Cattle feeders have heard for years they should treat manure as a resource rather than a nuisance, but never has it been as true as it is today. Prices for commercial fertilizers for the 2009 crop are, depending on ingredients, up to 150 percent higher than those in 2007. Those prices have doubled the value of manure in a corn-soybean over the past five years.

Joe Lally is a nutrient management specialist with IowaStateUniversity, working with livestock producers to develop comprehensive nutrient plans. The goals for a feedlot nutrient management plan, he says, begin with stewardship of land and water and compliance with environmental regulations. But, he adds, cattle feeders are in business to make a profit, and a key goal of nutrient management is to capture that value in ways that generate returns to the business. Cattle feeders, Lally says, are making a transition from compliance with regulations to systems approach for nutrient management, linking their livestock and crop operations in a single business model.

Nutrient management must continue to evolve as shifts in other management practices change the makeup of manure. Feeding distillers’ grains, for example, significantly changes the nutrient composition of manure compared with that from cattle on a corn-based diet. In University of Nebraska research, feeding 20 percent to 40 percent wet distillers’ grains resulted in a 40 percent to 130 percent increase in the value of manure relative to manure from cattle fed corn, even after accounting for added costs such as hauling the manure further.

Recover

The first step in this process is to recover the nutrients contained in feedlot manure and wastewater. Good wastewater containment to prevent runoff and capture nutrients is, of course, a standard feature at feeding operations. Lally says pen maintenance – specifically more frequent pens scraping – helps minimize runoff and the need to remove manure solids from settling ponds. Additionally, research shows that by scraping pens monthly, rather than just at pen closeout, feedlots can increase nitrogen recovery by 7 pounds per head. At today’s nitrogen values, the difference is a potential improvement of $3.85 per head from regular scraping.

Lally says many of the cattle feeders in his area are scraping pens more. One example is Doug Freund, who farms and feeds cattle with his three brothers near Lewis, Iowa. The family’s feedlot features covered, semi-enclosed pens with capacity for 2,400 head. Freund says they routinely scrape the pens about every two weeks, partly to recover manure nutrients, and also to provide a more comfortable, less muddy environment for cattle, less runoff and less manure entering settling ponds.

Retain

The next step is to retain those valuable nutrients. Nitrogen, Lally says, is the “leakiest” of the manure nutrients, with phosphorus and potassium less likely to escape to the environment. Land treatments, rotations, tillage practices, timing of application, and environmental influences all contribute to successful manure handling retention of nutrients for crop use.

Storage practices play a major role in nitrogen retention long before the product is applied to crop fields. Researchers at the University of Nebraska recently completed a study comparing stockpiling manure with a composting system in which windrows were turned and aerated four times during the 111-day storage period. In this trial, nitrogen retention was significantly higher in the stockpiled manure. Also, the researchers found that dry-matter content, volume and weight of manure after 111 days were fairly similar for both storage methods. Composting is typically seen as a means for reducing manure volume to reduce transport costs, but the researchers concluded that those savings might not be enough to offset the added costs of management, labor, land and equipment needed for composting.

Looking at ways to recover and recycle as much of the manure nutrient content as possible, the Freund brothers avoid spreading on frozen ground in the winter. Instead, they stockpile manure in a field through most of the year, spreading and incorporating it in the fall.

Recycle

The final step in the process, Lally says, is to recycle nutrients through crops that generate returns to the operation, while minimizing use of commercial fertilizers.

He advocates comprehensive nutrient management planning including testing, proper application and cropping systems designed to fully capture nutrients from manure and lagoon water.

In the case of wastewater, he says most medium- to larger-sized feedlots in the area have installed travelling-gun or center-pivot irrigation systems on nearby cropland to use the water from their lagoons.

Sampling of lagoon water, he says, indicates nitrogen levels up to two pounds per 1,000 gallons, more than needed for a corn crop and about double that of most application recommendations and permits. Excess nitrogen offers an opportunity for more intensive cropping systems, he adds.

