Winter wheat is commonly grown in dryland cropping systems in the Pacific Northwest region of semi-arid eastern Oregon. For agronomic, economic, and environmental reasons, it is important to understand the long-term sustainability of such dryland systems. The objective of this study was to evaluate the long-term effects of tillage, nitrogen (N), soil depth, and the influence of precipitation on wheat yields in dry land cropping systems of eastern Oregon. Data were taken from the Tillage/Fertility or "Balenger" experiment, which was established in 1940 by a Soil Conservation employee, and is one of the oldest replicated research experiments in the western United States. The experiment consisted of a winter wheat-summer fallow rotation arranged in a randomized block design with three replications. The main plot consisted of three primary tillage treatments (moldboard plow, offset disk, and subsurface sweep) and subplots consisted of six nitrogen treatments that changed over time and most recently ranged from 0 to 180 kg ha�����. Soil depth of individual plots ranged from 1.2- to 3.0-m. The study was divided into four main time periods (1940-1951, 1952-1961, 1962-1987, and 1988-1997) within which experimental treatments were consistently maintained. The moldboard plow tillage treatment significantly increased yields by more than 300 kg ha����� over the subsurface sweep tillage treatment in all four time periods. Yields with the moldboard plow system were significantly higher than with the offset disk system in time periods 3 and 4. The same trend was evident for mean yield in time periods 1 and 2, but differences were not statistically significant. In time periods 1, 2, and 3, mean yields were higher with the offset disk tillage treatment than the subsurface sweep tillage system, although the differences were not statistically significant. In time period 4, mean yield was higher for the subsurface sweep system than the offset disk treatment, but differences were not statistically significantly. The optimum amount of N for winter wheat differed from year to year, within, and between experiment periods. This was apparently in response to rainfall patterns and improved management factors, specifically more N responsive semi-dwarf varieties. For time period 1, the maximum fertilizer rate was 11.2 kg N ha�����, which tended to produce higher mean grain yields than an application rate of than 0 kg N ha�����, regardless of the quantity or distribution of precipitation. For time period 2, the maximum fertilizer rate was 33.7 kg N ha�����, which produced significantly higher grain yields than an application rate of than 0 kg N ha�����, regardless of the quantity or distribution of precipitation. For time period 3 (1962-1987), which had below-normal annual and growing season precipitation, yield increased with the addition of 45 kg N ha�����. For time period 4 (1988- 1997), which had above-normal annual and growing season precipitation, yield increased with the addition of 90 kg N ha�����. Yield increases at greater rates of N were insignificant. For time periods 3 and 4, maximum mean yield was obtained at an application rate of 135 kg N ha�����. The response of wheat yield to N during dry years was greater for deep (> 2.8 m) soils than for shallow soils. In addition to amount, rainfall distribution during the winter (October to March) and growing (April to June) season significantly affected yield. Results demonstrate the importance of rainfall and nitrogen to winter wheat production in eastern Oregon, and that the most environmentally sound tillage systems are not necessarily the most profitable from farmers' point of view. / Graduation date: 2000

