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Biosolids Nitrogen Availability During Summer Fallow

Grant Miller
with: Dan Sullivan and Andy Bary, WSU Puyallup; Dan Sturgill, Seattle Metro;
and Mikki Kisson, O’Neill and Sons

Objective

Measure the amount of plant-available nitrogen released from biosolids (municipal sewage sludge meeting all regulatory standards for land application) during the first year after application.

Location: 15 mi. SE. of Lind, WA; 1 mi S. of Hwy 26
Annual precipitation: 10 inches
Soil: mapped as Ritzville silt loam; soil is sandier than the typical Ritzville soil.
Previous crop: winter wheat, 1993

Treatments

Check (No fertilizer)
Aqua ammonia - 45 lb N/ac with 5 lb S/ac as 12-0-0-26
Biosolids - 3, 4.5, and 6 dry ton/ac

Comments

Biosolids from the Renton wastewater treatment plant were applied with a manure spreader on 30 Nov 93. Each biosolids rate was applied to four 70 by 700 ft plots. Biosolids were incorporated the day after application by chiseling. The biosolids contained 109 lb total N and 22 lb ammonium-N per dry ton. During summer fallow, the field was disked to a depth of 4 to 7 inches on 15 Mar 94, and rodweeded about every 30 days (4 rodweedings during fallow period). Aqua ammonia was applied with an 18 inch shank spacing on 21 Apr 94. Soil samples were collected with hand probes (27 Apr 94) and with a hydraulic Giddings probe (27 Jul 94) in one foot depth increments. Fifteen soil cores (1’ depth) and 6 cores (2’ and 3’ depth) were collected from each plot.

Data

Soil N on 27 April 94 ( lb/ac). Ammonium to 1 ft, nitrate to 3 ft.

Treatment Rep 1 Rep 2 Rep 3 Rep 4 Average

Check 92 60 78 76 77a

Biosolids 6 T/ac 189 149 184 206 182b

LSD (5%) 28.5

CV 10%

Soil N on 27 July 94 ( lb/ac). Ammonium to 1 ft, nitrate to 3 ft.

Treatment Rep 1 Rep 2 Rep 3 Rep 4 Average

Check 116 82 74 91a

Biosolids 3 T/ac 203 150 158 170b

Biosolids 6 T/ac 275 251 332 286c

LSD (5%) 70.8

CV 17%

Conclusion

Available N increased during summer fallow. The amount of additional ammonium and nitrate produced by the biosolids application was equal to 16 percent of the total biosolids N applied (April) and 30 percent of the total N applied (July). One dry ton of biosolids supplied 33 lb of plant available N (July). Over 90 percent of the plant-available N measured was in the top foot of soil (April and July). We conclude that there was enough soil moisture at this site for normal plant-available nitrogen release from the biosolids. The amount of plant-available N released per dry ton of biosolids was similar to that observed at WSU research sites on irrigated cropland (Yakima Valley) and in high rainfall areas (western Washington).

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