Effects of Organic versus Conventional Agricultural Management on Soil Quality in Skagit County, Washington

The purpose of this thesis was to investigate the soil quality of selected farms in Skagit County, Washington, to determine whether conventional farming practices have resulted in lower soil quality than organic practices. Comparative organic and conventional farms were measured for percent soil organic matter content, annelids, soil moisture, soil compaction levels, infiltration, nitrogen, phosphorus, potassium, salinity, and soil pH. The hypothesis was that within conventionally managed fields, one would find degraded soil quality as evidenced by less soil organic matter; fewer annelids; lower soil pH and salinity; lower soil moisture; lower levels of nitrogen, phosphorus, and potassium; increased compaction; and, lower water infiltration rates. Such factors would reduce the farm's ability to respond to drought conditions, allow topsoil erosion, and result in an increased loss of soil. The results showed that, in terms of soil quality, the lower soil organic matter and annelids content in conventional farms was statistically significant. Indeed, the results show that SOM and annelids are soil properties which change relatively quickly, regardless of soil type, when organic practices are introduced. Thus, these two variables may provide the strongest evidence for soil improvement when changing to organic practices. It is possible that testing for these two variables alone, may be adequate for determining and categorizing soil quality in Skagit County, and elsewhere. Regarding organic practices and lower soil quality values for other variables tested, it is possible that conversion to organic is too recent for statistically significant differences between management practices to be apparent.