This paper describes how water content reflectometers (WCRs) were analyzed to develop a calibration equation. Time domain reflectometry (TDR) technique is the most prevalent method in in-situ moisture monitoring; and WCR is a type of low frequency TDR sensors, which is sensitive to soil type. Developing soil-specific calibration and investigating different environmental effects on WCR calibration is important. This study focused on investigation of the soil dry density and temperature effects on WCR calibration in RMA soil. Two series of tests to develop soil-specific calibration with dry density and temperature offset were conducted. Results from testing program showed that WCR response was positive related to volumetric water content, dry density, and temperature. Equations were developed to illustrate the response-density-temperature-moisture relation. Application to a field site was also presented to illustrate the difference in volumetric water contents obtained by using manufacturer method and the calibration procedure drawn in this paper. / text

Indiana University-Purdue University Indianapolis (IUPUI) / Non-rainfall waters such as fog and dew are considered as important source of water in drylands, and the knowledge of possible sources of its formation is very important to make future predictions. Prior studies have suggested the presence of radiation fog in drylands; however, its formation mechanism still remains unclear. There have been earlier studies on the effects of fog on soil moisture dynamics and groundwater recharge. On the contrary, no research has yet been conducted to understand the contribution of soil moisture and groundwater to fog formation. This study, therefore, for the first time intends to examine such possibility in a fog-dominated dryland ecosystem, the Namib Desert. The study was conducted at three sites representing two different land forms (sand dunes and gravel plains) in the Namib Desert. This thesis is divided into two parts: the first part examines evidences of fog formation through water vapor movement using field observations, and the second part simulates water vapor transport using HYDRUS-1D model. In the first part of the study, soil moisture, soil temperature and air temperature data were analyzed, and the relationships between these variables were taken as one of the key indicators for the linkage between soil water and fog formation. The analysis showed that increase in soil moisture generally corresponds to similar increase in air or soil temperature near the soil surface, which implied that variation in soil moisture might be the result of water vapor movement (evaporated soil moisture or groundwater) from lower depths to the soil surface. In the second part of the study, surface fluxes of water vapor were simulated using the HYDRUS-1D model to explore whether the available surface flux was sufficient to support fog formation. The actual surface flux and cumulative evaporation obtained from the model showed positive surface fluxes of water vapor. Based on the field observations and the HYDRUS-1D model results, it can be concluded that water vapor from soil layers and groundwater is transported through the vadose zone to the surface and this water vapor likely contributes to the formation of non-rainfall waters in fog-dominated drylands, like the Namib Desert.

Dielectric constant is a physical property of soil that is often measured using non-invasive geophysical techniques in subsurface characterization studies. A proper understanding of dielectric responses allows investigators to make measurements that might otherwise require more invasive and/or destructive methods. Previous studies have suggested that dielectric models could be refined by accounting for the contributions of different types of mineral constituents that affect the ratio and properties of bound and bulk water. This study tested the hypothesis that the dielectric responses of porous materials are mineral-specific through differences in surface area and chemistry. An experimental design was developed to test the dielectric behavior of pure quartz sand (Control), quartz sand/kaolin clay mixtures and ferric oxyhydroxide coated quartz sand. Results from the experiments show that the dielectric responses of quartz-clay and iron oxyhydroxide modified samples are not significantly different from the pure quartz Control. Increasing clay content in quartz sands leads to a vertical displacement between fitted polynomials. The results suggest that the classic interpretation for the curvature of dielectric responses appears to be incorrect. The curvature of dielectric responses at low water contents appears to be controlled by unknown parameters other than bound water. A re-examination of the experimental procedure proposed in this study and past studies shows that a properly designed study of bound water effects on dielectric responses has not yet been conduct / Master of Science

Bermudagrass (Cynodon spp.) is the most common turfgrass used on golf course putting greens in the southeastern United States (Lyman et al., 2007). In 2013, the National Turfgrass Evaluation Program (NTEP) started a 5-year trial of warm-season putting green cultivars. One of the bermudagrass cultivars in the study is MSB-285 (experimental cultivar). MSB-285 is a sister plant of MSB-264 (Philley and Munshaw, 2011) and is a distinct cultivar of C. dactylon × C. transvaalensis. MSB-285 has a more extensive root system and upright growth habit than traditional bermudagrass putting green cultivars (Philley and Munshaw, 2011). Due to MSB-285’s unique genetic makeup and growth habit, the objectives of this research were to determine if best management practices used to maintain ultradwarf bermudagrasses would be suitable for MSB-285 and to determine the water-use characteristics of MSB-285 compared to industry standard cultivars.

