The purpose of the study was to determine the soil moisture content by measuring the naturally occurring gamma radiation in the soil. A calibration procedure was developed both in laboratory and in the field. In the laboratory, two different sample sizes were used: three-inch diameter, and 18-inch diameter columns, both 15 cm long. Small size soil samples (three-inch diameter) cannot be used to predict the calibration curve in the field, whereas the larger soil samples (18-inch diameter) calibration may be used to predict the field calibration curve. The prediction limits for the calibration curve done in the field are of ±5%, which is an unacceptable level of precision. It was also observed that the distance between the detector and the soil should always be kept constant, and that the top 15 cm of the soil contribute to approximately 95% of the radiation measured at the soil surface.

New methods were tested to evaluate the ground cover parameters used in the WEPP model. Rainfall simulator plot data, collected from fifteen rangeland ecosystems across the western United States, were used to evaluate modifications to the ground cover components for rill and interrill areas in the model. Observed and predicted values of average sediment yield were compared for six different configurations of the model. The modifications made to WEPP to incorporate measured ground cover distributions resulted in a lower r2 for predicted sediment yield than any of the configurations in which ground cover distribution was not modified. This result was due to a reduction in the calculated value of total interrill ground cover. The model equations used to adjust interrill erodibility for the effect of interrill ground cover were adversely affected. The result was that interrill erodibility values were increased for many of the plots tested.

A three-point hitch, mounted implement was developed to control the injection rate of trickle irrigation tubing. Power to the implement was supplied by the tractor's electric and hydraulic systems. A doppler radar velocity sensor measured ground speed and provided a signal to a single board computer. The computer generated an output signal which operated a throttling valve that controlled the hydraulic flow to the motor coupled to one of two pulling wheels. The wheels, mounted on parallel shafts with their faces in contact, utilized friction to feed the tubing. An error feedback loop controlled the pulling wheels speed with satisfactory operation being obtained over a range of travel speeds of 3.7 km/h to 5.6 km/h. Extra tube dispensing and cutting systems were incorporated in the design. These were manually activated by the operator when required.

Enzymes can be used to catalyze reactions in non-aqueous media, which can be particularly useful for the processing of materials with low water solubility. One such reaction is the lipase-catalyzed esterification between citronellol and acetic acid, in a medium of hexane. Both reaction conditions and special pretreatments on the lipase impact the lipase's catalytic performance. This project focuses on improving lipase performance by optimizing its pretreatment. The pretreatment factors studied include pH adjustment, lyophilization time, addition of buffer salts, non-buffer salts, denaturants or active site protectants to the lyophilizate, and flash-freezing in the presence of phase interfaces. The effectiveness of a particular pretreatment is presented in terms of 'relative performance' (RP), which is equal to the number of times faster the pretreated lipase catalyzes the reaction relative to untreated lipase. The individual and interactive effects of the pretreatment factors were studied in detail and compared. Buffer salts had a much stronger performance enhancing effect than non-buffer salts; pretreatment with 90% (w/w) sodium phosphate yielded lipase with an RP of ∼64 (catalyzed the reaction ∼64 times faster that untreated lipase). A strong interaction between the treatments with sodium phosphate and pH adjustment was found. Both these treatments may mitigate the inhibitory effect of acetic acid, one of the substrates. Activating effects of phase interfaces and active site protectants are shown to be complementary to other treatments, demonstrating that they act by a distinct mechanism. An optimization process known as 'the method of steepest ascent' was used to simultaneously optimize the pH and buffer salt pretreatments, as well as the concentration of acetic acid in the reaction mixture, This process succeeded in rapidly developing pretreatment combinations that yielded lipase with RP as high as 170. Studies were also conducted to develop methods for recovery, reprocessing and reuse of lipase from completed reactions.

Remote sensing is being used in agriculture for crop management. Ground based remote sensing data acquisition system was used for collection of high spatial and temporal resolution data for irrigated broccoli crop. The system was composed of a small cart that ran back and forth on a rail system that was mounted on a linear move irrigation system. The cart was equipped with a sensor that had 4 discrete wavelengths; 550 nm, 660 nm, 720 nm, and 810 nm, and an infrared thermometer, all had 10 nm bandwidth. A global positioning system was used to indicate the cart position. The study consisted of two parts; the first was to evaluate remotely sensed reflectance and indices in broccoli during the growing season, and determine whether remotely sensed indices or standard deviation of indices can distinguish between nitrogen and water stress in broccoli, and the second part of the study was to evaluate remotely sensed indices and standard deviation of remotely sensed indices in broccoli during daily changes in solar zenith angle. Results indicated that nitrogen was detected using Ratio Vegetation index, RVI, Normalized Difference Vegetation Index, NDVI, Canopy Chlorophyll Concentration Index, CCCI, and also using the reflectance in the Near-Infrared, NIR, bands. The Red reflectance band capability of showing stress was not as clear as the previous indices and bands reflectance. The Canopy Chlorophyll Concentration Index, CCCI, was the most successful index. The Crop Water Stress Index was able to detect water stress but it was highly affected by the solar zenith angle change along the day.

