When should we think about phosphorus availability?

The other day I had the opportunity to provide a guest lecture to a class of juniors and seniors in Agricultural Systems Technology here at Iowa State. The class is about animal production systems and I was asked to provide a lecture on “manure.” It is always interesting when you get general requests like this as there are literally hundreds of issues about manure and it seems like you could pick almost any of them. However, in cases like this I usually talk about methods for determining appropriate manure application or in a case like the how to fill out an Iowa Manure Management Plan. There are lots of skills that I think would be useful, but when it comes down to it, making sure they understand the steps in determining manure application rates is the one I’d really like them to know.

As we talk about it, we use the check book analogy, i.e., there are two things you need to keep track of, the ins and the outs and we want to try to keep those in balance. When I do this for manure the two things we want to know are the demand side (how much of this nutrient do we need) and the supply side (how much of that nutrient is our manure going to provide). We do this first for nitrogen and talk about how losses might occur during application and how this might cause you to adjust your rate and what nitrogen availability means. Then we do this for phosphorus, talking about situations when your manure application rate might be limited by the amount of phosphorus you put on (based on the Phosphorus Index here in Iowa). Normally I do nitrogen first as its more complicated due to volatilization losses and having to worry about availability that it makes phosphorus seem easy.

However, the other day I got a good question… it was, “why don’t you worry about phosphorus availability when you do this?” I thought for a second, it seemed I done these calculations so often and usually just glossed over the phosphorus availability assumption that it was second nature to me, but now with an interested student in my office asking why I’d get a chance to explain it. So I answered, well usually we think of the fields getting manure as one that get repeated applications year after year, and since typically our manures supply more phosphorus than the crop needs we have built up phosphorus levels in the soil so we aren’t really concerned about availability since there will be enough there to satisfy our crop.

I’ve always thought this approach was fair, and was quick to accept it, but the student’s question got me thinking… is this still true? Recently we’ve seen lots higher N:P ratio’s in swine manure; this has occurred for numerous reasons including improved availability of phosphorus in DDGS as compared to more traditional ingredients as well as the inclusion phytase into the swine diet to improve phosphorus digestibility, but it might mean that we start to care more about phosphorus availability in swine manures. And just the other day I was writing about how far you could move manure if you were getting it to fields were there was a need for this phosphorus. What about these cases, i.e., fields with low soil test phosphorus, what does phosphorus availability mean in these instances?

Well, in general, a large fraction of the phosphorus in manure is considered to be plant available immediately after application (often 60-90%). The fraction that isn’t immediately plant available is often an organic fraction that will become available as microbes in the soil break apart those organic molecules and free up the phosphorus. The other part of phosphorus is very much soil dependent, there are lots of things (iron, aluminum, calcium) that can react with the phosphorus and make it more difficult for our crops to obtain. This is why soil sampling is so important, it gives us an estimate of the potential of seeing a yield effect with phosphorus application. Fields in the high or very high category see little to no response in yield with additional phosphorus, so considering phosphorus availability has no effect. In fields with very low or low soil phosphorus concentrations though we have much greater potential for a yield impact, and in these cases it would be important to make sure we are applying sufficient available phosphorus to supply what the crops need the first year or two. So if you are applying your manure to fields with low soil test phosphorus, you just might want to look at some of those first year phosphorus availability numbers to make sure your crops have what the need. For more information on phosphorus recommendations in Iowa see PM 1688: A General Guide for Crop Nutrient and Limestone Recommendations in Iowa.

Protect your soil to reduce erosion

As I’m sure we all recognize, soils are an important part of our agricultural systems, but they to far more than just provide a place for plants to grow roots and anchor themselves. Soils are really an ideal growth medium, they maintain spaces that are filled with oxygen to help, others that are filled with water, they hold nutrients in a place where plants can get them, and they insulate roots from drastic daily changes in temperature. As such, it acts as an ideal growth medium. That means protecting it an making sure it remains in the field for years to come is vital for maintaining our agricultural productivity.

