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Biosolids Fertilization in Low Precipitation Dryland Cropping Systems - Summary

Biosolids are a valuable resource for dryland cropping systems. They provide many essential plant nutrients and organic matter. With the current low metal levels in biosolids, application rates are based on nitrogen. The plant-available nitrogen (N) content of biosolids is less predictable than commercial fertilizers. Because of the high pH (8 to 8.5) of anaerobically-digested biosolids, ammonium (about 25% of the total N in biosolids) can be lost as ammonia gas after biosolids application. Organic nitrogen (about 75% of the total N in biosolids) must be converted to plant-available forms (ammonium and nitrate) by soil microorganisms.

Five on-farm test locations were established in the low (10 to 14 inch) precipitation zone to measure biosolids effects on grain yield, grain quality, grain N uptake, and postharvest soil nitrate to compare biosolids with aqua or anhydrous ammonia fertilization.

Biosolids, 3 to 5 dry tons per acre; average rate: 3.6 dry tons/ac (292 lb total N/ac)
Anhydrous or aqua ammonia, 40 to 60 lb N per acre, injected
Check (no fertilizer applied)

Biosolids were produced by anaerobic digestion of wastewater solids at Renton and Spokane treatment plants. Dewatered biosolids (about 20% solids; 80% water) were applied with a manure spreader. The 3 dry ton rate is the minimum rate for accurate spreading with most manure spreaders.

Data shown in the tables is the average of 3 or 4 replications per location. Biosolids were applied to one acre plots (usually 50 by 1000 ft). Grain was harvested from the center of each plot (approximately 25 by 950 ft strips). Soil samples were collected in the fall after grain harvest in one foot depth increments. For conversion of soil nitrate test values, we assumed an average soil bulk density of 80 lb per cubic foot: soil nitrate-N (lb/ac/ft) = 3.5 * (ppm nitrate-N). For statistical analysis for average treatment effects, we treated locations as replications in a randomized complete block design.

Biosolids On-Farm Test Locations

County	Harvest Year	Annual Precip (in)	Biosolids Source	lb N/ac	dry ton/ac	Wheat Variety
Douglas	92	10.5	Renton	161	3.1	Penawawa
Douglas	93	10.5	Renton	312	3.0	Eltan
Douglas	94	10.5	Renton	433	5.1	Eltan
Lincoln	93	14.0	Spokane	296	3.7	Rely
Adams	94	11.5	Renton	258	3.0	Tres
All Locations				292	3.6

Conclusion

Biosolids produced equal (4 locations) or better (Douglas 93 location) grain yields compared to anhydrous or aqua ammonia. An application rate of 3.6 dry tons provided greater N than needed for maximum yield. This greater N availability is indicated by higher protein, lower test weight (Douglas 93 and 94 locations), and higher postharvest soil nitrate with biosolids fertilization. At the end of the first cropping cycle, an average of 10 percent of the applied N was removed by grain harvest, with another 16 percent of the applied N present as soil nitrate. The remaining N (74 % of applied) was either lost as ammonia at application, or was still present as organic N in the soil and crop residues. The distribution of nitrate in the soil profile suggested that leaching losses were low. Biosolids application rates cannot usually be reduced below 3 dry tons per acre because of spreading equipment limitations. We recommend that N fertilizer applications for the crop following a biosolids application be reduced from normal, based on soil nitrate testing

Grain yield, bu/ac

Treatment	Douglas 92	Douglas 93	Douglas 94	Lincoln 93	Adams 94	Average
Check	13.1	71.3	37.9	49.7	46.1	43.6a
Anhydrous ammonia	17.5	76.7	57.0	52.0	51.2	50.9b
Biosolids	17.3	89.9	56.4	50.9	55.0	53.9b
LSD (5%)						7.2
CV						10%

Grain protein, percent

Treatment	Douglas 92	Douglas 93	Douglas 94	Lincoln 93	Adams 94	Average
Check	15.8	10.4	8.1	10.2	7.7	10.4a
Anhydrous ammonia	16.4	11.6	9.9	10.6	8.3	11.4a
Biosolids	17.0	14.7	14.4	10.4	11.4	13.6b
LSD (5%)						1.9
CV						11%

Grain test weight, percent

Treatment	Douglas 92	Douglas 93	Douglas 94	Lincoln 93	Adams 94	Average
Check	57.9	60.3	58.6	59.3	60.5	59.3a
Anhydrous ammonia	56.6	60.9	59.8	59.1	60.7	59.4a
Biosolids	56.2	57.6	57.2	58.6	61.1	58.1a
LSD (5%)						1.3
CV						1.5%

Grain N uptake, lb N/ac

Treatment	Douglas 92	Douglas 93	Douglas 94	Lincoln 93	Adams 94	Average
Check	20.4	77.7	31.4	52.1	37.4	43.8a
Anhydrous ammonia	28.0	94.0	59.2	56.8	45.0	56.6ab
Biosolids	28.9	132.1	80.6	53.8	66.9	72.5b
LSD (5%)						18.1
CV						22%

Postharvest soil nitrate-N, lb\ac

Treatment	Douglas 92	Douglas 93	Douglas 94	Lincoln 93	Adams 94	Average
	3 ft	4 ft	4 ft	4 ft	3 ft
Check	39	28	24	29	19	27.9a
Anhydrous ammonia	43	25	21	59	22	34.0a
Biosolids	68	56	74	126	83	81.3b
LSD (5%)						22.0
CV						32%

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU