By Andy Bary, Washington State University-Puyallup
Soil health is a function of various soil attributes (physical, chemical and biological) which respond to land management and vary in space and time (Soil Quality Institute, 1999). Soil quality or soil health has become of increased interest over the last few years. They have been studied on a number of locations in the Pacific Northwest. There is currently a large interest in soil health Nationwide. The Soil health Institute is currently measuring soil health on about 150 locations in North America. This project is in its infancy this year with sampling starting this spring. That project is measuring about 30 different soil health parameters at already existing long term research plots. Several of the sites have used biosolids as one of their treatments. The Long-Term Dryland Grain Research Site (GP-17) in Douglas County was chosen as one of the intensively sampled locations. There will be more about that project forth coming as the data is available. As we wait for that information there is much we have already learned from existing research. This site has been receiving biosolids since 1994 and receive biosolids every 4th year. Biosolids rates are low, medium and high (2, 3, and 4.5 dt/a). The site also includes a fertilized (50 lb N/a) and zero N treatments. A number of tests have already been measured that are indicators of soil health. The most recent look in 2017 shows that biosolids at all rates have increased soil carbon. Increase in soil carbon is associated with reduced run off, improved soil water storage, and improved plant productivity. In addition in 2012 soil bulk density was measured and found similar results as to the total carbon all biosolids rates were less than the fertilized or unfertilized control. Lower bulk density are related to improved water infiltration and soil aeration and in some cases improved rooting ability.
Table 1. Total soil carbon and soil bulk density. Means within a column followed by different letters are significantly different (P < 0.05) by protected LSD