At the Freund operation, a center-pivot system irrigates 130 acres of continuous corn with water from the feedlot’s lagoon. High levels of nutrients in the water, Freund says, allow the family to bale corn stalks for bedding after harvesting for grain, rather than tilling the residue in, and the field rarely needs any commercial fertilizer.

The excess nitrogen also could produce an additional crop. Lally has been working with cooperating cattle feeders to test double-crop systems to use more of the nitrogen and return it to the cattle enterprise. They are planting a small-grain cover crop such as rye in late summer, to be cut for silage the following April. Early irrigation, he says, allows them to speed up germination and early growth, resulting in a strong stand going into winter. Abundant nitrogen in the topsoil facilitates rapid growth in the spring.

The following crop in the rotation – typically short-season corn for silage – probably won’t need much nitrogen, Lally says, adding that he recommends testing the soil when the corn is six to 12 inches high to determine whether additional nitrogen is needed.

Jeremy Singer is a research agronomist at the USDA/ARS National Soil Tilth Laboratory in Ames, Iowa. He has been working with Lally to assess nutrient cycling in crop fields irrigated with feedlot wastewater. Singer and his team have taken core samples from under the center pivot and outside the pivot’s coverage, to measure levels of nitrogen and other nutrients down to four feet deep in the soil. The fall rye crop, he says, does a good job of capturing nutrients, and grows well in response to the early irrigation. Outside the pivot, the rye produced 0.63 tons of dry matter per acre and accumulated 58 pounds of nitrogen per acre. Under the pivot, production was 0.97 tons of dry matter per acre and the crop accumulated 76 pounds of nitrogen per acre.

Using a cover crop for manure or wastewater application achieves three primary goals, Singer says.

  • It protects the soil from erosion.
  • It helps capture nitrogen for the following crop.
  • It provides carbon-rich organic matter to improve the soil.

There are, naturally, some costs associated with the fall cover crop, including seed, tillage and planting. Some producers, Singer says, harvest the crop in the spring for silage, which provides immediate value to help offset the costs. Others spray the field in the spring to kill the plants, then either plow the crop into the soil or use no-till equipment to plant corn. In these cases, the payoff is more in the long-term, with improved soil organic matter and recycled nutrients from the plant material returned to the root zone.

The cover crop also is a good candidate for a spring application of manure, especially if the producer plans to plow it under. Singer says trials have shown that when manure is incorporated with a rye cover crop, there is no yield reduction in the following crop of corn silage, while incorporating the cover crop without manure tends to suppress silage yields.

In the case of solid manure, Lally says, one application of manure typically provides enough phosphorus and potassium for four crop years in a corn-soybean rotation. Along with the nitrogen provided by the soybean crop, there typically is enough nitrogen for three years, with an additional application of 100 pounds of nitrogen per acre for the second corn crop.

In continuous corn, the manure generally provides enough P and K for three to four years, but Lally says the field will need more nitrogen. With management practices designed to preserve manure nitrogen, Lally believes manure potentially can provide all the nitrogen for one, and possibly two years in a continuous-corn system.

The Freunds test the soil in every field, and the nutrient content of the manure, and base application rates on the analysis. Continuous corn typically requires some supplemental nitrogen, and manure applications boost the need for lime to maintain the right ph levels, but commercial phosphorus and potassium usually are not needed.

Freund says that as fertilizer prices rise, he’s been able to justify hauling manure further, to a farm 11 miles from the feedlot. He says these more distant fields that received commercial fertilizers in the past benefit noticeably from manure applications as the organic material improves soil tilth and water retention in addition to adding nutrients.

Average U.S. farm fertilizer prices

2006                2007                2008

Anhydrous ammonia                                       521                  523                  755

Nitrogen solutions (30%)                                232                  277                  401

Urea (45 % N)                                                 362                  453                  552

Ammonium Nitrate                                         366                  382                  509

Super phosphate (45 % phosphate)                 324                  418                  800

Diammonium phosphate (18-46-0)                 337                  442                  850

Potassium chloride (60 % potassium)             273                  280                  561

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Source: USDA/ERS


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