Partial manure injection - a compromise solution to combat nitrogen loss

Saturday, November 3, 2012

Testing shows that partial injection decreases ammonia nitrogen volatilization by one quarter to one third. But too much incorporation damages the alfalfa, so some ammonia loss will happen

by DON STONEMAN

Livestock farmers face a dilemma when making the best use of their liquid manure asset to fertilize crops. Expensive nitrogen is the most volatile of the three basic fertilizer elements.  It can also be a major pollutant, either as ammonia vaporized into the air or as nitrate leached into the soil and ending up in drinking water.

Specialists with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) have been looking at how to spread livestock slurry manure into growing crops so that farmers can retain more home-grown crop nutrients and reduce the environmental impact from manure spreading. The additional benefit is that farmers can reduce the pressure on manure storage capacity and disperse their work loads. "Partial injection," scratching the soil lightly with coulters while applying liquid manure, may be one answer, with the challenges being different for pork and dairy farmers.

Corn industry program lead Greg Stewart says a big question is whether manure can be injected into a growing crop without damaging it. OMAFRA has looked at injecting manure into winter wheat at about the same time as nitrogen fertilizer would be applied in the spring. The trick is to create enough of a disturbance with the coulter to get manure into the ground so that ammonia volatilization is minimized without hurting the wheat stand.

A soil and crop improvement demonstration at Jake Kraayenbrink's farm near Drayton in August was looking at using tool bars behind slurry tanks to see how they work under different conditions and on different crops. Christine Brown, nutrient management field crop lead, says if one tool bar was proven to be versatile in different crops and soil conditions, farmers would be more inclined to inject manure.

It is a balancing act, Brown says. "The research has shown that the closer we can get to applying nutrients to when the crop needs them, the better off we are both environmentally and economically. If compaction and timing weren't an issue, in a perfect world that's what people would do."

But farmers are pressed for labour and have to do a lot of work on clay soils that don't dry in the spring. That's why they compromise and apply manure in the fall. Dairy farmers want to spread some manure in early June, after they have taken a first cut of alfalfa, Brown says. Pork producers often have a winter wheat crop as part of their rotation, and they need to apply nitrogen in early spring to stimulate its growth.

Both the dairy and the pig farmer want to spread manure into a growing crop without damaging it, Brown points out, and therein lies the dilemma. How can they reduce nitrogen losses for both economic and environmental reasons, whilst not damaging the crop? The more complete the disturbance is of the soil, the more likely there is to be damage to the crowns of alfalfa. With less injection, however, ammonia escapes into the air.

Partial injection itself is a compromise. Testing using dosimeters – devices that measure gases, placed in upside-down recycling blue boxes with holes punched in them – shows that partial injection decreases ammonia nitrogen volatilization by one quarter to one third. With more incorporation, there is less ammonia loss, Brown says. But too much incorporation damages the alfalfa. So if alfalfa yields are to be maximized, "we are going to have some ammonia loss," she notes.

Dairy farmers "don't think about the nitrogen loss" on alfalfa because the crop produces its own N, Brown says. "They think about an opportunity to apply manure to a crop that needs phosphorus and potassium," and they count on the nitrogen that the alfalfa or clover produces itself to feed that crop.

Brown points out that there is an effect from nitrogen application even with crops that produce their own. If N is added, the yield will increase partly because "you are feeding the nodules," she explains.

Hog farmers can also apply liquid manure to their wheat fields in early April, when nitrogen fertilizer is normally put on to green up the crop.

Wheat growers also want to spread manure after harvest when it isn't causing compaction but, when high ammonia converts to nitrates, it can become risky to drinking water. Avoiding nitrates is the reason that farmers are planting cover crops such as oilseed radish, Brown points out.  Stewart says some farmers are putting eight to 10 pounds of oilseed radish seed per acre into manure tankers with agitators.

Surface-applying manure creates a risk from ammonia volatilization, not to mention odour, so injecting is better. It also increases the uniformity of the application. The effectiveness of typical splash plates used for surface-spreading of slurry can be influenced by wind or by the angle of the slope where the application is being made, Brown says. Use of injection units seven to 12 inches apart means that the applicator is treating the manure more like a fertilizer.

As well, manure is being applied at a lower rate and it infiltrates more easily, which should reduce the volatilization rate, Brown says. Tests using the meters have shown that when liquid manure is ponding, ammonia volatilization occurs at rates 16 to 40 times higher than if the manure is injected.
Testing also shows that the highest volatilization occurs in the first 12 to 24 hours after application, Brown says.

Typically, dairy manure is spread on forages at rates of around 4,000 gallons per acre, "not high, high volumes," Brown says. In the fall, dairy slurry is spread at about 8,000 gallons an acre, enough to supply a corn crop with nitrogen the following year.

Typical dairy manure contains half of its N as ammonia and half in an organic form. Pig manure likely has two thirds to three quarters of its N in the ammonia form.  Putting it into bare ground is a true injection. Volatilization would be very low.

Usually sow barn manure has a lower concentration of nutrients than feeder barn manure. That's another reason why it is important to sample manure before spreading, Brown says. BF

Manure injection comes of age

by DON STONEMAN

Ten years ago, Wayne Graham, operations manager at Leading Edge Equipment in Burgessville, was selling Aerway systems for working manure into the ground because of nutrient management legislation.

"Today, we see demand because of fertilizer prices," says Graham, who showed off some of his company's equipment at the Heartland Soil and Crop Improvement demonstration at Drayton in August. A decade ago, liquid manure was spread via tanker or drag hose spreaders with splash plates over soil that had been recently worked. Modern equipment puts the liquid manure into the ground directly behind an injection coulter.

"As fertilizer costs go up, you are looking at liquid gold here," says Larry Prong, the GPS specialist at Premier Equipment Ltd. in Elmira. Spreading manure has gone high-tech, for producers who can afford it.

Prong says using GPS while spreading manure makes a lot of sense. Applicators avoid skips across the field as well as overlaps. And if a corn crop was planted with a GPS unit, the rows would be "bullet straight" and the GPS-equipped applicator has the option of side-dressing manure into the growing crop "very accurately."

Applying manure with a GPS-equipped unit has benefits when it is treated as a hazardous material as well. The map and associated records serve as an audit of how much manure was applied in relation to the distance from rivers, streams and also wellheads.

Dennis Nuhn, president of Nuhn Industries Ltd. at Sebringville, says that 10 years ago injection was a hard sell." Fertilizer was cheap." The research sponsored in part by Ontario Pork and conducted by Agriculture and Agri-Food Canada "was not appreciated as much then as it is now," he says.

Farmers are going to give a higher value to manure as a crop nutrient source as they get better at using it, Nuhn predicts. "If everybody spread fertilizer as bad as most people spread manure it wouldn't work very well either." BF