The relationship between remotely sensed canopy temperature and soil moisture was studied. The objectives were to relate two remotely sensed canopy temperature-based indices, the Crop Water Stress Index (CWSI) and the Water Deficit Index (WDI), to soil moisture through the water stress coefficient, to estimate soil moisture depletion with the CWSI and the WDI, and to develop a remote sensing system aboard a linear move irrigation system that would provide field images of the WDI at one-meter spatial resolution. Studies were conducted in Maricopa, Arizona during the 1998 and 1999 seasons with cotton (Gossypium hirsutum, Delta Pine 90b). In 1998, the field was surface irrigated (low frequency irrigation), and the CWSI was calculated from canopy temperature measurements using stationary infrared thermometers. In 1999, the field was irrigated with a linear move system (high frequency irrigation), and the WDI was calculated using measurements made by the on board remote sensing system. Both the CWSI and the WDI were correlated to soil moisture through the water stress coefficient. Soil moisture depletion could be estimated using the CWSI under low frequency irrigation, but could not be estimated using the WDI under high frequency irrigation. These differences were attributed to the range of soil moisture resulting from infrequent surface irrigation vs. frequent irrigation using the linear move. High spatial resolution images of the WDI could nonetheless monitor water stress throughout the field from partial to full canopy cover, which demonstrated that ground-based remote sensing is feasible for irrigation management in precision agriculture. This application of remote sensing provides an opportunity to improve water use efficiency.

A new water deionization method was conceived and investigated. Bench scale reactors were designed and tested. Numerical analysis of ion movement in water in the presence of electrical, hydraulic, and chemical gradients was conducted. The new water treatment technology uses bicomponent fibers (BCF). Ions in water are concentrated near charged bicomponent fibers. Bicomponent fibers are composed of two materials. The outer annulus is made of nylon and has an inside diameter of 10 mum and outer diameter of 50 mum. The inner annulus is composed of carbon powder and has an outer diameter of 10 mum. For the bench scale reactors, approximately one kilometer length of fibers was wrapped around a series of plastic panels and placed in a plexiglass container containing sodium nitrate solution. The ends of the fibers were covered with electrically conductive epoxy and connected to a DC power supply. In experiments which lasted up to 96 h., the solution showed up to 50 percent decrease in nitrate concentration after the power supply was applied. Preliminary studies indicated that distance between panels, polarity of panels and voltage magnitude influenced observed concentration. Two one dimensional analytical solutions and finite element solutions for two dimensions were derived for no flow condition between parallel plates. For the first finite element model, the continuity, Navier-Stokes, and species equations were solved for solute concentration with rectangular coordinates. For the second model, Poisson-Boltzmann equations were included in a finite element scheme. The models were applied to irregular-shaped bodies and the finite element solutions were compared with analytical solutions. The solutions for Poisson-Boltzmann equations were obtained for both linearized and non-linear forms. Boundary conditions included no chemical reactions and no transport across boundaries. The formulations did not solve for concentration in bicomponent fiber reactors because insufficient data and knowledge of the bicomponent fiber process is available. However, future numerical models of the bicomponent fiber treatment process may be based on solutions derived in this research.

