Keith E. Saxton

WIND EROSION AND FUGITIVE DUST FLUXES ON AGRICULTURAL LANDS IN THE PACIFIC NORTHWEST

With recent emphasis of agricultural wind erosion and associated dust emissions impacting downwind air quality, there is an increased need for a prediction method to estimate dust emissions and ambient particle concentrations on a wind event basis. Most current wind erosion methods predict average annual or seasonal erosion amounts, and only very approximate estimates of suspended dust emissions are available. A project in the Columbia Plateau of eastern Washington State was initiated to develop an empirical method to estimate dust emissions for this region. Field measurements, wind tunnel tests, and laboratory analyses were combined to provide an empirical wind erosion equation and a related vertical flux dust emission model. While based on measured data, the model has not been independently verified. When combined with a transport-dispersion model and calibrated, estimates of downwind particulate concentrations compared reasonably with those measured.

Wind Erosion and Its Impact on Off-site Air Quality in the Columbia Plateau — An Integrated Research Plan

With the advent of the 1990 Clean Air Act came the responsibility to monitor and control fugitive air particulates with diameters less than 10 micron (10 ¥ 10–6-m, PM10). Many urban areas, particularly in the Western United States, have experienced concentrations of these particulates which exceeded the federal health standards of this legislation a sufficient number of days that costly remedial measures have been required. In several of these cases, it has been evident that a significant amount of this material was generated by wind erosion on upwind agricultural fields, entrained in the regional air mass, and impacted downwind urban areas. There is an urgent need to better define the hazards and controls of PM10 particulate material emitted by wind erosion on agricultural lands. It is not possible with current knowledge to determine the quantity of PM10 material emitted from agricultural areas or to prescribe appropriate control methods. An extensive research and evaluation plan has been developed and initiated for the Columbia Plateau of Eastern Washington State with multi-disciplinary and multi-agency involvement.

A Predictive Model of Water Stress in Corn and Soybeans

ABSTRACT THE previously developed SPAW model for estimat-ing daily soil water and evapotranspiration using readily available climate, crop and soil data was expand-ed to include estimates of crop water stress and the effect of this stress on canopy development, plant phenology and crop grain yield. Crop yield susceptibility was represented by a bell-shaped weighting factor with peak at tasselling or flowering. A water stress index was com-puted for the growing season as an accumulative daily water stress multiplied by the daily yield susceptibility factor. Calibration of the water stress index for corn and soybeans was with data from research sites in western Iowa and central Missouri. The results showed that this daily soil water and crop water stress method is a prac-tical and accurate approach for assessing water stress ef-fects on crop yields.

Design and Aerodynamics of a Portable Wind Tunnel for Soil Erosion and Fugitive Dust Research

A portable wind tunnel was designed and built to research wind erosion of soil and simultaneous emissions of fine dust from agricultural fields. This approach allowed for time efficient, in situ measurements of erosion processes under controlled wind conditions. The tunnel had an overall length of 13 m with a working section 7.3 m long, 1.0 m wide, and 1.2 m high. Power was supplied using a 33-kW gasoline engine driving a 1.4-m industrial fan.

An equation for separating daily solar irradiation into direct and diffuse components

Abstract An equation suitable for separating daily total solar irradiation into direct and diffuse components is presented. It incorporates an easily-determined physically based coefficient which reflects the maximum clear-sky transmissivity at the study site. Data collected at Pullman, Washington State, U.S.A. were used to establish the separation equation, and it has been tested on an independent data set from Townsville, Queensland, Australia. Results of these tests indicate that this separation equation can account for more than 90% of the variation in diffuse radiation incident on a horizontal surface. Application of the separation equation for estimating daily total solar radiation incident on non-horizontal surfaces is discussed.

Irrigation Optimization Under Limited Water Supply

ABSTRACT Atwo-stage simulation/mathematical programming model was developed to determine the optimal intraseasonal allocation of irrigation water under conditions of limited water availability. The model was applied to a representative surface irrigated farm in Washington States Columbia River Basin. Results from applying the model to a series of incifeasingly severe water shortage conditions indicated a large potential for water conservation in the assumed production setting. Farm-level water supply reductions of 40% translated to about 10% decrease in economic returns. Income losses resulting from water shortages were minimized through the conjunctive management of irrigation scheduling, irrigation labor practices, and several other short-run responses to water deficits. The combination of crop water simulation and farm-level economic optimization models was shown to be a compatible merger of techniques for representing the engineering and economic irrigation environment.