Have you seen this video of raindrops hitting a sand surface that was captured a team of scientists in the Chemical Engineering and Material Science department at the University of Minnesota. Their video shows the impact of water drops on the surface of sand particle. The high-speed photography reveals the detailed liquid-drop impact dynamics at various impact velocities. As you watch the video look at how the soil particles are struck and scatter when the drop hits; drops can be up to 6 mm in diameter and hit the soil at up to 20 miles per hour. As you can see this force from the raindrops can dislodge soil particles and splash them up to three feet away. If there is no residue coverage left, then our soil is exposed to these pounding forces that breaks apart our soil aggregates and facilitate the formation of a crust that seals the soil from taking in additional moisture as quickly as it otherwise would. However, if we keep crop residue on the surface or grow cover crops, we can reduce the impact this raindrop impact has. Residue provides a cushioning effect that absorbs the impact of the rainfall, and helps protect your soil.

So what are some ways that you can help protect your soil resources by leaving more residue? Here are three tips:

1. Try to follow a crop rotation sequence where a high-residue producing crop is grown every couple years. Or if you have need for a forage, consider planting a perennial like alfalfa that will maintain surface residue coverage for several years.

2. Wait until spring for tillage operations.

3. Try planting a cover crop, especially in fields where low residue crops where grown. For example, focus on fields where your corn was harvested as corn silage and lots of the residue removed.

Assessing Hazards in Manure Storages & Handling Systems

As I was installing a new circuit in my garage the other day, it got me thinking about where I learned this useful skill. To no surprise, my first experiences with wiring were at the farm with my dad. One day he decided it was time to replace all the lights in a barn (no doubt due to some university research saying better light encourages cows to give more milk). As with most farm projects, it of course goes better with a little help, and as a result I was drafted into service as the “flashlight holder” and the “where did I set the (insert tool name here) locater.” Now this might not appear to be an important job, but let me tell you it really is, for both the flashlight holder and the guy trying to get the wiring done. Any time you’re wiring the power is off and you are in the dark, so someone to hold the flashlight for you gives you two hands to work with, and if you are the one holding the flashlight it’s your chance to learn a new skill from someone who knows what they are doing. So what’s that got to do with safety… well, although most projects went well, every now and then one went differently than what we expected and at the end we’d say, “that was lucky.” In those cases it wasn't that we didn't realize that there were things that could go wrong in what we were doing, it was that we didn't take the time to think about what those things were and the best ways to minimize those risks.

So, now the fun part, where I say something that is supposed to inspire you to take the next step, walk around your farm, and identify the risks associated with your manure management system. Then of course, I finish by trying to provide you with a tool, tip, or technique to help you in the process. This all sounds like a simple process, 1, 2, 3, and it all comes together and your safety issues are solved. However, in trying to come up with my story about why safety is important only one thing came to mind… family. So I hope you take the time this winter to think about the safety program at your farm, and help develop a culture of doing things correctly and safely so your family has happy holidays for years to come.

In terms of developing a safety program, I think there are about four steps to work through, with your manure system being no different. 1. Select the job to be analyzed, 2. Break that job into a sequence of steps, 3. Identify potential hazards associated with each step, and 4. Determine preventative measures to address that hazards identified. Before we get stated, just two thing to remember, Safety is not optional and Safety is more than signs!

That are lots of activities that go into your manure system and even more into your farm, but since this is a manure blog we’re only going to focus on the manure portion of safety. Any manure system really accomplishes five tasks these are manure collection, transport to treatment/storage, storage, transport to land application area, and land application. It’s important that you consider all five steps, understanding that in many ways the steps that happen infrequently (transport to the land application area and the process of land application) might present more risk not only from the activity itself, but also because these tasks are so rarely performed.

So, here I’m going to focus on the manure storage. What safety hazards are there? The risks differ for each type of manure handling systems and the activity you are performing. Enclosed structures are commonly associated with asphyxiation hazards related to gases from manure decomposition, while open structures are often associated with drowning risks. In the case of open manure structures, one way to reduce the risk of drowning is by purchasing and installing a fence around the storage. This can work really well at keeping children and animal out and just as importantly identifies to people entering that there is a risk present. Though this is a great start, and focuses on just the general day to day risks, there still may be times when we may have to enter inside the fence, for example if we are collecting a manure sample or getting ready to agitate and remove the manure. Having a safety harness available that can be attached to anchor points on the storage might be one to reduce the risk of this activity of manure sampling.

