Winter 2004
Soil sampling requirements for manure management plans
by Jeremy Klatt, Iowa Department of Natural Resources
The DNR’s manure management plan (MMP) rules were recently revised to include the phosphorus (P) Index as required by state law. The P Index considers factors such as soil P, erosion and location of the field to estimate the risk of P delivery from fields to surface waters. This article explains the minimum requirements that must be met when taking soil samples for a P Index based MMP.
The soil sampling depth and analysis methods needed to run the P index are those that are recommended for crop production in Iowa. Therefore, the samples taken for the P Index can also be used for making nutrient and lime recommendations.
Sampling Method
Soil samples can be taken according to any credible
sampling method. For instance, grid sampling, sampling
by soil type or elevation, or sampling by designated
management zones within a field. Two good sources of
soil sampling information are: Iowa State University
Extension publication PM 287 Take a good soil sample to help
make good decisions available on-line at:
www.extension.iastate.edu/Publications/PM287.pdf
NCR-13
Report 348 Soil Sampling for Variable-Rate Fertilizer and Lime Application
available on-line at: www.extension.umn.edu/distribution/cropsystems/DC7647.html
Collecting a soil core for soil sampling requirements.
Minimum Sampling Requirements
Regardless of what sampling method is used to take the
samples, there are minimum requirements that must be
met.
- Samples must be analyzed for P and pH once every 4 years (the P Index and MMP must be updated with the new soil samples every 4 years)
- Each soil sample can represent no more than 10 acres. For fields 15 acres or less, only one sample is necessary.
- Each sample must be a composite of 10 cores taken at the depth of 0-6 inches.
Using Existing Soil Samples
Soil samples can be used for the plan if they
are 4 years old or less and meet the above
requirements. Therefore, producers who need
to submit a P Index MMP update in two or
four years could plan ahead and begin thinking
about soil sampling.
For producers who must submit an original plan now, existing soil samples that do not meet the above requirements can be used for the original MMP, if they are four years old or less. In this case, soil samples that do meet the requirements must be taken no more than one year after the MMP is approved.
Use Phosphorus-Based Rates to Reduce Soil-
Sampling Requirements
One way to reduce the soil sampling requirements
associated with the MMP is to apply
manure at P-based rates. If P-based application
rates are used between soil sampling
periods, soil sampling can be reduced to 1
sample per 20 acres for fields with a Very Low,
Low, or Medium P Index. So while samples
must initially be taken at one sample per 10
acres for all fields, if P-based application rates
are adopted after the soil sampling, the next
soil samples taken can be reduced to one
sample per 20 acres.
A P-based application rate replaces the P that is removed from the field with harvest or is based on a P soil test recommendation. Because up to four years of P removal can be applied in a single application (if the N requirement of the crop is not exceeded), P-based application rates may not be much different than N-based rates. When developing a P-based manure plan, not applying to the same fields every year is often more important than the actual application rate.
Reducing the P concentration of the manure (e.g. with phytase) will also make a P-based manure plan more achievable.
Soil Laboratory Analysis
Soil samples must be analyzed by a lab enrolled in the
Iowa Department of Agriculture and Land Stewardship
soil testing certification program. A list of certified soil
testing labs can be found at http://www.agriculture.state.ia.us/certlabs.htm
The Bray P1 soil test method should not be used if the pH of the soil is greater than 7.4, as this test does not provide an accurate measurement of available soil P under these conditions. If the Bray P1 test is used and the pH is greater than 7.4 in one or two samples in a field, do not include these samples in the field average for the P Index. If the majority of samples have a pH greater than 7.4, use the Olsen or Mehlich-3 soil test when samples are taken again. For moreinformation, Iowa State University has a soil fertility Web site that includes information about soil sampling at extension.agron.iastate.edu/soilfertility/.
Who needs an MMP? Confinement feeding operations (totally roofed) with an animal unit capacity of more than 500 animal units, i.e., 1250 finishing swine. When submitting an “original” MMP for a new or expanding operation, a P Index-based plan is needed when the plan is submitted. For those who submitted an MMP prior to April 1, 2002, the P Index will be due with the first update after Aug. 25, 2008. For those who submitted their original MMP between April 1, 2002 and Oct, 25, 2004, the P Index will be due with the first update after Aug. 25, 2006. |
If you have questions about the requirements contact your regional DNR field office. Manchester (563) 927-2640 |
