Figueroa-Viramontes, Uriel (The University of Arizona., 1999)
Denitrification is a microbial process of anaerobic respiration in which nitrate (NO₃⁻) is chemically reduced to gaseous nitrous oxide (N₂0) and molecular N2. Fertilizer N can be lost to the atmosphere through this process. Subsurface drip irrigation may create favorable conditions for denitrification, such as high moisture and NO₃⁻ content. The objectives of this research were to: 1) determine the denitrification rate in drip-. irrigated cauliflower and sweet corn crops; 2) evaluate the effect of soil water tension on the denitrification rate, and; 3) estimate an N balance under subsurface drip irrigation, including denitrification losses. Two field experiments with subsurface drip-irrigated cauliflower were conducted during the 1996-98 winter growing seasons at the Maricopa Agricultural Center, in Maricopa, AZ. An additional study with subsurface drip-irrigated sweet corn was conducted at the Campus Agricultural Center in Tucson, AZ. All the experiments were complete factorial designs with two soil water tension levels (low, high), two levels of N fertilizer (zero, adequate), and three replications. The denitrification rates evaluated at ambient temperature were <12 g N ha⁻¹ d⁻¹ during the cauliflower winter seasons. When soil cores taken during the 1997-98 winter season were incubated at room temperature (24 ±2°C), denitrification rates were five to 50 times higher than the rates evaluated at ambient temperature. The denitrification rate measured at room temperature in the cauliflower winter season was similar to the rate observed in the sweet corn during summer. Soil cores from the cauliflower 1997-98 season that received 100 kg N ha⁻¹ had denitrification rates from 10 to 45 g N ha⁻¹ d⁻¹ ; when these cores were amended with additional soluble carbon, the denitrification rate increased to 800 to 3500 g N ha⁻¹ d⁻¹. All of the three experiments showed higher denitrification rates at the end of the season. This trend coincided with increases in denitrifying enzyme activity and soluble organic carbon. The denitrification loss of fertilizer N was <1% in cauliflower and almost 2% in summer sweet corn, when irrigated at the higher soil water tension. Lower soil water tension did not increase the denitrification rate in the winter, but in the summer the loss of N due to denitrification increased to almost 6% of the applied N.
McGee, Eric Arthur. (The University of Arizona., 1996)
Nitrogen (N) cycling involves the gains, losses, and transformations of N from sources such as soil organic matter, crop residues, and fertilizers. These sources are the primary N supplies potentially available to non-leguminous crops. Through the use of a stable N isotope tracer (¹⁵N), transformations among various soil N pools can be studied. We conducted three separate studies using ¹⁵N. Two studies dealt with methodologies of ¹⁵N use and analysis, while the third study investigated mineralization of ¹⁵N labeled crop residues under field conditions. The first study evaluated a new apparatus for applying ¹⁵N by fertigation to subplots under buried drip irrigation. We determined that this method was an effective means of uniformly applying tracers using buried drip irrigation. The second study evaluated a new method for fine-grinding soils based on particle size distribution and variability of organic N and ¹⁵N analyses. Soils of varying texture were rapidly ground to achieve acceptable analytical precision for N and ¹⁵N analysis. The objectives of the third experiment were to: (i) evaluate mineralization of inorganic N from ¹⁵N -labeled crop residues with different C/N ratios and at different loading rates and (ii) evaluate the influence of residue loading rate and type on the percent net mineralization from ¹⁵N-labeled crop residues in a basin irrigated wheat cropping system in Southern Arizona. Mineralization of crop residues in this hyperthermic soil was rapid and was often followed by periods of re-immobilization. Net end-of-season mineralization of residue N was 30-50% for lettuce, and 30-40% for wheat.
Tavassoli, Abolghasem, 1940- (The University of Arizona., 1980)
Reclamation of four salt-affected soils collected from southern Arizona was studied in the greenhouse and laboratory. Two rates of four amendments (sulphuric acid, gypsum, ammonium polysulphide, and ammonium thiosulphate) were applied in triplicate. Results were evaluated in terms of changes in nutrient availability, ions removed by leaching, plant growth, and infiltration rates. In most cases the high rates of sulphuric acid and gypsum increased the solubility of the major cations (Na, K, Ca, and Mg) in the soil. If the required amount of leaching water were applied to the soil, a significant amount of these cations, especially Na, was leached from the soil. For the Gothard soil (saline-sodic) two pore volumes were sufficient to accomplish leaching, but were insuffcient for the Guest (nonsaline-slightly sodic) and Gilman (highly saline-sodic) soils. High rates of sulphuric acid and gypsum decreased the pH and increased the EC for all soils, although the EC was not significant at the 5% level for the Mohall (nonsaline-nonsodic, calcareous) soil. All treatments decreased the pH of the Gothard soil significantly; however, the greatest increase in EC and least pH were obtained from acid application. Regarding changes in phosphorus (P), all treatments increased the amount of soluble P in the leachates from the Gothard and Guest soils; whereas available soil P increased significantly only with the acid treatments. None of the treatments affected the amount of P in the Gilman soil leachates, but acid and gypsum increased the available soil P. Ammonium polysulphide and ammonium thiosulphate tended to increase available P but the increase was not significant at the 5% level. None of the treatments affected the P parameters for the Mohall soil. Sulphuric acid increased growth and P uptake of alfalfa plants on all soils except the Mohall. Gypsum and ammonium polysulphide increased P uptake on the Gothard and Guest soils whereas ammonium thiosulphate increased P uptake only for the Guest soil. Sulphuric acid and gypsum increased the infiltration rates for all four soils. Thiosulphate produced intermediate infiltration rates while the lowest rates were found with ammonium polysulphide and the untreated soils. Although amendment rates were based on equivalent amounts of sulphur and their effectiveness in supplying soluble calcium, and the exchangeable sodium status of each soil, results varied according to such factors as rate of oxidation of the amendment, lime content of the soil, soluble salts present in the soil, and soil texture.
