Thursday, November 20, 2014

Winter Manure Application Tips

Challenging weather conditions are causing some tough manure management decisions. When injection/incorporation is not an option, surface application should be considered. However, surface application can result in additional nitrogen loss so application rate adjustments may be appropriate. Surface application on frozen or snow-covered ground pose additional runoff risks. Based on potential nutrient losses and water quality impacts, winter manure application is not recommended. However, if you do need to apply manure yet this fall or winter because of limited available storage capacity, there are several things to consider to minimize nutrient loses and water quality impacts.

Best management practices for winter manure application include applying to level ground and where soil erosion is controlled. If you do need to apply, timing and weather conditions are two of the most important factors affecting the amount of manure nutrient we lose.  Nutrient loss requires something to move the manure nutrients from the field to a water body; this is usually either snowmelt or a rainfall event onto the frozen soil.  If these events are small, nutrient losses tend to be low; if it is a larger runoff event then nutrient losses are higher. In general, the more time that passes between the manure application and the first runoff event, the less risk of environmental impact from nutrient transport. This means watching the weather forecast and avoiding manure application for a few days before anticipated snowmelts or rainfalls can make a big difference in limiting manure nutrient loss.

The other thing to remember is that the amount of snow in the field is a critical component in how much runoff will occur. Although it may seem counter intuitive, often times fields with lots of residues will tend to accumulate deeper amounts of snow. Research by Jeff Lorimor showed that runoff losses where higher from standing corn stubble than from soybean stubble, which they attributed to the deeper snow cover in the cornfield as compared to the soybean field. Additional recommendations include incorporating the manure when you can, avoiding areas of concentrated flow such as waterways, ditches, or similar areas,  using setbacks from sensitive areas like stream banks, sinkholes, and similar, and if possible avoiding application near areas that drain to surface tile inlets. If these areas can’t be avoided add protection around drainage tile intakes to prevent entry by manure or runoff water.
There are a few other legal requirements to keep in mind. Most importantly, follow the required separation distances (available at, make sure to update your manure management plan to reflect surface application rates, and if your Master Matrix said you’d use injection or incorporation contact Iowa DNR before applying to get written permission to surface apply. Additionally if you have an NPDES permit or comprehensive nutrient management plan, make sure you know what’s in them and follow them accordingly. Finally, keep records of the rate, date, method of application, field, and other application precautions taken when applying the manure.

Iowa’s restrictions on application to frozen or snow covered ground will be in effect this winter for confinement operations with more than 500 animal units. Iowa law prohibits liquid manure application from these larger operations between Dec. 21 and April 1 if the ground is snow-covered, unless manure can be properly injected or incorporated or an emergency exemption is granted. Snow-covered ground is defined as soil having one inch or more of snow cover or one-half inch or more of ice cover. Also, once the calendar reaches Feb. 1 confinement producers with 500 or more animal units are limited to emergencies only for applying liquid manure on frozen ground unless the manure is injected or incorporated. A press release from the Iowa DNR at provides additional clarification of these requirements.

If winter manure applications are not avoidable,
  • Take into account soil and weather conditions
  • Avoid applying before a snowmelt or rainfall event
  • Apply to areas of level ground and where soil erosion is controlled
  • Apply to areas with less snow cover
  • Follow appropriate setback distances
  • Update your Manure Management plan to reflect surface application rates and if subject to Master Matrix requirements for injection or incorporation get approval before surface applying
Stay safe and happy hauling,

Monday, November 17, 2014

Commercial Manure Applicators in Iowa - The Manure Business

As you may be aware Iowa has a Manure Applicator Certification Program that is mandatory for all commercial manure applicators (businesses that are paid to  transport and haul manure) and confinement site applicators (farmers who apply their own manure and have more than 500 animal units raised in confinement buildings). This is an annual training where attendees learn about safety aspects of handling, transporting, and land applying manure, how to best utilize their manure resources, and how to minimize the impacts that manures can have on the environment.