The pursuit of agricultural sustainability is necessary to ensure global food security into the future. To achieve sustainability, production systems around the world use different approaches. Utilizing several biological and physical indicators, this study investigates two agricultural production systems and assesses how management has affected the long-term health and sustainability of the soils. The first study assessed the effect of variable intensities of tillage on three Saskatchewan soils under low-disturbance (LD) management for the ten years prior to tillage. The soils represented were in the Grey, Black and Brown soils zones at sites located near Tisdale, Rosthern and Central Butte, Saskatchewan, respectively. A completely randomized block design utilized four treatments of varying tillage intensity. Samples were taken in spring before planting and after harvest at all sites. The soils were analyzed for microbial indicators of health by assessing dehydrogenase, urease, protease, and alkaline phosphatase activities. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial quotient nitrogen (MQN) also were analyzed. Traditional soil nutrient and physical parameters were measured. The tillage intensities affected each parameter differently likely due to the differences in litter quality at each site. The high intensity tillage treatment decreased dehydrogenase activity at Tisdale at May, while in Rosthern dehydrogenase activity was increased in the moderate intensity tillage treatment and decreased by the high intensity tillage treatment. At Central Butte no effect was detected until October when dehydrogenase activity was increased by the low and moderate tillage intensity treatments. Protease and urease activities were affected at Rosthern only where the moderate intensity tillage treatment decreased activity relative to the control treatment. Soil physical parameters were not affected by tillage intensity; however nutrient levels were impacted by the increasing tillage intensity. Specifically, NO3- was reduced at Tisdale and was increased at Rosthern. Phosphate levels were reduced by the high tillage intensity in Rosthern whereas, with increasing tillage, the opposite occurred at Tisdale and Central Butte. The responses were strongly influenced by site characteristics, especially soil zone, organic matter content and surface litter abundance and quality. These effects were short-term, having no long-term impact on the agricultural sustainability or health of the soil, although knowledge of litter condition and quality is agronomically beneficial in order to predict soil responses to intense tillage events. iii The second part of the study was to assess the success of grass terraces on preserving the soil health of hillslope farm plots with Oxisolic soils in southern Ethiopia. Soil erosion has a devastating impact on hillslope agriculture in Ethiopia causing severe land degradation. An adjacent terraced and unterraced hillslope was chosen and sampled, along with a second unterraced slope for comparison. These soils were analyzed for dehydrogenase, alkaline phosphatase, and urease activities, as well as total C and total N. The plots above the terraces [terraced upper and unterraced upper] had higher urease activities than the plots below [terraced lower and unterrraced lower]. The impact of a vegetative strip that had formed a terrace 20 years ago was still evident in consistently higher alkaline phosphatase, urease, and dehydrogenase activities than the other plots. Simple methods of erosion prevention on erosion prone hill-slopes indicated that vegetative strips leading to terracing have a positive effect on soil health and functionality, promoting the long-term agricultural productivity and sustainability of these landscapes.

This study considered using a relatively new method to study soil-tool wear which could drastically reduce the time and associated costs of traditional wear studies. The goal was to utilize discrete element method (DEM) simulations to recreate the results of a circular soil bin test in order to develop a relationship that could be used to predict wear under different conditions. Through the application of DEM, simulations could be used to study different materials or designs intended to result in improved wear performance.<p> Three replications of aluminum cylindrical bars were worn during 400 km of travel in a circular soil bin. Wear was quantified by measuring the change in radius of the cylinders at 18-degree intervals around their circumference. Mass data were also obtained to provide an overall average of wear occurring on the bar and to validate the radii measurements.<p> The DEM simulations were executed using EDEM software. Conditions present in the physical soil bin trials were simulated by recreating components in the soil bin and incorporating soil properties that were directly measured, using representative soil samples. Forces exerted on the bar by the soil and the relative velocities between the soil and tool were used to generate a relationship to predict wear of the bar. The wear equation was verified using a portion of the experimental data from the soil bin.<p> The wear model showed promise in predicting the amount of wear recorded in the soil bin through the application of DEM-predicted compressive forces and relative velocities between the tool and soil particles. The Archard equation for wear was modified to create a non-linear equation. Plotting the measured wear against the wear predicted from the fitted equation produced a trendline with a slope of 0.65. Although a perfect correlation would have produced a slope of 1, the model was able to predict a large portion of the wear that occurred. Refinement of the model could further be achieved with changes in the design of the geometry used in the simulation and through verification of force predictions with experimental data. Because of the variable nature of wear, additional replications of tools in the soil bin would have increased the number of data points available to create the model and reduced the impact of outlying data. With these recommended improvements, the wear model has the ability to very accurately predict the wear of a cylindrical bar.