Now that we've  talked about safety , I’m going to try to help show you a way to organize the process. In the table below I've identified a specific item, the day-to-day operation and maintenance of a manure storage. The next step is to identify examples of potential hazards. In this case it might include the risk of falling in (that drowning hazard) or the risk of hazardous gasses. The final step is then to think about what we could do to reduce or manage that risk, so for example placing a fence around the storage to help prevent entry or in the case of under building storages, making sure pump-out covers are in place.

How is the storage operated and maintained.	Examples of Potential Hazard	Example Preventative Measures
If the storage takes place in an open or closed tank…	Falling into the tank leading to: possible trauma, drowning, and potential life-threatening situations Such tanks or pits are often confined spaces and would be expected to have hazards: oxygen deficiency, hydrogen sulfide toxicity, methane exposition potential; as well as others, especially under certain conditions like the presence of foam or during times of manure agitation	Avoiding entry into the manure storage area. Place a fence around the storage or in case of under barn pits, make sure the access points have sturdy covers.

If you are interested in learning manure about manure storage safety ASABE has a standard EP 470: Manure storage safety that can be a nice resource. It details several safety risks and some things to consider in managing those risks.

How far can I afford to haul my manure?

When debating the economics of manure there are many things that can be considered, whether it be costs associated with manure collection in the barn, building or maintaining the manure storage, or moving the manure to the field and land applying it. How these costs are accounted for can make a big difference in whether we think the manure is providing a cost effective fertilizer resource, or if its use doesn’t pencil out compared to commercial fertilizers.

In evaluating the costs of manure application, the first choice a farmer has to make is whether to hire a commercial manure applicator to apply the manure for them, or to perform the application themselves. There are numerous reasons to consider both options, whether it be the ease of allowing someone else to handle the application, bio-security issues of bringing different equipment onto your farm, control over when manure application occurs, costs, or availability of equipment and labor. Here I'm going to base my cost estimates on information on what our commercial applicators are charging and use this to get some rough estimates. This is meant to be illustrative only, not an analysis for any particular farm.

When using manure as a fertilizer one of the most common questions is, how far can I afford to haul it and still have it be a viable, cost-effective fertilizer? What this question usually means is how far can I transport the manure and still have it be cheaper to use than commercial fertilizer. Like most thing in life, it depends. Things like what the nutrient content of the manure is, which nutrients are we getting value from (nitrogen, phosphorus, potassium, trace minerals, or even organic matter), what sort of crop rotation are we using, or even whether we are applying it ourselves or hiring a custom applicator to apply it can all impact the results. In addition, current prices of commercial N, P, and K fertilizers can affect this distance as this sets the value on the nutrients in our manure.

Let’s look at an examples; we are going to work with corn-soybean rotation, set current nitrogen, phosphorus, and potassium prices at $0.44 per lb N, $0.49 per lb P2O5, and $0.40 per lb K2O, and focus on swine manure first. Current nutrients concentrations (average ± standard deviation) in deep-pit slurry from a swine finishing operation are around 58 ± 25 lbs N/1000 gallons, 18 ± 8 lbs P/1000 gallons, and 20 ± 7 lbs K/1000 gallons (average ± standard deviation). Our commercial manure haulers on average are charging  around $0.02 per gallon, plus a millage fee of $0.0035 per gallon per mile transported. These prices are only rough guidelines that may vary throughout the state depending on your manure, soil, and crop production characteristics.

If a farmer is getting value from the N, P, K than they can afford to haul their swine slurry manure about 12 miles and have it be as cost effective as commercial fertilizer. Transport distances of 5 to 20 miles are possible depending on the manure’s nutrient content. However, if only the nitrogen is of value then the hauling distance equivalent to the fertilizer value is only about 1 mile. This illustrates that moving the manure further from the farm may be justified if it provides the opportunity to better utilize all the nutrients in the manure and take advantage of the phosphorus and potassium it contains.

Similar analysis can be conducted for dairy slurry, beef manure solids, layer manure, and turkey litter. Results of all manure types are summarized in table 1. In that case of solid manure, application costs were set at $6 a ton plus an additional $2.20 for every mile the manure had to be hauled. Again, these prices are just a rough estimate and could vary considerably based on your manure, field, crop, and equipment characteristics.  If all nutrients (N, P, and K) are being valued, manures can be transported between 2 and 34 miles while still being as cost effective as commercial fertilizer; however, if only nitrogen is being valued than economically justifiable transport distances are typically only 0 to 2 miles. In general, these results suggest that solid manures could be more economically transported further distances than the liquid manures, and that finding ways to capture the value of the phosphorus and potassium can really increase how far we are able to move our manure.