As I’ve mentioned in a previous post, Iowa is number 1 in both pork and layer production, and this leads to lots of manure; somewhere around 8.6 billion gallons of liquid/slurry manure and another 6 million tons of solid manure. Although this may sound like a lot, crop production in Iowa has plenty of capacity to utilize all these nutrients (check out How much manure is there in Iowa at to get the scoop). Using these resources is just a question of getting the manure to the right place at the right time, that’s where our commercial manure applicators come in. In 2014 we had over 600 business certified as commercial manure applicators representing over 90 counties in Iowa and six of the surrounding states.

A recent survey of these businesses suggests that our commercial manure applicators are applying more than 3 billion gallons of our liquid/slurry manure, or at least 30% and over 1.5 million tons of solid manure or at least 25% of the solid manure in Iowa. With an average price of about $0.02 per gallon of slurry applied or $6 per ton applied that means these companies are doing about $70 million worth of business annually, while moving and applying the equivalent of about $250 million worth of fertilizer value!

As you can see, the business of manure is booming and as a result, our applicators are doing what they can to ensure their customers are getting the most from their manures while protecting the environment. This might include incorporating the latest technology to get the manure out to the field faster, better control how over how it’s getting in the ground and how well its covered, or even better documenting when, where, and how much as applied at the field scale level by using gps mapping technologies.

Wednesday, November 12, 2014

Soil Structure - Tillage, no-till, and that elusive "tilth"

Well, as you might be able to tell from the title, this is an article on soils, not manure. What's up with that? Well, the discussion of soil structure in relation to tillage and no-till will focus on what it means for us in terms of our manure management and utilization decisions, and how it can impact nutrient export from our fields. This week we are focusing on basics, so hopefully in the future we can chat about them in a bit more detail and what we can do to build our soil's tilth and manure's role in that.
Soils can retain water for substantial periods of time. Despite the incessant pull of gravity, water entering the soil surface by rainfall or irrigation stays in the upper zone long enough for plant roots to extract what they need to survive. Water is held in such a manner that under normal conditions gases can also move through air spaces, allowing oxygen to reach plant roots and maintaining aerobic conditions. While doing all this it can hold and eventually release some crop nutrients, holds our plants in place, and helps in the breakdown of old organic residues. In this way, soil is much more than just a water storage reservoir, it is an ideal growth medium for plants.
The two most important characteristics of the soil water phase are the amount of water in a given amount of soil and the forces holding water in the soil. Many processes (gas exchange with the atmosphere, diffusion of nutrients to plant roots, soil temperature, microbial activity) are controlled by the amount of water in the soil, while others (efficiency of water absorption by plant roots, amount of drainage occurring, and the extend of movement of water and solutes) are influenced by the forces exerted on water.

Figure 1. Recently tilled soil, not it has fluffy aggregates.

Figure 2. Tilled soil after it is consolidated and crusted after several rainfalls.
Above you can see two different pictures of soils and soil pores.  The photo on top (figure 1) shows a field that has been recently tilled. In this case you can see that the soil is fluffy and pores are well connected, this allows water to more easily move through the soil. You might also note that the tillage has reduced the size of the soil aggregates. This means that if runoff was to occur these particles may be susceptible to erosion since they are smaller and not stuck together. This is in contrast to the soil on the bottom (figure 2). This soil is what a tilled soil may look like after a few rainfall events. You can see the surface aggregates have broken apart from the rainwater crashing on them and a crust has developed. This crust makes a layer where it is more difficult for water to enter the soil which may promote more soil runoff. You can also see that the soil is more consolidated with generally smaller pores.

Thinking about your crop production fields, this might give you some insight into why maintaining surface residue can do a lot to reduce your erosion. The soil particles at the surface are no longer subjected to the pounding forces of the raindrops. Instead, the residue can protect the soil aggregates. This keeps the soil particles bigger and less available for transport in runoff water and also reduces the opportunity for the soil to form a crust since the aggregates weren't broken apart and reformed in a continuous layer.