Strip-tillage implements remove the residue from previous crops and form a seedbed ready for planting. An experiment was conducted to evaluate 5 row-cleaning devices. The proportion of residue removed by the implement was used as the performance indicator. Each of the 5 devices was evaluated at 2 speeds and orientations on the implement. The devices were tested in two blocks (fields) of corn residue (one high residue and one medium residue), and one field of wheat residue. An analysis was conducted, using a mixed-effects model, to compare the performance of the cleaners operating in the different conditions. All cleaners performed well, with no statistical difference in mean performance. All row cleaners performed more consistently in wheat residue, compared with performance in corn residue. Numerically, the consistency of the different cleaners was different, with one configuration performing less consistently than the other four. Edge-effects of the outside row unit of the implement had, in most cases, an insignificant effect on the row unit's cleaning performance.

Strip-tillage implements remove the residue from previous crops and form a seedbed ready for planting. An experiment was conducted to evaluate 5 row-cleaning devices. The proportion of residue removed by the implement was used as the performance indicator. Each of the 5 devices was evaluated at 2 speeds and orientations on the implement. The devices were tested in two blocks (fields) of corn residue (one high residue and one medium residue), and one field of wheat residue. An analysis was conducted, using a mixed-effects model, to compare the performance of the cleaners operating in the different conditions. All cleaners performed well, with no statistical difference in mean performance. All row cleaners performed more consistently in wheat residue, compared with performance in corn residue. Numerically, the consistency of the different cleaners was different, with one configuration performing less consistently than the other four. Edge-effects of the outside row unit of the implement had, in most cases, an insignificant effect on the row unit's cleaning performance.

Cadmium (Cd) from the soil can accumulate in our bodies via the consumption of our crops and cause serious health problems. While it has been documented that long-term cultivation affects physical and chemical properties of soil, little is known about its effect on the phytoavailability, solid-phase speciation, and profile distribution of soil Cd. The objectives for this study were to determine the effect of long-term cultivation on: (1) a cadmium availability index (CAI) that reflects phytoavailable Cd for durum wheat, and related soil properties, (2) the solid-phase species of soil Cd and relationships between the CAI and the solid-phase species of soil Cd and related solid-phase soil component properties, and (3) the profile distribution of total soil Cd in the past, and the profile distribution of total soil Cd over the next 100 years. One Orthic Chemozemic soil profile was investigated from a virgin and an adjacent long-term cultivated field at eight sites in the Brown, Dark Brown, and Black soil zonesof Saskatchewan, Canada. Long-term cultivation significantly decreased the CAI. A decrease in total Cd, total Zn, and CEC, and an increase in aromaticity of the soil organic matter and soil pH all contributed to the decrease in the CAI. Both the virgin and cultivated soils had the same solid-phase Cd species with the same order of relative abundance: metal-organic complex-bound > easily reducible metal oxide-bound > H2O2 extractable organic-bound > crystalline metal oxide-bound > exchangeable. However, metal-organic complex-bound Cd and H2O2 extractable organic-bound Cd decreased significantly with long-term cultivation. In the virgin soils two solid-phase Cd species correlated significantly with the CAI: exchangeable Cd (r = 0.93) and easily reducible metal oxide-bound Cd (r = -0.88). In the cultivated soils three solid-phase Cd species correlated significantly with the CAI: exchangeable Cd (r = 0.95), metal-organic complex-bound Cd (r = 0.71), and crystalline metal oxide-bound Cd (r = 0.86). For both the virgin and cultivated soils, the concentration of A horizon Cd > C horizon Cd > B horizon Cd. In the past, A horizon Cd concentration decreased significantly with long-term cultivation. However, it is estimated that in 100 years, with the use of phosphate fertilizer made from Idaho ore, the total A horizon Cd content in these soils could be 3.5 times higher and reach a concentration of 1.18 mg Cd kg-1 soil which is in the critical region where the phytoavailability of soil Cd could increase dramatically. The present study has advanced the frontiers of knowledge on the effect of long-term cultivation on the Cd content and distribution in the soil profile, its phytoavailability index, solid-phase species, and the soil properties related to its phytoavailability. Extending research such as this to other major agricultural soil types and farming practices will assist in the development of innovative management strategies to curtail Cd contamination of the terrestrial food chain.