Understanding the spatial and temporal dynamics of soil water and crop water stress within a field is critical for effective Variable Rate Irrigation (VRI) management. Proper VRI can result in improved protection of the crop from early onset of crop water stress while minimizing runoff and drainage losses. The objectives of this study are (1) to examine zone delineation for informing irrigation recommendations from volumetric water content (VWC) and field capacity (FC) to grow similar or greater wheat yields with less water, (2) evaluate the ability to model soil and crop water dynamics within a season and within a field of irrigated winter wheat, and evaluate the sensitivity of crop water stress, evapotranspiration and soil water depletion outputs within a water balance model with Penman-Monteith evapotranspiration (ET) in response to adjusted soil properties, spring volumetric water content (VWC), and crop coefficient model input values. Five irrigation zones were delineated from two years of historical yield and evapotranspiration (ET) data. Soil sensors were placed at multiple depths within each zone to give real time data of the VWC values within each soil profile. Soil samples were taken within a 22 ha field of winter wheat (Triticum aestivum ‘UI Magic’) near Grace, Idaho, USA multiple times during a growing season to describe the spatial variation of VWC throughout the field, and to assist in modeling soil water dynamics and crop water stress through energy balance and water balance equations. Spatial variation of VWC was observed throughout the field, and on a smaller scale within each zone, suggesting the benefit of breaking portions of the field into zones for irrigation management purposes. Irrigation events were triggered when soil sensors detected low values of VWC, with each zone receiving unique rates intended to refill to zone specific FC. Cumulative irrigation rates varied among zones and the VRI approach saved water when compared to an estimated uniform Grower Standard Practice (GSP) irrigation approach. This method of zone management with soil sampling and sensors approximately represented the VWC within each zone and proved beneficial with effective reduction of irrigation rates in every zone compared to an estimated GSP. As such, there was a delay in the premature onset of crop water stress throughout some areas of the field. Variability in soil properties and spring soil moisture were key in giving accurate values to the model in order to make proper VRI management decisions. When assessing the model sensitivity, changing the inputs such as FC, wilting point (WP), total available water (TAW), spring VWC and crop coefficient (Kc) by -4 to +4 standard deviations away from their spatially average values, impacted the outputs of the model, with Kc having a large impact all three of the outputs. Further work is needed to improve the accuracy of representing VWC throughout a field, thus improving VRI management, and there is potential benefit in using a variable crop coefficient could to more accurate VRI management decisions from a soil water depletion model.

Moisture in a sandstone body plays a notable role in hydrological, weathering, biological and other processes. Knowledge about presence and movement of moisture within porous medium of natural sandstone exposures is, however, rather limited. Aim of the doctoral thesis was thus to quantify selected moisture characteristics of several natural sandstone exposures in Český ráj (Czech Republic). According to long-term logging, mean annual temperature at studied areas was between 8.5 řC to 11.5 řC, mean annual relative humidity was between 73 % to 85 %. Deforested area was found warmer and drier and amplitude of the values was higher there than at the forested areas. Values of water content (more than 400 measurements) and suction (more than 150 measurements) of the exposures including their spatial-temporal changes were obtained. Mean volumetric water content in zone from the sandstone's surface to 12 cm depth was from 3 % to 10 % and mean suction in depth 2-12 cm was from 2 kPa to more than 130 kPa. Using uranine powder coloring, spatial distribution of moisture near the sandstone's surface was visualized repeatedly for the first time. The coloring divided the surficial area of the sandstone into capillary (wet) and diffusion (dry) zone. The sharp transition between the two zones was represented by...

