Thesis (Ph. D.)--Oregon State University, 1989. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Virginia Polytechnic Institute, 1951. / Vita. Includes bibliographical references (leaves 56-58). Also available via the Internet.

Thesis (M.S.)--Oregon State University, 1999. / Typescript (photocopy). Includes bibliographical references (leaves 70-72). Also available on the World Wide Web.

Written for the Dept. of Plant Science. Title from title page of PDF (viewed 2009/06/10). Includes bibliographical references.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 148-156). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 148-156). Also available on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1957. / Typescript. Abstracted in Dissertation abstracts, v. 17 (1957) no. 11, p. 2362. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 59-61).

The study included field, greenhouse and laboratory experiments with sawdust used as mulch and incorporated with soil. The field experiments were conducted with hemlock sawdust mulches on Lynden silt loam at Abbotsford and on Everett sandy loam at Aldergrove. In both cases the crop was strawberries. Two depths of sawdust were used, two and four inches, and these were compared with clean cultivation, with and without sprinkler irrigation. Soil samples were taken in triplicate from three depths at intervals throughout the 1951 growing season and used for the determination of soil moisture. The 1951 season was one of the driest recorded and both depths of sawdust were very effective in conserving soil moisture. On the Lynden silt loam the sawdust maintained soil moisture at a satisfactory level for growth throughout the growing period and was as effective as sprinkler irrigation for this purpose. However, on Everett sandy loam, sprinkler irrigation maintained soil moisture in a more satisfactory manner. Samples taken from the Lynden soil after the mulches had been down a year, indicated a reduction in Humin I nitrogen and nitrate nitrogen had occured as a result of mulching. However, the differences were not great and a more significant reduction of total nitrogen and nitrate nitrogen was noted on the irrigated plots. In the greenhouse experiment, two sizes of cedar and hemlock sawdust were incorporated at two rates with Alderwood sandy loam, fertilized at two rates and planted with lettuce. After one year it was found that hemlock sawdust had increased the moisture equivalent and wilting percentage more than cedar had, but that the cedar mixtures gave a higher yield of lettuce. In all cases the differences were small but significant. Sawdust, when incorporated with the acidic soil, raised the pH slightly and increased the moisture equivalent, permanent wilting percentage and cation exchange capacity of the soil, the effect being greater for the higher rate of incorporation. Sawdust had the opposite effect on available moisture and lettuce yield. Apparent specific gravity of the soil was noticeably decreased as a result of the sawdust additions and a very large increase in non-capillary pore space occured. This was associated with a large increase in percolation rate. Capillary porosity was affected to a very small extent by the sawdust. Nitrogen fertilization (NH₄NO₃) increased soil acidity in the control soil and in the soil sawdust mixtures. Tests were conducted to determine the absorptic capacity of sawdust for water and ammonia. Size of sawdust affected the amount of water absorbed but not the amount of ammonia absorbed. / Land and Food Systems, Faculty of / Graduate

Modern agriculture, the basis of our civilization, provides sustenance for over 7.9 billion people. However, considering the increasing global population and rising living standards, our food production must to grow by ~50% by 2050. Further constraints of limited arable land, freshwater resources, and the threatening effects of climate change, put our food security at risk and call for multifaceted technological intervention. Currently, irrigated agriculture, while only accounting for 20% of cultivated land, contributes 33%-40% of the total food production. Therefore, irrigated agriculture in arid and semi-arid lands can help us address this complex food–water–climate challenge. However, aridlands are characterized by low precipitation, immense evapotranspiration losses, which is often compensated unsustainably by colossal amounts of freshwater. Evaporation from the topsoil in aridlands remains inadequately tackled. For instance, while plastic mulches have been demonstrated to restrict evaporation, their cost, fragility, lack of reuse, and eventual disposal in landfills limit widespread acceptance. In response, we have conceptualized, developed, and field-tested superhydrophobic sand (SHS), a bio-inspired enhancement of common sand with a nanoscale coating of wax. When a 5-10 mm mulch of SHS is applied on top of subsurface-irrigated soil, the evaporation is dramatically reduced; higher soil moisture boosts plant health, biomass, and yields. Our multi-year field trials of SHS application on tomato (Solanum lycopersicum), barley (Hordeum vulgare), and wheat (Triticum aestivum) crops have consistently demonstrated significant enhancement in grain yields ranging from 17%–73%. In this dissertation, we present our translational surface science research spanning materials development and characterization, mass transfer studies and mathematical modeling, and greenhouse and field experiments. To gain insights into the mulching capacity of water-repellent granular media such as SHS, we present an encompassing novel modeling approach based on particle–particle and liquid–particle forces to accurately capture the fate of evaporating liquid marbles. Then, we explain the origins of SHS superhydrophobicity and provide mechanistic insights into SHS mulching action. Subsequently, we present the data from the field trials to demonstrate how SHS shifts the water balance towards higher crop yields. We close the dissertation with SHS lifecycle analysis and environmental impact and practicality considerations.