Conservation tillage reduces PM10 emissions in dairy forage rotations

The San Joaquin Valley (SJV) is a United States Environmental Protection Agency (USEPA) serious non-attainment area for PM10, particulate matter with an aerodynamic diameter <10 μm. At certain times of the year, PM10 is composed mostly of soil-derived material. The correspondence of air quality violations with intense tillage activities and PM10 composition has focused attention on row crop agriculture as a potential major contributor to PM10. This two-year study compared conservation (CT) and standard tillage (ST) systems in dairy forage production to determine if, and to what extent, CT can reduce agricultural PM10. Vertical profiling methods were used to calculate PM10 emission factors for both systems at two farm locations. Test results showed CT reduced PM10 emissions by about 85% on both farms in spring 2004 and by 52% on one farm to 93% on another farm in spring 2005. PM10 reductions were mainly due to the fewer number of tillage operations in CT systems (zero or one operation compared to three to six in ST) and the higher soil water contents at which CT operations can be performed. Aside from soil moisture, degree of soil pulverization, characterized in the second year of this study by weighted mean ped diameter (WMPD) also proved to be an important determinant of PM10 emissions. The ST second disking always had a higher PM10 emission factor than the first disking despite any change in soil water content. The WMPD decreased 39% between the two diskings. Large discrepancies between PM10 emission factors measured in this study and those used for regulatory purposes in California emphasize the continued need to refine monitoring strategies under varying field conditions to improve accuracy of emission factors and to understand how soil and cropping management affect dust production.