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Unfenced Answers: Incorporating Manure into Your Fertility Plan


Unfenced Answers: Incorporating Manure into Your Fertility Plan

Q: What are the main considerations when making manure a part of your fertility plan? - Brian Gordon, via CropNutrition.com Facebook page

According to Mike Ballweg, a University of Wisconsin Extension soils and crops expert, there are a number of important things to consider before you can successfully include manure in your farm fertility plan.

“A nutrient management plan using manure looks at three things,” Mike Ballweg says. “First, you’ll want to consider the nutritional needs of the crop to be grown, then the soil test levels of nutrients, especially phosphorus, and finally, the ‘P-Index,’ or Phosphorus Index.”

The P-Index is a numeric value that combines the soil test level of P, the topography of the field and the farming practices being used, such as tillage, buffer strips and the crop rotations being implemented. It is a measure for the potential of phosphorus leaving a particular field. The higher the P-Index value is, the greater the potential for phosphorus running off.

“Without the basic soil test, showing P and K levels along with pH, the farmer doesn’t know where he’s starting,” Ballweg explains.

In addition to soil testing, growers should routinely check the manure source for the amount of available nutrients.

“Sampling the manure gives farmers a better handle on the potential nutrient input,” Ballweg says. “We have book values, but book values are averages, and there can still be a wide range.”

Knowing soil nutrient levels and manure nutrient levels helps to better determine a soil fertility plan for your farm. It will also help to avoid possible overapplication, which can bring environmental concerns.

Farmers with low phosphorus levels who are interested in adding manure to their crop nutrition plans could work with livestock operations that may have built up phosphorus levels. Purchase manure from livestock facilities nearby, spread it on fields to assist in building up phosphorus levels, and you may find there is nitrogen and potassium in the manure, too.

“But the phosphorus is where all the attention is focused,” asserts Ballweg. “That’s the source of greatest water quality concern.”

The crop being grown, as well as the crop rotation, become key considerations in deciding if manure is an appropriate crop nutrition source.

“Corn is probably the crop with the highest nitrogen requirement, so manure applications made before planting [each] corn crop make sense, assuming phosphorus levels aren’t already too high,” Ballweg advises. “Most nutrient management plans, when they are developed, include determining a rotation: maybe three years of alfalfa, two years of corn, a year of soybean and then maybe back to corn. Winter wheat also works well in the rotation in this part of Wisconsin.”

Getting the manure into the soil helps maintain the highest level of nutrients, and there are a few things to keep in mind when applying.

“From a sound agronomic perspective, we like to see manure injected; or, if it is broadcast, to be incorporated as soon as possible,” Ballweg says. “There are three reasons for that: One, you save more of the nitrogen in the manure; two, it reduces the probability of manure runoff in the case that you would receive a significant rainfall; and three, farmers want to be good neighbors, and injecting that manure will significantly reduce odor issues.”

He adds that one of manure’s chief benefits is adding organic matter to the soil.

“Organic matter is very beneficial in building up soil tilth,” says Ballweg. “It increases the water-holding capacity of the soil. In periods when it is dry, the soil holds moisture a little better. Likewise, higher organic matter levels increase the water infiltration rates and help reduce soil erosion.”