Irrigated agriculture is the largest user of freshwater in a world experiencing increased water scarcity and water demands. Variable rate irrigation (VRI) aims to use water efficiently in crop production, resulting in good yields and water conservation. With VRI, the grower is able to employ custom irrigation rates for different parts of a field. Adoption of VRI has been limited due to the complexity of matching irrigation to spatiotemporal crop water needs and the cost/benefit economics of VRI equipment. The goal of this study was to quantify spatiotemporal variability of VWC in a field that has uniform soil type and discuss the driving factors that contribute to that variability. Soil samples were acquired at 66 and 87 locations during the 2019 growing season at two study sites. Soil samples from 32 and 48 locations within each study site were selected to be analyzed for soil texture properties. The USGS Web Soil Survey was also referenced. Both, the USGS data and the data collected for this project showed very uniform soils across both fields. The objectives of this study were i) to show variability of VWC within fields that contain uniform soil texture using univariate Local Moran’s I (LMI) and ii) to compare static VRI zones based on spatial patterns of readily available field data that might serve as surrogates for VRI zones created from measured variation of soil volumetric water content (VWC). Management zones created using readily available field data had reasonable correlations with VWC. In both study sites, elevation was found to be the best variable for delineating VRI zones that imitate measured VWC.

Water availability and arable lands are increasingly limiting resources in many parts of the U.S., particularly in semi-arid and arid regions. As a means of addressing food and fuel demands associated with burgeoning population growth, highly productive and water-use efficient crops need to be identified. One potential crop, Agave, merits consideration and evaluation due to its putative capability to provide sustenance and energy despite growing in water-limited regions and on marginal soils. However, little is known regarding the productivity these succulent plants will have under growing conditions of the Southwest, where high concentrated saline soils are abundant, and water is often limited. The objectives of these studies were to determine the effects of high levels of salinity and different volumetric water content levels (VWC) on plant growth, biomass accumulation, and nutrient uptake. I used a hydroponic study to compare the effects of four salinity treatments (0.5, 3, 6, and 9 dS m-1) on productivity of four Agave species (Agave parryi, Agave utahensis ssp. kaibabensis, Agave utahensis ssp. utahensis, and Agave weberi). In a second study, an automated irrigation system was established to examine four pre-determined VWC threshold set-points and simulated a gradient of well-watered to drought conditions, to evaluate how A. weberi would respond to varying levels of water availability. Salinity concentrations did not significantly affect root and plant dry weight accumulation in A. weberi, but all other agave plants experienced less biomass accumulation under high saline conditions (>6 dS m-1). Seedlings of A. utahensis were two times more likely to die in the two highest saline treatments (6 and 9 dS m-1) than the two lower treatments (0.5 dS m-1 and 3 dS m-1). Calcium, Mg, S, Mn levels decreased in both A. parryi and A. weberi at higher salinity levels. Agave weberi was able to tolerate salinity, but it also experienced lower biomass production ≤3 dS m-1. In the water-stress study, Agave weberi plants experienced a decrease of 2.11 g as compared to plants in the highest treatment. Plants in the intermediate VWC treatments had similar dry mass values as those in the highest treatment, which suggests that this species could have moderately high yields under limited water conditions, and consequently should be evaluated as a potential bioenergy crop for semi-arid regions, such as the U.S. Southwest. Agave shows considerable potential to be grown in arid and semi-arid regions that are moderately high in salinity and have limited water availability. Indeed, the cultivation of Agave as a crop appears to be a viable option for many areas of the Southwest. While some of the Agave species evaluated were quite productive under moderate salt and water stress, it is uncertain if growth will be significantly reduced if under these stress conditions for periods longer than 3 months.

Measuring soil moisture content (SMC) in mining waste rock is important for assessing and modelling hydrological processes which influence pollutant release. Here, an experimental setup containing mining waste rock is established to compare the performance of 4 Arduino capacitance moisture sensors to one single Time Domain Reflectometry (TDR) sensor. Furthermore, the performance of these sensors is evaluated in both sieved and unsieved mining waste rock. Fitted calibration curves are provided for both the TDR- and Arduino-sensors individually and in combination. These calibration curves are evaluated using the RMSE and R 2 of each curve and compared between sensors and soil texture. It is concluded that using more capacitance sensors significantly improves the fit statistics of the calibration curves and that using at least 4 capacitance sensors can enhance calibration curve fitting. For both the TDR and capacitance sensors, the calibration curves in sieved soil provided the best fit, meaning that soil specific calibration of sensors is recommended. On a sensor individual basis, the temporal precision of the TDR sensor was superior to each individual capacitance sensor. Use of 4 or more Arduino capacitance sensors may especially be justified in circumstances where the spatial variability of SMC is addressed by executing a large number of measurements. Here, the feasibility of the Arduino sensor system means that the use of these low-cost sensors, despite their reduced temporal precision, can be upscaled at relatively small costs.

