Manure Management and Biosecurity

 

The prevention of disease transfers due to manure handling equipment moving from one farm to the next is essential for your operation. Biosecurity advice often revolves around owning your pumping equipment dedicated to your farm. It also ensures manure equipment was washed, disinfected, and in some cases, had a “downtime” before moving to the following site. These techniques still hold today, but new ideas and innovations have made biosecurity more convenient.

 Owning your manure pumping and handling equipment still provides the most biosecure option. It gives complete control over what sites the equipment has been on, how recently it was cleaned and disinfected, and the amount of downtime before it is used.

 When working with custom manure haulers, make them aware of any biosecurity requirements for your farm upfront. Please take a moment to inspect their equipment as they arrive to make sure it is clean. Try to work with them to provide cleaning and disinfecting options as they finish your site—review lines of separation and routes through the farm site to maintain biosecurity. Be clear about the health status of a facility. As custom applicators organize their jobs, they can ensure proper biosecurity is maintained. Work from farms with the highest to lowest biosecurity requirements and current health status. Switch the feces species you are hauling as the risk of disease transfer between different livestock is typically lower; when possible, add a cattle job between pig sites.

 However, we have also seen equipment changes help make manure withdrawal more biosecure. One challenge with maintaining biosecurity of manure removal is removing a pump-out cover from the barn and dropping an agitator into the manure. The pump-out opening modifies the ventilation system. It often serves as an air inlet; in filtered barns, this weakens biosecurity as  air isn’t forced through the filter before entering the pig space. As a result, some farms have begun to switch to a straw or a “mass agitation” system. Rather than opening a pump out cover, the manure pump is hooked directly to the straws built into the pump-out lid to recycle manure back into the barn and one port for manure removal.

 In addition to often being the weak link in terms of maintaining the integrity of the barn ventilation system, the drop-in agitation pump is often the hardest to clean and disinfect. These systems, with manure straws, allow pump trailers to be pulled alongside the barn and speed cleaning and disinfecting as because they are not lowered into the manure, they stay cleaner.

 An alternative option is to use a pump dedicated to the site to move the load station further away from the building, making maintaining lines of separation much more straightforward. In this way, tractors and tanks have greater maneuverability. There is less risk of manure haulers and farmworkers crossing paths and inadvertently contaminating the clean side of a clean/dirty line. Similarly, the farm site provides the lead pump and a short distance of hose dedicated to the facility when using the dragline application. In this case, it is vital to ensure that the pumping capacity of the supplied lead pump and the rest of the pump system align.

 

Figure 1. The load station is located away from the facility and in the field to help maintain lines of separation.

Higher Fertilizer Prices, Manure Opportunities

 

Last fall, fertilizer prices were trending higher (Figure 1), and with supply change issues and soaring fuel prices, that trend has continued into the spring. Even with potentially higher crop prices, this offers challenges to finding ways to increase or maintain farm profitability. However, one available option is to explore the use of manure on your farm. Many livestock owners have long known the value manure has to offer. With skyrocketing commercial fertilizer prices, this offers the opportunity to make even better use of the manure resources.

 

Figure 1. Weekly anhydrous ammonia prices.

Farmers who historically have relied on synthetic fertilizer, and even those who have used manure, but have limited experience with spring application, should consider using some manure this spring. While there is never a guarantee of what fertilizer prices will do in the future, current prices are unprecedented. Until 2021, most years showed a lower average price in the fall than in the spring. Even if your manure resources are limited and applying some manure this spring means you won't be able to cover as much ground next fall, it still represents an opportunity to save some money now since fertilizer prices haven’t stabilized.

ISU research evaluating the impact of swine manure timing on the yield of corn has consistently shown moving manure application closer to the growing season has a yield benefit. In 2021, with a dry fall and spring nitrogen loss via leaching and denitrification was at a minimum. The yields between fall and spring-applied manure were similar. We also compared spring UAN fertilizer to spring manure application and found, on average, the spring manure to corn (following soybean the previous growing season) out yielded the spring UAN application by 13 bushels per acre.

Figure 2. Average corn yields for 2021 at the Nashua site.

 

Similarly, this may be a good time to reexamine the nitrogen application rates you are selecting. Manure management plans typically utilize the yield goal method to set nitrogen application rate maximums, intended for environmental protection, not to maximize profit. Rate selection tools, like Maximum Return to Nitrogen, can be used to determine rates that will help you maximize your manure fertility value and typically will help you stretch the manure across more acres.

