Investigations involving four cultivation treatments were conducted at the Utah State University Greenville Experimental Farm to determine the effect of these treatments on yields of beans and sweet corn. The effects of the different treatments on soil water content, soil temperature, and weed control in beans and corn were investigated. The effect of cultivation on the degree of root rot infection and the effect of different planting dates were also investigated in the bean study. The pre-emergence treatment (ridged just before the plants emerge) produced a 48 percent greater bean yield and a 40 percent greater corn yield than the control treatment (no cultivation). The planting-ridge treatment (ridged at planting time) produced 21 percent greater bean yield than the control treatment. The post-emergence treatment (cultivated after the plants emerged) yielded 10 percent more beans and 20 percent more corn than the control treatment. The second and third planting dates produced 16 and 42 percent, respectively, greater bean yields than the first planting date. The pre-emergence treatment had a higher soil water content and soil temperature than the other methods in both the beans and corn. The pre-emergence treatment had 50 percent less root rot infection than the control treatment. The planting-ridge treatment had 30 percent less root infection than the control and the post-emergence root infection was 17 percent less than the control. The root rot infection in the second and third plantings was 15 and 32 percent, respectively, less than the first planting. The order of best weed control was: pre-emergence, planting-ridge, and post-emergence. The pre-emergence treatment produced the most favorable results in all aspects of the study.

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Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Soil Science" Title from author supplied metadata (automated record created on Sep. 15, 2006.) Vita. Abstract. Includes bibliographical references.

The formation of Fe oxides is influenced by pedogenic factors including ionic environments However, the surface chemistry of Fe oxides formed under different ionic conditions remains obscure Tins study reveals the impact of the structural chemistry of the Fe oxides formed under the influence of low-molecular-weight organic acids and inorganic ligands on their surface chemistry. The selected ligands at optimal ligand/Fe(II) molar ratios (MRs) promoted the crystallization of the Fe oxides formed and decreased their specific surface area through fundamental structural changes. At relatively high ligand/Fe(II) MRS, the ligands inhibited the crystallization of the Fe oxides formed, resulting in the development of micropores, the increase in their surface roughness and irregularity as revealed by atomic force microscopy, as well as the increase in their specific surface area. The net negative surface charge of the Fe oxides consistently increased as the ligand/Fe(II) MR increased. The ligands altering the surfaceproperties of the Fe oxides generally followed the order of the stability constants of the Fe-ligand complexes: silicic acid > citrate > tartrate > oxalate > sulfate > carbonate. The kinetics and mechanisms of adsorption/desorption of P and Ph on the Fe oxides formed at various citrate/Fe(II) MRs were investigated by conventional batch method, pressure-jump relaxation spectrometry and differential Fourier transform infrared spectroscopy. The apparent rate constants, intrinsic rate and equilibrium constants, activation energies, pre-exponential factor values of P and Ph adsorption by the Fe oxides formed and the coordination of P and Ph on the Fe oxide surfaces greatly varied with the amount of the citrate ligands coprecipitated with Fe and their surface properties. The mechanistic rate laws of P and Pb adsorption by the Fe oxides formed at the citrate/Fe(II) MRs of 0 and 0.001 were different. The P adsorption occurred in two sequential reactions whereas the Pb adsorption included two parallel reactions. The role of organic and inorganic ligands in influencing the surface properties of Fe oxides through their effect on crystallization is profound. The subsequent impact on the dynamics of nutrients and pollutants in terrestrial and aquatic environments merits close attention.

Five methods to measure the saturated hydraulic conductivity of Arizona irrigated soils were evaluated using the in-situ single ring, double ring, compact constant head permeameter methods, and with tempe cells (soil cores) in the laboratory. Ten Arizona irrigated soils were studied, and the textures of these soils ranged from sand to silty clay. Three water qualities were evaluated, namely the local water, gypsum in local water, and gypsum water (0.005M CaSO₄ · 2H₂O solution). Sites were selected to provide soils having a wide range of soil characteristics and detailed laboratory and field morphology data were measured including soil texture, bulk density, soil aggregation, stickiness, plasticity, moisture retention at various tensions, ECₑ, and pHₑ. The results showed that the double ring method was the better in-situ method. The relationships between soil properties and K(sat) were evaluated, and soil properties were examined as predictor variables for K(sat) in stepwise multiple-regression. Stepwise multiple-regression criteria were set at a probability of F to enter ≤ 0.5 and probability of F to remove ≥ 0.1. Six models are presented that can be used in predicting K(sat). Each model has a subset of field and laboratory predictor variables selected based on stepwise multiple-regression criteria, and with some personal judgment. Casewise diagnostics were used to test model performances.

