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The real value of manure

Maria F. McGinnis Published on 30 June 2015

In the dairy industry, we know manure is valuable. But how valuable? Typically we look to nutrient composition as the major indicator of dollars and cents.

However, examining when, where, how, how much and even how well manure is applied can help dairy farms of all sizes start to realize its real value.

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“We all know that manure has value, but we have to know a few things if we want to use manure as a fertilizing product,” says Dr. Brad Joern, professor of agronomy from Purdue University.

The factors that help determine the value of manure are:

1. Manure nutrient content

2. Application rate

3. Losses between application and crop uptake

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4. Where to apply manure to get the biggest return

How valuable is valuable?

Focusing on a few major nutrients (nitrogen, phosphorus and potassium), a 75-cow dairy (for example) will generate about 440,000 gallons of liquid manure per year, which is equivalent to $15,000 worth of fertilizer.

Dairy cow nutrition plays a large role in the nutrient content of manure. “When we start looking at the phosphorus requirements of the dairy cow, byproduct feed sources (such as dried distillers grains or DDGs) result in much more phosphorus in the manure,” Joern says.

Manure does not supply nutrients in ratios that match crop need, so it’s important to pay attention to soil test results. “The value of your manure depends on where you put it,” Joern says. “If your soil tests are high, there is no point in spreading manure at that location.”

Hidden costs and manure application

Labour and fuel costs should also be factored into the value of manure. “It’s always the farthest fields that need the most fertilizer,” Joern jokes. “It might not pay to apply manure to those fields until your labour demands are lower, for example when the crops are off in the fall.”

Unfortunately, improper manure application can reduce the value of manure and even cause field damage.

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Spreaders that are not calibrated correctly can run out of manure too quickly and lead to soil compaction when the farmer drives over the ground to reload. Further, the time it takes to continuously reload leads to additional labour costs.

“The rate of application ought to be a function of your application equipment and the width of the field,” Joern says.

Examining total kilometers spent hauling manure during the year can help determine if application equipment is appropriately sized or even if hiring a custom manure hauler is necessary.

“How big is your honey wagon? If you have a 2,500-gallon manure spreader, upgrading to 5,000 gallons will cut your miles and trips in half,” Joern says. “There might also be certain periods of the year where being on a tractor for an extended amount of time isn’t practical – you might consider hiring a custom operator.”

Get with the program

Improved computer software could lead to answers and solutions for better nutrient management. Considerations need to be made for fertilizer price, soil tests, build times and even the farmer’s budget.

Joern has created a software model that looks at soil moisture (rainfall) and soil temperature along with the farmer’s location, soil texture, soil pH and fertilizer protocol.

The output of the model predicts nitrogen crop uptake and shows the level at which the crop will no longer make use of applied fertilizer.

To test the performance of the model, Joern collaborated with colleagues Dr. Jim Camberato, extension soil fertility specialist at Purdue, and Dr. Charles Wortmann, professor of agronomy and horticulture at the University of Nebraska – Lincoln.

“The model was almost flawless,” Joern says. “I can’t believe how good this is working.”

What’s next?

“In the real world, we are not farming 20 feet by 80 feet [like in a research trial]. You are farming big acres and the topography is varied,” Joern adds.

Preliminary testing of the model has been successful, and now different crops, soil conditions and climate are being tested.

With better tools to determine crop and soil fertilizer needs, removing policy barriers will be the real key to success with nutrient management plans in the future.  PD

Maria F. McGinnis is a freelance writer based in Sun Prairie, Wisconsin.

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