By this time of year, many farmers are dealing with liquid manure storage at capacity. As farmers consider how to use manure in spring, Glen Arnold, field specialist in nutrient management, Ohio State, urges farmers to understand how stored nutrients affect crops.

“About 50% of the nitrogen, phosphorus and potassium is actually in the nitrogen, so if it’s in the ammonium form and ready to use, you can use it on a growing crop,” said Arnold. “If manure goes out in fall, in most areas, about half of the nitrogen will be lost over winter.”

Dairy manure analyses are typically returned with values for total nitrogen, ammonium nitrogen and organic nitrogen. “As dairies have moved away from organic bedding and more to inorganic sources of bedding, we’re seeing the ammonium nitrogen percent rise in dairy manure,” said Arnold. “Sometimes we see as high as 18 to 20 pounds of ammonium nitrogen in dairy manure.”

Both swine and dairy manure are reliable sources of potash for alfalfa and similar crops. “It’s important to emphasize the balance for phosphorus with any manure,” said Arnold. “You can put on enough for two or three years of crop rotation, but we don’t want to build phosphorus levels.” Swine and dairy manure are also good sources of sulfur.

Arnold referenced a farmer who has ample wheat fields that are ideal for spreading swine finishing manure in early spring. However, not all farmers have that option.

“Some commercial manure applicators use a coulter with a depth control rim on the outside, hooked up behind a tanker,” said Arnold. “It creates knife marks through the wheat field and puts manure directly on top of the knife marks.” Depending on the state, this method may qualify as incorporation.

An alternative for manure application on wheat is a drag hose. Arnold cited an applicator who applied sow manure at approximately 10,000 gallons/acre. In most cases, sow manure will be lower in ammonium nitrogen and other nutrients compared to swine finishing manure. For correct total nitrogen, some farmers apply swine manure twice, spaced appropriately.

“You should not over-fertilize wheat,” said Arnold. “The wheat will go down and no one enjoys combining fields that have gone down badly. With high rates of nitrogen on wheat, you can get into that situation quickly.”

If wheat is becoming too tall for surface application, drop nozzles help direct manure to the ground instead of depositing it on the leaves. If the wheat is used for silage or wheat haylage, manure isn’t a problem because the drop nozzles have placed it on the ground.

Fields that had manure applications the previous autumn will still have nutrient benefits the following spring, but technique is critical. Arnold explained a field study in which manure was knifed-in in strips with the intent of planting corn directly on top of the strips the following spring. A similar study in Canada involved knifed-in manure in April followed by planting in May.

“They had real problems getting decent emergence,” said Arnold, adding that less than 50% of the corn grew. “If the planter is moved over about six inches from the manure, it might work, but it’s hard to get the ground fit for equipment after liquid manure has been knifed into the ground.”

For autumn manure applications, Arnold suggested considering whether manure was incorporated or left on the surface for weeks before being worked in. “Most ammonium loss happens in the first few days,” he said. “After that it doesn’t leave as fast.”

For soil testing to determine manure needs, pull the soil core from the proper depth – likely deeper than for a standard six-inch soil sample test. If there’s a known manure history for the field with recent manure applications, a pre-sidedress nitrate test (PSNT) may be useful for determining nitrogen application. Farmers who use a commercial applicator to manure sidedress corn should plan ahead for availability.

“Some farmers are applying manure with tankers with Dietrich sweeps or rolling coulter toolbars,” said Arnold. “Do the math ahead of time and make sure you can get to the other end of the field. You don’t want to go across fields twice with heavy tankers. We like to run Dietrich sweeps behind the toolbar or behind the wheel row to take out some of the compaction.”

The industry trend is moving toward using a “wavy” coulter, which tills soil to two to three inches, puts the manure on top of the loose soil, then covers it. There may not be as much covering in a no-till system, but it should be enough to take care of worm holes and preferential flow treatment.

Many farmers had a tough time establishing and/or replanting crops in 2024. To find potential solutions for dairy and swine manure application in rough years, Arnold conducted a comparative manure application study. Manure was either incorporated or surface applied at a higher rate in a planted field.

“They planted corn, and the dairy needed manure storage space,” said Arnold, explaining the dilemma. “Rather than putting manure on first and waiting until the field was fit, the applicator drove across the field at an angle. They sidedressed fertilizer but backed off about 40 pounds per acre, assuming the dairy manure would make up the difference.”

When Arnold pulled leaf tissue samples at pollination, both the dairy and swine farm reports came back within sufficient range.

Familiarity with crop growth stages is important in dragline manure application. Arnold prefers drag application at V3 and no later than V4. Another way to determine crop suitability for a drag is to step on the corn – if the plant snaps, it’s too tall and won’t come back as it should. If the plant bends over and just looks bad, it’ll straighten up the next day and will be fine.

“Not every field is a candidate for a drag,” said Arnold. “On a loamy soil, nitrogen may be moved around due to soil piling up as the hose moves across the field. Sometimes dirt is piled up enough that the hoses pull apart. If you deep work it in spring and haven’t had any rainfall, odds are good it’s too soft for a drag hose. If it’s a stale seed bed or has a cover crop, it should work well.”

For drag lining manure on hay fields, consider biosecurity issues such as Johne’s transmission through baled dry hay. “Don’t wait until a week before harvest to splatter manure on a field, make hay from it and then be surprised when there’s disease transfer,” said Arnold.

by Sally Colby