I investigated whether rapid-maturing medics (genus Medicago) could establish and produce seed under the relatively dry winter conditions of southern Arizona. Hardseededness is common in many medics and may limit germination before fall rains. Therefore, I was also interested in the amount of medic germination that occurred following summer rainfall. Five accessions from four Medicago species (laciniata, polymorpha, truncatula and littoralis) were sown with or without a companion grass (Oryzopsis hymenoides) and grown with or without weekly 2 cm irrigation. While single-plant forage yields were over 8 times higher with irrigation, each accession established and produced up to 14 seeds for every seed sown under rainfed conditions. The companion grass had no influence on medic performance. Natural reestablishment occurred in all accessions from pods. Seedlings established in summer did not survive to flowering. M. littoralis appeared particularly well adapted to establishment under rainfed conditions in this environment. (Abstract shortened with permission of author.)

Two experiments using lambs were conducted to obtain additional information on the potential nutritional value of halophyte forages for ruminants. In experiment one, Salicornia bigevolii Torr. planted in mid-March and harvested at three dates (July, August and September) replaced wheat straw (30%) in a 65% forage diet. Nutrient composition and digestibility of Salicornia forage declined with advancing maturity. Forage from the July cutting was superior to wheat straw, while that from later cuttings was approximately equal to straw. In experiment two, digestion coefficients were lower when Atriplex deserticola replaced 50% of the alfalfa hay in a 70% roughage diet. Even when all of the alfalfa hay was replaced using a mixture of 85% Atriplex barclayana and 15% Atriplex deserticola consumption by lambs was not adversely affected. It is concluded that Salicornia bigevolii and Atriplex deserticola have potential as feedstuff for ruminants, especially in geographical areas where conventional feedstuffs are not available.

Protoplasts were isolated from mesophyll tissue, callus and seedling cotyledons of Medicago sativa L. cv. Regen S and the halophyte M. marina L. Cotyledon protoplasts of Regen S were cultured in protoplast and cell culture media used previously for alfalfa protoplast culture and in media that had been simplified. There were no differences in the plating efficiencies of protoplasts cultured in the simple and complex media, but cells produced in the latter were greener and they colonized sooner. Protoplasts of M. marina grew at one-half the rate of Regen S protoplasts. Etiolated cotyledon protoplasts of Regen S were fused at 31°C using a solution containing PEG, DMSO and calcium at high pH. The frequency of fusion was 16% of the surviving protoplasts. These methods for protoplast isolation, culture and fusion should be useful in the somatic hybridization of alfalfa and M. marina.

Laser light scattering (LLS) is an alternate method for determining soil particle size. Since the majority of information on particle size analysis has traditionally been derived from sedimentation methods, it is important to be able to draw a relationship between these two methods. Twenty four soil samples from a set of 214 samples analyzed by LLS were selected and also analyzed using sedimentation techniques. Particle size percentages were obtained in five different size ranges and then these two techniques were compared. Linear regression equations were developed that convert numbers obtained from the LLS method to a pipette analysis equivalent. This data was then utilized to eliminate the variation of soil moisture due to soil texture to obtain a moisture content independent of soil moisture. This "adjusted moisture" was displayed on a geographic information system to locate areas in the soil profile where soil moisture is relatively high. The high "adjusted moisture" contents occurred predominately below 2.44 meters (8 ft.) depths suggesting that the pre-irrigation applied to this soil reached this depth.

Nine physically and chemically different soil samples from five study sites in which agaves grew, or were grown, were investigated to evaluate the effects of soil physical and chemical properties on the growth habits of agaves. In five Arizona study sites, biomass data of seven agave species has been recorded for the past ten years. Agaves were grown experimentally in the greenhouse using two widely different soil types from the five sites to evaluate growth under controlled conditions. Influence of edaphic factors on agave growth for the study sites and greenhouse experiment was evaluated. The results show that the determinant primary factors were water availability and temperature. Soil texture, soil pH, soil CO2 concentration, nitrogen, and soluble salt concentration were placed as influential secondary factors for the growth of agave. The degree of influence of these soil factors depends highly upon the genetic characteristics of agave species.

