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10 things everyone utilizing manure should know

Progressive Dairy Editor Karen Lee Published on 31 July 2020
Manure spreader

Balancing manure and fertilizer applications, crop production and environmental conservation is an ongoing challenge.

Having the knowledge and understanding of several foundational principles of nutrient management can aid in making better farming decisions.

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Robb Meinen, a senior extension associate in the Department of Animal Science at Penn State University, provides the following 10 key points to his nutrient management students when he wraps up a semester’s worth of instruction.

“I do this to bring all the science we learned into simple messages,” Meinen said during a presentation at the 2019 North American Manure Expo in Fair Oaks, Indiana. These foundational nutrient concepts extend beyond the classroom and can be used by anyone working to manage nutrients.

1. Nitrogen and phosphorus imbalances are present in manure

“This is why we have issues that drive nutrient management planning, manure management planning and why one farm will have one rate and another farm will have another rate,” Meinen said. He showed the average amount of nutrients in dairy manure and the amount of nitrogen, phosphorus and potassium needed to grow corn. If the amount of dairy manure is applied to fulfill the nitrogen need of corn, then it is likely phosphorus will be over-applied. In areas of the country where soils are high in phosphorus and manure applications need to be based on corn’s need for phosphorus, then the amount of nitrogen needed for the crop will be under-applied, and the crop would need to be supplemented with a commercial nitrogen fertilizer.

2. Nutrient sources have variations

Manure at one farm will have a different nutrient content than another. The amount of nutrient availability in manure varies from farm to farm and species to species.

3. Variation of nutrient delivery

The type of soil, among other factors, impacts how nutrients are delivered to a water source. For example, the Chesapeake Bay watershed contains a wide variation of soils. Meinen said, “Fifty-eight percent of phosphorus delivered to the Chesapeake Bay comes from agriculture, but there’s a great variation depending on where you are at.” The western side (Maryland) has about 50% of the phosphorus coming from agricultural sources, whereas the eastern shore with sandy soils shows that 80% of the phosphorus comes from agriculture.

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4. Natural processes are important for nutrient cycling and utilization

Natural processes in the soil make a big difference in nutrient cycling, such as the nitrogen cycle. Microbial processes can change how nutrients are delivered. They can enhance the uptake of nitrogen and phosphorus but also increase the potential for nutrient loss.

5. Timing is important

The nitrogen uptake in corn starts slowly. When the plants get to be 12 inches to 24 inches high, the corn growth can suddenly take off and more nitrogen is needed. “The timing is very important. Where’s the best spot to put our nitrogen? Right here before the crop really needs it,” Meinen said, pointing to the early growth stages on a chart. One way of adjusting that timing is to sequester nitrogen in cover crops. They pull in and hold nitrogen as they grow in the fall and early spring, when there traditionally isn’t any crop growth. “I would encourage you, wherever you are, to adopt cover cropping or double cropping if you can,” he said.

6. Placement is important

The nutrient source combined with the risk of transport is the basis of phosphorus indexing, Meinen said. Sources can be soil, fertilizer or manure, while transport can be erosion, runoff, leaching or volatilization. Either a large source with little risk of transport or a small source with high risk of transport may be OK; but when source and transport are both high, it could result in a critical area with a high chance of phosphorus loss. Phosphorus indexing identifies those critically high areas on the landscape.

7. Dissolved phosphorus is necessary, but understanding and management are necessary too

What’s been happening for the past several decades in Lake Erie shows the impact of phosphorus fractioning. Going back to 1967, the amount of phosphorus loss into the lake was increasing. It steadied out with more soil conservation. Then the practice of no-till became highly popular. Eventually, tile drains were added to an area in western Ohio, known as the Great Black Swamp, to convert it to better farmland. Dissolved phosphorus is readily available for plants and is in the form that goes where the water goes, whether it’s through the tile drain or across the soil surface.

In no-till farming, the fertilizers and manure are more likely to build up on the surface and therefore are more susceptible to becoming dissolved phosphorus. As the amount of dissolved phosphorus began to increase in the mid-90s, so did the algal blooms in the watershed. “Total phosphorus didn’t change much, but a little bit of dissolved phosphorus did. If you think about that, that is a really important thing to understand in phosphorus management,” Meinen said.

8. Lower rates can increase plant response and limit risk of nutrient loss

The way plants respond to nutrients can be set on a curve. Any fertilizer added over the maximum production level won’t yield any more than what the plant is capable of. Also, as plants near their maximum-yield capacity, the response to nutrients begins to diminish. “That’s an important principle to think about when you’re looking at fertilizer and manure management,” Meinen said. “How much do you spend or want your application rate to be to try to squeak out those last bushels? You might be able to be the best corn producer in your neighbourhood, but you might do it at a cost.”

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That cost may come in dollars, but also to the environment. He recommended if you’re in a position where you have a lot of acres and only a limited amount of manure, it is better to put the manure across more acres than to concentrate it on a smaller land base. “That gets you more response with your initial application and, by the way, environmentally it’s probably better too,” he said.

9. Soil test interpretation allows for maximum production while limiting risk of loss

The same principle transfers to soil testing. Soil test recommendations are likely going to recommend nutrient applications to fall within a high response area while not being abusive to environment.

10. Soil health is so important

Soil health is the foundation for nutrient management, as microbes in the soil are the drivers of natural nutrient processes. For example, Meinen said, the organic matter of soil impacts the nitrogen cycle as it helps immobilize nitrogen and hold it in the soil until the plant wants it. Microbes are more active in warm, moist climates. In the summer, higher microbe activity can coincide with nutrient uptake when the crops need them to grow. Good soil health and organic matter helps to hold and immobilize nutrients during cold weather. Cover cropping is a way to accomplish this too.  end mark

PHOTO: Nutrient imbalances and variations of livestock manure are two of the foundational concepts to understand when working with nutrient management plans. Photo by Karen Lee. 

Karen Lee
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