So what does this mean to you? Current market conditions seem to indicate that crop prices over the next year or two might be lower than what we experienced in the past couple years. Finding ways to reduce expenditures as we try to get the crop in the field and to harvest might help in reducing our risk. Manure can play a role in this, if you have fields in need of phosphorus and others that don't strive to get your manure resources to the fields where you can take advantage of the fertility it has to offer.

Some of you may be wondering, if I can really economically justify moving manure this far, we don't we see more of it moving these kinds of distances. Well, there are really lots of reasons, but one of the most important is we generally don't have to move manure anywhere near this far to find fields that can benefit from its application, and if those fields can benefit from all those manure nutrients why not save a little money in the costs of hauling them. Another, important consideration is the amount of time it would take to apply the manure. As I'm sure most of us are aware, there are a limited number of days available in the fall and spring to get our manure application accomplished. Hauling further distances either requires us to get new, bigger equipment, to haul on more days, or to haul under some less than ideal conditions to get the job done. Thus like most things, finding the right balance so that you can take advantage of your manure resources and get the job done is critical.

As a note, in determining the value of the manure I only considered nitrogen that would be available for crop production in the first year. More information about the amount of nitrogen available in the manure can be found in the ISU publication "Using manure nutrients for crop production," which you can find at http://store.extension.iastate.edu/Product/Using-Manure-Nutrients-for-Crop-Production. 

Table 1. Break-even hauling distances for manures from different types of operations and different cases of how manure are valued. The first number represents the average manure, values within parenthesis represent how farm manure within 1 standard deviation of the average could be transported.

	Manure Type
	Swine Slurry	Dairy Slurry	Beef Solids	Layer Manure	Turkey Litter
Break-even Hauling Distance (mi) All Nutrients Value	12 (5 - 20)	8 (2 - 13)	14 (9 -20)	25 (16 - 34)	16 (13 - 19)
Break-even Hauling Distance (mi) Only Nitrogen Valued	1 (0 - 4)	0 (0)	0 (0)	1 (0 -3)	2 (1-2)
Break-even Hauling Distance (mi) P & K only (P-limited)	5 (0 - 10)	6 (2 - 11)	13 (8 - 13)	21 (13 - 28)	11 (9 - 13)

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 www.iowadnr.gov/Environment/LandStewardship/AnimalFeedingOperations/AFOResources/AFOFactsheets.aspx), 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 http://www.iowadnr.gov/insidednr/socialmediapressroom/newsreleases/vw/1/itemid/2304 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,
Dan

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 http://themanurescoop.blogspot.com/2014/10/how-much-manure-is-there-in-iowa.html 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.

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.

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 athttp://www.iowadnr.com/afo/file/hqwr2.pdf, 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.

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.

Economic Value of Manure Sampling and Testing

As you may recall, last week we talked about a bit about manure in relation to precision farming. We said there are really three aspects to precision farming, measuring something, making a decision based on that thing we measured, and then implementing our decision. Today we are going to look at these concepts in terms of manure management, specifically in terms of manure sampling and testing.

To start with we need to understand a little bit about manure. One of the most common questions asked about manure “what is the fertilizer value of manure.” This question usually means, “How much nitrogen is in the manure?” or stated a slightly different way, “how much manure should I apply to fertilize my crop?” This question doesn’t have an easy answer, because unlike commercial fertilizer (anhydrous ammonia, MAP, DAP, or urea) we might usually purchase, manure doesn’t come with a guaranteed composition. Instead, there can be substantial variation in nutrient content from one-farm to the next, year-to-year on the same farm, and to a lesser extent the manure that we are pumping out during a single land application event. This variation makes “book values,” i.e., estimated nutrient contents available in Midwest Plan Services or state extension materials a good starting point for planning purposes, but means that we really need to measure the nutrient content of our own manure to understand what is in it.

