Story Posted: November 03, 2011

Canola Watch: Soil tests, Tillage, Variety performance, Check bags

Topics for the month: A good time to test soils. Hold off on tillage. The seed decision. New insights for canola storage. Please fill in our Canola Watch survey.

A good time to test soils. Soil tests will help growers estimate nutrient removal and nutrient reserves to set fertilizer rates for next year. Ask for organic matter results for each test. Fields with high organic matter tend to provide more mineralized nitrogen to the crop, which may explain why some fields consistently yield higher than others even when treated the same way.

Hold off on tillage for next year’s canola fields unless you’ve truly weighed the risk versus reward. Is it really the best decision?

The seed decision. Variety comparison data from the new Canola Performance Trials should be available later this month. For grower who don’t want to wait to make some of those early buying decisions, there are also some other information sources that can provide insights regarding varieties’ agronomic characteristics and performance.

New insights for canola storage. As the outside air gets cold heading into winter, air cycles within stored canola until its core temperature reaches equilibrium with the outside air. This air movement can concentrate moisture, increasing the chances of heating. Preliminary research into bag storage systems is shedding some light on how this process in bags compares to our past experience with canola in bins, and implications for safe storage.

Please fill in our Canola Watch survey. You can help us improve Canola Watch for 2012. The survey has 37 questions and should take about 10 minutes. All survey replies received by November 30, 2011 will be entered into a prize draw. Three winners will be selected. Thank you to everyone who has already completed the survey. Click here for the survey.

Good time for soil tests
Fall is a good time to do soil tests. Growers may have a extra few hours to take samples, unlike in spring. And with results and recommendations in hand before winter, growers have more time to plan their fertilizer programs for 2012, to order fertilizer, and to take advantage of reduced pricing opportunities that may occur.

The ideal time is to take samples when soil temperatures drop below 7 C. Because microbial processes in the soil slow down as temperatures cool, sampling late in the fall will provide a better indication of what nutrient levels will be next spring.

Growers can use results from soil nutrient analysis to determine if the fertilizer rates they have been applying are in line with current industry recommendations.

Which lab to choose? Different labs may use different chemical extraction methods for determining nutrient levels in soil samples, so labs will not always come up with the same recommendations. If you already have a favorite lab, it’s important to send samples to the same lab for year to year comparison of test results. Many labs base recommendations for next year on soil test analysis plus yields for the current year. If, for example, wheat yielded 50 bushels per acre, the lab will consider the nutrients removed by that wheat crop when setting canola fertilizer recommendations for next year. The CCC factsheet “Understanding Soil Test Recommendations” has more information.

Ask for an organic matter test
When submitting samples to the soil lab, ask the lab to provide an organic matter (OM) analysis, and ask whether the lab considers OM when setting fertilizer recommendations. Soil with high OM can release a high amount of plant available nitrogen throughout the year. The amount released each year varies. High moisture and high temperature tend to increase mineralization rates, which may explain why, with good moisture and warm weather this past summer, some growers who fertilized for 40 bushel crops were surprised to harvest 50 bushel crops.

Soil organic nitrogen levels in the top 6” of soil can range from 2,500 to 7,500 pounds per acre. Around 1% to 3% of that soil organic N mineralizes and becomes available for plant uptake each year. If soil has 5,000 pounds of soil organic nitrogen in the top 6”, it could provide anywhere from 50 to 150 pounds of nitrogen to the crop using those numbers. These numbers are from the article “Nitrogen Mineralization: What’s Happening in Your Soil?” by Fran Walley from the U of S Department of Soil Science. Here is a PDF of Walley’s full article: Fran Walley – Nitrogen Mineralization 2005 Canola College

Many herbicides are also broken down by microbes or water, so high OM soil that can hold more moisture and house more microbes can have more rapid herbicide breakdown.

Click here for more on organic matter.

Other tests to consider

Soil pH. Soil pH will influence nutrient availability, especially phosphorus. Phosphorus availability is highest at a soil pH around 6.5 and drops as pH gets lower or higher than that point. Adequate phosphorus fertilizer is important for all crops, but precise placement where seedlings can access it easily is especially important with pH below 5.5 or above 7.0.

