biosolids agricultural land application

By Bill Pan and Andy Bary, Washington State University

Data mining a WSU soil vault has supported biosolids’ reputation for building soil organic matter.  A research paper recently published in Soil Science Society of America describes how repeated biosolids applications promote organic carbon accumulation, including very stable fractions that contribute to long-term carbon sequestration.   A twenty-year experiment near Waterville, WA, conducted by Andy Bary and Craig Cogger, has featured biosolids applications to a wheat field every four years.   Earlier publications reported that biosolids are able to produce comparable wheat yields to commercial fertilizer, while also improving soil chemical and biological health.  More detailed analysis of the stored soil samples from this experiment revealed high efficiency of soil carbon recovery from biosolids in this dryland wheat cropping system, and that a chemically stable fraction of soil organic matter is accumulating.    

As part of USDA-funded REACCH (Regional Approaches to Climate Change for Pacific Northwest Agriculture), our cropping systems team identified recycling organic byproducts as a best management practice for wheat farmers to help mitigate climate change by storing soil carbon and reducing commercial fertilizer N inputs.  Sally Brown at University of Washington earlier modeled with life cycle analysis that climate mitigation benefits were achievable from biosolids land applications.   Results from the soil vault suggest the rate of organic carbon and nitrogen buildup in this system is even higher than projected earlier. In addition, chemical analysis of biosolids samples used in the study indicated there may have been sufficient chemically stable organic carbon and nitrogen in the biosolids to potentially account for the buildup of soil organic matter fractions that are even resistant to decomposition by strong acids.  While the total supply of regional biosolids is insufficient to treat all of the wheat-producing soils of the inland Pacific Northwest, biosolids transport and redistribution of organic matter provides a good model for other organic byproducts like manure to address climate change and improve soil health in Washington State. 

Acknowledgement: This research was supported in part by USDA-NIFA Award #2011-68002-30191 from the USDA National Institute of Food and Agriculture.

Related publication
Pan WL, LE Port, Y. Xiao, AI Bary and CG Cogger. 2017. Soil carbon and nitrogen fractionation balances during long-term biosolids applications. Soil Science Society of America Journal (in press). Available online doi: 10.2136/sssaj2017.03.0075.