GHGMP Feature Articles
Manure value depends on proper handling
New friendlier image of manure gradually emerging
Describing unglamorous manure as a valuable soil nutrient might sound like a Cinderella story. But research shows the long-regarded "waste" can play an important role in sustainable farming practices without compromising soil, air and water quality.
Management is the key to capturing the value of manure without affecting the environment, say soil fertility specialists. Applying manure to the land at proper rates and quickly getting it incorporated into the soil will solve many of the negative aspects associated with all forms of livestock manure.
Mishandled it can produce a wide range of negative social and environmental effects from strong odour, to contributing to greenhouse gas emissions, to leaching nutrients into ground water.
"It can be a valuable part of a fertility program," says Dr. Ross McKenzie, a veteran researcher and soil fertility and crop nutrition specialist with Alberta Agriculture Food and Rural Development in Lethbridge. "But producers first need to know what they are dealing with from a nutrient standpoint and then calculate that into their soil fertility program. Soil and manure testing to determine nutrient levels is critical to development of a sound manure management plan."
The cost of mismanagement
Although there are climatic differences across Canada, manure handling issues have a national scope. Producers in all regions and climatic zones are looking for the best ways to handle manure to benefit from its nutrient and soil improvement qualities, while at the same time minimize the environmental impact.
It does have value, but if not handled properly, manure can have a serious impact on the environment at various stages. In storage, either in liquid or dry form, it can contribute to greenhouse gas emissions with release of methane, carbon dioxide and ammonia to the atmosphere. Both methane and carbon dioxide are produced during the decomposition process as organic acids are being degraded.
Land application of manure without incorporating it into the soil can quickly result in a process known as volatilization. That's where the nitrogen in manure, exposed to the sun and warm temperatures, changes to ammonia gas and is lost to the atmosphere.
"Not only does it produce a strong odour, but it also means the nitrogen is being lost," says McKenzie. "Manure spread on a field, but not incorporated, soon loses its nitrogen value. Depending on weather conditions, anywhere from 20 to 30 percent of nitrogen can be lost within the first few days after application. There is greater loss under warm, dry conditions and less under cool, wet conditions."
Ammonia volatilization isn't just specific to manure, however. Many nitrogen fertilizers surface or broadcast applied without incorporation, are subject to volatilization if conditions are favourable. Ammonia itself isn't a greenhouse gas, but it can contribute to greenhouse gas emissions. After being released in the atmosphere, ammonia will eventually settle back to earth, contributing to the nitrogen load already found in the soil and water. Under the proper conditions as this nitrogen breaks down it can produce nitrous oxide, a harmful greenhouse gas.
Incorporating manure into the soil within 24 hours of land application is recommended to minimize nitrogen loss. With dry livestock manure this means cultivating a field after manure has been spread. While with liquid manure, a knife or injector system can be used to place manure in the ground at the time of application.
Application rate is important
It takes a lot more manure to deliver the same nutrient value as chemical or commercial fertilizers. While nutrients levels vary, it will take, for example, several thousand gallons of liquid hog manure per acre and several tons of dry cattle manure per acre to supply the same nutrients as found in a relatively few pounds of commercial fertilizer.
There's a real risk of over applying manure - applying more to the land than crops can use - for a couple reasons. First, the nutrient levels in manure can vary widely making it difficult to estimate its nutrient value, and second, because raw manure contains a high percentage of water, it is expensive to haul. This means many producers apply heavier rates of manure within a short radius of manure storage.
High manure levels, even if it's incorporated into the soil can increase the risk of nutrients leaching into ground water. Also under wet conditions a process known as denitrification takes place, which means the nitrogen is converted into gases including nitrous oxide.
"Repeated yearly applications of manure at rates, which greatly exceed crop nutrient requirements, result in excess accumulation of nitrate in the soil as well as gaseous denitrification losses to the atmosphere," reports Dr. Jeff Schoneau, a researcher and soil fertility specialist with the University of Saskatchewan's Department of Soil Science. "The accumulation and potential escape of manure nutrients to ground or surface water as well as emissions to the atmosphere are significant environmental concerns associated with over applications of manure."
Recommended management practices for manure handling, first include a nutrient analysis to determine the nutrient value of the manure, say specialists. The manure analysis, along with a soil test, will give producers the best handle on how much overall manure and/or chemical fertilizer is required to meet crop needs.
"With solid beef manure, for example, there can be a lot of variability in nutrient levels from one pen to another," says Curtis Cavers, a land management specialist with Manitoba Agriculture, Food and Rural Initiatives in Carman. Nutrient levels will be affected by the type of feed ration, age of animal producing the manure, season of the year and other factors. "Producers will need to take samples from several areas of a feedlot to get a representative sample for analysis," he says.
Producers also need to know how manure releases nutrients in the soil. Not all the nitrogen in manure is available to the crop the first growing season, Cavers says. With solid beef manure, for example, about 25 percent of the nitrogen is plant available the first year, compared to injected liquid hog manure where nearly 100 percent is available to the crop. The remaining nitrogen is mineralized over the next few growing seasons. That information will help producers determine proper application rates for the crop.
Timing and method of application of manure are also factors. In Western Canada, for example, with most of the nitrogen in liquid hog manure available in year one, a late fall application just before freeze up will reduce the risk of leaching and denitrification of the manure. The same applies to proper fall application of anhydrous ammonia. Research also shows injecting manure into the soil improves crop uptake of the nutrients, which can improve yields.