EM 8646 • February 1996 75¢
NUTRIENT MANAGEMENT FOR DAIRY PRODUCTION
Assessing your manure management for water quality risk M. Gamroth and J. Moore
N
utrients and microorganisms in manure can cause water quality problems. When you collect, handle, and land spread manure, this material can get into surface or groundwater supplies.
The level of risk depends on many factors. You can control some of these factors, while others, such as weather, are beyond your control. However, you generally can predict weather trends, and can use this information to manage storage facilities and spreading activities to reduce risk.
Rating your risk The tables on pages 2–3 identify several factors involved in managing manure and assign a risk value to each. These tables are not designed to be an absolute scale; rather, they identify areas of concern and assign a relative risk to each.
Mike Gamroth, Extension dairy specialist, and Jim Moore, Extension agricultural engineer; Oregon State University.
For each category, risk values of 1 to 4 are assigned, with 1 representing the lowest risk and 4 the highest. For each item, find the description that best fits your operation. Then fill in your score in the right-hand column. Begin with your analysis of the receiving site (Table 1). Your capability to handle the manure and wastewater also affects the risk potential of your manure handling system. Next, evaluate your facilities and equipment (Table 2) and your nutrient management (Table 3).
Table 1.—Land Receiving Site Low Risk
High Risk
Risk Score
1
2
3
4
Season when spreading
summer
spring
fall
winter
Ground slope of receiving site
less than 5%
6 to 10%
11 to 15%
greater than 15%
Score
Distance to surface water If rainfall in your area is: more than 50"/year 30" to 50"/year
And distance from receiving site to surface water is: Over 300' 150 to 300' 75 to 150' Over 200' 100 to 200' 50 to 100'
under 75' under 50'
Over 100'
50 to 100'
25 to 50'
under 25'
Crop grown or field surface
growing crop
crop residue
seasonal cropping
fallow ground
Soil type
loam
clay loam
sandy loam
sand or clay
Application with drain tile flow
none
yes, but recycled
yes, drains capped
yes, drains open
Depth to groundwater
more than 50'
50 to 15'
15 to 5'
less than 5'
Climate region
eastern Oregon
Willamette Valley
coastal
—
less than 30"/year
Total
Table 2.—Facilities and Equipment Low Risk
High Risk
Risk score
1
2
3
4
Application method
injection
tanker
traveling big gun
stationary big gun
Solids storage structure
curbed and covered
covered
curbed
uncontrolled
Open lots
none used
2 dikes— above and below
1 dike—either above or below
uncontrolled runoff
Lot maintenance (cleaning) and season used
4 times/year summer only
3 times/year used when dry
2 times/year used when wet
1 time/year used most of year
Total storage capacity If rainfall in your area is: more than 50"/year
And storage capacity is (in number of months' production that can be stored): 6 months 4 months 2 months less than 2 months
30" to 50"/year less than 30"/year
4 months 2 months
3 months 1 month
2 months —
1 month less than 1 week
Overall maintenance
regular, monthly
quarterly
annually
only when broken
Clean water control
control all
roof gutters
some curbs
little or none
Total
Score
Table 3.—Nutrient Management Low Risk
High Risk
Risk score
1
2
3
4
Determine manure nutrient values
analysis obtained
use book value
uniform application empty storage
Determine application required
crop or soil test
recommended or book value
best estimate
not considered
Calibrate application rate
measure field application
book value for equipment
best estimate
no calibration
Nutrient balance
apply to most limiting nutrient
apply to meet N requirement
estimate and apply
empty storage
Score
Total
Reducing your risk
For further reading
After evaluating your facility and practices, review the results. If you have any risk value of 4, take a closer look at this item. Can you do anything within reason to reduce the risk? Receiving site. If your land receiving site’s total score is greater than 24, try to identify ways to reduce the risk of spreading manure. For example, although you can’t change the soil type or climate, you can increase the width of the buffer strip between the surface water and the spreading site, or you can spread on the steeper ground only during the summer. A good manager can make these choices. Facilities and equipment. Review any risk values of 4. If your total risk value is greater than 21, try to improve some part of your system to reduce the risk. Nutrient management. Your total score should be no more than 12. Again, any 4s should prompt a serious review. This section suggests many ways to lessen your risk. Simply using nutrient and soil analysis and calculating application rates can reduce your risk sharply. Most of the factors that influence the movement of manure to surface and groundwater are management related. Therefore, you can change your score with little or no financial investment. You decide how to manage your livestock manure and how your operation will influence water quality.
Calculating the fertilizer value of manure from livestock operations, EC 1094, by J. Moore and M. Gamroth (Corvallis, Oregon State University, reprinted 1993). $1.00 Dairy manure as a fertilizer source, EM 8586, by J. Hart, M. Gangwer, M. Graham, and E. Marx (Corvallis, Oregon State University, reprinted 1996). 75¢ How to take a soil sample. . . and why, EC 628, by J. Hart (Corvallis, Oregon State University, revised 1995). No charge Managing dairy grazing for the most efficient yields, EM 8412, by L. Cannon, M. Gamroth, and P. Ballerstedt (Corvallis, Oregon State University, reprinted 1993). 50¢ Manure management practices to reduce water pollution, FS 281, by J. Moore and T. Willrich (Corvallis, Oregon State University, reprinted 1993). No charge Using constructed wetlands to improve water quality, EC 1408, by J. Moore (Corvallis, Oregon State University, reprinted 1993). 75¢ To order copies of the above publications, or additional copies of this publication, send the publication’s complete title and series number, along with a check or money order for the amount listed, to: Publications Orders Agricultural Communications Oregon State University Administrative Services A422 Corvallis, OR 97331-2119 Fax: 541-737-0817 We offer discounts on orders of 100 or more copies of a single title. Please call 541-737-2513 for price quotes. You may order up to six no-charge publications without charge. If you request seven or more no-charge publications, include 25 cents for each publication beyond six.
This publication was produced and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Extension work is a cooperative program of Oregon State University, the U.S. Department of Agriculture, and Oregon counties. Oregon State University Extension Service offers educational programs, activities, and materials—without regard to race, color, religion, sex, sexual orientation, national origin, age, marital status, disability, and disabled veteran or Vietnam-era veteran status—as required by Title VI of the Civil Rights Act of 1964, Title IX of the Education Amendments of 1972, and Section 504 of the Rehabilitation Act of 1973. Oregon State University Extension Service is an Equal Opportunity Employer.