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

Graduation date: 1986

Weed management in sustainable farming systems often requires the integration of several different pest management techniques. Cultural, biological, and chemical pest control efforts can be utilized to contribute to the common goal of reducing weeds in vegetable row crop systems. This research addresses how common disturbances such as tillage and insecticide use affect: carabid beetle assemblages; predation of weed seeds by invertebrates; and weed seed recruitment. Field experiments were conducted over three years at two different locations on the OSU Vegetable Research Farm, Linn Co., OR. We found that activity-density of carabid beetles varied seasonally and peaked in late August-September each year. Insecticide applied in year 1 affected seed loss in year 2, suggesting possible long-term effects of land management on weed seed removal. Weed recruitment was highly variable between treatment, site, and year. Conserving biological weed control agents in combination with cultural techniques such as reducing tillage and the use of cover crops, helps growers shift from expensive, density-independent control efforts to more ecological, long-term solutions for weed management in agroecosystems. / Graduation date: 2011 / Access restricted to the OSU community, at author's request, from Dec. 15, 2010 - Dec. 15, 2011.