Bill Schillinger, Craig Cogger, and Andy Bary, Washington State University
 
Research in Washington State has demonstrated that biosolids applications can reverse the decline in soil organic matter and improve grain yields in traditional dryland wheat production. We do not know if biosolids can produce similar benefits to the soil in conservation tillage systems.
 
To address that question, Washington State University scientists Bill Schillinger, Andy Bary, and Craig Cogger are conducting a field study to evaluate the effects of combining biosolids applications with conservation tillage on wheat production and soil quality. The study is located at the WSU Lind Dryland Research Station, in the low rainfall wheat-fallow zone of eastern Washington. The experiment began in 2011 and is planned to continue for 8 years.  As the cropping system is winter wheat-summer fallow (i.e., one crop every two years), we established two sets of plots, one with wheat harvests in even years beginning in 2012, and one with wheat harvests in odd years beginning in 2013.
 
Treatments include biosolids with traditional tillage, biosolids with conservation tillage, inorganic N and S with traditional tillage (control treatment), and inorganic N and S with conservation tillage. Biosolids are applied once every four years to the appropriate plots, while inorganic N and S is applied to the appropriate plots every crop cycle (2 years). Conservation tillage is done with an undercutter sweep implement to preserve more surface residue compared to the traditional tandem disk treatment.  The undercutter method of wheat-fallow farming is considered a best management practice for controlling wind erosion.
 
Significant findings to date include:
  1. Using the undercutter method during fallow resulted in more than 30% residue cover remaining after planting in early September of  2011, 2012, and 2013 whereas there was less than 30% surface residue remaining after planting with traditional tillage.  Thirty percent residue cover after planting is the minimum amount required by USDA-NRCS to be considered “conservation tillage”. 
  2. Biosolids treatments had more spikes (heads of grain) per unit area compared to chemical fertilizer treatments in both 2012 and 2013.  Spikes per unit area is considered the most important grain yield component for dryland wheat.  
  3. Biosolids treatments produced 3.6 bushels/acre higher grain yield than chemical fertilizer treatments in 2012, and 1.9 bushels/acre higher yield in 2013, although these differences were not statistically significant in either year.  In 2014, biolsolids (applied in 2011) and chemical fertilizer treatments again produced statistically equal grain yields. 
  4. Wheat in biosolids treatments produced more than 20% more straw than the chemical fertilizer treatments in both 2012 and 2013. The increased number of spikes per unit area in the biosolids treatments may have resulted in these large straw dry weight increases. The high straw values with biosolids are important for leaving the farmer with a good “starting point” to begin the 13-month-long fallow cycle. The increased straw levels also provide more raw material for building soil organic matter. 
  5. For plots that will be planted to winter wheat for the 2015 crop year, phosphorus content in the soil is presently significantly higher (19 versus 13 ppm) in treatments that received biolsolids in April 2012 compared to inorganic N and S. Increased straw production may be the result of phosphorus provided by the biosolids treatments. The soils at the site have marginal levels of P, and P fertilizer is typically not applied.
  6. Grain protein trended higher in biosolids treatments compared to inorganic N treatments in both 2012 and 2013.
Additional future research:
The next round of biosolids applications will begin in 2015. We will collaborate with a USDA-ARS wind erosion specialist based in Pullman, WA who will use a 60-ft-long wind tunnel machine to compare erosion from plots with and without biosolids applications. This will help measure and document potential wind erosion protection benefits observed by farmers following commercial biosolids applications.