This research developed a method for parameterizing a physically-based distributed rainfall-runoff model to more effectively model erosion on small semiarid watersheds. Topographic survey was done to characterize the form of a small watershed near Tombstone, Az. Soil samples were collected to characterize the spatial variability of soils. It was found that a relationship between slope and area can be used to determine the critical source area necessary to initiate a channel. These estimates agreed with the location of channel heads identified in the field. This provided a basis for partitioning the watershed into subcatchment elements based on process-scale rather than topographic map scale. The Engelund and Hansen (1967) transport capacity relationship in the KINEROS2 model can be parameterized using soil particle size data. Soils on the surface of the hillslopes are the least variable, while soils in the channels are the most variable. The coarsest soils on the watershed occur at the transition from hillslope to channel. Particle size in channels were estimated using drainage area and channel slope as predictors, because downstream fining occurs in channels. Particle size distributions on hillslopes were estimated using geostatistics and regression relationships. To see whether these methods improved model estimates, simulations from a simplified 18 element representation of the watershed using lumped parameter estimates were compared to simulations from a 312 element partitioning of the watershed using distributed parameter values. Data from six events could be precisely modeled (model efficiencies > 0.9) which minimized the effect of hydrologic error on erosion modeling. A multiplier was placed in front of the raindrop impact sediment entrainment term, and in front of the transport capacity term, the two primary erosion mechanisms. The model predicted sediment yield for some events well (model efficiencies 0.85 and 0.97). Results from the complex configuration of the watershed were better than the simple configuration. Multiplier values on the splash term were 5 (complex) and 12 (simple). The multiplier on the transport capacity term was between 1.2 and 1.70. These multiplier values are unrealistic suggesting that the multipliers are acting as fitting coefficients, and may not have any physical significance.

The assessment of crop evapotranspiration (ET) has received intensive research due to its critical role in irrigation management and water conservation studies. Because weather conditions largely determine ET, various methods based on meteorological factors have been developed to estimate ET rates. In order to accommodate the concept of reference crop ET (ETo), evaluation of weather data quality has been addressed. In this research, 9 year (1989-1997) weather data from the AZMET weather station at the Maricopa Agricultural Center were used to compare daily and 10 day average ETo estimated by the Hargreaves (HARG), FAO 24 Penman (FAOP), and FAO Penman-Monteith (FAOPM) methods. Before ET calculation, the weather data were evaluated for the influence of aridity at the weather station site and sensor calibration/malfunctioning problems. Corrections were made on temperature and solar radiation data. Reference ET as reported by the AZMET was also considered for comparison purposes. In general, the weather data correction decreased ETo estimates 18.3%, on average. The highest reduction (23.5%) was obtained with the FAOPM method. When this method was used as the standard for ETo estimate comparison, the FAOP method corrected for site aridity ranked first as predictor of ETo despite its tendency for overestimation. At the Maricopa Agricultural Center, a two year field research (Fall-Winter of 1996/97 and 1997/98) was carried out to derive head lettuce (Lactuca sativa L.) crop coefficient (Kc) and to investigate the effects of ETo method in the shape and values of the crop coefficient curve. For the periods of low crop ET, the 2 year (Kc) from the HARG, FAOP, and FAOPM methods did not differ significantly. However, in the peak demand period, crop coefficients derived from the three methods peaked at different values. The predicted peak (Kc) was 0.87, 0.72, and 0.82 for the HARG, FAOP, and FAOPM methods, respectively. These results reflect the tendency of ETo underestimation by the HARG method and overestimation by the FAOP method under and conditions. Crop coefficients derived in the 96/97 growing season were then used to investigate the effects of (Kc) and ETo mismatching in the water use and yield of lettuce during the 97/98 growing season. To reach such objectives, an experiment design in Latin square with four replications and four treatments was carried out. Differences in seasonal water depth were as high as 33 mm among treatments. The analysis of variance revealed that the treatments did not induce lettuce marketable yield statistically different at the 5% significance level.

A Sediment-Resistant flume has been tested and analyzed in the laboratory and field to measure flow rate with high sediment concentration for natural and irrigation streams. This flume is basically an improvement of the well studied long-throat flume which has an additional chute proposed by J. A. Replogle. The chute, where a new gauging station is located at the half-way point of its length equal to two times the throat length, worked satisfactory for a chute slope of 3%. For clear-water flow the chute showed a supercritical and curvilinear flow having a hydrostatic pressure consistently located at the halfway of the chute. For sediment-laden flow with a concentration of 3% by weight of clear mortar sand, behavior was similar to the clear-water. Sediment deposits filled the approach channel of the flume and plugged the intake pipe of the supercritical gauging station causing it to fail. This failure was compensated for by the use of the new supercritical additional gauging station located in the chute, which remains clean and continues to measure the flow-rate. Hydraulic behavior of the stage-discharge curves for the sediment-laden flow flume was similar to the clear-water flow after the approach channel was filled. Prior to filling an inconsistent condition existed caused by the sediment movements in the approach channel. It was shown that this flume might be used in the field with errors of 5% or less. In addition, a computer program was developed to compute the stage-discharge curve using the dynamic equation of gradually varied flow, which may be used to compute the stage-discharge curve in new flumes. Further laboratory and field research is to be expected to compare these results with future data to improve reliably.