LETHBRIDGE – Producers who want their crops to recover the most nitrogen possible from liquid hog manure are encouraged to pay attention to application rates and methods of placement.
“In the case of liquid swine manure, (applied) at an agronomic nitrogen rate, we see recovery of about 50 percent of added nitrogen in the crop in the year of application,” says Jeff Schoenau, a soil scientist from the University of Saskatchewan.
He is currently working on a way to add a nitrification inhibitor to liquid hog manure to maximize crop recovery of the available nutrients.
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When applied at 3,000 gallons per acre, he told a recent manure management conference in Lethbridge, hog manure provides about 100 pounds of nitrogen per acre.
“Those kinds of recoveries we’re getting, at 50 percent recovery in the crop in the year of application, come close to what we see with commercial urea nitrogen fertilizer,” Schoenau said.
“We also know that when you do it wrong, when you over apply, that automatically equates to low recovery. The crop can only use so much nitrogen. The excess you apply tends to accumulate as nitrate and is either leached or denitrified – converted to nitrous oxide and N2 gas and lost to the atmosphere.”
Much of the nitrogen contained in liquid swine manure is present in the form of ammonium. Schoenau said ammonium has a positive charge, so it is adsorbed to the negatively charged particles in soil, such as clay and organic matter.
“That holds the ammonium and protects it from leaching. It’s also not highly susceptible to gaseous loss. It would be nice if the inorganic nitrogen applied as liquid swine manure stayed as ammonium nitrogen. It would go a long way towards reducing the risk of loss by leaching or denitrification,” he said.
In a matter of weeks, ammonia gets converted to nitrate, a form which is easily lost. Schoenau said commercial products are available that can be added to soil or fertilizers and inhibit this nitrification process, such as N-Serve, or nitrapyrin trichloromethyl, and Super-N, or dicandiamide, also known as DCD.
“This is not new technology. N-Serve is sold by Dow AgroScience and used in the Midwest U.S. by corn growers, added to nitrogen fertilizer to help reduce the nitrification process and reduce nitrogen losses. That increases nitrogen recovery and increases yield response to the nitrogen,” he said.
“DCD is sold commercially by Agrotain International. This is the product we used in our trials, where we looked at the effect of adding a nitrification inhibitor to liquid manure. This DCD inhibitor adds from five to eight cents per pound to the cost of the nitrogen, whether it was commercial urea or liquid swine manure.”
Schoenau and grad student Chadrick Carley recently conducted a study to find out what would happen if they added this inhibitor to liquid hog manure under typical prairie conditions.
They were testing the hypothesis that adding a nitrification inhibitor could potentially improve the recovery of the liquid hog manure nitrogen by field crops.
Schoenau said the trial compared a 15,000 litre per acre rate of hog manure, injected into the soil – one with the DCD inhibitor and one without. The application rate added 40 kilograms of nitrogen per acre.
“We looked at the net effect of adding this inhibitor in terms of yield, protein content, nitrogen recovery and some early season effects,” he said.
Schoenau and Carley took soil and plant samples immediately after seeding the crop. They also used plant root simulator resin membrane probes to look at how the inhibitor was affecting nitrogen dynamics in the soil.
They took zero to 15 centimetre soil samples and plant biomass and nitrogen concentration samples and measured available ammonium and nitrate.
Crops included hard red spring wheat in 2005 and linola in 2006. Schoenau said they had perfect growing conditions in 2005, with the wheat yielding 50 to 55 bushels per acre. The next year had excessive rain in late May and early June. The linola wasn’t seeded until the end of May.
The manure treatment was applied in April 2005, with the wheat seeded in early May. The manure treatment was then applied again in the fall of 2005 after harvest for the 2006 growing season. Early season supply rates of ammonium and nitrate were tested with the soil nutrient probes.
“We see the inhibitor resulting in higher supply rates of ammonium. That’s what we expect if the inhibitor is doing its job. It’s keeping more nitrogen in the ammonium form earlier on in the season,” Schoenau said. “Without the inhibitor, there’s more nitrate, and with the inhibitor there’s less nitrate. It’s doing what it’s claimed to do – keeping the nitrogen in the ammonium form and working most effectively early in the season.”
With regard to biomass, Schoenau said the July 25 and Aug 1 biomass sampling showed a small effect of the inhibitor, with more biomass being produced. But in 2005, the grain yield showed no significant difference.
“We also didn’t see any effect on the grain or straw nitrogen concentration, uptake or percent nitrogen recovery. They were all similar,” he said.
“In 2006, with the flax, there was no difference in the ammonium or nitrate supplies through 2006. There was no significant effect of the inhibitor on the yield, nitrogen content, uptake or the percent nitrogen recovery.”
Based on two years of results, Schoenau said the nitrification inhibitor was doing what it claimed to do – keep the nitrogen in the ammonium form longer.
“It was most effective early in the season. And spring application was most effective. The odds were stacked against its performance in 2006 because it went on in the fall. There wasn’t a large potential for early spring loss of nitrogen as nitrate in 2006. Instead, the rains and high loss potential came later in May and early June. By then, the nitrification inhibitor effect was gone,” he said.
“Addition of a nitrification inhibitor might prove beneficial under conditions of higher potential loss than we experienced in this study. We’re going to continue this work for another three years to see if there’s any effects down the road, but under the conditions we experienced under the two years of this study, we didn’t see a lot of benefit from that nitrification inhibitor addition.
“It points to the idea that most important is the rate and method of placement. Injecting it and at an agronomic nitrogen rate are the key things that help you maximize the recovery of that manure nitrogen.”
