The objectives of this study were to describe demographic change in an alfalfa population and determine whether genetic changes were associated with stand loss in an alfalfa field during the year of establishment. A nondormant composite population (AZ-88NDC) was sown at 1944 seeds per square meter in Oct. 1988 at Tucson, AZ. Only 29% of the seeds sown germinated and emerged. Survivorship curve of the emerged seedling population had some characteristics of Deevey type III. Two heavy mortality periods were observed. Low temperatures might be the major cause of the first heavy stand loss. The second significant stand loss could be explained by increased density stress. Isozyme profiles were produced from 60 day survivors dug from the field, unselected greenhouse-grown AZ-88NDC (='Unsel') and 300-d progenies produced by intermating plants surviving 300 days. Significant differences were observed in overall level of population heterozygosity of 60-d and unselected populations based on fixation indices of six isozyme loci. This suggests that genetic changes may be associated with establishment of an alfalfa stand.

Three maize populations developed for their ability to withstand drought and salinity, and their reciprocal F1 crosses were tested under induced water stress and normal moisture conditions. Two commercial hybrids and one open-pollinated variety were also included in the study. The objective was to investigate yield and its components under induced drought. Significant differences in yield were observed in both irrigation treatments. DeKalb 689, one of the commercial hybrids, outyielded all the other entries under wet conditions, whereas under dry conditions the open-pollinated variety, Page Ranch, had the highest yield. Significant differences between populations and their hybrids were also observed. Significant correlations were noted in grain yield as observed in wet and dry conditions and the reduction in the number of ears per plant was positively correlated with the reduction in grain yield resulting from drought.

Understanding patterns of genetic diversity in crop species may enhance the efficiency of germplasm conservation and utilization. Nondormant alfalfa (Medicago sativa L.) is an important forage crop in southwest Arizona, and originates from low elevations of the Middle East and India. This study examined 60 accessions of nondormant alfalfa from India, north Africa and Arabia in a field trial in Tucson, AZ during 1989-91. Nondormant Indian and African alfalfas have previously been considered independent germplasm sources. Principal components of 6 morphological and 15 agronomic traits were used to classify accessions using average linkage cluster analysis. Low elevation Indian accessions did not differ phenotypically from most African and Arabian alfalfas. This indicates that Indian alfalfas are not an independent source of germplasm in need of conservation as such, but western Arabian alfalfas may be.

A study of electro-osmotic draft reduction was conducted to determine the effectiveness of electro-osmosis content and apparent resistivity, tillage speed, and electrical voltage and current were measured to determine a relationship which predicts the effectiveness of electro-osmosis in reducing draft force. The application of electro-osmosis resulted in a reduction in draft force for all tested conditions in the loam soil, with a maximum reduction of 39.4 percent. Water content was a good predictor of resistivity with a regression coefficient of 0.944. Resistivity was a significant predictor of draft force for all test configurations with an average regression coefficient of 0.8173. A comparison of water content and resistivity regression coefficients indicates that the difference between the coefficients is not large enough to choose one variable as a better predictor than the other of the effects of electro-osmosis on draft force.

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.

The spatial and temporal variability of water content, soil water tension, and derived hydraulic conductivity parameters are analyzed using geostatistical methods. The measured data sets were obtained from a 1985 experiment near Las Cruces, New Mexico. Post-irrigation water content and tension measurements had been recorded over 44 days at 455 sampling locations along a 91 x 1.5-meter transect. Unsaturated hydraulic conductivity values are derived using the instantaneous profile formula, and an exponential model is used to obtain values of saturated hydraulic conductivity and pore-size distribution parameters. The exponential model is found to inadequately describe the conductivity data for tensions near saturation, because excessively large saturated hydraulic conductivity values are derived. Semivariogram analysis shows ranges of dependence of three to 32 meters for water content and six to 34 meters for tension. As water content decreases, the coefficient of variation and variance are found to increase.

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.

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.

Mortality is substantial in alfalfa stands and may be due to random and natural selection. The effects of selection for persistence on single-plant yield are not well understood. This study examined relationships between yield, nonstructural carbohydrates (TNC), and other agronomic characteristics, and persistence in nondormant alfalfa. S₁ progenies were produced on 60 plants dug from a five-yr-old field of 'CUF-101' (Persistent population) in central AZ and 60 greenhouse-grown CUF-101 plants (Random population). Progenies were sown in a replicated field trial at Tucson, AZ in Oct. 1989. Spring and fall forage yield was significantly lower in the Persistent population than in the Random population. Rate of stem regrowth following harvest was also lower in the Persistent population. S₁ progenies from the Persistent population contained approximately 7.1% more TNC in roots and crowns than the Random population, suggesting that TNC and persistence may be positively correlated. These data suggest that plants in the Persistent population exhibited more conservative growth patterns and that a negative genetic correlation may exist between single-plant yield and persistence. Simultaneous selection for traits associated with productivity and persistence may be necessary.

<p> Two field trials were conducted to determine the impact of water management on the efficacy of insecticide seed treatments against rice water weevil, <i> Lissorhoptrus oryzophilus</i> Kuschel, in rice at the Delta Research and Extension Center during 2011 and 2012. The performance of thiamethoxam, chlorantraniliprole, and clothianidin was evaluated when the permanent flood was established at different timings (6 and 8 weeks after planting) and the effect of flush number (0, 1, or 2) on seed treatment performance was evaluated. Seed treatment efficacy was not impacted by delayed flooding, but 2 flushes reduced efficacy of some seed treatments. </p><p> Experiments were also conducted to determine the impact of reduced seeding rates found in hybrid rice production on the efficacy of insecticide seed treatments targeting rice water weevil. Efficacy was similar when comparing currently labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin with higher rates of these products.</p>