Take home message - the condition of the soil plays a key role in its ability to retain water and for water to move through the soil, all pores and aggregates are not created equal, and the method we use to apply our manure and how it is protected from these aggregates plays a key role in how manure nutrients can move through soil.

Monday, November 10, 2014

Delayed Harvest and Manure Application – What does it mean?

The challenging weather conditions of the past summer led to slower crop development, sluggish harvest, and delayed manure application this fall. Winter arrived early as snow and bitter cold weather gripped the state by mid-November bring freezing temperatures and frozen fields. With freezing temperatures occurring, it is essential to consider the impact weather has on manure management on the farm.

“If you were unable to get manure applied this fall, or didn’t get as much applied as you normally do, it is essential to consider the impact it will have on manure management on your farm this winter,” says Dan Andersen, an Iowa State University Extension ag and biosystems engineer. “It’s especially important for farmers to ensure that adequate storage for manure is available for winter months.”

He noted that it is crucial for farmers to get their storages pumped down so that they have adequate capacity to make it through critical storage periods, such as winter. “Confinement feeding operations must retain all manures produced by the farm during periods between land applications,” Andersen said.

Manure agitation and pumping into a tanker wagon.

According to state law, all manure must be applied in a manner that does not cause surface or groundwater pollution. No matter the time of year, manure application requires adhering to setback distances as a means to minimize environmental impacts. Manure that is not injected or incorporated into the soil on the date of application must be applied at least 200 feet from a creek, well or other water body. High quality waters, listed on the Iowa Department of Natural Resource’s website at, require an 800-foot setback. If a National Pollution Discharge Elimination System permit is in place, additional requirements may also apply.

If the operation is required to follow Iowa DNR’s Master Matrix, farmers should ensure compliance with the land application requirements previously selected. If you specified that you would either inject or incorporate your manure, written permission must be obtained from the Iowa DNR to surface apply. State law requires manure applicators in Iowa be certified. Personal application of manure, even a couple of loads, needs proper certification.

Wet soils absorb manure and water at a slower rate because of their capacity to hold liquids is already utilized and they are prone to compaction and surface runoff. While there are options to reduce the risk of environmental impacts, there are no guarantees of complete prevention. When applying manure using tankers, the risk of environmental impacts is reduced when the tankers are not filled to full capacity, which reduces the weight limit and reduces compaction. Applying manure to the driest fields or driest portions of the fields first and then adjusting the application rate ensures that the soil is capable of holding the manure and its nutrients in the soil profile.

Wet falls can lead to higher soil water contents, as you apply think about how much manure and manure nutrients your soils can hold.

“Looking ahead, Iowa’s restrictions on manure application to frozen or snow covered ground will be in full effect this winter,” said Andersen. “The law applies to all confinement animal facilities with liquid manure that have more than 500 animal units.”  This amounts to about 1,250 finishing pigs, 5,000 nursery pigs, 500 steers, immature dairy cows, or other cattle, and 357 manure dairy cows.

“We want to remind farmers that the law prohibits manure application from these operations between Dec. 21 and April 1 if the ground is snow-covered, unless the manure can be properly injected or incorporated,” says Andersen. He noted that starting Feb. 1, manure application from these operations is also prohibited on frozen ground.

Tuesday, November 4, 2014

Fall vs. Spring - the whats and whys we need to think about in terms of manure application timing

Storing our manure reduces or eliminates the need to collect and spread the manure on a daily basis. The primary reason to store manure is to provide the capability for the farm to land apply the manure at a time that is compatible with both the climatic and cropping characteristics of the land receiving the manure. For example, in the Midwestern United States, we generally try to avoid applying manure in the winter as the snow cover and frozen soils make it difficult to get the manure where we want it and to do a good job. Similarly, during the summer when our crops are actively growing it can be difficult to find good places to land apply our manure. This leaves us with two big windows for manure application, in the spring after the soils start to warm up and before we plant crops for the up-coming year and in the fall after our crops have been harvested but before the soils freeze.

