Top up canola fertility now (June 17, 2005)

June 17, 2005: Canola growers who cut fertilizer rates this spring may want to top up fertility levels now. Canola Council of Canada agronomist Jim Bessel says there are many extremely pressing reasons for considering adding fertilizer.


Bessel points out that the abundant moisture available in many regions has allowed plants to develop a very shallow root system, thereby reducing the volume of soil from which available nutrients can be extracted. As well he says warmer soil temperatures will increase microbial activity and may temporarily immobilize some nitrogen on fields with large amounts of crop residue, if the carbon to nitrogen ratio is high, tying up plant available nitrogen. This means that all of the plant’s required nitrogen may not be available during early plant development.


“Balanced soil nutrient levels will turn an average canola yield into above average,” says Bessel, senior Canola Council agronomist for north central and north eastern Saskatchewan.


He adds that in some regions, soils are moisture saturated, causing less oxygen to be available and increasing the risk of denitrification. “This scenario,” he says, “increases losses of gaseous forms of nitrogen to the atmosphere and consequently reduces nitrate nitrogen amounts. These higher rainfall areas may also have more leaching of mobile nutrients within the soil profile of lighter textures soils.”


Now that temperatures are rising, Bessel says it’s especially important that growers make sure they’re top dressing the right form of nitrogen For instance, he explains, forms of urea are much more volatile now than during colder air and soil temperatures in spring. Ammonium nitrate, ammonium sulphate and urease inhibitors are more stable resulting in less volatilization and immobilization of nutrients. Bessel advises growers to use a dribble banding system rather than broadcasting.


“In areas with good to excellent moisture, the crop will be set to take off with warmer temperatures, but it won’t have the nutrient levels needed. The best way to determine if the crop is lacking nutrients is to tissue test,” says Bessel.


Collect samples early--from rosette through very early flowering. For many growers that’s right now. It takes about two to three days to get results once the test lab receives samples. The earlier samples are collected, the more likely any in-crop fertilizer application will be applied in time.


Submit 30 whole plants at the early rosette stage or 15 plants at later rosette stages, cutting them just above the soil surface. Collect 50 leaves from bolting or very early flowering plants or 30 leaves from more mature plants.


Bessel stresses that the key to getting accurate tissue test results is to sample when plants are actively growing. "Don't sample after an extended dry period because although the plant is not producing much biomass, it continues to take up nutrients. This raises the nutrient levels in the plant, which can cause false high or adequate nutrient level readings. Also, don't sample if it was dry for an extended period followed by a recent rain. This can cause a growth spurt that will lower the tissue nutrient level."


Bessel cautions growers not to rely solely on the tissue test when making a decision to apply in-crop fertilizer. For example, if soil tests have normally shown sufficient sulphur (S) and boron (B), but a plant analysis says these nutrients are low, take a look at the most recent soil test results. If nutrients are available at lower depths, as roots continue to grow they may be able to access those nutrients and recover. It's not unusual after good spring moisture for S and B to move lower in the soil profile he adds.


Bessel advises growers to work closely with their local fertilizer dealers and test labs to ensure the right decisions are made.


"And don't get carried away with applying in-crop nitrogen (N) if you cut back on other nutrients this past spring. Plants will not be able to take advantage of extra N if they are lacking other nutrients," says Bessel.


An over abundance of N may result in an imbalance of total nutrients and limit plant development and yield potential. As well, the Canola Council agronomist sasy growers need to set realistic target yields when considering application rates. Late seeded crops and crops that have suffered from excess moisture will have reduced yield potential. Warmer temperatures combined with ample moisture will increase mineralization of organic nutrients, and these will more available for later maturing crops.


He advises growers to look for the visual symptoms of plant stress due to nutrient deficiency. But be aware that various other factors can cause plant stress including frost, herbicide residue, and/or insects. Also, plants that are slightly nutrient deficient may not display visual stress symptoms. For details on diagnosing nutrient deficiencies, refer to page 911 of the Canola Council's new Canola Growers Manual.


Bessel notes that growers also need to be aware that foliar applications should be applied at the right crop growth stages, at rates that will minimize crop injury. Plants take up nutrients at different rates during their growth. For example, the optimum time to apply foliar N is between the five-leaf stage and first flower. And the optimum time to apply S is from five-leaf stage to full flower. Consult with your fertilizer dealer to determine the optimum time to apply foliar treatments on your farm.


For more information in your area, contact:

John Mayko, Agronomic Research & Extension Manager, 780-764-2593


Derwyn Hammond, Manitoba, 204-729-9011


Jim Bessel, North Central & North Eastern Saskatchewan, 306-373-6771


David Vanthuyne, Eastern Saskatchewan, 306-782-7799


David Blais, Western Saskatchewan, 306-895-2122


Christine Mardell, Peace, 780-518-1513


Doug Moisey, Central Alberta, 780-645-3624


Matthew Stanford, Southern Alberta, 403-758-6660