Regional Prediction of Crop Water Stress by Soil Water Budgets and Climatic Demand

ABSTRACT Apreviously developed model for simulating soil water, evapotranspiration, and crop water stress for corn was tested for regional application to corn at 49 sites in two transects across the variable climatic regions of Missouri, Kansas, Iowa, and South Dakota. Ten years (1967-1976) were computed for correlation with observed corn yield, plus the near-drought year of 1977 was used for model verification. The detailed method of soil water prediction utilizing daily climatic data with crop and soil characteristics provided a sensitive estimation of crop water stress and its effect on crop yield. Specific parameters that represent crop and soil characteristics are yet sufficiently difficult to define so that each local region needs some calibration; but once a parameter set is established, water stress effects on crop yields in future years can be predicted with moderate-to-good accuracy. More experience and knowledge with the method will reduce required calibration. Even though the method is complex as compared with current applied procedures, its relatively minor cost of 1 to 2 cents/station/day (IBM 360 computer) make such an approach feasible on a broad regional basis with todays computing capability.

Predicting Wind Erodibility of Loessial Soils in the Pacific Northwest by Particle Sizing

ABSTRACT Wind tunnel tests on silty textured loessial soils throughout the Columbia Plateau of eastern Washington state and northern central Oregon were used to define soil erodibiltiy for wind erosion predictions. Aggregate and primary particle size distributions were determined by common techniques and correlated with the wind tunnel erosion values. Dry aerodynamic particle sizing by a laser method was not useful due to disaggregation caused by the method, although it verified the upper size of sieving cuts. Neither wet dispersed nor aerodynamic techniques provided useful results for discriminating among the wind tunnel erodibility of the tested soils. A combination of standard wire-mesh and sonic sieving of dry aggregates from 30 µm to 2000 µm proved most applicable for correlation to soil mass eroded during wind tunnel field trails. Separate correlations were made for silty soils that are readily suspendible and sandy soils that are largely moved by saltation. Application of these correlations to wind erosion predictions will rely on developing additional relationships with the natural wind erodibility for these same soil classes.

Optimum sorghum planting dates in western Sudan by simulated water budgets

Abstract The Soil-Plant-Air-Water (SPAW) model previously developed and tested was used to simulate soil water budgets and crop water-stress for sorghum in the dryland region of western Sudan. Limited climatic data were combined with general observations of sorghum growth and soils to provide daily water budgets at one site for 11 years. Probability distribution of computed water budget components and water-stress index resulting from simulation of nine possible planting dates for each year were used to determine the optimum planting period for minimal crop water-stress. The water budget analysis showed a distinct optimum planting period of June 20 to July 10 with planting in early July as the most likely for best production. These results agreed well with general experience. The technique will be similarly useful for other locations, for research designs of soil water management, yield forecasting, and planning and management of agricultural resources.

Agricultural wind erosion and air quality impacts: A comprehensive research program

With the passage of the 1990 Clean Air Act came the responsibility to monitor and control particulates in the size range 10 um and smaller (PM10). Many urban areas, particularly in the western U.S., have experienced concentrations of fugitive dust particulates from upwind sources that exceed the federal health standards. Often a significant amount of this material is generated upwind on agricultural fields, and then is entrained and transported in the regional air mass, thus degrading the air quality in downwind urban regions. Current technology cannot adequately quantify the fugitive dust emitted and transported from agricultural sources, nor specify adequate control methods. A comprehensive research plan recently was developed and initiated for the Columbia Plateau of eastern Washington State that involves multiple disciplines and several state and federal agencies. This research has several components: characterizing the soil, vegetation and climate in a region of 136,000 km; developing wind erosion and fugitive dust emission relationships for individual farm fields; developing and applying transportdispersion-deposition models of the region; selecting and testing farm-level control strategies; and providing public information to both the urban and farm communities for understanding the problem and developing management plans. Simultaneous receptor analyses and public health research combine to make this a comprehensive regional research effort on fugitive dust emissions and impacts.