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Precisely Placing Manure Significantly Offsets Fertilizer Costs

The nearly 8,500 tons of manure Jon Greenfield’s 1,000 head of Black Angus cattle produce annually is a valuable nutrient resource for his crops. The brown gold not only contains nitrogen, phosphorus, potassium, and other nutrients but also adds organic matter to the soil. In turn, this can amend soil structure, aeration, soil moisture-holding capacity, and water infiltration.

“A local insurance adjustor has said numerous times that he can tell whether or not growers have livestock by looking at their field’s actual production history,” says Paul Bruns, a precision agriculture consultant. “On average, their yields are 10% higher than the grain farmer next door with no livestock manure to apply on fields. There’s that much potential benefit from manure.”

For years Greenfield, who grows 1,400 acres of corn and soybeans in Balaton, Minnesota, has been applying a flat rate of manure across his fields. “Once Paul and I started looking at soil tests and the nutrient recommendations, I was amazed at how much manure I was underutilizing,” he says.

With the help of Bruns, who owns Precision Consulting Services in Canby, Minnesota, Greenfield found a way to combine the technology he was already using in crop production to precisely apply the eight loads of manure he hauls weekly, which totals 32,000 pounds.

“The idea for variable-rate manure began when we did some variable-rate lime,” says Bruns. “Up until about five or six years ago, if you put lime on ground in southwest Minnesota, most people thought you were crazy because there are high calcium carbonates in the soils.”

However, there can be a wide range of pH levels in any given field. When ground was grid soil-sampled, it really drove that point home. 

“Yes, pH will run from 4.7 to 8.4 in the same 80-acre field,” explains Bruns. “Variable-rate lime turned out to be one of the fastest paybacks compared with just a flat rate.”

Working with a technician to set up the variable-rate lime application, Bruns realized he had the same Artex spreader that Greenfield was looking to purchase. “It made me realize we could do this for manure just as easily,” says Bruns.

“The best part was that I already had Ag Leader’s Integra monitor, which can be moved effortlessly from the planter or combine to the spreader,” says Greenfield. “All it cost me to have the ability to variable-rate the manure was $3,000 to add a flow valve and a speed sensor. Being able to get the most out of the technology when I don’t have the extra funds to spend on an entire system is a smart strategy.”

crunching the numbers

Ag Leader
Although Greenfield is in the first year of varying the amount of manure being applied to his fields, early estimates show an impressive return on investment.

“My annual P and K costs are close to $60,000 for both my corn and soybean acres,” says Greenfield. “By variable-rating the manure, I will be able to save roughly $30,000 on my corn ground and $26,000 on beans. My return on investment for a technology that only cost me $3,000 is huge.” 

As a bonus, that amount doesn’t even include the savings he’ll see in nitrogen. “It’s going to cost me $43 per acre to buy nitrogen commercially this year,” says Greenfield. “My cost went from $150 per acre to less than $50 per acre because of the way I’m applying the manure.”

“At the same time, he is still pushing yields,” adds Bruns. 

To accomplish this, Bruns closely evaluates yield maps and yield goals, and he takes soil samples on 2½-acre grids. 

“I also look at Jon’s extensive yield data history to determine the potential of each field, and I use that as a guide,” says Bruns. “We use a lot of variable-yield goals in the equation because his heavy clay soils can produce anywhere from 80 to 220 bushels in the same field.”

Correctly calculating the rate of manure per acre starts with knowing its nutrient value.

“We take manure samples at least two to three times a year and treat that manure just like we would a starter credit,” says Bruns. 

Based on all this information, prescription maps are developed to accommodate his varying soil. “I have one field that is getting zero manure in one area and 12 tons in another,” says Greenfield. 

A scale on his spreader also verifies how much is being hauled to each field. “I know exactly what I’m applying and where. If there is ever a question and I need to go back and look at the records, I can easily do that,” he says.

Because manure is being placed so precisely, he may see another benefit. “After next year, I might have extra manure to sell,” says Greenfield. “Every ton is worth a minimum of $11.

“Technology like variable-rate manure is going to make me money in good times and keep me farming in tough times, especially when I can take a piece of hardware I already have and use it for another application,” he says.

Test manure first

Before manure is applied, make sure it’s tested. Studies by the University of Minnesota (UMN) find nutrient values for nitrogen, phosphorus, and potassium vary 300% from farm to farm for the same species. More livestock producers recognize the value of testing manure, yet fewer than half in Minnesota do so, estimates Michael Schmitt, UMN.

“Testing manure IS extremely critical in sound nutrient management, from an agronomic, an economic, and an environmental perspective,” Schmitt says. “Precision application is a great technology to use since the nutrients needed do vary across a field. If you don’t know the analysis of the manure you’re applying, it diminishes the value of the variable-rate application.”

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