The pursuit of agricultural sustainability is necessary to ensure global food security into the future. To achieve sustainability, production systems around the world use different approaches. Utilizing several biological and physical indicators, this study investigates two agricultural production systems and assesses how management has affected the long-term health and sustainability of the soils. The first study assessed the effect of variable intensities of tillage on three Saskatchewan soils under low-disturbance (LD) management for the ten years prior to tillage. The soils represented were in the Grey, Black and Brown soils zones at sites located near Tisdale, Rosthern and Central Butte, Saskatchewan, respectively. A completely randomized block design utilized four treatments of varying tillage intensity. Samples were taken in spring before planting and after harvest at all sites. The soils were analyzed for microbial indicators of health by assessing dehydrogenase, urease, protease, and alkaline phosphatase activities. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial quotient nitrogen (MQN) also were analyzed. Traditional soil nutrient and physical parameters were measured. The tillage intensities affected each parameter differently likely due to the differences in litter quality at each site. The high intensity tillage treatment decreased dehydrogenase activity at Tisdale at May, while in Rosthern dehydrogenase activity was increased in the moderate intensity tillage treatment and decreased by the high intensity tillage treatment. At Central Butte no effect was detected until October when dehydrogenase activity was increased by the low and moderate tillage intensity treatments. Protease and urease activities were affected at Rosthern only where the moderate intensity tillage treatment decreased activity relative to the control treatment. Soil physical parameters were not affected by tillage intensity; however nutrient levels were impacted by the increasing tillage intensity. Specifically, NO3- was reduced at Tisdale and was increased at Rosthern. Phosphate levels were reduced by the high tillage intensity in Rosthern whereas, with increasing tillage, the opposite occurred at Tisdale and Central Butte. The responses were strongly influenced by site characteristics, especially soil zone, organic matter content and surface litter abundance and quality. These effects were short-term, having no long-term impact on the agricultural sustainability or health of the soil, although knowledge of litter condition and quality is agronomically beneficial in order to predict soil responses to intense tillage events. iii The second part of the study was to assess the success of grass terraces on preserving the soil health of hillslope farm plots with Oxisolic soils in southern Ethiopia. Soil erosion has a devastating impact on hillslope agriculture in Ethiopia causing severe land degradation. An adjacent terraced and unterraced hillslope was chosen and sampled, along with a second unterraced slope for comparison. These soils were analyzed for dehydrogenase, alkaline phosphatase, and urease activities, as well as total C and total N. The plots above the terraces [terraced upper and unterraced upper] had higher urease activities than the plots below [terraced lower and unterrraced lower]. The impact of a vegetative strip that had formed a terrace 20 years ago was still evident in consistently higher alkaline phosphatase, urease, and dehydrogenase activities than the other plots. Simple methods of erosion prevention on erosion prone hill-slopes indicated that vegetative strips leading to terracing have a positive effect on soil health and functionality, promoting the long-term agricultural productivity and sustainability of these landscapes.

