonstrates groundwater informatics for the aquifer. Considerable water-level data collected by multiple agencies over a seven-state area exist (18,903 wells; 287,272 measurements [April 22, 2019]). Data and metadata quality assurance methods, basic statistics, hydrograph visualization, outlier identification, hypothesis testing, and time-series modeling are described. Two approaches (generalized additive models [GAMs] and support vector machines [SVMs]) are used for data interpolation and extension to monthly water-level estimates. Numerical congruence between GAM and SVM estimates will be useful to limit inclusion of monthly estimates from subsequent science activities.