Soil water and particle size distribution influence laboratory-generated PM 10

Abstract

Management of soils to reduce the amount of PM 10 emitted during agricultural tillage operations is important for attainment of air quality standards in California's San Joaquin Valley (SJV). The purpose of this study was to improve and expand upon earlier work of predicting tillage-generated dust emissions based on soil properties. We focus on gravimetric soil water content (GWC) and soil texture. A mechanical laboratory dust generator was used to test 23 soils collected for this study. Averaged results showed PM 10 concentrations (mg m −3) increased logarithmically as GWC decreased below soil water potentials of −1500 kPa. Soils with clay contents less than about 10% by weight began to emit PM 10 at GWCs 1.5–4 times their GWC at −1500 kPa. Soils with clay contents greater than about 10% began to emit PM 10 at GWC values closer to −1500 kPa. We found no correlation between maximum PM 10 concentrations, measured at low GWC values, and the %sand, %silt, or %clay in a soil. However, there was a significant correlation between the %silt to %clay ratio and PM 10 concentrations. This not only suggests the dependence of dust emission magnitudes on the supply of particles of PM 10 size, but also the importance of clay in stabilizing aggregates and maintaining higher amounts of capillary water at lower water potentials. Based on modeled results of pooled data, PM 10 concentrations increased linearly (slope = 564) for every unit increase in the %silt to %clay ratio. However, when soils were separated into groups based on clay content, the slopes for PM 10 concentrations vs. %silt to %clay ratio were texture dependent. The slope for soils with <10% clay (slope = 727) was 3.3 times greater than for soils with >20% clay (slope = 221). Improved PM 10 emission prediction based on soil properties should improve management decisions aimed at reducing tillage-generated PM 10.