So, this brings up the question is spring manure application better than fall application? Well, applying in the spring leaves less time for decomposition of organic material in the manure and conversion of manure nitrogen into nitrate before the crop is up and actively growing. This can be a good thing as it can reduce the loss of nitrate, but often times spring is a busy time with planting and other fieldwork and any delay caused by waiting for manure application might reduce our yield potential. Additionally, in the spring we are often dealing with wet soils that might make soil compaction a concern. If we apply in the fall, it gives microbes in the soil time to decompose the manure, which can make the manure nutrients available to the crops as soon as they are planted. On the other hand, it gives us more time for nitrogen loss before the crop is up and growing.

A recent summary of nitrogen application time was performed as part of the Iowa Nutrient Reduction Strategy.  The summary was not specific for manure, but was geared at how timing of nitrogen application influenced losses through leaching and crop production. They estimated that switching from fall fertilizer application to a pre-plant nitrogen application in the spring would reduce nitrogen losses by 6% on average. These studies also indicated that switching from fall application to spring application would increase corn yield by 4% on average, (For completeness they found that switching from spring nitrogen application to sidedress application or a split pre-plant/sidedress application would reduce nitrate leaching by 4-7 %.)

In summary, I don’t think there is a perfect answer for when we should apply our manure, both fall and spring application have different opportunities and challenges. The potential benefits of reduced nitrogen losses from less fall application need to be balanced with practical concerns such as time and equipment availability in the spring and the soil conditions we will be applying our manure too. However, before moving on let’s dive into a bit of the science on this and see what we can find.


Although it is actually a cycle, it is often convenient to think of it as a flow of nitrogen, where the organic nitrogen will first be converted to ammonium nitrogen, and then eventually nitrate nitrogen. To be usable by plants the nitrogen has to be either in the ammonium or nitrate form, so conversion of organic nitrogen to ammonium makes it more plant available. Once it is in the ammonium form there are three things that can happen, plants and microbes can use the ammonium immediately, it can be converted to ammonia and lost to the air via volatilization, or it can be converted to nitrate which is susceptible to denitrification and leaching. Many of these processes (mineralization of organic nitrogen, nitrification, denitrification) are performed by microbes in the soil. The rate these microbes perform these processes at is related to the soil temperature, warmer temperatures faster reaction, colder temperatures, slower reactions. To conserve as much of our nitrogen as possible, we don’t want to let it get to nitrate nitrogen. This is because nitrate is the form most easily lost from the soil as it is extremely water soluble, making it easy to leach into groundwater or tile drains. Ammonium on the other hand will often stay in the soil as long as it isn’t exposed to the atmosphere where it can be lost by volatilization.

So what this means to use if we are using manure as a fertilizer source is if we have ammonium rich manures we want to wait until our soils are cooling before we apply it. Otherwise, it will be converted to nitrate yet this fall and be susceptible to losses all winter and spring before our crops have the opportunity to use it. If we are using manures that are mostly organic nitrogen we still want to be aware of this but probably can apply a little sooner as are manure nitrogen has to go through several conversions before it can be leached. As a general recommendation, ammonium rich manures should be applied after the soil temperatures are 50-degrees and cooling. If manure applied to soils when soil temperatures are above 50 degrees F, the inorganic nitrogen converts rapidly to nitrate-nitrogen, which is a very mobile form of nitrogen and increases the risk of nitrogen leaching into the ground waters.

  This desire to delay manure application until the soil is cooler needs to be balanced again the availability of equipment and the risk of a quick change in weather conditions (frozen soils) preventing manure application. So like most choices in life, there isn’t one easy answer that will work for everyone, it’s all about balancing your risk of not completing your manure application with your desire to maximize its fertilizer value.