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Climatic variables have been used to calculate evapotranspiration loss by many researchers. Evapotranspiration formulas have been developed for local use in predicting soil moisture in many parts of the United States. The objective of this study was to develop a method to estimate soil moisture in Virginia using data collected by the Agricultural Engineering Department, Virginia Polytechnic Institute, Blacksburg, Virginia. The first step in the study was to determine the relationship between soil moisture and loss pan evaporation. This relationship was found on a seasonal cumulated basis. For shorter periods, the results were poor. No workable relation could be found that would satisfactorily estimate soil moisture from any of these procedures. A soil moisture accounting system based on the soil moisture balance principle was then devised in which daily evapotranspiration loss was calculated by Van Bavel’s nomogram method. Daily soil moisture and measure soil moisture were compared by the student t-test for paired observations. The results of the statistical analysis indicated it could be used to estimate soil moisture in local conditions. Finally, the correlation between daily evapotranspiration and pan evaporation was determined. A high correlation was found. The problem encountered in analyzing the data available for this study indicated the need for a detailed statistically controlled experiment. Hence an experimental design has been formulated that, hopefully, will allow an systematic investigation and evaluation of the problem. / Master of Science

Soil water movement and desorption studies were conducted on two agriculturally important soil series. The soils selected were the Norfolk soil (a fine loamy, siliceous, thermic, Typic Paleudult) and the Cecil soil (a clayey, kaolinitic, thermic, Typic Hapludult). Water desorption properties were investigated in the laboratory and in situ. The soil water desorption curves developed in the laboratory for both soils were relatively uniform. This observation was also true for most horizons for the desorption curves developed from the field data. The results for the B horizons of the Cecil soil showed the greatest variability, with the field data being the most variable. Comparisons of the field and laboratory water contents at given tensions show the field values were lower than laboratory values for horizons with over 40 percent sand and less than 30 percent clay. Field values were higher than laboratory values in the B horizons of both soils. In all other horizons, the field values were close to those obtained in the laboratory. The Norfolk soil was found to contain more plant available water than the Cecil soil. The selection of an upper limit for plant available water estimation is critical, especially for the Norfolk soil. The Cecil soil yielded little water between -.05 and -.30 bars, whereas the Norfolk soil yielded a relatively large amount of water (more than 3 times greater) in this range. This would nearly double the predicted plant available water for the Norfolk soil. Results of this study show that the irrigation management of the Cecil soil would require smaller amounts of water applied frequently, whereas the Norfolk soil could hold larger amounts of plant available water applied less frequently. This would allow more time between irrigations. / Master of Science

Master of Science

Effects of media, soil moisture, fertility rate, and plant growth regulators on plant growth were investigated for 13 taxa of succulents. Media: Liners were grown in five common greenhouse substrates: 80% peat, 60% bark + 30% peat moss, 80% pine bark/20% Permatil (v/v), 100% composted pine bark, or whole tree substrate until market ready. Overall, higher percentage bark mixes yielded smaller plants, with lower shoot dry weights, shoot heights and widths. Soil Moisture: Liners were potted into a 60% bark/30% peat soilless potting mix. In group 1 , irrigation to container capacity occurred when volumetric soil moisture content fell below 30%, 20%, or 10%,. Group two (seven species) irrigation thresholds were shifted to 35%, 25%, and 15%. Effects of irrigation rate were significant in three of the 13 species studied, and those effects were species-specific. Fertility Rate: Liners were potted into60% bark/30% peat substrate. Fertility reatments in group were 0, 50, 100, or 200 mg.L-1 nitrogen. Group 2 plants received treatments of 50, 150, 250, or 350 mg.L-1 nitrogen. Four of the 11 species studied were affected by nitrogen rate, with rates up to 200 mg.L-1 generally producing the largest plants. PGRs: Seven species were potted into a 60% bark/30% peat substrate. Group one plants were treated with a foliar application of benzyladenine (Configure) at rates of 0, 400, 800, or 1600 mg.L-1. Group 2 plants were treated either BA at 0, 250, 500, or 1000 mg.L-1, dikegulac sodium (Augeo) at 400, 800, or 1600 mg.L-1, or a tank mix of 500 mg.L-1 Configure and 800 mg.L-1 Augeo. BA caused an increase in branches leaders or offsets in two species. / Master of Science

