GHGMP Project Reports by Region

Balancing fertility to the crop improves profits, saves environment

Nitrogen unused or lost is money out of your pocket, and raises risk of increasing the environmental impact of greenhouse gas emissions

A soil test can't make it rain, but it will provide the best snapshot of what nutrients are available to the crop once moisture is available.

The value of soil testing is anything but a new message for Prairie farmers. But it's one that often bears repeating, say soil conservation specialists. With growing awareness and in some respects, increasing pressure to better balance soil nutrients with crop needs, the initial late fall or early spring soil test is an important step to prevent over or under fertilizing the crop.

"Probably the greatest risk of not soil testing is missing out on potential crop yield," says Tim Nerbas, a soil conservation agrologist with the Saskatchewan Soil Conservation Association (SSCA) based in North Battleford, Sask. "Without the soil test, producers run the risk of not achieving a nutrient balance. If one of the key nutrients or micronutrients is missing, the crop isn't able to make full use of the available nutrients." Whatever is missing becomes the limiting factor for potential yield.

Canola is a good example of a crop dramatically influenced by balanced fertility. A producer might apply adequate rates of nitrogen or phosphorus, but without a soil test he or she might be short on the 10 to 15 pounds of sulphur the crop needs. "That could mean the difference between a good crop and an excellent crop," says Nerbas.

Balanced fertility has several benefits, he notes. It helps optimize crop yields, which means producers are getting the best value from their fertilizer dollars. After a dry year some residual nutrients can remain in the soil following harvest. If moisture conditions improve, surplus nitrogen, for instance, can be leached below the rooting depth, or lost as a harmful greenhouse gas such as nitrous oxide through the process of denitrification. Thus annual soil tests are an important tool to not only determine what residual nutrients remain in the soil, but for setting realistic yields goals.

Demonstration project

Different approaches can be used to balance crop nutrients, says Rich Szwydky, of Borden, an SSCA soil conservation agrologist for west central Saskatchewan. Szwydky developed a couple demonstration projects in 2003 funded jointly by SSCA and the federal Greenhouse Gas Mitigation Program.

One project near Kindersley looked at a split application nitrogen treatment applied post-emergent. Some nitrogen was put down with the seed and the balance was applied in-crop with two different liquid application methods.

The other project looked at the effectiveness of delayed-release nitrogen fertilizer. This is conventional urea or UAN solutions treated with Agrotain, an additive that delays the release of nitrogen. The potential value in this is that higher rates of fertilizer can be applied at seeding with reduced risk of seedling damage and minimum nitrogen losses.

Both projects started with a soil test to determine additional nutrient requirements of crops, says Szwydky.

In the post-emergent fertilizer application project, on a 25-acre producer/co-operator plot the soil test recommended about 55 pounds of added nitrogen. Crop check strips received 55 pounds of nitrogen banded with the seed at time of seeding.

On one test plot, about 20 pounds of nitrogen was applied with the seed at time of seeding. A 42-foot-wide coulter-type liquid applicator was later used to apply another 35 pounds of urea-ammonium nitrate (UAN) liquid fertilizer as an in-crop treatment. The raised coulters dribbled fertilizer on the soil surface. On different plots, the post emergent nitrogen application was made at the two-leaf and also at the five-leaf crop stage.

On another plot, the same 42-foot-wide coulter-type applicator was used, this time, to inject 35 pounds of top-up nitrogen into the soil at the two-leaf crop stage. The low-disturbance coulters caused minimal crop damage and appeared to have little adverse impact on wheat plant numbers, says Szwydky.

"Unfortunately the weather didn't co-operate for the post-emergent demonstration," he says. "It was just too dry for the crops to fully benefit from the post-emergent nitrogen." The check crops, which received all fertilizer at time of seeding, yielded about 36 bushels/acre, while yields from the post-emergent fertilizer plot ranged from 30 to 32 bushels/acre.

"It does demonstrate, however, this type of post-emergent fertilizer application can work," he says. "It can be a useful tool, for example, in a dry spring, enabling farmers to put a lower amount of fertilizer on at the time of seeding, and then if moisture improves, nitrogen can be topped up in-crop." In 2003 moisture conditions did not improve.

By applying fertilizer in stages as the weather and crop dictates, it better matches nitrogen to crop needs, reducing the risk of surplus nutrients being leached from the soil or lost as nitrous oxide.

"Split applications of nitrogen gives producers greater flexibility in their fertilizer program," says Szwydky. "This practice minimizes the risk of placing all the nitrogen at the time of seeding, especially in drier soils. Also, by providing nitrogen to meet the changing demands of a growing crop, producers can potentially increase nitrogen-use efficiency.

"Under high moisture conditions, split application reduces the risk of nitrogen losses through leaching and denitrification. It also reduces the amount of product a producer must handle during the busy seeding period."

Crop benefit

The delayed-release nitrogen demonstration showed improved crop safety with fertilizers and improved nutrient uptake, says Szwydky. Agrotain is an additive to urea or UAN solutions. It temporarily inhibits the activity of the naturally found urease enzyme in the soil. The urease enzyme is needed to convert the urea fertilizer into ammonia, therefore reducing volatility losses especially for surface applied nitrogen. It was developed primarily to reduce nitrogen losses in broadcast or surface applied fertilizer, but works with banded fertilizer, as well.

"One of the dangers of applying seed-placed urea at higher rates or in drier soils is that the ammonia released from the urea can create seedling toxicity, which can reduce plant counts," says Szwydky.

With Agrotain the release of ammonia nitrogen is delayed for up to 14 days after application, depending on the treatment rate. This allows for timely rains to move surface-applied urea into the soil, or with banded fertilizer it allows time for seedlings to better establish so they can make better use of the available nitrogen.

Along with check strips with untreated-fertilizer, Szwydky applied various rates of treated fertilizer to different plots. "We found with the fertilizer treatment we could increase the nitrogen rate to 50 percent more than the recommended seed safety rate without crop injury," he says. Beyond that rate, however, crop injury was evident.

The technology, in most cases, will allow producers to increase nitrogen rates at time of seeding without risk of crop injury. "It reduces the risk of nitrogen being lost to the atmosphere, and also makes the nitrogen available to the crop when it is better able to use it," says Szwydky. "It's a tool that can help improve nutrient-use efficiency and benefit the environment."


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