Hands-on manure study sheds light on phosphorus

Farmers know that manure is an excellent source of nitrogen, phosphorus and potassium for our field crops, and it provides other benefits for soil quality. Here in Michigan, there are key assumptions that are used when determining the actual amount of nutrients that are available in the first year of application.

Nitrogen is highly variable depending on species, storage and handling. Potassium is considered 100% available from manure. Agronomically, 80% of phosphorus is available for crop growth in that first field season. (By the Right to Farm Act’s generally accepted management practices and for regulatory purposes, we need to assume 100% of the P as it is applied.) However, this key assumption on P availability varies throughout the Midwest and is based most often on laboratory study data rather than field-based studies. It is for this reason that I spent more than two years of my education working hands-on with a large supply of manure.

That large supply of manure was intended for an even larger field-based study in Wisconsin. This study involved applying fertilizer, dairy slurry, dairy semi-solid pack, swine slurry and poultry pellets at rates to supply approximately 80, 160 and 240 pounds of phosphorus per acre, as well as involving a control area that received no phosphorus. All of these treatments were applied to cornfield locations with low to very low soil phosphorus levels. These lower phosphorus levels were used with the goal of being able to measure a response to increased phosphorus application in corn yield.

Getting the results

After hours of labor, a few manure baths, and 3,000 soil and plant samples later, we had some results. When comparing yields, the type of phosphorus source used did not affect yield. Basically, in the eyes of your corn plant, phosphorus is phosphorus regardless of where it comes from. The lack of difference between fertilizer and manure also implies that manure phosphorus is 100% available in the first year of application. However, it’s always good to remember that, unless you’re hand-applying manure as evenly as possible, there will be application inconsistencies that can be accounted for by using a more conservative percentage such as the 80% currently recommended in Michigan.

Additionally, corn yield did not increase as the amount of phosphorus applied increased, showing that applying phosphorus above crop needs on low-testing soil won’t earn you a yield boost. If this is the case in low-phosphorus soils, you can easily make the connection that the majority of our agronomic soils that have high beginning phosphorus levels have an even lower chance of seeing yield boost from increasing phosphorus applications. The take-home message: If your phosphorus levels in your soil are already high, you are probably wasting your money on applying more phosphorus fertilizer.

Finally, we looked at how soil phosphorus levels changed from the beginning to the end of the season. We observed that for every pound of phosphorus per acre applied, manure and fertilizer increase the phosphorus levels in soil tests equally. This hints that equal overapplications of manure and overapplications of fertilizer will increase the phosphorus levels in the soil by the same amount.

The study’s take-home points:

• The current agronomic recommendation of 80 availability of phosphorus from manure the first year of availability appears to be a good, conservative, yet accurate, assumption.

• A yield boost was not observed in low-testing soils, showing that if you have high-testing soils, the likelihood of seeing a yield boost with additional phosphorus applications is much lower.

• Regardless if you’re using fertilizer phosphorus or manure phosphorus, overapplication beyond crop need will lead to an increase in soil phosphorus.

Using your manure fertilizer wisely will help you maximize yields and minimize costs. To get the most from your applications, use your soil tests and always test your manure for nutrients.

Sneller is a Michigan State University Extension field crops educator based in Saginaw County. You can reach her at snellere@msu.edu.

MSU dairy farm earns top honor — again

Operating a modern dairy farm means being responsible for and committed to caring for animals around the clock. Owners and farm managers must keep a close eye on all the details to keep the farm running smoothly. Add to the typical daily routine the mix of research trials and a revolving student labor force, and it becomes even more challenging.

The crew at the Michigan State University dairy farm has been able to overcome these obstacles for two consecutive years to be awarded the distinction of being a National Dairy Quality Award Platinum level dairy farm. Winning the top-rated NDQA Platinum award essentially means that the farm produces the highest-quality milk.

This award is considered the “gold standard” of awards. This year the award was presented to the top seven dairy farms in the country that achieve extraordinarily high marks for milk quality. Official bacteria and somatic cell count tests measure the milk quality level; low bacteria and SCC levels indicate higher levels of milk quality.

Bob Kreft manages the 135-cow dairy farm, located on the MSU campus in East Lansing. Kreft, along with four other full-time employees, oversee the day-to-day operations on the farm. The dairy farm work force also includes 22 part-time college students.

“Achieving high-quality milk takes a commitment to detail each and every time the cows are milked,” says Gary Trimner, director of quality control for Michigan Milk Producers Association, the cooperative that markets the milk from MSU. “It is quite remarkable that the MSU Dairy has achieved this award for two consecutive years. It is not an easy task.”

Management details

Kreft attributes the dairy’s success to changes in animal bedding and training the employees.

“It has been a lot of small things that have had a cumulative effect,” he says.

The first step the dairy made to improve the milk quality was to change the type of bedding material used in the cow stalls. Switching from green sawdust bedding to kiln-dried sawdust lowered the number of mastitis cases in the herd and subsequently lowered the SCC in the milk.

As the somatic cell levels dropped, the employees were challenged to see how low the count could go. “It became a bit of a game for the students to see how low the count could get,” Kreft says. “Everyone was getting excited to see the quality levels go up, and they worked harder than ever to achieve the best results we could. It was really a team effort by everyone.”

The MSU crew also made changes in the milking routine. Using lab reports from Dairy Herd Improvement, the employees spot any cows that may need individualized medical attention.

Winning national recognition for high-quality milk is nice, Kreft believes, but the motivation for producing high-quality milk goes further than winning awards. “We take pride in knowing that we are shipping a high-quality product every day that consumers can trust and enjoy,” he says.

The MSU farm herd consists of 150 milk cows and 150 heifers and calves.

Source: MSU College of Agriculture and Natural Resources

This article published in the April, 2010 edition of MICHIGAN FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.