 

Farms that have not historically used manure in the past may be more interested in purchasing manure due to either inability to obtain other fertilizers or because of the high prices. If you are working with someone new to using manure, you can do a few things to help facilitate the exchange.

 

1. Set a price that works for both sides. Manure has value, and the value moves with the price of other fertilizer sources. Can selling some manure now potentially help you obtain acres for manure application in the future? If you are selling manure, look for fields that can utilize the N, P, and K to maximize value and price.
2. Know your regulations. Suppose the manure is coming from a confinement animal feeding operation. In that case, it needs to be applied by a certified applicator. Unless it is sold under Chapter 200A, through an independent manure broker, the field needs to be in a manure management plan (and have appropriate soil tests and erosion assessment).
3. Share the experiences you had in what helps you get the most value and best benefits of your manure. Discuss improvements to soil health all the nitrogen won't be available right away, and then state how the injection units will leave the field or best practices you've found to make planting a success.
   
   

Higher fertilizer prices make getting the most from your manure essential. Spring application has consistently shown similar or improved yields. Moreover, with the high fertilizer prices, getting manure nutrients to the right field at the right time makes manure more valuable than ever.

Energy Embedded in Fertilizer and Impacts on Manure Carbon Management

 

Last month we looked at how a few different manure management decisions impacted carbon cycling in the manure. This time, we are going to look at a different aspect of carbon, that being energy. While we often think about the economics of fertilizer, with the greater emphasis on climate change, greenhouse gases, and sustainable energy, it is important to look at how different manure management decisions impact energy from a fertility perspective.

 

Obtaining fertilizers takes energy. In the case of phosphorus and potassium, this energy is related to the difficulty of mining and processing the fertilizers (for P₂O₅, this is 5600 Btu per pound, and for K₂O, it is 4700 Btu per pound). For nitrogen, it is the energy required to synthesize nitrogen from diatomic nitrogen in the air (18,100 Btu per pound of N). Considering what this means in terms of carbon emissions, it implies every pound of P₂O₅ is worth 0.65 lb CO₂, a pound of K₂O is worth 0.55 lb CO₂, and a pound of N is worth 2.1 lb CO₂.

 

Let’s look at what this implies for beef finishing farms employing different manure management.

 

Table 1: Summarizes the N, P₂O₅, and K₂O contents of typical manure from different systems and what this means for differences for CO₂ use.

	N	P2O5	K2O	CO2	CO2/savings
Manure System	lb	lb	lb	lb	Savings per Head
Bedded Pack	44.5	25.9	26.4	125	34
Deep Pit	42.7	26.8	37.3	128	37
Open Lot	30.0	21.8	24.5	91	-

 

If we compare these options by holding onto the manure’s fertilizer value, we save approximately 34-37 lb of CO₂ per animal in extra nutrients that have been saved in manure. While this is important and useful, one thing to keep in mind is that the carbon cycle itself accounts for around 500-1000 lbs of CO₂ per pig space per year, which is a fair amount more than the energy in the fertilizer value of the manure. However, some of that CO₂ was recently recycled from the atmosphere to plant material and then through the animal. In terms of energy not used to make or obtain new fertilizer, carbon that has not been emitted represents a true change in the carbon cycle.

Carbon Footprint on Swine Deep Pit Finishing Farms

Carbon cycles can be as complex as we make them. In this case, I’m only going to focus on the manure portion of the carbon cycle; that is to say, I’m not looking at how diet and the crops are grown impact the carbon footprint, but only the manure management choices we make.

In terms of carbon, if we assume that the average weight of our pigs is 70 pounds and they excrete manure at a rate of the ASABE standard (0.375 kg VS/animal-day), with approximately 58% of the volatile solids being carbon, then every pig space will generate 80 kg of carbon in the manure every year. All we can do is control the form this carbon takes as we move it around.

 

Daily Haul

Although this system is minimally used in practice, it still gives us something to compare against. One quick note, I won’t be accounting for the amount of energy used to hauling the manure, only where that 80 kg of the carbon ends up. Most research suggests about 13% of the carbon in manure is stabilized in soil, which amounts to 10 kg. The other 70kg of carbon is converted into carbon dioxide, so this system generates about 257 kg CO₂ per pig.