One way to think about this is based on probability. This is demonstrated for a swine manure from a deep-pit manure storage in figure 1 below. What you see is that the manure has the greatest probability, or the highest chance of having at a nitrogen content of 7 kg/1000 L (or right around 58 lbs. of Nitrogen per 1000 gallons of manure). However, what’s harder to tell is that there is something like a 20% chance that swine manure might have more than 9 kg N/L (75 lbs./1000 gallons) or a 20% chance that swine manure will have less than 5 kg N/L (41 lbs./1000 gallons). This means if we were basing our manure application off “typical” or average swine manure and trying to applying 150 lbs. N/acre, there is a 20% chance we apply more than 190 lbs. N/acre and a 20% chance we apply less than 110 lbs. of N per acre. So what does this mean to us? Well, it implies there is a pretty good chance we won’t be applying the amount of nitrogen we think we are. This is costing us lost revenue from either not fully utilizing our N (if we end up applying more nitrogen than we need) or from nitrogen limitation in our crop growth (if we are applying less N than we think we are).

Figure 1. Probability or a swine manure from a deep-pit manure storage having different nitrogen contents.

Based on this I think we have an interesting question we can ask ourselves, and that is, what is the return on investment of manure sampling. That is, how much value does manure sampling add to our operation? In determining the value of the manure test, it is important to understand how a farmer can use the information gained from the test results, i.e., how having this information alters the farmer’s nutrient management and affects the farm profit. This is a complex topic, as almost limitless possibilities exist, but to get a general idea I’m going to make a few assumptions and approximation about common cropping and manure management systems in the Midwestern United States. This may mean the results don’t give you an exact value for your operation, but they give you a pretty good starting point.

In this evaluation, I assumed that the manure application method would be either injection or immediate incorporation to maximize N utilization. Additionally, I assumed that best management practices for manure application timing were followed; as a result, the yield response to available N (defined here as the sum of ammonia N and organic N expected to mineralize in the first growing season) would be the same as the yield response to mineral N fertilizer. Finally, we limited crop rotation choices to continuous corn and corn-soybean rotations, as these represent the dominant rotations in the upper Midwestern U.S. The impacts on the value of the manure test of N-limited or P-limited application, as well as when sampling or testing was conducted, were handled by evaluating all cases. Finally, the basis of this effort was that farms intend to use their manure resources to support crop production. In cases where farmers have insufficient land to use all their manure resources, they can only extract the value of the manure test if they can find buyers for the manure nutrients.

The value of the manure test was calculated by estimating the profit that would have been made if the manure was assumed to have a “typical” nutrient composition and then to compare this to the profit generated if the actual nutrient composition was known. The profit graphs for these steps are shown in figures 2, 3, and 4. As a note, I performed this analysis earlier this spring when corn price was $5 per bushel.

Figure 2. Probability of different profits due to different nitrogen contents of manure assuming manure standard rates.

Figure 3. Expected profit from applying manure of a known composition at the maximum return to nitrogen (rate changed to account for measured nutrient content).

Figure 4. Expected value of the manure test, based on graph 3 minus graph 2 (adjusted based for sampled manure nutrient content case minus assumed nutrient content case).

To put these results in perspective I used the model to evaluate what manure sampling would be worth for a 1000-head capacity swine finishing farm using a deep-pit manure storage. On average, the facility generated 4 L of manure per head per day. This farm has collected and tested manure samples every year for the last five years. The first four years of manure sample values were 0.84%, 0.72%, 0.98%, and 0.62% N, with an average and standard deviation of 0.79% ±0.16% N. The N content for the current year was 0.92% N. If no sample was tested, this operation assumed that the manure had an available N content of 0.79%, the average of the previously collected samples. Using pre-application sampling and assuming that manure application was N limited, the value of the manure test would be $30.96 ha^-1. Assuming that the manure sample is representative of all the manure from this building, the overall value of the sample was $1,759 (the farm would have applied manure to 56.8 ha). This represents a good return on investment, as the approximate cost of obtaining this information would be $50 for manure testing, $50 for shipping the manure to the testing lab, and $100 for the farmer’s time to collect, label, and ship the sample, giving a return of almost 9:1. If manure application was P limited and manure was sampled during application, the estimated value would be $14.20 ha^-1. In this case, the manure was applied to 112 ha, so the actual value of the test would be $1,589

The same analysis was performed for other manure types and estimated values of manure testing are shown in table 1.Overall, the results indicated that sampling and testing the manure provided enough economic value that it would pay for itself.

