If corn is king in the Midwest, hog manure is certainly a member of the royal court.
“Not too many years ago, if you had hog manure, you just wanted to get rid of it,” says Gyles Randall, professor and soil scientist at the University of Minnesota (U of M) Southern Research and Outreach Center. “But with increased fertilizer costs and the nice growth responses (corn) growers have seen, hog manure has taken on a real positive light.”
U of M trials have demonstrated that corn yields average 10.7 bu./acre more when soil is fertilized with hog manure (applied during spring) compared to commercial fertilizer applied at a non-limiting nitrogen (N) rate.
Northern Illinois grower Kim Huntley built two 2,000-head swine finishing barns in 2002 to diversify his 3,000-acre corn and soybean enterprise. The resulting manure has been a nice boon, says Huntley. The two barns provide fertilizer for approximately 400 acres near the site. In 2006, Huntley constructed a 4,800-head finishing facility, which will supply manure to an additional 600 acres.
Huntley pays $50/acre to a custom applicator each fall to pump manure directly from the 8-ft. pits underneath the facilities and inject it in select fields. Manure is applied to any given field every three years:
Year 1: Liquid manure is injected at agronomic rates; no other commercial fertilizer is used.
Year 2: No manure is injected. Commercial N (as anhydrous ammonia) is applied at a rate of 140 units with adjustments based on soil productivity. No added phosphorus (P) or potassium (K) is applied.
Year 3: No manure is injected. A full rate of commercial N (as anhydrous ammonia) is applied with no added P or K.
At today's fertilizer prices, Huntley figures the manure is worth $60/acre in year 1 ($110 in comparable commercial fertilizer cost minus $50 for manure application), $40-60 for year 2 (based on total P and K credits and some N credit) and $35 for year 3 (based on total P and K credit and no N credit).
The manure has benefited Huntley's bottom line and enhanced crop performance and yield. “Occasionally, when you put on anhydrous ammonia, you'll see some streaking (leaf discoloration), but I haven't seen that with this,” says Huntley. “The fields are more uniform.”
In 2007, GPS yield maps revealed a 15-bu. average yield advantage in a field split between corn on corn and corn on soybeans. Each side of the field had similar coarse, sandy clay loam soil and Huntley managed both sides alike, other than fertilizer application.
If some would argue that the N rate on the corn on soybeans seems low, Huntley answers he is convinced that carryover from the previous manure treatment, plus residual N from the soybeans, provides adequate levels for the agronomic conditions.
So why does corn love manure? “My agronomist says an increase in organic matter and the way the microbes in the manure interact with the soil make the tilth better,” Huntley says, adding that the soil is easy to work up and free of clods. “It makes a good seedbed.”
Randall says soil scientists have yet to determine exactly why corn thrives in manure-treated soils. He agrees that micro-organisms may be a factor, as well as the presence of micronutrients, such as sulfur or zinc, not provided in commercial fertilizers. In addition, research has shown there are changes to the soil's aggregation or structure that may curb water and P runoff.
Minnesota farmer Irv Sether, who grows corn and soybeans with his family near Jackson, credits manure application for transforming what he once considered the poorest yielding of their 40-plus fields into their best-producing ground. Last year, the Sethers pumped 7.5 million gallons of liquid hog manure onto 1,420 acres, including 280 acres' worth of manure sold to neighbors.
“It seems to have brought out yield increases in ground we couldn't improve with commercial fertilizers,” says Sether. “It has a combination of various nutrients that are lacking in the soil.”
Soil scientist Randall cautions that soil should be 50° or less before manure is applied in the fall to reduce risk of N loss. This occurs when N in manure is converted to the nitrate form, which is susceptible to loss via leaching or denitrification when excess spring rainfall occurs. He says spring applications pose less risk because N doesn't have as much time to convert to nitrate before plant uptake.
Nutrient availability can vary with the manure source and age of pigs. However, the N and other nutrients in liquid manure from swine finishing facilities remain fairly constant. “Approximately 75-80% N in swine manure from finishing facilities is available to crops so long as it is injected or incorporated into the soils immediately,” Randall says.