Surface soil samples from a climosequence were studied with the purpose of relating color, reflectance variations and texture to contents of organic carbon and free iron oxides. Information on the physicochemical properties of the soils were obtained with a fine resolution spectroradiometer, a chromameter and by laboratory analyses. The effect of soil organic carbon and free iron oxides is shown by the varying shape of the soil spectral curves. Both the chromameter and the spectroradiometer detected the varying amounts of organic carbon and free iron oxides in soil. Silt had a positive, highly significant relationship with organic carbon. Clay and silt had a positive highly significant relationship with free iron oxides.

Cu(II) binding characteristics of bulk, <30,000, <10,000, <5,000, <1,000, and <500 dalton molecular weight (MW) fractions of soil fulvic acid were determined from Cu(II)/dissolved organic matter interactions. Manual complexometric and potentiometric titrations measured Cu(II) MW fraction binding capacities and acidities. Ionic strength, temperature, and pH were varied. Cu averaged 7.3 x 10⁻⁴ micromoles per liter and carbon ranged between 0.5 and 3.5 ppm. Total Cu(II) binding capacity differed among all but bulk and <30,000 fractions due to site concentration differences; binding was insignificant for the <500 fraction. A three-site discrete ligand model determined conditional stability constants 10⁷˙⁰ 10¹¹˙⁰ and 10¹³˙⁸ and site concentrations 1.8 x 10⁻⁶ 8.5 x 10⁻⁶ and 7.6 x 10⁻⁵ M L⁻¹ for the bulk and 30,000 fractions (pH 6.2, 0.01 M, 22°C). Similar stability constants were determined for lower MW fractions. Cu(II) complexation capacity was pH-dependent; Ionic strength effects were significant at pH 7.0, not at 6.2. Temperature effects were insignificant.

Gravity bubbler irrigation is a new mode of irrigation activated by the existing pressure in conventional irrigation supply channels. In gravity flow systems on steep slopes, pressure increases in the downstream sections of the pipe and must be dissipated for uniform application. A design procedure for gravity bubbler irrigation systems on inclined steep slopes or converted to bench terrace systems is described in detail. The design is based on the use of orifices as energy dissipating devices. Laboratory tests were conducted to determine graphical relationships and coefficients for estimating the head loss for an orifice made from PVC. The head loss coefficient is a function of the orifice to pipe diameter ratio and can be expressed by an equation of the form Ko = abetab where a and b are constants determined from test data and beta is the ratio of diameters. A prototype gravity bubbler irrigation system was designed and installed.

Remote sensing and geographic information system techniques have proved to be effective tools to detect, analyze, and evaluate land cover and land use changes over time. In this research project, changes in land cover and land use were detected in northwestern Sonora, Mexico between 1972 and 1992 using Landsat MSS imagery. About 40% of the entire land cover in the study area changed during that period of time. Of the six classes assigned to the imagery, cropland had the highest rate of change being modified into riparian areas by more than 60%, more than 20% into plains vegetation, and about 8% into bajadas with vegetation. From the two classification methods utilized in this study, the seeding pixels method yielded an over all accuracy over 96%, while the seeking polygons method generated overall accuracy values smaller than 82% probably to user's error.

A comparative study was performed to investigate the tolerance levels of beet armyworm to three insecticides, cyfluthrin, profenofos, and methomyl. The field strains were collected from Yuma and Marana, AZ whereas the susceptible laboratory strain was obtained from California. Dosage-mortality data were obtained by topical application on third instar larvae. Compared to the susceptible strain, both Yuma and Marana strains exhibited an increase in the LD50 to cyfluthrin by 15.65 and 5.45-fold, respectively. Both strains also exhibited an increase in the LD50 to profenofos and methomyl by 14.10, 17.77 and 2.95, 8.07-fold, respectively. The cyfluthrin-selected strain (Marana strain) tested for cross resistance to profenofos and methomyl and exhibited an increase in LD50 by 24.68 and 3.32-fold,respectively.