Capturing, storing and applying swine manure as crop fertilizer are increasingly important objectives both in terms of maximizing its value and reducing or eliminating commercial fertilizer costs.

Without a doubt, manure has value as a fertilizer, but due to varying nutrient levels in the manure as well as fluctuating fertilizer costs, its value changes and is often difficult to measure. 

One of the challenges in capturing its value for cropland is matching the manure’s nutrients with the crop’s requirements. Another challenge is choosing storage and application methods that maximize manure’s nutrient value. The closer that the nutrients match the crop's requirements the greater value you will realize from the manure.

Nitrogen, phosphorus and potash are the big three when considering manure’s value. So, how do you capture maximum value from these nutrients?

 “Producers receive maximum value from manure by applying it to their own fields which require nitrogen, phosphorus and potassium,” says John Lory, Extension nutrient specialist, University of Missouri. “Seek out fields that require nitrogen, phosphorus and potash so you get value for all the ingredients.”

Most manure sources will oversupply phosphate and potash. “When you apply manure based on a field’s nitrogen requirements, you will be applying nearly as much phosphorus and often nearly as much potash as nitrogen,” Lory says.  To address that, you need to find fields that have a high demand for phosphorus and potash.                

The nitrogen, phosphorus and potash in manure can vary due to your storage system. But your feed management programs also play a role.

Manure storage systems vary in the ability to preserve manure nutrients. If manure matters to your operation, the deep-pit-slurry system is far superior to most lagoon systems, as it preserves more nutrients as well as organic matter.

“When land-applying manure from a typical lagoon system, you’re applying a small fraction of nutrients excreted by the pigs,” Lory says.

Agitating the lagoon will mobilize nutrients in the sludge for land application. However, it is difficult to fully agitate a lagoon to get the consistent nutrient concentration needed to collect fertilizer’s full value.

Too often overlooked is manure’s organic matter contribution, which improves soil structure and water-holding capacity, and helps moderate nutrient release within the soil. All manures are not created equal, Lory says. “Swine manure has lower levels of organic matter compared to manure from other species.”

Deep-pit-slurry systems again hold an advantage over lagoons when it comes to organic matter.

Manure also is useful as a micro-nutrient fertilizer. “With manure application, sulfur, zinc, magnesium and other micros are usually delivered in quantities that exceed crop removal,” Lory says. “If you’re applying manure, you likely won’t need additional micro-nutrients.”

Keep Manure in its Place

For manure to be a reliable fertilizer and to receive its full value, you must keep it where it belongs, Lory stresses. He provides four critical factors to address:

  • Analyze manure —The nutrient level varies with feeding and manure storage strategies. Because of these variables, sampling is a critical step in getting a reliable nutrient estimate to know what you’re applying. Collect samples of each manure batch and have a laboratory run an analysis.

    “Ask for total nitrogen, ammonium nitrogen, phosphorus, potassium and moisture content,” Lory says.  (For manure sampling and analysis information, go to porkmag.com/environment.)

  • Estimate the nutrient availability — Request that the analysis report be expressed in terms you can work with on your operation.  Phosphorus and potassium will be 100 percent available. However, not all of the nitrogen is available to the crop. “Use state-based recommendations for calculating nutrient availability,” Lory says.           

    Manure application methods will affect the nitrogen availability. Volatilization and the resulting nutrient loss will occur with surface application, whereas injection preserves more nutrients. “An important factor when injecting manure is to make sure you’re getting good soil closure over the injected manure,” Lory says.

  • Apply at the target rate — When irrigating manure, adding extension hoses or changing nozzle size will affect the application rate. Periodically calibrating manure application equipment helps ensure that you’re applying manure at the target rate. Maintaining the correct application speed also is important in this effort.
  • Apply uniformly over the field — Lory says uniform manure application is important to maximizing manure’s fertilizer value. If you don’t apply manure evenly and in a uniform pattern across the field, it will result in gaps that will hurt yields. Lory warns that field areas near manure storage facilities may inadvertently receive more manure than areas farther away due to varying hose lengths and pressure.
           
    Inadequately spaced risers also may interfere with even application.  Avoid fluctuation in hose pressure due to elevation changes which affects the application rate. “Watch those injection channels, especially on side hills,” Lory warns. “Make sure the manure is not running down the hillside instead of being absorbed into the ground.” Make sure the manifold on injection units is evenly distributing to all injectors and that none are plugged.

Injecting manure adds to the predictability factor of application. That’s because it gets nitrogen and the other nutrients under the soil and prevents volatilization which reduces the manure’s value. “Use a known nutrient concentration to ensure the levels of each nutrient you’re applying and then inject the manure to increase the predictability,” Lory says.

Since manure offers extra value to most pork producers today, it pays to adopt strategies and tactics that can help you tap the full value from this important asset.


Feed Management and Manure Value

Changes in feed management strategies can impact the nutrient make-up of manure. Certainly, the dietary nutrient balance plays an important role in the economics of both feed and manure fertilizer value.

So when making feed decisions, it’s worth considering the consequences for the manure’s nutrient level. “When you bring feed onto the farm, think in terms of bringing fertilizer onto the farm,” suggests John Lory, Extension nutrient specialist, University of Missouri.

Typically, the pig excretes at least 65 percent of the nitrogen consumed, 95 percent of the potassium and 55 percent of the phosphorus. 

Lory calculated the numbers to estimate the annual nutrient excretion of a typical finishing barn with 4,800 animals and 2.2 turns. Excluding an estimated 30 percent loss of nitrogen in a slurry system, plus losses through handling and application, the expected plant-available nutrients from that finisher will be 48,000 pounds of nitrogen, 45,000 pounds of potash and 33,000 pounds of phosphate.

Lory then calculated an average manure value based on recent values of commercial fertilizer. “There’s around $30,000 in nitrogen, $30,000 in potash and $10,000 in phosphate for a total of $70,000 of fertilizer value in the manure,” he estimates.

Some ingredients can actually help you customize your fertilizer needs and reduce your feed costs without impacting your pigs’ growth rate. Distillers’ dried grains with solubles is one such example; it adds additional phosphorus in the manure. So, if your fields need phosphorus, DDGS may offer additional benefit.