Worksheet for Calculating Biosolids Application Rates in Agriculture

Dan Sullivan and Craig Cogger
Oregon State University and Washington State University-Puyallup

A paper copy of this worksheet (PNW 511) and other biosolids publications can be ordered from OSU Extension and Experiment Station Communications at http://eesc.orst.edu/agcomwebfile/edmat/. Type the key word "biosolids" in the search box.

Copies of the paper publication are also available from Washington State University Cooperative Extension and will soon be available from the University of Idaho Cooperative Extension System at http://info.ag.uidaho.edu/.

The Web version of the worksheet is updated periodically to make it more useful. You can send your suggestions for improving the worksheet to Dan Sullivan.

Worksheet

Fill your data in the yellow highlighted cells, and the calculations in the blue cells will be done for you.

The green color is for explanatory data not used directly in the calculation of the agronomic rate. In these spaces, record the soil and crop management at the field site, the processing methods used to produce biosolids, and biosolids application method. You will need this information to obtain an accurate calculation of the agronomic rate.

Don't forget to click on the Done button at the bottom of the page when you have entered all of your data into the worksheet.

Step 1. Collect Site Information

Soil and crop information:

Line No.		Your Information	Example
1.1	Soil series and texture (NRCS soil survey)		Puyallup sandy loam
1.2	Yield goal (grower, agronomist) (units/acre*)		5 tons/acre/yr
1.3	Crop rotation (grower; e.g., wheat/fallow/wheat)		perennial grass
1.4	Plant-available N needed to produce yield goal (fertilizer guide; agronomist) (lb N/acre/yr)		200

*Yield goals may be expressed as a weight (tons, lb, etc.) or as a volume (bushels).

Plant-available N provided by other sources:

Line No.		Your Calculation	Example	Units
	Pre-application testing
1.5	Nitrate-N applied in irrigation water		10	lb N/acre
1.6	Preplant nitrate-N in root zone (east of Cascades)**		—	lb N/acre
	Adjustments to typical soil N mineralization
1.7	Plowdown of cover or green manure crop**		—	lb N/acre
1.8	Previous biosolids applications (Table 1)		30	lb N/acre
1.9	Previous manure applications		—	lb N/acre
	Grower information
1.10	N applied at seeding (starter fertilizer)		—	lb N/acre

1.11	Total plant-available N from other sources (sum of lines 1.5 through 1.10)		40	lb N/acre

**Do not list here if these N sources were accounted for in the nitrogen fertilizer recommendation from a university fertilizer guide.

Step 2. Estimate the Amount of Plant-Available N Needed from Biosolids

Line No.		Your Calculation	Example	Units
2.1	Plant-available N needed to produce yield goal (from line 1.4)		200	lb N/acre
2.2	Plant-available N from other sources (from line 1.11)		40	lb N/acre
2.3	Amount of plant-available N needed from biosolids (line 2.1 – line 2.2)		160	lb N/acre

Step 3. Collect Biosolids Data

Application Information:

Line No.		Your Information	Example
3.1	Moisture content of biosolids (liquid or solid; see Table 3)		liquid
3.2	Biosolids processing method (see Table 3)		anaerobic
3.3	Method of application (surface or injected)		surface
3.4	Number of days to incorporation of biosolids		no incorporation
3.5	Expected application season		Mar. – Sept.

Laboratory Biosolids Analysis (dry weight basis):

If your biosolids analysis is on an "as is" or wet weight basis, you will need to divide your analysis by the percent solids (line 3.10) and multiply the result by 100 to convert to a dry weight basis.

Line No.		Your Calculation	Example	Units
3.6	Total Kjeldahl N (TKN) ³		50,000	mg/kg
3.7	Ammonium N ³		10,000	mg/kg
3.8	Nitrate N ¹ ³		not analyzed	mg/kg
3.9	Organic N ² (line 3.6 – line 3.7)		40,000	mg/kg
3.10	Total solids		2.5	percent

¹ Nitrate-N analysis required for composted or aerobically digested biosolids, but not for anaerobically digested biosolids.
² Organic N = total Kjeldahl N – ammonium N.
³ If your analysis is in percent see Table 6 to convert to mg/kg.

Step 4. Estimate Plant-Available N Per Dry Ton of Biosolids

Convert biosolids N analysis to lb per dry ton:

Line No.		Your Calculation	Example	Units
4.1	Total Kjeldahl N (TKN) (line 3.6 x 0.002)		100	lb N/dry ton
4.2	Ammonium N (line 3.7 x 0.002)		20	lb N/dry ton
4.3	Nitrate N (line 3.8 x 0.002)		not analyzed	lb N/dry ton
4.4	Organic N (line 4.1 – line 4.2)		80	lb N/dry ton

Estimate Inorganic N Retained:

4.5	Percent of ammonium-N retained after application (Table 2)	60	percent
4.6	Ammonium-N retained after application (line 4.2 x line 4.5/100)	12	lb N/dry ton
4.7	Calculate biosolids inorganic N retained (line 4.3 + line 4.6)	12	lb N/dry ton

Estimate Organic N Mineralized:

4.8	Percent of organic N that is plant-available in Year 1 (Table 3)		30	percent
4.9	First year plant-available organic N (line 4.4 x line 4.8/100)		24	lb N/dry ton

Plant-available N:

4.10

Estimated plant-available N
Add available inorganic N and available organic N (line 4.7 + line 4.9)

lb N/dry ton

Step 5. Calculate the Agronomic Biosolids Application Rate

Line No.		Your Calculation	Example	Units
5.1	Amount of plant-available N needed from biosolids (from line 2.3)		160	lb N/acre
5.2	Estimated plant-available N in biosolids (from line 4.10)		36	lb N/dry ton
5.3	Agronomic biosolids application rate (line 5.1/line 5.2)		4.4	dry ton/acre

Step 6. Convert to "As Is" Biosolids Basis

Desired Units		Your Calculation	Example
Gallons per acre =	(line 5.3/line 3.10) x 24,000		42,240
Acre-inches per acre =	(line 5.3/line 3.10) x 0.88		1.55
Wet tons per acre =	(line 5.3/line 3.10) x 100		176

Support for the development of this on-line worksheet was provided by the Oregon State University Extension Projects program.

Worksheet for Calculating Biosolids Application Rates in Agriculture, PNW 511-W
by Dan Sullivan and Craig Cogger
(Oregon State University and Washington State University-Puyallup)
March 2, 2000