This study considered using a relatively new method to study soil-tool wear which could drastically reduce the time and associated costs of traditional wear studies. The goal was to utilize discrete element method (DEM) simulations to recreate the results of a circular soil bin test in order to develop a relationship that could be used to predict wear under different conditions. Through the application of DEM, simulations could be used to study different materials or designs intended to result in improved wear performance.<p> Three replications of aluminum cylindrical bars were worn during 400 km of travel in a circular soil bin. Wear was quantified by measuring the change in radius of the cylinders at 18-degree intervals around their circumference. Mass data were also obtained to provide an overall average of wear occurring on the bar and to validate the radii measurements.<p> The DEM simulations were executed using EDEM software. Conditions present in the physical soil bin trials were simulated by recreating components in the soil bin and incorporating soil properties that were directly measured, using representative soil samples. Forces exerted on the bar by the soil and the relative velocities between the soil and tool were used to generate a relationship to predict wear of the bar. The wear equation was verified using a portion of the experimental data from the soil bin.<p> The wear model showed promise in predicting the amount of wear recorded in the soil bin through the application of DEM-predicted compressive forces and relative velocities between the tool and soil particles. The Archard equation for wear was modified to create a non-linear equation. Plotting the measured wear against the wear predicted from the fitted equation produced a trendline with a slope of 0.65. Although a perfect correlation would have produced a slope of 1, the model was able to predict a large portion of the wear that occurred. Refinement of the model could further be achieved with changes in the design of the geometry used in the simulation and through verification of force predictions with experimental data. Because of the variable nature of wear, additional replications of tools in the soil bin would have increased the number of data points available to create the model and reduced the impact of outlying data. With these recommended improvements, the wear model has the ability to very accurately predict the wear of a cylindrical bar.

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on December 2, 2009. Major professor: Brent G. Hallock, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Agriculture with specialization in Soil Science." "November 2009." Includes bibliographical references (p. 67-71). Also available on microfiche.

Laboratory soil columns, 0.3 m diameter $ times$ 0.7 m long, and two computer simulation models, LEACHM-N and NTRM, were used to investigate nitrate-nitrogen ($ rm NO sb{3 sp{-}}$-N) leaching in a sandy loam soil. The following treatments were studied: no-till (NT), reduced tillage (RT), and conventional tillage (CT) practices, with residue (R) and without residue (NR). Nitrogen fertilizer was applied at a rate of 180 kg/ha in granular form (experiment I), and in solution form a year later (experiment II). In both experiments, water was applied 5 times over 3 to 4 weeks duration, with each application lasting for 30 minutes. Each column received an average of 24 mm water in experiment I and 32 mm in experiment II. Soil moisture contents were measured and water for $ rm NO sb{3 sp{-}}$-N concentration determination sampled at 0.1, 0.2, 0.4, and 0.6 m depths, following each water application. / In each experiment I, higher nitrate-nitrogen concentrations ($ lbrack rm NO sb{3 sp{-}}$-N)), occurred at the 0.1 and 0.2 m soil layers in RT and CT treatments initially, but less leached to lower layers, while more $ rm NO sb{3 sp{-}}$-N leached to lower depths (below 0.4 m) in the NT treatment. In experiment II, more $ rm NO sb{3 sp{-}}$-N leached below 0.4 m in RT and CT than in NT treatments. Conventional tillage exhibited the lowest drainage rates. Tillage and residue effects were significant only at early stages (4 hours or before) at some depths of experiment I ($P<0.05$). Maximum $ lbrack rm NO sb{3 sp{-}}$-N) occurred at 0.4 m depth in all treatments. / LEACHM-N estimated more $ rm NO sb{3 sp{-}}$-N leaching below 0.4 m in RT and CT treatments than in NT treatment. The model performed poorly only immediately after fertilizer application, showing up to 50% deviation from observed data. Although LEACHM-N overpredicted $ lbrack rm NO sb{3 sp{-}}$-N) in the 0.2 m soil layers in all treatments, estimations remained within standard deviations of observed data. NTRM performed well below 0.4 m depths, but often underpredicted $ rm NO sb{3 sp{-}}$-N leaching at shallower depths. / From both the laboratory experiments and mathematical simulations it was concluded that when fertilizer is applied in granular form, no till practice is undesirable because deeper $ rm NO sb{3 sp{-}}$-N leaching (below 0.4 m) occurs. Reduced tillage may be the preferred choice in such a situation. When fertilizer is applied in solution, reduced and conventional tillage practices are undesirable because deeper $ rm NO sb{3 sp{-}}$-N leaching occurred. No till practice may be a better choice in such a case.