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Proper agronomic rate key to liquid manure management

More Saskatchewan producers are using environmentally sound manure management practices

Though often misunderstood and underrated, manure can be a valuable and environmentally sound nutrient source when producing annual and perennial field crops, says a soil science professor at the University of Saskatchewan.

After evaluating a wide range of manure application, soil and environmental parameters on a number of sites across Saskatchewan over several years, Dr. Jeff Schoenau says manure not only benefits soil and crops, but can be managed in an environmentally sustainable farming system. His research at the University of Saskatchewan, primarily involving liquid hog manure, but also includes beef cattle manure at some sites as well as poultry manure. Along with research, Schoenau is also a member of the Saskatchewan Taking Charge Team. Taking Charge which is the provincial steering committee involved in selecting demonstration projects funded in part by the federal Greenhouse Gas Mitigation Program.

Agronomic rates

It's important for producers to target proper agronomic rates with manure, says Schoenau. An agronomic rate can be defined as the level of applied nutrients to the crop that meet, but don't exceed crop nutrient requirements and removal over time.

"We find with excessive rates of manure - rates greater than what the crop can use - applied year after year, we end up with high nitrate concentrations in the soil," he says. "With those treatments, we also see an elevated production of nitrous oxide, which is one of the more serious greenhouse gases.

"Not unexpectedly, when you load the system with nutrients it starts to become 'leaky.' There's increased potential for movement of nitrate either by leaching through the soil or by being lost as nitrous oxide through denitrification."

Manure applied at proper agronomic rates becomes an important nutrient source and soil amendment. So what is the proper agronomic rate? That varies with manure type and nutrient content, soil type and nutrient availability, crop grown and climatic conditions as it influences yield potential and nutrient requirements, says Schoenau. The key tools in determining the proper rate are a soil test and a manure nutrient analysis. With that information, producers and crop advisers can determine rates that best match crop needs and adjust nutrient balance if necessary by supplementing with commercial fertilizer.

Sustainability

"Based on our research so far, we have a very good idea of sustainable rates of applications," he says. "Although producers need to determine rates for their particular situation, in the Black Soil Zone, for example, annual application rates of about 100 pounds of nitrogen per acre per year, which is the equivalent of 3,000 to 4,000 gallons of injected liquid hog manure, would be a sustainable application rate.

"At that rate we see good crop response, no evidence of nutrient loading in the soil, no salt accumulation and no evidence of large losses to the atmosphere or through leaching."

Over the past eight years at sites across the province, Schoenau's research has evaluated a range of factors including manure application rates, sequence, timing and application methods, such as injection versus broadcast and incorporation. Schoenau says the research has been an important contribution to improving manure management.

"With the improved understanding and awareness of manure best management practices we're seeing producers using reduced application rates and improved application techniques. By far the trend now is to inject liquid manure in bands into the soil just like commercial fertilizer. We're seeing greater adoption of management practices, such as using manure analysis and soil testing to determine the appropriate rate to meet crop nutrient requirements."

Nutrient balancing

Along with proper rates, Schoenau says nutrient balancing is also important. While manure from one source, for example, may be high in nitrogen, it may be low in sulphur and supplemental commercial fertilizer may be needed to improve the nitrogen/sulphur balance. "In sulphur deficient soils near Melfort, we see a big response to the addition of supplemental commercial sulphur fertilizer," he says.

Similarly, the nitrogen and phosphorus availability or levels can vary depending on manure type. The amount of nitrogen available from straw-based cattle manure is quite low in the year of application, ranging between 10 and 50 percent. By contrast, 60 to 80 percent of nitrogen is available with liquid hog manure. "Additional commercial nitrogen may be needed with cattle manure in the first years to help the crop use the phosphorus that's being added with the manure," says Schoenau.

Other management issues include monitoring soil type to avoid build-up of salts and sodicity. The risk of increasing salinity is low on well-drained soils where manure salts can be flushed below the root zones. Use of liquid hog manure on naturally saline-sodic soils should be avoided. Both solid and liquid manures will improve soil organic matter, although it's a slower process with liquid manure. At the same time, application of either liquid or solid manure has been shown to increase water infiltration in research involving Black and Grey soils.

Produce the yields

As with any nutrient source, with decent growing conditions, manure can increase the yields, says Schoenau. For example, in one canola trial, under good moisture conditions, injected swine manure produced a 38 bushel crop, compared to an eight bushel crop on land that received no fertilizer. In a forage stand, liquid hog manure produced 2.4 tonnes per hectare of crested wheatgrass, compared to only one tonne per hectare on an unfertilized plot. In a dry year, however, liquid hog manure supplying 100 pounds of nitrogen per acre produced a 13 bushel per acre wheat crop with 18.7 percent protein. A control plot with no fertilizer yielded 12 bushels per acre at 15.5 percent protein.

Applying agronomic rates of liquid hog manure is a good fit with the environment, says Schoenau. Sustainable rates reduce the risk of leaching and the production of nitrous oxide, increase soil organic carbon content and low-disturbance injection fits well with zero till and soil conservation objectives.

"Manure application technology has improved greatly in recent years, thanks to research and development efforst by agencies like the Prairie Agricultural Machinery Institute, as well as equipment manufacturers," says Schoenau. "There is a lot of good equipment on the market. The low disturbance injection technology we have worked with in Western Canada is compatible with zero till production and can be used equally well with annual cereal and oilseed crops as well as with forages."


Regional reports will be posted as information becomes available. Please check back regularly for updates.