 

Deep Pit Manure Storage

In a deep pit manure storage, the average is approximately 12.2 kg CH₄ generated per animal space per year. This is approximately 9.1 kg of carbon, but as methane, it is 25 times stronger greenhouse gas than carbon dioxide, which works out to 305 kg CO₂ equivalents. While the manure is stored in the pit, CO₂ is also generated and released; most manure-based biogas is approximately 60% methane and 40% carbon dioxide. Assuming this ratio, we will generate another 8 kg of CO₂, accounting for 2 kg of C.

 

We started with 80 kg of carbon and have converted 17 kg into gasses before application, leaving 63 kg of carbon in the manure. Again, 13% of this carbon will be stabilized in the soil, so approximately 8.2 kg, while the remaining 54.8 kg of carbon gets converted into CO₂, another 201 kg of CO₂.

 

Thus, in this system, 508 kg of CO₂ equivalents are generated per pig space per year. This is about double what we saw from the daily haul system because some carbon is converted into methane, a potent greenhouse gas. This provides our first insight into how to minimize our carbon footprint; reducing or eliminating methane emissions is critical.

 

Anaerobic Digestion of Manure

In this case, we will again, not be accounting for any energy that goes into moving manure for land application or getting it into the digester, but I will account for energy used in heating the anaerobic digester and for cleaning and compression of the generated methane to put it on in a natural gas pipeline.

 

Starting with our previous assumptions, pigs are 70 pounds. They excrete manure at a rate of the ASABE standard (0.375 kg VS/animal-day), with approximately 58% of the volatile solids being carbon giving the 80 kg of carbon per pig space per year. But in this case, we also need an estimated methane production potential, which I will estimate as 0.4 m³ CH₄/kg VS.

 

Anytime manure is stored anaerobically, some of the organic matter will break down and release methane and carbon dioxide. In an anaerobic digestion system, we want to minimize this time so more of the methane is captured in the digester. I assumed methane generated before manure collection and movement to a digester as 0.05 m³ CH₄/kg VS. This amounts to 4 kg CH₄ (3 kg of carbon, 75 kg CO₂ equivalents). Manure decomposition will also generate 2.6 kg CO₂ (0.7 kg C).

 

This leaves 0.35 m³ CH₄/kg VS of potential; I assumed the digester would be 75% efficient at converting potential into production. In the digester, we would hope to generate 21 kg CH₄ (16 kg C), which will all be combusted into CO₂ for power (58 kg CO₂); however, this means we don’t need to combust a fossil fuel for power, saving that CO₂ from being emitted, making this a negative emission of 58 kg CO₂. During digestion, we will generate 14 kg CO₂ (4 kg C).

 

The effluent from the digester needs to be stored, and as it is stored, more methane and CO₂ will be emitted. I assume that 10% of the remaining potential will be converted to methane. This is 0.7 kg CH₄ (0.5 kg C, 2 kg CO₂ equivalents) and 0.45 kg CO₂ (0.1 kg C).

 

These emissions leave us with 55 kg C in manure. Again, assuming 13% will stabilize in the soil (7 kg C) and the rest will become CO₂ (48 kg C, 176 kg CO₂).

 

Doing some math, we are at 212 kg CO₂ per pig space per year. I still need the energy to heat the digester and compress biogas. How much heat is needed is dependent on location, digester design, insulation value, and operation scale. As a best guess, I estimate this as 0.144 MMBtu per pig, with each MMBtu time 53 kg CO₂/MMbtu giving 7.6 kg CO₂. Cleaning and compressing the biogas from a pig space would take approximately 30 kWh, with every kWh generating about 0.38 kg of CO₂. Compression and cleaning of the biogas take 11.6 kg CO₂ gives a carbon balance of 231 kg CO₂ equivalents per pig space per year.

 

Implications:

What does this tell us? If we can find a way to encourage the adoption of anaerobic digestion systems, we can save around 277 kg CO₂ equivalents per pig space per year, a reduction of 55% compared to our baseline, and even slightly lower than the daily haul system. More importantly, we get that without wasting as much fertilizer value the manure would offer as daily haul systems will typically result in large amounts of nitrogen loss (next Scoop, we’ll look at energy in fertilizers and what that means for different manure systems).

Impact of Variability of Cattle Manure Application on Soil Nutrients and Crop Yield

 A study from 2011 and 2012 up in Saskatchewan looked at how the rate and uniformity of solid cattle manure application impacted crop yield under two fertilizer practices, manure application only and manure with supplemental urea fertilizer. This study is unique because it focuses on solid manure application uniformity with and without supplemental fertilizer. It used three different manure spreaders to give different manure application uniformities.

