Biosolids and Conservation Tillage: Long-Term Effects on Grain and Straw Yield of Dryland Wheat.

Biosolids and Conservation Tillage: Long-term Effects on Grain and Straw Yield of Dryland Wheat

William F. Schillinger, Andy I. Bary, and Craig G. Cogger

Department of Crop and Soils Sciences, Washington State University, Pullman, WA 99164

Biosolids produced from municipal wastewater treatment plants are applied to many agricultural fields around the world as a source of nitrogen, phosphorus, and other plant nutrients. Biosolids also provide stable soil organic carbon (SOC) and, therefore, can replenish some of the SOC lost to oxidation and wind erosion during the past 135 years of dryland farming in the wheat-fallow region of the Pacific Northwest. An 8-year biosolids field experiment was initiated at Lind, WA in April 2011. We used a split-block experimental design with tillage method (either traditional double disk or conservation undercutter) for main-plot treatments and sub-plot treatments were fertilizer type (either chemical fertilizer or biosolids). There are two sets of plots to allow for data collection every year in the 2-year wheat-fallow rotation. Biosolids were applied with a manure spreader at a rate of 2.8 dry tons/acre to meet the nutrient requirements for two winter wheat crop years (2012-2015). Biosolids were reapplied to both sets of plots at the same rate for the 2016-2019 crop years. The chemical fertilizer treatment receives 50 lbs N and 10 lbs S/acre as aqua + thiosol for every wheat crop. Results from the first five years show equal winter wheat grain yield between tillage treatment and fertilizer treatment combinations. More spikes were produced with biosolids, but this was offset by greater kernel weight in the chemical fertilizer treatment. These yield component differences primarily occur during the first crop after biosolids application when relatively more nitrogen is released compared to the second crop cycle. Significantly more wheat straw is produced with biosolids compared to chemical fertilizer. There have been no differences to date in any of the yield components or in straw production between the tillage treatments. However, undercutter primary tillage retains significantly (p<0.001) more surface residue through the fallow cycle compared to double disk primary tillage. Data show that use of biosolids combined with low-soil-disturbance conservation tillage is an agronomically sound practice for dryland wheat production.