Saraiva Leao, Moies Custodio,1939- (The University of Arizona., 1975)
A field study was conducted to determine water and salt distribution patterns in a soil irrigated by pairs of double-chamber, perforated polyethylene tubes. The study consisted of two experiments: a water distribution experiment and a salt distribution experiment. Both experiments were conducted at the same site with experimental plots having two perforated lines 9 m long, spaced 0.60 m. The tubing had outer orifices 0.5 mm in diameter spaced 0.30 m along the tubes. The water distribution experiment consisted of water application to the bare soil for periods of time of 3, 6, 9, and 12 hours. After each test a trench was dug normal to the irrigation tubes and samples were taken to determine soil moisture on a dry weight basis. Moisture profiles are presented for the various tests. The salt distribution experiment was conducted in the Fall of 1973 and repeated in the Spring of 1974. It consisted of four irrigation treatments comprising two irrigation levels and two levels of salt in the irrigation water (327 and 2000 milligrams per liter of salts). Experimental plots were planted with lettuce and soil samples taken after planting and after harvesting the lettuce. Soil samples were analyzed for electrical conductivity of the soil saturation extract, pH, calcium, magnesium, sodium, potassium and nitrates. Saturation extract conductivity profiles in the soil are presented for different treatments. After planting and after harvest concentrations of calcium, magnesium, sodium, potassium, nitrates and pH values are also shown. Seasonal water application and lettuce yields are presented for both trials Water movement in the soil was 2 to 3 times greater in the horizontal than in the vertical direction. Wetted soil volume showed a high positive correlation with both the volume of water applied and with time of application. Salt accumulation occurred mainly at the soil surface between the irrigation tubes and away from the main root zone of the plants. The surface accumulation was followed by a leached zone. There were no significant differences in yield among plots receiving different treatments. Seasonal water application was less than half of the seasonal amount of water normally applied for furrow irrigated lettuce in the Tucson area. It was higher than experimental determinations of seasonal consumptive use for lettuce at Mesa, Arizona. The study indicated that trickle irrigation with water of high salt content is likely to cause a high surface concentration of salts. Application of extra amounts of water by the trickle system, or another method, is recommended to leach the salts to a depth below the crop root zone.
Miscible displacement experiments were performed with solutes of different size and structure to examine their mass transfer, sorption, and transport in homogeneous and heterogeneous porous media. In homogeneous porous media, the contribution of axial diffusion becomes significant at pore-water velocities less than 0.1 cm/h, and the use of a tracer-derived dispersivity for solutes of different sizes would not be valid in this case. Comparison showed that dispersivities measured with a non-sorbing single-solute solution should be applicable to multi-component systems. Breakthrough curves exhibited both early breakthrough and tailing for solute transport in aggregated, stratified, and macroporous media. The extent of non-ideality was consistent with the impact of solute size on the relative degree of "non-equilibrium" experienced by solutes whose transport is constrained by diffusive mass transfer. Flow-interruption experiments with dual tracers of different size, performed for various interruption times, provided additional evidence regarding the effect of solute size on diffusive mass transfer. The relationship between sorbate structure and rate-limited sorption was examined using the QSAR (quantitative structure-activity relationship) approach for sorption of low-polarity compounds by two soils. The first-order valence molecular connectivity (¹xᵛ), accounting for the size and structure of the solutes, was found to be the best topological descriptor. This supports the contention that rate-limited sorption in these systems is analogous to the polymer diffusion model. Based on this model, the calculated diffusion-length ratios for two soils compare favorably to the values determined from the measured rate data. The synergistic effects of rate-limited sorption and mass transfer in heterogeneous porous media were examined. Independent predictions produced with the multiprocess non-equilibrium model (MPNE) provided very good descriptions of the experimental data for transport of several organic solutes with different solute structures in a saturated aggregated medium. The success of describing the mass transfer, rate-limited sorption, and transport of contaminants has important implications for understanding contaminant transport in the subsurface and for remediation practices of contaminated sites.
