Thesis (M.Sc.(Agric.))--University of Western Australia, 2006.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Washington State University, May 2007. / Includes bibliographical references.

Dissertation (PhD(Agric))--University of Stellenbosch, 2008. / Accompanying CD-ROM in back pocket of thesis. Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 87-95).

The effects of a straw mulch, applied either uniformly or in strips, on the surface energy balance and soil thermal regimes are investigated using a numerical solution to the two-dimensional soil heat transfer equation. The numerical technique used is an extended version of Barakat and Clark's (1966) alternating direction explicit method. The modified technique can solve problems that are periodic in time and/or space, on either rectangular domains or domains with a curvilinear upper boundary, and in which the soil thermal properties may vary with position, time, or temperature. The method also incorporates non-uniform grid spacings to reduce computation time and to increase efficiency. The straw mulch is represented as a single layer of constant shortwave and longwave transmissivities and reflectivities. Vertical transport of heat and water vapour through the mulch is evaluated by bulk transfer equations. Shading of the bare strip and reflection of radiation onto it by the sides of the mulch strip, as well as the reduction of the sky-view factor seen by the bare strip, are included. Solar irradiance, air temperature and water vapour density, wind speed, soil thermal properties and mulch parameters are the required inputs. Evaporation is estimated using a surface resistance model to vapour flow. The model is compared with micrometeorological measurements made in soils covered with barley straw, either uniformly at rates of 2, 10 or 20 t/ha or in 0.30 m wide mulch strips (10 t/ha rate) alternating with 0.10 m wide bare strips, with the strips oriented in north-south, northeast-southwest, or east-west directions. The results show that for the uniformly applied mulch soil temperatures can be adequately predicted but evaporation is underestimated. Both soil temperatures and evaporation are underestimated in the bare strip. The differences are attributed to the penetration of wind eddies into the straw mulch and the microscale advection from the warm straw strips onto the relatively cold bare strips. / Land and Food Systems, Faculty of / Graduate

Soil erosion research in the fields of agronomy, soils science and mechanics, agricultural engineering, hydrology, climatology, and other scientific disciplines has economic dimensions. In general, measurable and, at times, significant economic effects are associated with the effects of erosion in the other disciplines. Interactions between climate, soils, hydrology, and tillage practices are incorporated into a stochastic simulation model that considers twenty six combinations of five tillage systems, three initial soil depths, two soil associations, two slope classes, and two annual precipitation levels over one hundred years. The model endogeneously determines stochastic annual soil loss. Yield is a function of varying soil depth and technological advance. The model maximizes the wheat producer's objective, 100-year discounted quasi-rents from wheat production. Cumulative or total rent distributions that derive from alternative tillage systems in the different ecological circumstances are compared under stochastic dominance. In low rainfall, shallow soil areas, annual tillage systems were preferred to fallow ones, while conservation tillage dominated plow tillage. In high rainfall areas, for either shallow or deep soil, conservation tillage dominated plow tillage, while plow tillage dominated no-till. Manipulation of the tillage-associated rent distributions permitted the estimation of value-of-marginal product or willingness to pay curves (ordinary, profit-maximizing, input demand curves) that express the depth of soil as a function of its economic worth. Properties of these curves are discussed. Comparison of expected total returns and marginal returns to topsoil increments under alternative tillage systems in defined ecological circumstances paralleled the stochastic dominance results. Rankings of tillage systems by expected total returns differed between ecological areas and differed from rankings by marginal returns. Regardless of tillage system or ecological circumstances, the economic worth of each added soil increment diminished. The experiment showed that differential rates of soil loss associated with different tillage systems influence the decision to continue using or to initially invest in alternative tillages, and also influence the economically rational wheat producer's willingness to incur costs associated with soil conservation. Total and marginal rents associated with single tillages were found to vary greatly across ecological circumstances. The ability and the willingness to invest in soil conservation were somewhat divorced. This result has significance for soil conservation targeting. / Graduation date: 1986

4 pp. / Wheat Production on Lettuce Beds / In 2009, over 56,000 acres were planted to wheat in Arizona, all of which following either a lettuce or cotton crop. For wheat grown in the region, the conventional tillage sequence prior to planting can be tied to as many as seven field operations that consume valuable time, labor, and resources. In this study, our aim was to determine the effectiveness of reducing the number tillage (minimum till) operations in fields immediately following lettuce harvest. And demonstrate to Southwest wheat producers a means for conserving time, fuel, and resources. Growing wheat on lettuce beds immediately following lettuce harvest did not significantly reduce grain yield or quality. Although the regrowth of the previous crop can have significant implications for Durum grown with minimum tillage if not managed effectively, lodging was not a significant factor in this study as the degree of lodging was similar in both growing systems. The significant savings in fuel, labor and time, with no apparent reduction in Durum yield or quality, may be a significant benefit to wheat producers who incorporate minimum tillage practices following a lettuce crop.

While many spring and winter wheat (Triticum aestivum) varieties have been evaluated for yield characteristics under Utah's conventional dryland cropping systems, little is known about these same varieties under new conservation tillage farming management techniques. Farmers are rapidly adopting various reduced tillage systems and need information regarding proper varieties, fertility practices, weed control , etc. A two year field study, in Box Elder County, Utah on a DeJarnet Gravelly silt loam (Loamy-skeletal, mixed, mesic, Calcic Pachic Haploxeroll) and on a Mendon silt loam (fine-silty, mixed, mesic, Calcic Pachic Argixeroll) examined total dry matter, grain yield, percent protein, kernel weight, kernel volume, and average bushel weight responses to four fertility treatments superimposed upon five spring wheat and four winter wheat varieties. Also compared were one spring wheat variety "Komar" and one winter wheat variety "Weston" in a conventional verses conservation tillage dryl and c ropping system. Soi 1 moisture and soi 1 temperature (20 em and 10 em, respectively bel ow the soi 1 surface) readings were compared between the conventional and conservation tillage planting systems. The conservation tillage plantings were done with an air-seeding tillage planter and the conventional plantings were done with standard deep-furrow drills. Dry granular fertilizer (27 -12-0-4 sulfur) was applied to both deepfurrow and conservation tillage plots with the air-seeder. Rates were 0, 168, 224, 280 kg/ha fertilizer material applied. Significant differences were obtained for all spring wheat varieties. Conservation-tilled "Komar" yielded significant yield increases ove r conventio na l- tilled "Komar". The opposite held true for "Weston" , with the conventional-tilled plots yielding a slightly significant increase in grain over conservation-tillage "Weston". No relative difference in soil water or soil temperature were observed in either variety through time. However, at certain growth stages the differences were clearly discernable. Very littl e significant differences were established amoung the winter wheat varieties. Because of heavy infestations of snowmold (Calonectria graminicola) on all winter wheat plots, the true potential yield characteristics of conservation verses conventional tillage remain unproven on these winter wheat varieties.

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