Research Summary:
How dryland wheat responds to biosolids fertilization at eleven field sites

D.M. Sullivan, A.I. Bary, C.G. Cogger, E.A. Myhre, T.E. Shearin and T.N. Cramer
Oregon State and Washington State Universities

Materials and Methods

Experimental Locations

Central Washington and Oregon

Experimental locations

• Eleven locations over 7-yr period
• Randomized complete block design
• 3 or 4 replications per location

Location identification

• County-year of biosolids application e.g. Douglas County, 1991 is "D-91"
• Washington State (9 locations):
  • Counties: Adams (A), Douglas (D), Kittitas (K), Lincoln (L), Spokane (S)
• Oregon (2 locations):
  • Both locations in Sherman County
  • "State-year" of biosolids application, e.g. "Ore-95"

Crop: Soft-white winter wheat

• Wheat-fallow cropping system (crop every 2 yr)
• Biosolids applied during fallow (usually to stubble)

Soil

• Mostly silt-loam soils derived from loess
• Sandier texture at location S-92 and A-93
• Depth: most 4 to 6 + feet
• Shallower soil (2 to 4 feet) at location Ore-95

Biosolids and Fertilizer Treatments

Biosolids

• Dewatered (20 % solids)
• Four wastewater treatment facilities
  • Washington: Renton, Ellensburg, Spokane; Oregon: Rock Creek)
• One biosolids source per location

Agronomic biosolids rate

• Dewatered, anaerobically-digested biosolids (180 to 250 g solids/kg)
• Applied during fallow year
• Chosen application rate is the lowest rate that can be spread evenly
Application rate: 200 to 400 kg total N/ha (about 6 to 9 Mg dry solids per ha)
• The “agronomic rate” supplied 60 to 120 kg available N/ha in our wheat-fallow cropping system, as verified by soil testing for ammonium + nitrate-N

Fertilizer N

• Applied during fallow year
• Source: Ammonium nitrate (3 locations) or anhydrous/aqua ammonia (8 locations)
• Rate: 50 to 80 kg N/ha

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