Potatoes in the Eastern Shore of Virginia are traditionally planted between late February and early April and harvested between early June and late August. Potato prices are usually higher early into the harvest season and decrease slowly as the season progresses. Early planting dates are desirable for farmers, as it allows them to perceive higher prices for their product, but early planting is also associated with lower air temperature during the early season, which in turn can affect plant development, water and nutrient uptake, and overall yield. Additionally, variations in soil properties often affect nutrient and water availability for plants, as well as the distribution of soil-borne insect pests. Additionally, several techniques are available to map the variations of soil properties in commercial potato fields, but little effort has been made to relate this information to the potential presence of soil-borne pests. Hence, the objective of this project was to evaluate the effect of planting dates, nitrogen (N) rates, and irrigation regimes on potato production. Two comprehensive studies were conducted between February and July 2022 and 2023. The objective of the first study was to evaluate the effect of N rates, planting dates, and soil physicochemical properties in potato production and the presence of soil-borne pests. This study was established in a split-plot design with four replications, with planting dates on the main plot and N rates and time of application on the sub-plot. Late March planting resulted in the highest total tuber yield, while early planting produced significantly larger tubers. Early March planting reduced plant development and emergence, probably due to lower air and soil temperatures. There was no interaction between planting dates and N applications. Using N rates higher than 147 kg ha-1 resulted in no significant differences in total tuber yield. Regression analyses showed that the Normalized Differences Red Edge (NDRE) is an excellent predictor of N content in plant tissue and tuber yield. Moreover, Ca and H saturation percentages were linked to wireworm damage levels using classification algorithms. Similarly, K saturation percentage was identified as a potential predictor of nematode presence in this region. A second study was established with the objective of evaluating the effect of N rates and irrigation regimes on potato production. The study was established in a split-plot design with four replications, with the irrigation method on the main plot and total N rate on the subplot. Results from these experiments showed higher growth and tuber yield when combining overhead irrigation with crop evapotranspiration (ETc) estimation. Moreover, there were no significant differences when using N rates higher than 112 kg ha-1. Overall, results from these experiments suggest no changes in current N rate recommendations for this region. Additionally, these results suggest planting in late March and using irrigation regimes based on evapotranspiration with overhead irrigation systems. Future research should focus on adaptive fertilization based on growing degree days and refinement irrigation determination practices. / Master of Science in Life Sciences / In the Eastern Shore of Virginia, nearly 4,000 acres are annually dedicated to fresh white potato farming. The established planting window extends from early March to early April, aligned with peak market demands in late April. However, this traditional planting strategy exposes crops to varying temperatures, potentially affecting water and nutrient demands, as well as overall yield. A research project consisting of two studies was conducted with the objective of evaluating the effect of planting dates, nitrogen (N) rates, and irrigation regimes on potato production. The first study was conducted with the aim of optimizing yield and nutrient management by exploring the interplay between planting dates, N rates, and application timing. The second study evaluated overhead and subsurface drip irrigation systems with irrigation regimes determined either by crop evapotranspiration (ETc) or by soil moisture content through soil water sensors (SWS). Results demonstrated that early March planting resulted in delayed emergence and overall growth due to colder temperatures, while late March plantings produced the highest tuber yields. On the irrigation front, overhead irrigation integrated with ETc estimation consistently improved plant health and augmented yield. In addition, the Normalized Differences Red Edge (NDRE) index, obtained from multispectral drone imaging, produced a significant correlation with N content in plant tissue and with total tuber yields for both studies. This suggests its high potential as a yield prediction tool. Overall, results from these studies reinforce current N rate recommendations for Virginia. Furthermore, they not only refine regional potato cultivation practices but also suggest the need for research pivoting around adaptive fertilization based on growing degree days and the potential refinement of irrigation regimens.