by Sally Colby
Kevin Erb, Certified Crop Agronomist with University of Wisconsin extension, encourages farmers to understand the value of farm manure in crop production systems.
“The number one benefit of manure for cash grain operations is nutrients and financial,” said Erb. “Manure is an excellent source of macronutrients (nitrogen, phosphorus and potassium) and also a very significant source of micronutrients; particularly as coal-fired power plants have switched from using low sulfur coal to natural gas.” Erb added that about 30 years ago, farmers could count on five, 10 or more pounds of elemental sulfur equivalent per acre/per year in rain. “In many cases, normal precipitation doesn’t provide as much as the crop is removing.”
Erb points out that this issue is more critical in some of the sulfur demanding crops such as alfalfa, but manure can be an excellent economic source of some micronutrients; particularly boron, sulfur and zinc; and the impact from micronutrients can last five to seven years after the initial manure application.
The other obvious benefit of manure is its soil building aspects, particularly after heavy rain events followed by runoff and drying in summer. While farmers often think of manure as just manure, Erb says if feed doesn’t become milk on a dairy farm or meat on a swine, beef or poultry operation, it ends up in the manure stream. That manure stream includes urine/feces, animal bedding, waste feed and feed storage runoff, waste milk and dairy parlor wash water.
Erb noted there’s concern about whether sawdust bedding ties up the nitrogen in the corn. “What we’ve seen in farms that use sawdust for bedding, we need to be more watchful of what’s going on in the subsequent growing season,” he said. “If they’re using straw or rice hulls, we don’t see the problem nearly as much.”
Depending on the animal species and how much precipitation water and other waste is added to manure, the estimate is that every 1,000 gallons of liquid dairy or swine manure will have $6 to $35 worth of nitrogen, phosphorus and potassium per thousand gallons. When done properly, a farm can replace all of the corn’s fertilizer application with manure, and at the same time, reduce future phosphorus and potassium applications. “Most of the time, if we’re applying dairy or beef manure to the corn’s nitrogen need, we’re applying more phosphorus and potassium than the crop needs,” said Erb. “That’s going to build the soil for the future. With the phytase that’s been added to swine rations, nitrogen and phosphorus are where they need to be, but we are building soil test potassium.”
A manure analysis is the most accurate way to determine nutrient levels. Rather than collecting one sample from the edge of the pit, Erb suggests filling four to five coffee cans from every other load leaving the agitated pit, mixing them, and taking the sample from that mix.
Erb says the analysis is the starting point in determining the value of manure for economic agreements between farms. “I always recommend that it’s the certified crop advisor (CCA), the agronomist, who makes that agreement between operations and negotiates rather than the farmers themselves because of that independence factor,” said Erb. Erb also noted that while the majority of manure’s nitrogen, phosphorus and potassium are available the first year, those components break down slowly in soil over time and there will be an increase in soil test phosphorus and potassium levels in the future based on long-term availability.
Manure differs among species, and there can be inconsistencies throughout the year. “Swine manure smells stronger than dairy manure so there will be some different neighbor considerations,” said Erb. “Primarily because of the ammonia content. Factors such as whether the storage is underground or on the side that receives more rainfall will influence nutrient yield per ton and application rate, so again, manure analysis is a critical step in determining application rates.” Erb says dairy manure analysis is, in general, 31-15-19 per 1,000 gallons and solid beef manure is usually about 14-9-10 per ton.
“Fields that have seen manure seem to do better in drier summers when it’s hot during corn pollination,” said Erb. “Part of the reason is that we’re adding organic matter back to the soil, which increases soil water holding capacity. The other thing we’re seeing, particularly in some tighter soils with more clay content, is that the increased organic matter increases infiltration rate.”
Erb says this is a critical point because as the season progresses into the heat of summer and into the pollination window, the right amount of rain at the right time means significantly higher yields. “Conversely, we get into situations where we just get hammered with rain,” he said. “In spring, we can’t get the corn in and every day we’re losing one-half bushel to a bushel per acre because of delayed planting.”
According to Erb, a southern Wisconsin farmer who averaged 140 bu/acre in a drought year (2012). That farmer’s neighbors, who had the same soil, didn’t bother to combine their corn because it did so poorly. “Part of it is due to his long-term rotation of adding organic matter through cover crops and manure,” said Erb. “It’s an example of how the little things like cover crops and managing manure properly can have a huge impact in drought-stressed years.” Erb added that many of the cash grain farmers he has worked with see the benefit of manure for up to five years following application; not only in the nutrients in soil but also in increased water holding and infiltration capacity.
While using manure can build organic matter and improve soil quality, there are some negatives. “Weed seed is one,” said Erb. “Weed seed is an issue when we’re bringing in outside protein sources such as cottonseed or other feeds from outside the area. You need to be on top of scouting — the crop consultant needs to know that you’ve taken manure in.” Erb says farmers should watch for new weeds that haven’t been seen in the area, and also weed subtypes that may be more or less susceptible to herbicides.
Another potential negative with manure is neighbor relations. “Manure smells,” said Erb. “If we’re taking livestock manure for the first time, we need to be proactive. Manure that’s injected or incorporated immediately will cut odor by 90 to 95 percent.”
Erb also suggests developing good relationships with neighbors and paying attention to clues such as balloons tied to a mailbox or a large tent going up that indicate an event such as a wedding or picnic might be taking place.
“I strongly suggest that you pop in and say, ‘hey, I’m going to be doing this, I just want to make sure you don’t have something planned,’” said Erb. “The other thing I recommend is touching base with landlords to keep them in the loop.”