 

Manure rates tested were 0, 9, and 27 tons per acre, respectively, with three different coefficients of variation of manure application achieved (10, 50, and 110%). The low application rate supplied approximately 150 lb total N/acre, while the high rate supplied around 450 lb total N/acre. No statement on the fraction estimated to be plant available was provided, but it is fair to assume approximately 50%. On half of the plots, an additional 71 lb N/acre was applied using urea. They repeated two years growing oats in year one and barely in year two. Each year's yield was scaled to the percent of max for that year and then averaged.

Figure 1. Illustration of how solid cattle manure application rate (tons/acre) and uniformity (coefficient of variation) impacted crop yield (for oats and barley) as a function of maximum yield achieved.

 

Important notes and take-homes:

In all cases, the use of urea increased crop production, causing a significant increase (p = 0.0005) in yield. Solid manure can provide sufficient nitrogen to support crop nitrogen need on an annual basis. Still, in many cases, the higher carbon content of the manure causes early-season nitrogen tie-up, so while overall availability may be sufficient, there could still be periods of inadequate nitrogen supply.

 There were no statistical differences among treatments where urea was applied. These treatments all had sufficient nutrients to maximize yield. Urea on its own was sufficient to provide the nitrogen the crops needed.

 There was no statistical difference between manure application rates (p = 0.22). While we think more is often better, adding more manure didn't improve yield, presumably because while overall nitrogen supply was increased, a greater tie-up of nitrogen occurred with the greater manure application rates, causing a more seasonal deficiency.

 While no impact of application variability was seen on the urea applied plots, in the manure-only plots, application variability of 50% had more significant yields than 10% statistically but was no different than 110%. Generally, the data suggest improved uniformity increased yield at the higher application rate, where manure had to supply fertility.

How does uncertainty impact the manure nitrogen application rate you select?

 Selecting an appropriate nitrogen fertilizer rate is critical for optimizing profit from cornfields. Applying too little N reduces profit by reducing grain yield; too much N and you don’t get a return on the nitrogen you bought and can cause damage to the environment. In Iowa, most manure management plans are filled out using the yield goal method, with current university guidelines suggesting the use of the maximum return to nitrogen approach. If you are a long-time reader of this blog, you’ve probably seen both of these discussed before, so don’t worry, that isn’t the topic today. Instead, I’m focusing on uncertainties in the application and what that means for how we make decisions.

A lot of uncertainties exist when using manure as a fertilizer. Some examples include:

 · Nitrogen need of the crop (every growing season is a bit different)

· Spatial variation in nitrogen need to support crop production (because all soils aren’t the same)

· Nutrient content of the manure

· Nutrient variation from start to finish of manure application

· Application Rate Control and Variation in Application Rate

· Availability of the manure nitrogen to the crop

· Amount of nitrogen lost to volatilization

· Non-uniformity in application rate

 For now, I want to look at the manure application parts of this uncertainty and assume we know the crop response to nitrogen perfectly. How do all the variations and uncertainty impact the nitrogen application rate we should select? To answer this question, I first parameterized the yield response curve from the maximum return to nitrogen. The price of corn was set at $5.65 a bushel and nitrogen price at $0.40 a pound, which in a corn-soybean rotation gave an optimal nitrogen rate of 150 lb N/acre.

 The manure nitrogen content was set at 40 lbs N/1000 gallon, nitrogen availability at 95%, the nitrogen volatilization coefficient at 98%, and the desired application rate of 3706 gallons/acre calculated. A Monte Carlo simulation was then performed. For each variable that added uncertainty (manure N/content, Application rate, Volatilization coefficient, Nitrogen availability, and the knife-to-knife coefficient of variation), a normal distribution was constructed using the average value listed above and standard deviations of 2.75 lb N/1000 gallons, 250 gallons/acre, 0.01 % volatilization, and 0.05 % availability, respectively. Knife-to-knife variation varied between 0 and 100% were evaluated. I then performed 3500 simulations drawing randomly from the distributions I created to determine the nitrogen application rate for each knife (for distributions with natural limits, such as volatilization coefficient, no values over 100% were allowed).

 A lost value from application variability and uncertainty was calculated. If the actual amount of available N applied was greater than the MRTN rate of 150 lb N/acre, the value was set at the differences between the amount of N used minus 150 lb N/acre times a nitrogen price of $0.40 a pounds. If the nitrogen application rate was less than the MRTN rate, the value was set at the difference between corn yield at MRTN and the projected corn yield at the N rate applied times a corn price of $5.65 a bushel. The average loss in profit for all 400 knife simulations for each of the 3500 simulations was calculated, and then the average and standard deviation of the 3500 simulations were calculated.