Lumbuenamo, Sinsi Dianza. (The University of Arizona., 1990)
In order to study the effect of standing dead biomass on vegetation canopy spectral response, the normalized difference, the soil-adjusted vegetation index, the green vegetation index and the perpendicular vegetation index were used to examine and compare the spectral behavior of a mostly green (regrowth after burning) vegetation canopy to a perennial vegetation stand. Results showed all greenness indicators to be strongly affected by the presence of standing dead vegetation. The burned plots which had less green biomass in the first growing season (February-June) exhibited higher vegetation index values through the entire growing season. The observed discrepancies in the vegetation indices seem to stem from the attenuation of the near-infrared flux combined with a lack of responsivity of the red channel. Overall, there was no correlation between green biomass and greenness measures in the perennial stand. Furthermore, in the perennial environment, a steady increase in "greenness" was observed while the green biomass was actually decreasing. The problem seems to be more of visibility than quantity of green biomass present.
King, Chad Eric (The University of Arizona., 2005)
As we have come to depend on aquaculture to supplement natural fisheries, intensive culture methods have increased production. Accompanying environmental damage--non-point source pollution, loss of biodiversity and struggle for water--has offset food and financial gains. Problems surrounding food production are amplified in arid lands, as the potential of irrigated agriculture is weighed against the value of water. Through the following research, I studied integration of aquaculture and agriculture through multiple uses of water and nutrients, to reduce environmental impacts. When managed properly, integration can provide multiple cash crops, increased food and fiber production with reduced inputs. Integration allows for groundwater and nutrients in water and solid waste to be reused. Shrimp farms in Arizona use low-salinity ground water from aquifers for shrimp ponds and agricultural irrigation. On one of these farms, effluent is reused for irrigation of olive trees and other field crops. In Chapter 3, I described an experiment designed to quantify changes in the height of olive trees due to irrigation with shrimp effluent. Trees receiving effluent grew an average of 61.0 cm over the two-year experiment, 70.4 cm with fertilizer and 48.4 cm in the well water treatment. No negative effects due to effluent irrigation were found, while increases in water use efficiency were realized by producing two crops with the same irrigation water. Multiple uses of water are also possible in smaller scale agriculture systems. I performed a financial analysis of a small-scale aquaponics system, integrated hydroponics and aquaculture, in Chapter 4. Biological viability of such systems is clear. By building and managing this system for five months, I examined economic viability, by analyzing annual costs and revenue. Calculating net present value showed that the system was not financially viable unless labor costs were excluded. Financial returns were between 3,794 and 10,640 over six years. In five months, this system produced 181.4 kg of food, with fish feed, iron and water as the only inputs. This study showed potential for using small-scale aquaponics as a hobby, in schools, and as a tool for agricultural economics education, but not as a business opportunity.
Al-fatesh, Ibrahim Yahya. (The University of Arizona., 1990)
Field and greenhouse studies were carried out to determine the effects of Al and Mn individually or collectively on the growth and elemental composition of various grape cultivars. Soil and plant tissue analyses were evaluated in two vineyard locations on which several grape varieties were established on a White House soil series. Soils at both locations were treated with soil amendments and N fertilizers. The results show that both soils are acidic at the top 30 cm surface and have a high extractable Al, Fe and in some cases Mn content. The field results further indicate that grape varieties respond differently to soil acidity in terms of their mineral composition. High soil Al, Fe and Mn resulted in a higher accumulation of these elements in grape leaves whereas the cation uptake especially P, Ca, Zn, and Cu were reduced. Field plants exhibiting P deficiency symptoms resulting from high soil Al and Fe had a 950 Mg kg⁻¹ Al and 400 mg kg⁻¹ Mn in their leaves. Furthermore, these plants had a deficient range of P, K, Ca and Zn. The Al treatments reduced shoot growth and decreased number of leaves. The growth reduction resulted from higher Al, Mn and Fe content of plant leaves and lower P, Ca and Cu. Furthermore high Al treatments of 30 mg 1⁻¹ and more in the nutrient solution resulted in lower accumulation of P, Ca, K, Mg, Fe and Cu. The different parameters were affected by Al levels to different degrees and were more pronounced at a later stage of growth than the earlier stage of growth. The concentration of Al in plant tops at which Al toxicity symptoms appeared was 800 mg kg⁻¹ Al or more. Mn treatments reduced plant growth, decreased number of leaves and induced toxicity symptoms. The percent reduction of growth parameters was greatest at highest Mn levels. The reduced growth resulted from the deficiency of several mineral elements such as Ca, Fe, Zn and Cu and higher accumulation of Mn in plant tissue. The effect of Mn levels on the elemental composition especially Fe, Zn, Cu, Ca and P increased progressively as plant growth progressed. The 10% reduction in growth occurred when plant had accumulated 400 mg kg⁻¹ Mn in their tops. The accumulation of elements in plant leaves was varied at various stages of growth as a function of time and Mn and/or Al concentration in the nutrient solution. The growth reduction and the severity of toxicity symptoms were proportional to either Al, Mn or Al + Mn concentrations in the nutrient solution as well as their accumulation in plant tops.
The export option will allow you to export the current search results of the entered query to a file. Different
formats are available for download. To export the items, click on the button corresponding with the preferred download format.
By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.
To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export.
The amount of items that can be exported at once is similarly restricted as the full export.
After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.