Christopher Hay

Estimation of Evapotranspiration from Fields with and without Cover Crops Using Remote Sensing and in situ Methods

Estimation of actual evapotranspiration (ETa) based on remotely sensed imagery is very valuable in agricultural regions where ETa rates can vary greatly from field to field. This research utilizes the image processing model METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) to estimate late season, post-harvest ETa rates from fields with a cover crop planted after a cash crop (in this case, a rye/radish/pea mixture planted after spring wheat). Remotely sensed EToF (unit-less fraction of grass-based reference ET, ETo) maps were generated using Erdas Imagine software for a 260 km2 area in northeastern South Dakota, USA. Meteorological information was obtained from a Bowen-Ratio Energy Balance System (BREBS) located within the image. Nine image dates were used for the growing season, from May through October. Five of those nine were captured during the cover crop season. METRIC was found to successfully differentiate between fields with and without cover crops. In a blind comparison, METRIC compared favorably with the estimated ETa rates found using the BREBS (ETλE), with a difference in total estimated ETa for the cover crop season of 7%.

Comparative Analysis of METRIC Model and Atmometer Methods for Estimating Actual Evapotranspiration

Accurate estimation of crop evapotranspiration (ET) is a key factor in agricultural water management including irrigated agriculture. The objective of this study was to compare ET estimated from the satellite-based remote sensing METRIC model to in situ atmometer readings. Atmometer readings were recorded from three sites in eastern South Dakota every morning between 8:15 and 8:30 AM for the duration of the 2016 growing season. Seven corresponding clear sky images from Landsat 7 and Landsat 8 (Path 29, Row 29) were processed and used for comparison. Three corn fields in three sites were used to compare actual evapotranspiration ( ). The results showed a good relationship between estimated by the METRIC model ( -METRIC) and estimated with atmometer ( -atm) ( = 0.87, index of agreement of 0.84, and RMSE = 0.65 mm day−1). However, -atm values were consistently lower than -METRIC values. The differences in daily between the two methods increase with high wind speed values (>4 m s−1). Results from this study are useful for improving irrigation water management at local and field scales.

Estimation of Crop Evapotranspiration Using Satellite Remote Sensing-Based Vegetation Index

Irrigation water is limited and scarce in many areas of the world, including Comarca Lagunera, Mexico. Thus better estimations of irrigation water requirements are essential to conserve water. The general objective was to estimate crop water demands or crop evapotranspiration ( ) at different scales using satellite remote sensing-based vegetation index. The study was carried out in northern Mexico (Comarca Lagunera) during four growing seasons. Six, eleven, three, and seven clear Landsat images were acquired for 2013, 2014, 2015, and 2016, respectively, for the analysis. The results showed that was low at initial and early development stages, while was high during mid-season and harvest stages. These results are not new but give us confidence in the rest of our results. Daily maps helped to explain the variability of crop water use during the growing season. Based on the results we can conclude that maps developed from remotely sensed multispectral vegetation indices are a useful tool for quantifying crop water consumption at regional and field scales. Using maps at the field scale, farmers can supply appropriate amounts of irrigation water corresponding to each growth stage, leading to water conservation.

Estimating Evapotranspiration from Fields With and Without Tile Drainage using Remote Sensing

Subsurface (tile) drainage on agricultural land with poor natural drainage allows timelier field operation and contributes to improved crop yields. Considerable uncertainty exists regarding the impact of the tiles on the water balance at the field scale, including impacts on crop consumptive water use. The objectives of this study are to estimate and compare the water use from a field with and without tile drainage for four days during the growing season in order to determine its impact on evapotranspiration. Suitable models and algorithms applied to high resolution (30 m) satellite imagery provide a cost effective and time efficient method to obtain evapotranspiration estimations from bare soil and vegetation. METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) is a model utilizing satellite imagery that can be used to estimate water use with high resolution (30 m) over a large area, thereby enabling the evaluation of the water consumption on a field-by-field basis. This is advantageous because of the ability to compare crop consumptive use from fields with and without tile drainage. The normalized difference in ET rates between the two subfields estimated using METRIC was 10% or less. This is less than eddy covariance measurements from the same field that found normalized differences between the field with and without tiles of 18%.