A maximum return curve was calculated by taking the profit that would have been generated with perfect information (200 bu/acre x $5.65/bu – 150 lb N/acre x $0.40/lb N) minus the profit lost from uncertainty and application variability using the procedure listed above. Here we see an interesting trend – the uncertainty of ammonia volatilization and nitrogen availability and the variation in volumetric application rate and manure nitrogen content during the application, make it advisable to apply six pounds more available nitrogen per acre than if we didn’t have these variations. This occurs as the economics of nitrogen application is non-symmetrical, with the cost of being a pound short greater than being a pound heavy. Suppose we factor in any knife-to-knife application variability. The story gets more interesting, with the ideal application rate first increasing (until we reach a knife-to-knife application variability of about 40%, where the ideal rate is 167 pounds of N/acre, or 17 pounds/acre higher than the known nitrogen response curve we put in. Ideal nitrogen rate then decreasing to 137 lb available N/acre.

 

Figure 1. Impact of knife-to-knife variability of the effects of the maximum return to nitrogen for spring-applied swine manure to corn in a corn-soybean rotation. The ideal rate varies with our machinery variation.

 

But what about a fall application? As the MRTN curve is based on spring nitrogen applications, I added a term to the model to account for N-loss from fall to spring. For fall applications, I assumed an average of 15 lbs N/acre with a standard deviation of 15 lb N/acre and performed the same Monte Carlo simulation as above (but with the available N corrected for estimated nitrogen loss.

Figure 2. Impact of knife-to-knife variability on the impact of the maximum return to nitrogen for a fall and spring-applied swine manure to corn in a corn-soybean rotation and continuous corn rotations. The ideal rate varies with our machinery variation.

Almost all the curves looked the same. For example, the Maximum Return to Nitrogen in a continuous corn rotation was approximately 50 pounds higher in the continuous corn rotation than in the corn-soybean rotation, whether the manure was applied in the fall or the spring. The difference was impacted slightly by the knife-to-knife variability of the application equipment, but only slightly. Similarly, while the nitrogen loss from fall application was set at 15 lb N/acre, the fall application rates were on average 22 lb N/acre higher to hit the optimal rate.

So overall, where does this leave us. There is uncertainty and variability in every decision we make. The more confident we are about our equipment and manure, the closer our rate should be to the “true” MRTN. However, from an economic perspective, if there is uncertainty or variability in what we are doing, the right rate for us sneaks upward just slightly. This insurance N helps us in years we’d otherwise be short. And this is why we still talk about the 4Rs of right rate, right place, right timing, and the right type of fertilizer.

Manure Scoop: The Value of Real Time Nutrient Sensing

 

A few years ago, I became interested in the value of manure sampling and how obtaining good information helped us make better nutrient management decisions. I tried to use the theory of value of data to determine how much a manure sample was worth. Read a summary here.

 

Many factors cause variations in manure's average nutrient concentration: diet, housing type, manure storage type, environmental conditions, management techniques, and treatment practices. Just as critically, our ability to agitate and create a uniform, homogeneous mixture is often limited by our ability to stir manure storages.

 

A repeated sampling at five manure storages was used to assess the average, standard deviation, and coefficient of variability. The data were summarized as averages across the sampling data set to determine the variability in manure concentrations from each manure application event. Average manure nutrient concentrations were 28, 16, and 21 pounds of N, P, and K, respectively, per 1,000 gallons with standard deviations of 4, 7, and 3.

 

In determining the manure test's value, it is essential 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. This evaluation assumed the manure application method would be either injection or immediate incorporation to maximize N utilization. Additionally, we assumed 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.

 

Our methodology was to estimate 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. To make this evaluation, an economic model was developed as an Excel spreadsheet. The model compared the costs and revenue of corn production. Corn yield was calculated as the product of maximum yield and the estimated percent yield that was achieved.

 

For a corn-soybean rotation where the manure is going to corn, this means that the real-time nutrient correction for manure would be worth approximately $3.13 per acre. However, in a continuous corn rotation, which is more sensitive to nitrogen application in terms of crop response, it would be worth around $4.29 per acre. However, understanding just how big this variability is from load-to-load or pass-to-pass is critical for putting value to this technology.