Numerical simulations were performed to study two-dimensional infiltration from furrows. The simulations were carried out using the models SWMS_2D, HYDRUS-2D and HYDRUS-1D. The first model was used to evaluate the individual effect of soil and furrow parameters on cumulative infiltration and deep seepage. Cumulative infiltration was found to be more sensitive to saturated hydraulic conductivity, wetted perimeter and furrow spacing than the other parameters for relatively long times, while cumulative deep seepage was more sensitive to the same parameters except to the furrow spacing. It was verified that two-dimensional cumulative infiltration can be approximated using one-dimensional models, for example HYDRUS-1D, by combining the vertical and horizontal infiltrations. The two-dimensional cumulative infiltration is underpredicted by no more than 35% using this calculation. When steady state is reached the steady infiltration rate may be linearly related to the depth of the furrow. As a result, steady infiltration rate is dependent only on type of soil, water depth in the furrow and furrow width. Broocks-Corey soil hydraulic parameters were matched to the van Genuchten parameters by four different procedures. The method based on matching sorptivities produced the closest results to the van Genuchten solution for one- and two-dimensional cumulative infiltration. However, cumulative deep seepage was not accurately simulated. The SCS infiltration parameters were also matched but using an inverse problem methodology. The parameters obtained described cumulative infiltration reasonably well.

In the riparian corridor of the San Pedro River in southeastern Arizona, the fluxes of water and energy over three riparian vegetation groupings were monitored and modeled in order to determine their annual water use and water sources. In situ micrometeorological and soil moisture measurements were made from 1996-1998 at a floodplain grassland site composed mainly of the perennial floodplain grass, Sporobolus wrightii (sacaton), and a tree/shrub grouping dominated by Prosopis velutina (mesquite). The results indicate that the grassland obtained water only from the near-surface (recent precipitation), while the mesquite accessed moisture from deeper in the vadose zone and/or from the water table. Both of these sites exhibited little interaction with the underlying groundwater, suggesting that the majority of the groundwater use from riparian vegetation is limited to the areas of dense mesquite and the forest gallery adjacent to the river. Measurements of the forest gallery water use composed mainly of Populus fremontii (cottonwood) and Salix gooddingii (willow) were available for some shorter term periods in 1997. These measurements were used to calibrate the Penman-Monteith model for evaporation in order to determine the water use from the forest gallery for the entire growing season. The total seasonal water use from the forest was considerably less than potential evaporation estimates. Observations of soil moisture under two rangeland sites in the San Pedro Basin were examined in order to determine the magnitude and the depth of root zone recharge characteristics in this semiarid region. Intermittent TDR observations made from 1990 to 1998 show that deeper root zone recharge occurred primarily during the wintertime, when the plants were senescent and evaporation demand was diminished. A physically-based variably-saturated flow model was used to determine the wintertime recharge. Using an automatic calibration algorithm, the model proved capable of reproducing the observations with small error. Simulated wintertime infiltration amounts indicated that substantial, deeper root zone recharge did occur during wet winters, but that the large year-to-year variability of this recharge implies that deeper-rooted plants would still need access to moisture in shallow root zone.

The quantity of quartz and its size distribution was determined in soils formed from quartz free basaltic tephra on Greens Peak, Apache County, Arizona. The soils showed a decrease in quartz content from the east side to the west side of the peak. The percentage of averaged weighed quartz content in the upper soil horizons ranged from (36.1%-13.9%) on the east side and (19.9%-12.3%) on the west side. The content of quartz was higher in the surface soil horizons than in the lower horizons. Large amounts of quartz occurred in the sand and silt fraction, whereas no quartz was detected in the clay fractions. Quartz is concentrated mostly in the coarse silt (22-53 μm) fraction (50%). Quartz particle size distribution in these soils is dominantly in the range of 17-53 μm particle count based, and (17-63 μm) mass based. The abundance of silt and very fine sand quartz, and the paucity of aerosolic quartz 1-10 μm in these fractions is indicative of dust transported short distances from the local sources. It is suggested that the quartz was added as loess sized material of mainly local origin brought into the profiles by eolian transport.