Table 1. Estimated value of the manure test for different manure type and crop rotations.

Precision Farming and Manure

Recently, I have been hearing a few buzzwords (precision agriculture, big data, and even precision conservation) that really got me thinking about what these ideas mean in terms of our manure management. Often times when we hear the word precision agriculture it brings to mind the newest equipment being controlled precisely to drop a seed exactly where we want it. While I think this is an important part of precision agriculture, to me at its heart it is all about providing site-specific management practices within our fields to improve our crop production and lessen impact on the environment. This means we need innovative ways to understand our agriculture decision and then methods to take this information, determine an optimum way to move forward, and then implement the management practice we determined would work the best. I break it down into three important steps – measurement, decision-making, and implementation.

The first two steps, measurement and decision-making aren't always what gets the most glamorous, but they are probably the two most critical steps, and this is really what the new buzz term “BIG DATA” is. In agriculture, there are all kinds of information available at our fingertips: market prices, weather forecasts, soil types, planting population maps, past yield maps, or maybe even aerial photos of what are crops currently look like. This means there are many pieces that we need to take into account as we try to make a decision about our best course of action on what we should do to “get the most from our field.” In many cases, we rely on our experiences in similar situations to make our decision based on our current condition.

 I like to think of this in terms of sports, practice and then do. I don’t know if any of you are basketball fans, but with the season starting up again I thought this would be the perfect chance to mention it. You may recall last years’ NBA finals pitted the Lebron led Heat against the Spurs, but here I’m going to focus on the a mall moment earlier in the Spurs season. Spurs down by 2, 9.5 seconds left, Spurs ball… Park takes the ball and using a Duncan screen attacks from the left wing for a layup, but at the last second sends a pass to Leonard on the weakside for a corner three, which of course he makes for the win. Why did this happen? Well, of course practice and experience, but at a more data driven level (good old sabermetrics) we know corner threes are the best shot in basketball (most points per attempt, but corner threes are typically assisted) so the Spurs drew up a play to give them the motion to get one of their better shooters into this position. Did it mean it would work? Of course not, but it gave them the best chance to succeed. Precision agriculture is the same thing, it might not always work like we wanted, but it’s the idea of putting us in the best chance to succeed.

So how do these precision concepts fit with the world’s oldest fertilizer, manure? Well, in the long run it may mean trying to implement more site-specific manure management practices, but in the short run it means making sure we are getting the right data to inform us and then using this data to make decisions. When I think of this “precision ag” concept in terms of manure nutrient management, there are really four basic steps/or principles. 1. Measure the nutrient content, 2. determine the application rates needed, 3. control the rate applied, and 4. produce a record of where and when that application occurred.

Many factors cause variations in the nutrient concentration of manure, including diet, housing type, manure storage type, environmental conditions, management techniques, and treatment practices. Given the variability in composition, manure sampling and subsequent testing for nutrient composition is a critical component of proper management. For example, while “book values” are reasonable averages, they are just that, averages, they don’t represent your farm. It’s not uncommon for one farm’s manure to vary by 50% or more different from that average manure. For example if you asked me what I thought was the typical nutrient content of swine manure I’d probably say something like 50 lbs of N/1000 gallons, but I look at sample results all the time that have 60, 70, or even 75 lbs of N per thousand gallons. This means we can get a big financial advantage if we can manage to make the best use of these manure nutrients.

Next time I’ll provide you will some more details on how to use the results of manure sampling and testing and provide some insight into the economic value this decision making might have on your farm, but for right now I just wanted to make you aware of some resources on how to collect a good manure sample. The resources is “How to Sample Manure for Nutrient Analysis” and you can find it at http://store.extension.iastate.edu/Product/How-to-Sample-Manure-for-Nutrient-Analysis. 

What's that smell? LECA as a Permeable Cover for Manure Odor Reduction

Manure - we all know that it provides some great nutrients that can help support crop production, but even its most adamant supporters will recognize that in some situations is can have a smell. Here I'm going to provide a short discussion on the science of manure odor and then discuss one specific management practice, the use of LECA as a permeable cover on a manure storage, that can be used to mitigate odor in some situations. The use of LECA is by no means  the only option, it only receives highlighting here due to a recent question I received about its use. More information on the use of LECA as well as other permeable covers can be found at http://www.agronext.iastate.edu/ampat/storagehandling/pc/homepage.html, while information about other odor and greenhouse gas mitigation options for animal production systems can be found at http://www.agronext.iastate.edu/ampat/homepage.html.