Careful when comparing pH results from different sources. Soil pH listed in soil survey (and often research) reports is based on a saturated paste test — where enough water is added to the soil to saturate it without leaving any free water. This more closely approximates the pH at the root surface. Not all soil test lab do the saturated paste test. Some use a simpler 1:1 or 2:1 soil to water ratio, which produces a pH reading about 0.5 units higher than the saturated paste test.

	This graph shows nutrient availability based on pH. Source: Page 602 of the Canola Growers' Manual, online at www.canolacouncil.org.

Electrical conductivity. Soil labs use EC tests to measure salinity. The higher the salinity, the higher the conductivity of that soil. Greenhouse studies at AAFC in Swift Current found that soil with an EC above 5.6 deciSiemens per metre will reduce canola plant survival. This is in the “moderately saline” range. As with pH, labs will often use a simple 1:1 or 2:1 soil to water ratio for the EC test. This produces an EC salinity measurement that is about half the amount of the saturated paste test used for soil surveys.

Cation exchange capacity. CEC is a measure of a soil’s ability to hold on to key positively charged nutrients, such as calcium, magnesium and potassium, and keep them close for when the crop needs them. Soils with high clay and high organic matter tend to have a high CEC, so these soils are more likely to have an adequate supply of these nutrients on hand. A CEC of 1 milligram of hydrogen equivalent (meq) per 100 grams of soil is very low. CEC is ideally between 10 and 30 meq/100g.

Is that tillage really helping?
Growers have made great strides in advancing no tillage and conservation tillage practices. General benefits include reduced fuel use, reduced soil erosion, higher soil moisture reserves (which are welcome most years), and a general increase in profitability. Any return to tillage, even if only one field or across the whole farm for only one year, should be weighed carefully. Growers may consider tillage for:

Residue management
Tillage is often used to correct uneven residue distribution during harvest. Uneven residue can be a problem for proper stand establishment the following spring. But growers who find they have to till soil to manage residue may need to consider more sustainable long-term steps to improve their combine’s spreading capacity. An after market chaff spreader may help. Straw chopper performance can be improved with sharp blades and tight belts to ensure maximum power transfer to the unit.

Heavy harrowing on a hot, dry day may help spread residue without full tillage, but heavy harrows don’t always do a great job of spreading chaff strips, and they often rip out standing stubble, which is actually the best kind of crop residue. Standing stubble holds the snow, prevents soil erosion and is off the soil surface and out of the way for drill openers. Chopping down all the standing stubble just adds to the matt of residue on the soil surface. For long-term residue management solution, consider cutting crops higher and improving the combine’s chaff spreader and straw chopper, particularly if a move to wider header widths in recent years has increased the density of those chaff and straw rows.

	Canola can establish well in tall cut stubble.

Extreme moisture. Zero tillage tends to preserve moisture, so if fields are excessively wet, tillage is seen as one way to dry out the top layer. But the way the Prairies can switch from wet to dry from one year to the next, anticipating next year’s moisture is difficult. Tilled fields will warm up faster next spring, but that may not be much help for emergence of small, shallow seeded canola seeds if the tillage also leads to dry surface soil, which is a possibility after the dry fall.

Disease management. If you think tillage is going to help control canola diseases, think again. Tillage accelerates the distribution of clubroot resting spores throughout a field once the disease is established. More tillage also creates additional opportunities for equipment to carry soil infested with clubroot spores to neighbouring fields, and can facilitate spread of infested soil through increased soil erosion. For blackleg, it was thought that tillage may reduce the disease by burying canola residue, but a recent study found this not to be the case. The study by Agriculture and Agri-Food Canada in Melfort, Saskatchewan, found there was no difference between tilled and untilled treatments in causing blackleg infection in canola the following year. For more information on best management practices for controlling blackleg, check out this article on the Prairie Soils and Crops website.

