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Effect of Biosolids Application on Soil Quality

Ron Jirava
with David Granatstein, Ann Kennedy, Astrid Andersen

Objective

To determine what, if any, measurable impacts a single application of biosolids has on soil quality and erosion potential on dryland grain fields.

Location: west of Ritzville, WA (Adams Co.)
Annual precipitation: 11.5 inches
Soil: Ritzville silt loam
Rotation: Canola 1990, fallow 1991, winter wheat 1992, fallow 1993

Treatments

Check (no fertilizer)
Aqua ammonia (50 lb N/ac)
3, 6, and 9 dry tons/ac biosolids

Comments

This project consisted of measuring a number of physical, chemical, and microbial parameters of soil quality on plots already established (see other report from Ron Jirava). Green cover was measured with a residue rope in November 1993. Infiltration was estimated by a measurement of initial absorption with a single-ring infiltrometer. The results are reported as the number of minutes required for infiltration of a ponded inch of water. Straw samples were collected just prior to harvest in July. Soil samples (0-4" depth) were collected in April and August for chemical and microbial analysis.

Data

NS=not statistically significant
	Green	Infiltration Rate				Organic
Treatment	Cover %	Apr 94 min/in	Aug 94 min/in	Straw lb/ac	Straw: Grain	Matter %	pH	P ppm	Zn ppm
Check	33	11.3	6.3	4669a	1.3	1.6a	6.1a	22.3a	0.9a
NH4	32	8.7	7.4	5812ab	1.4	1.6a	6.1a	20.1a	0.7a
3T biosolids	35	11.8	6.4	6697b	1.4	1.8b	5.5b	47.5b	3.4b
6T biosolids	34	8.1	6.0	6267b	1.3	2.3c	5.2c	77.1c	7.2c
9T biosolids	29	11.2	6.4	6891b	1.4	2.4c	5.2c	98.6cd	9.0c
LSD (5%)	NS	NS	NS	1432	NS	0.17	0.2	17.57	1.92
CV %	5	67	31	15	9	6	2	21	30

Conclusion

Overall, we were surprised to find measurable changes in soil organic matter which is generally slow to change. The reduction in pH with increasing biosolids rate is probably due to the sulfur and nitrogen oxidation and the increase in soluble salts. Also, biosolids tended to suppress the microbial populations (data not shown), perhaps due to the same cause. Levels of both P and Zn were elevated by biosolids, but a single agronomic application (3-4 T/ac) should not lead to any problems with these elements and would supply adequate P and Zn where deficiencies exist.

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