Manure odor chemistry is complex, there are more than 400 gases that contribute to the odor, but generally the majority of the odor comes from just a few gases, including ammonia, hydrogen sulfide, cresols, volatile organic acids, and amines. These compounds all can result from the partial decomposition of organic matter in the manure. These compounds are natural byproducts of anaerobic breakdown of the organic material in the manure. To be perceptible as odor, these compounds must escape from the liquid phase and be present as a gas. The release of these compounds is impacted by factors such as the compounds vapor pressure, solubility, the manure's pH, or even if a  crust is present on the manure preventing release of these compounds. Most of our developed mitigation techniques try to adjust one or more of these properties to prevent the release of the odorous compounds.

One option that is sometimes used for odor control is permeable covers. Permeable covers are materials that lie directly on the surface of the stored manure and provide a physical barrier between the manure and the surrounding air. Examples of permeable covers include natural crusts, layers of natural vegetative materials (such as straw, corn stalks,ground corncobs, etc.), vegetable oils, permeable fabrics (geotextiles), as well expanded clays, ceramics, and ground rubbers (examples include LECA and Macrolite). The success of permeable covers depends on achieving season-long floatation and continuous 100% coverage of the manure storage structure, in this post we'll focus on LECA.

LECA is a light-weight expanded clay aggregate. It’s basically a ceramic shell with a honeycomb core produced by firing natural clays at 1100-1200C in a rotating kiln. The bulk density of 8-12 mm diameter LECA is about 325 kg/m3, allowing it to float. It is highly durable to both chemicals and frost giving it a long life (10 + years). LECA covers are typically applied in a 2 - 4 inch layer to provide good coverage of the manure. LECA is one of the highest cost of permeable covers and has been hard to obtain. (The LECA that I can generally find is still from European companies.) Below, is a picture of LECA.

Below is an example of an in-ground circular concrete tank swine manure storage that has a LECA cover. This LECA had been in use for over 10 years and provided a coverage depth of about 3-4” on the manure surface. Occasionally the LECA would all drift to one side of the manure storage from wind blowing from the same direction continuously, but it would generally fix itself after the wind direction switched. One potential issue with expanded clays is that agitation and pump out must be conducted in a way that ensures the floating cover material is not removed from the storage. This can generally be performed with minimal changes to standard agitation and pumping practices.  Such as corralling the LECA away from pump inlets or providing screening so the LECA cannot go through.

LECA works in a manner to any permeable cover (like chopped straw) in that it provides a barrier that helps reduce wind disturbance of the manure surface and in doing so lessens the transfer of ammonia, hydrogen sulfide, and other odors into the air. That is the permeable cover shields the manure surface from contact with the air. The major advantage of LECA over a material like straw is that the LECA has a long life, it is basically inert, so it lasts for a long time. When you are using LECA as a cover you are generally trying to get a 2- to 4- inch thick layer on the surface, and it generally is management free except when you are trying to pump the manure.

As far as studies of its performance there have been a few, but they mainly come from Denmark as this is where most of the LECA is made, but they generally show somewhere around a 50-90% reduction in odor, 60-80% reduction in hydrogen sulfide, and 70-90% reduction in ammonia, with performance varying a bit based on how well the manure stays covered and the thickness of the LECA cover. Thicker covers generally due a little better, but performance doesn’t increase that much as long as about 1.5-2 inches are floating on the surface. The problem has generally been that every square foot of manure storage you are covering costs something like $1-3, which adds up pretty quickly (this price is actually pretty comparable with what some impermeable covers would cost to purchase and install).

Although I haven’t seen in agricultural settings, a similar in concept and has me intrigued is the use of circular plastic balls. The balls float on the surface and act very similar to the LECA in covering the surface. There are a few companies settling these types of plastic module balls to municipal wastewater treatment plants, the challenge would again be how do they hold up in agricultural manure storages and do they interfere with our typical agitation and pumping practices?