The development, yield and water use of six sorghum (Sorghum bicolor (L.) Moench) hybrids and their respective male and female parents were evaluated under stressed and well irrigated conditions during 1980 and 1981 at Tucson, Arizona. Changes in soil moisture storage were measured by neutron modulation on a semiweekly schedule. Transpiration, diffusive resistance and leaf-ambient temperature differentials were monitored biweekly using a steady state porometer. Meteorological data was collected on a daily basis. The 1980 season had higher maximum temperatures and pan evaporation than the 1981 season. Differences in soil moisture extraction among sorghum entries were not apparent within water treatments. Mean cumulative evapotranspiration (ET) for the stressed treatment was 270 and 261 mm, for 1980 and 1981, respectively. Mean cumulative ET for irrigated treatment was about twice that at 520 and 648 mm during 1980 and 1981, respectively. There were no apparent differences in cumulative ET for entries in the stressed treatment while genotypic differences were manifested under well irrigated conditions. Temperature differential demonstrated a significant and negative correlation with diffusive resistance especially under stressed conditions (r = -.64 in 1981). Temperature differential was positively correlated with transpiration (r = .70 in 1980 stressed treatment). Plant height was significantly affected by water level both years while stem weight was affected by water level only in 1980. Soil moisture treatments did not affect leaf area either year and genotypic differences were demonstrated only in 1981. Hybrids produced greater grain yield than their male parents under both water treatments. This was due to greater seed number for hybrids. Seed number was also more stable for hybrids under both moisture levels. Hybrids four and seven had the greatest grain yield in 1980 and 1981, respectively. Harvest index was improved with increased water application due to increased seed number. Hybrid four in 1980 and hybrid seven in 1981 were extremely efficient in water use exhibiting ET ratios of 283 and 378, respectively under high water application. Reduced water application had little affect on the performance of these entries.

Extreme variability of rainfall during the growing season in the Prairies underlies the need to improve means of quantifying the amount of soil moisture available for plant growth in real time. This study was conducted to modify and validate the Versatile Soil Moisture Budget (VSMB) for estimating volumetric soil water content. A network of soil moisture hydra probes and weather stations were installed for continuous soil moisture monitoring and real-time weather data collection at 13 sites across Central and Western Manitoba during the 2009 and 2010 growing seasons. The data from the probes were validated and calibrated. Both the laboratory and field validations showed that the root mean square error of the default factory calibration increased with increasing clay content of the soil. Outputs from these probes were used to test the modified VSMB model. The model was most effective at simulating soil water content at the surface layers.

Cover crops may be used as a management tool in modifying soil water content, helping lower agriculture’s impact on water quality and lead to greater crop yields. During the 2012 growing season, a field study was conducted in Albany, IN to determine: 1) the impact of cover crops on soil moisture throughout the growing season and 2) cover crops’ influence on corn (Zea mays) yield. Treatments of a monoculture of annual ryegrass (Lolium multiflorum) (AR), a mixture of annual ryegrass (Lolium multiflorum), crimson clover (Trifolium incarnatum), and groundhog radish (Raphanus sativus) (MIX), were compared with a no cover crop control (CTRL) in a randomized complete block design, with blocks positioned in moderately well drained (MWD) and poorly drained (PD) soils. Cover crop treatments were similar to each other in accelerating moisture removal before the corn growing season, resulting in soil profiles that were 47% drier in the MWD soil and 22% drier in the PD soil than controls. Abnormally hot and dry weather conditions made water availability a limiting factor and decreased the relative importance of soil nitrogen while corn was growing. In the MWD soils, corn grown after MIX treatments had 21% higher yields than CTRL treatments and 11% higher yields than AR treatments due to increased subsoil water usage. Corn grain yields in PD soils were related to surface moisture conservation, leading to 3-5% higher yields in MIX and AR treatments. Implications for improved field trafficability, reduced runoff and tile drainage flow, and enhanced water availability to crops are discussed. / Department of Natural Resources and Environmental Management

Extreme variability of rainfall during the growing season in the Prairies underlies the need to improve means of quantifying the amount of soil moisture available for plant growth in real time. This study was conducted to modify and validate the Versatile Soil Moisture Budget (VSMB) for estimating volumetric soil water content. A network of soil moisture hydra probes and weather stations were installed for continuous soil moisture monitoring and real-time weather data collection at 13 sites across Central and Western Manitoba during the 2009 and 2010 growing seasons. The data from the probes were validated and calibrated. Both the laboratory and field validations showed that the root mean square error of the default factory calibration increased with increasing clay content of the soil. Outputs from these probes were used to test the modified VSMB model. The model was most effective at simulating soil water content at the surface layers.