Evaluation of industrial by-products and natural minerals for phosphate adsorption from subsurface drainage

ABSTRACT Agricultural subsurface drainage has been recognized as an important pathway for phosphorus transport from soils to surface waters. Reactive permeable filters are a promising technology to remove phosphate from subsurface drainage. Three natural minerals (limestone, zeolite, and calcite) and five industrial by-products (steel slag, iron filings, and three recycled steel by-products) were evaluated for phosphate removal from subsurface drainage using batch adsorption experiments. Phosphate adsorption onto these materials was characterized by Langmuir isotherm and second-order kinetic models. The adsorption capacities increased by factors of 1.2–2.5 when temperature was increased from 5°C to 30°C. Industrial by-products exhibited phosphate adsorption capacities that were one order of magnitude higher than natural minerals. Medium-sized steel chips exhibited high phosphate adsorption capacities (1.64–3.38 mg/g) across different temperatures, pH values, organic matter concentrations, and real drainage water matrixes. The strong chemical bonds between phosphate and steel by-products prevented the release of adsorbed phosphate back to the solution. The steel by-product filter can be paired with a woodchip bioreactor for nitrate and phosphate removal. It is suggested that the phosphate filter be connected to a woodchip bioreactor after the startup phase to minimize the impact of dissolved organic matter on phosphate adsorption. The results of this study suggest that the low-cost steel by-products examined could be used as effective adsorption media for phosphate removal from subsurface drainage.

Measurement of Cover Crop Evapotranspiration and Impacts on Water Management in Crop Production Systems

The use of cover crops is an increasingly popular sustainable farming practice that provides many benefits to the soil and subsequent cash crops. This research examines how the water usage of a cover crop affects the water availability for the subsequent cash crop. A Bowen-ratio energy balance system (BREBS) was installed on a cooperators field in Day County, South Dakota in order to determine the evapotranspiration (ET) of a cover crop mixture of rye, field radish and field pea compared to that of the cash crops before and after, spring wheat and field corn, respectively. This information will then be used to calculate crop coefficient values for the region. The system was installed on May 24th, 2011 and collected data for the rest of the spring wheat season and the following cover crop. The results show that the cover crop used less than half of the water that the spring wheat crop used, and the cover crop has correspondingly lower crop coefficient values. This research is ongoing and water use by the subsequent field corn crop is not yet available.

Precipitation and Evapotranspiration Patterns in the Northwestern Corn Belt and Impacts on Agricultural Water Management

Crop yields can be negatively impacted by excess water as well as insufficient water. The northwestern portion of the Corn Belt, including South Dakota, North Dakota, Minnesota, and Iowa, is situated in a transition zone from moist subhumid to semiarid climates, and is, therefore, susceptible to both floods and drought. Precipitation has increased in the upper Midwest over the last 50 years, but less is known about changes in evapotranspiration (ET), which, along with precipitation, determines water excess or deficit. The objective of this research was to evaluate patterns of precipitation and ET in the four-state region over the last 49 years. The results confirm that precipitation has increased over much of the region in the last two decades, particularly outside the growing season. Fall and winter precipitation increases were more pronounced in the Dakotas, while precipitation increases in the spring were more common in Iowa. Areas of increased summer precipitation corresponded to areas of expanded row crop production. Reference ET has generally declined slightly over the region. However, more information is needed to fully evaluate the impact of changes in reference ET on actual ET. A better understanding of the impacts of these precipitation and ET patterns may help to evaluate potential mitigation and adaptation strategies for future crop production in the region under projected climate change.

Efficacy of Evapotranspiration-based Landscape Irrigation in Eastern South Dakota

Sioux Falls, SD is in the climate transition zone between the humid Midwest and semiarid Great Plains. Outdoor water use in Sioux Falls accounts for about half of the daily demand during the summer. To reduce the outdoor water demand, ET-based landscape irrigation control was compared to time-based control. For the 2009 irrigation season, 36 volunteer homeowners were divided into three treatments- replacement of 100% of the irrigation requirement (estimated ET minus rainfall), replacement of 70% of irrigation requirement, and traditional time-based control (the control treatment). Homes in the time-based and 70% treatments reduced their outdoor water application during 2009 compared to 2008. The reductions of the ratio of outdoor water application to irrigation requirement were 0.22 and 0.15 for the 80% and time-based treatments, respectively. Homes in the 100% treatment increased their water application slightly during 2009 (the change of the ratio of outdoor water application to irrigation requirement was 0.25). However, there were no statistical differences among the treatments. After one season of use, the ET-based controllers show promise for reducing outdoor (landscape irrigation) water application but the reductions were not significant.