biosolids in dryland wheat

By Dan Sullivan, Oregon State University

The OSU Extension Publishing unit will release a new publication by Dan Sullivan, Craig Cogger, and Andy Bary later this year.  This publication reviews the long-term effects of biosolids applications on soil health in dryland cropping systems east of the Cascades in Washington and Oregon. Findings reported here come from field trials that have continued for more than ten years.  Other Pacific Northwest Extension biosolids publications emphasize short-term outcomes of biosolids applications, especially the amount of plant-available N provided for the first crop following a biosolids application.  

Major long-term findings are:

  • Biosolids increase soil organic matter. Biosolids increased soil organic matter by more than 50% in the top 4 to 6 inches of soil as compared to a no-biosolids control.
  • Biosolids application enriches the supply of immobile nutrients (e.g. P, Zn) in the top six inches of the soil. Best use of these nutrients from biosolids is achieved when biosolids are applied infrequently to many fields, rather than frequently to a few fields.
  • The combination of increased soil organic matter, increased soil nutrients, and improved soil physical properties following biosolids application can sometimes produce higher cereal grain yields than fertilization with inorganic N and S. Grain yield in a long-term Douglas County, WA trial averaged 15% greater with biosolids compared to anhydrous ammonia.
  • Soil salinity is indicated by EC, an electrical conductivity measurement. Soil salinity has remained low in soils despite repeated biosolids applications.  
wheat application
Biosolids application to dryland wheat.  Photos courtesy of Natural Selection Farms.






Biosolids publications from the PNW team are found at:  

Other Publications

Fertilizing with manure and other organic amendments

Fertilizing with Biosolids

Worksheet for Calculating Biosolids Application Rates in Agriculture