IMMAG Updates

August 2015

Welcome to the monthly update for the Iowa Manure Management Action Group (IMMAG) Web site. This update is provided as a service to inform you about changes made to the IMMAG Web Page or items of interest dealing with manure management and air quality from animal feeding operations. If you wish to subscribe to this mailing please click here. You may also view this update with direct links on the CURRENT NEWS site on IMMAG.

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Manure: a complete, but not balanced fertilizer

Iowa DNR Spill Number
Iowa DNR Spill Number
Did you catch that the Iowa DNR spill number changed?  Make sure you that you update your phone to have the correct number this manure application season. The new number is: 515-725-8694.

Apply manure now or later?
(Written for the September 2015 Wallace’s Farmer)
Angela Rieck-Hinz, Iowa State University, Extension Field Agronomist

photoOne of the most frequent questions asked this time of year is "what do you think about putting on manure now {August/September}"? The response is fairly simple, "what do you want to achieve with manure application"?

Liquid Swine Manure
Liquid swine manure (LSM), is a source of manure where the nitrogen form is primarily ammonium-N. Ammonium-N is positively charged and thus attracted to negatively charged soil particles, consequently not available for losses such as leaching. However, this source of manure is very similar to high ammonium-N content fertilizer such as anhydrous ammonia and is subject to the same processes for nitrogen loss once it is converted to nitrate-N. If your goal is to use liquid swine manure as a nitrogen fertilizer source for corn the following year, then your primary objective would be to wait as long as possible in the fall to apply this manure source. As soil temperatures cool, microbial processes slow, and the conversion of ammonium-N to nitrate-N is also slowed down, thereby preventing losses of N as nitrate, primarily through leaching. Nitrate-N can also be lost through denitrification if soils become saturated. We saw this happen in 2014 when we had excessive rainfall and saturated soils in June.

Results of a two-year study in Minnesota showed when manure was applied in early September, corn yields averaged 10 bu./ac less than when manure was applied in October/November. Similar studies showed that soil nitrate concentrations in June of the following year were much less in the plots where liquid swine manure had been applied in August and September versus the November application date. (Hernandez, Conversion to nitrate is dependent of soil temperature and moisture, leaching is dependent on rainfall. The earlier the manure is applied, the more rapid conversion takes place, the greater the time available to lose N due to leaching prior to when the corn crop can access the N.

Incorporation and injection also slow gaseous losses of N by volatilization as the manure has time to react with the soil. Losses of phosphorus (P) and potassium (K) should be negligible if manure is injected, whereas if liquid swine manure is surface-applied losses can occur if water flows across the surface or if erosion occurs.

Solid and Bedded-Manure
Solid and bedded-manures have a higher concentration of N as organic N. This N must mineralize, or breakdown into inorganic N forms which are available to the plant. The process of mineralization is increased in warm, moist soil conditions. We often see the impact of residual N as these manures continue to slowly breakdown over time, often years. Application of this type of manure in early fall would allow more time for mineralization, but since most of these manure sources are surface-applied, we also have to consider the impact of N losses to the atmosphere and the duration of time this manure is exposed to potential losses from runoff.

If You Have to Apply Early
There are many reasons why manure is applied early in the fall. Sometimes manure storage is full, often we have longer periods of dry weather leading to good soil conditions for application, more time is available in the fall versus spring when we concentrate on planting crops. If you have to apply manure, especially liquid swine manure, early in the fall, consider 1) only applying enough to alleviate storage concerns, 2) applying only a half rate so you can apply the remaining rate of N in the spring- as commercial fertilizer or manure and 3) incorporate or inject manure appropriately to maintain the value of the P and K in the manure.

Update on DNR Inspections for the EPA Animal Feeding Work Plan

photoAs you may remember the Iowa DRN entered into a Work Plan Agreement with the EPA and just recently completed the second year of the five-year agreement. "Our biggest effort is to complete the required 8,582 inspections, working to identify any hog, cattle, dairy or other operations that need National Pollutant Discharge Elimination System (NPDES) permits," said Barb Lynch, chief of DNR’s field services and compliance. "We agreed to complete about 20 percent of the inspections each year. DNR staff have completed 41% of the required animal feeding operation inspections thus far.

The updated progress report on the work plan is available at under the EPA/DNR Workplan heading on the left side of the screen. In the report the Iowa DNR discuss what they are doing to meet each objective, including compliance evaluation and inspections of AFOs that are CAFOs. Barb Lynch stated "Since the majority of larger facilities in Iowa are confinements, with animals housed under a roof and state law requiring manure containment, most facilities we inspect do not have problems with manure runoff. We’ve worked to ensure those that do have problems receive the appropriate enforcement actions, some of which result in new NPDES permits."

Ongoing work plan efforts include enforcement actions, which are taken as needed, identifying previously unknown animal feeding operations and completing annual inspections. For more information on the inspection process check out What to Expect when DNR Inspects.

Corn Silage and Cover Crops

photoWhen we harvest corn as silage from the field, we are removing almost the entire plant from the field. This leaves very little crop residue remaining on the surface and leads to a soil surface that is less protected and more vulnerable to erosion. Often times these fields are also used for manure application. As the silage harvest removed much of the organic residue, applying manure provides an opportunity to add some organic material to the soil, some of which might eventually become stable soil organic matter. However, as there is less surface residue the manure nutrients can be susceptible to washing away if the manure isn’t injected or immediately incorporated.

The good news is that planting cover crops onto fields that were used for corn silage offers and easier entry point for trying out cover crops in your farming system. As corn silage is harvested earlier than corn grain or soybean, it would normally mean leaving an uncovered soil surface exposed to rain and runoff longer than in other cropping systems, creating more opportunity for erosion. However, the earlier harvest date offers the opportunity for earlier planting of a cover crop and more time for it to grow and establish in the fall to provide soil coverage and nitrogen cycling to protect or soils from erosion and potential nutrient leaching.

For more information on cover crops and considerations for getting started check out the ICM news article by Mark Licht and Tom Kaspar.


Fall manure application season is approaching, are you certified? Just a reminder that if you are in the business of applying manure (a commercial manure applicator) or have more than 500 animal units and apply manure from your  farm (a confinement site applicator) you must complete your annual manure application certification training. You can get certification by: 1) contacting your County Extension Office to make an appointment to watch the appropriate training video; or 2) contacting your local DNR field office to schedule an appointment to take the certification exam. All certification requirements must be met prior to applying manure. Final touches to the on-line training system are occurring and release is expected soon.


The IMMAG Events page is a compilation of manure management related events. Please check the events page often for new listings.

Land Application Methods of Animal Manure and Potential Environmental Impacts: The USDA Natural Resources Conservation Service Science and National Technology Support Centers will be hosting a webinar on September 22nd at 1 PM on Land Application Methods of Animal Manures and Potential Environmental Impacts. Pre-registration is not required. For more information on this webinar click here.


Angie Rieck-Hinz
(515) 231-2830
Twitter: @iowamanure

Dan Andersen
(515) 294-4210
Twitter: @DrManure

Iowa Manure Management Action Group

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