Skagit Soil Quality Study: Raw Data

High soil quality is
tantamount to agricultural sustainability. Soil quality refers to the soil’s
ability to function as a living system in sustaining biological productivity and
promoting soil organismal health. The ­­­­­­­­­­­­­­­­­­­objective
of this research was to investigate whether differences in soil quality between
organically and conventionally farmed fields could be determined in matched
pair comparisons. The soil parameters studied were soil moisture, soil
compaction, pH, electrical conductivity, soil organic matter, and annelids.
Research sites were vegetable fields in Skagit County, Washington, a county
characterized by climate, soil, and water resources highly favorable for
vegetable and bulb production. Farm fields were matched on farming and crop history, soil type, aspect,
hydrology, climate, parent material, and relief. All soil sampling and
associated field and laboratory work was conducted in the spring of 2013.
Statistical analyses, including Cohen’s d to indicate small and medium effects,
were conducted. Data averaged for all matched pairs showed statistically
significant differences for pH (conventional fields), soil organic matter
(organic fields), and annelids (organic fields). The Cohen’s d figures
indicated a small-to-medium effect in increased soil moisture, a medium effect
in decreased compaction, and a small effect in decreased electrical
conductivity in organic compared to conventional fields. One reason for low pH
in organic fields was the use of shallow tillage resulting in stratification
with a more acidic pH in the top 30 cm of topsoil. Higher values in organic
fields for soil organic matter are indicative of several factors, including the
systematic use of organic matter (green manures, some compost) as part of a soil
fertility management regimen. The statistically significant higher levels of
SOM and annelids, although qualified, suggest a greater biological soil quality
in organic farms in relation to their conventional counterparts. Confirmation of
this effect is not surprising as the majority of the available research
suggests similar results. At the very least, the results indicate a role that
organic farm systems may play in improving biological properties of soil
quality.