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This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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This dissertation deals with collapsing soils that are prevalent in Tucson, Arizona. Upon wetting, such soils generally swell under small loads but collapse under large loads. Since the recognition of such collapsing soils in Tucson, before about two decades, more collapsing soils were encountered due to booming construction. Therefore, the main goal of this research was to study in depth the mechanism by which these soils collapse and to investigate the effect of certain mechanical and chemical treatment on that mechanism. The research included studies of undisturbed, compacted, and lime-treated samples. Both mechanical and physicochemical tests were conducted. The mechanical tests included collapse, swell, and unconfined compressive strength. The physicochemical tests involved X-ray diffraction and scanning electron microscopy. Various sites of highly collapsing soils were classified with respect to collapse according to existing criteria and the soil of one site was selected for a detailed investigation. A predictive collapse criterion was developed and used to classify the collapse susceptibility of soils in Tucson. The microstructure of the selected soil was investigated before and after collapse. A physical model was proposed to explain the mechanism of collapse. The effects of initial water content, sequence of loading and wetting, and level of loading on the engineering behavior of the selected soil were investigated. Stabilization by compaction was studied using impact and static methods at seven points on the Standard Compaction Curve. The benefits of hydrated-lime additive and the short-term reactions of lime-treated samples were also studied. The research results indicated that the microstructure of the soil is highly porous due to many interassemblage pores. Fine clay particles were found either clothing or buttressing the larger silt particles. The collapse was due mainly to weakening or failure of the clay connectors between the larger soil particles due to swelling of the expansive clay minerals, reduction of the strength of clay connectors due to wetting, dispersion of the supporting buttresses, and reduction of capillary tension. Compaction by both impact and static methods minimized the collapse but not the swell of the soil. Lime treatment completely suppressed the soil's tendency toward collapse and swell.

Dry and wet fine earth spectral measurements were made on the Ap soil surface horizons on the Maricopa Agricultural Center by using a Barnes Modular Multiband Radiometer. Three subsets were used in the analyses 552, 101 and 11. There were three soil series, Casa Grande, Shontik and Trix, four soil mapping units, and three texture classes identified on the farm. The wet soil condition reduced the amplitude of the spectral curves over the entire spectrum range (0.45 to 2.35 μm). The spectral curves were statistically related to the soil mapping units to determine if the soil mapping units and texture classes could be separated. The wet soil condition and the smaller sample size increased the correct classification percentages for soil mapping units and texture classes. LSD tests showed there were significant differences between these groups. Simple- and Multiple-linear regression analysis were used to relate some soil physical (sand, silt and clay contents and color components) and chemical (iron oxide, organic carbon and calcium carbonate contents) to soil spectral responses in the seven bands under dry and wet conditions. There were high correlations levels among the spectral bands showing an overlap of spectral information. Generally, the red (MMR3) and near-infrared (MMR4) bands had the highest correlations with the studied soil properties under dry and wet conditions. Usually, the wet soil condition resulted in higher correlations than that for the dry soil condition over the total spectrum range. The predictive equations for sand, silt and clay and iron oxide contents were satisfactory. For organic carbon and color components, the greatest success was achieved when variation in spectral response within individual samples are smaller than that between soil mapping unit group averages. There was a poor relation between calcium carbonate and spectral response. A comparison of multi-level remotely sensed data collected by SPOT, aircraft, and ground instruments showed a strong agreement among the data sets, which correlated well to fine earth data, except for the SPOT data. Rough soil surfaces showed a reduction in reflectance altitude compared to laser level, and it appears to be directly proportional to the percent shadow in the viewing area measured by SPOT satellite and aircraft.

Fuel accumulation rate and total soil nitrogen, phosphorus, and sulfur following prescribed fires were studied. Three prescribed fires were conducted in S.E. Arizona ponderosa pine stands during the summers of 1979, 1980, and 1981. Samples of forest floor and larger diameter fuel and soil from the surface 1.5 inches and 1.5 to 3.0 inch layers were collected in the summer of 1981. Forest floor and total fuel accumulation averaged 5.4 to 6.7 and 6.3 to 8.9 tons/acre/year, respectively. Total nitrogen, phosphorus, and sulfur in the surface three inches of mineral soil were not significantly affected by burning. Soil nitrogen, phosphorus, and sulfur content averaged 0.21%, 344 ppm and 150 ppm, respectively, in the surface 1.5 inches and 0.11%, 285 ppm and 74 ppm, respectively, in the 1.5 to 3.0 inch layer.

A report produced through an agreement between the City of Coolidge and the University of Arizona.

Prepared by Richard A. Herbert with contributions from Coolidge Regional Park Interdisciplinary Team.

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