Deep ruts. Tillage can help to smooth deep ruts, which some fields may have after a couple of wet summers. In this case, tillage may be the best solution to correct the problem quickly, but severe ruts may require several passes, so consider the economic cost. If the ruts are not severe, the winter freeze-thaw cycle will provide some benefit, as will the retained moisture from snow in the stubble.

Weed control. Tilling this late in the fall to control weeds is only going to spread perennial roots around, not control the plants. A pre-seed burnoff at high rates next spring will be more effective to control these large perennial and winter annual weeds ahead of canola than tillage would be at this point of the season. Long-time direct seeders who decide to till may also experience:

• An intense flush of weeds from buried dormant seeds that can germinate when moved closer to the surface, or incorporation of seeds that were stranded in surface residue.
• Preservation of newly produced seeds as a result of seed dormancy due to burial of the seed. This deep seed bank could remain preserved for many years until disturbed again.
• Temporary loss of the community of predatory insects and small mammals that feed on weed seeds and other pests. This may allow weed seed banks to build up again until this community is returned.

Consider targeting tillage to those areas that are worst affected and leave as much long-term direct seeding intact to retain these benefits.

If fields are at full moisture recharge and you have to till, do it in the fall. Even though you lose the stubble to catch snow when tilling in the fall, spring tillage ahead of seeding canola will often result in a poor seed bed, resulting from large clods that limit seed to soil contact and drying out the top inch or two of soil. If fields are dry, avoid fall tillage and wait until spring to reassess the moisture situation.

What seed to buy?
Be careful with coffee shop talk and field to field comparisons when considering which variety or system to choose. There are many variables from field to field — including soil characteristics, seed date and rate, moisture, frost, residual fertilizer, weed competition and insects — that can distort yield and profit comparisons, even if the same grower managed each field.

Growers considering a new variety or a new system are encouraged to try it on a small portion of their acres before converting the whole farm. Growers who test new varieties on some of their acres each year achieve two goals: They can assess the potential agronomic benefits of new technology, such as yield advancements or improved disease tolerance, while maintaining some performance predictability by seeding the rest of the farm to varieties known to work well for them.

To help growers make the right choice, the Canola Performance Trial data, which compares new varieties against current industry leaders in small and field scale plots, will be released within the next few weeks in print and on the Canola Council of Canada website. Click here for background information on the Canola Performance Trials for 2011.

For growers eager to make early booking decisions, here are some other sources for variety performance information:

WCC/RRC. Seed registration trial data from the Western Canada Canola/Rapeseed Recommending Committee compares yield, maturity, lodging, height and blackleg ratings. Growers can get a summary based on first year private and second year public data. Contact Raymond Gadoua of the Canola Council of Canada at gadouar@canolacouncil.org or 306-683-2403 and he can email the summary. Gadoua reminds growers that rarely would any of these cultivars have been tested in the exact same set of head to head trials.

Crop insurance. Alberta and Manitoba publish summaries of crop insurance yield reports by variety and zone. Read the 2011 editions online: Alberta Manitoba. These provide average yields over all acres of each variety grown, but are based on grower responses, are field by field, and do not include other data such as maturity, lodging and disease resistance. The 2012 editions come out in February or March.

Local research groups. Some provincial commodity groups or local grower-directed research groups do variety comparisons. Check if yours conducted any trials that would be relevant to your typical growing conditions.

Seed company data. Seed companies often run their own variety trials and will post results on their own websites. Here are some companies to check: Bayer CropScience, Monsanto, Pioneer Hi-Bred, Viterra, Cargill, Dow AgroSciences, DL seeds, Canterra, FP Genetics and SeCan. Some local seed suppliers also have their own branded varieties and may have performance comparison data.

Retail trials. Many independent and line companies run their own yield trials. See your local retailer for results.

Listen to CCC senior agronomy specialist Doug Moisey talk about what to look for in a new variety.

The air is cooling. Are your bins?
We keep harping on this one, but even if we save one bin each time we repeat this message, the repetition has paid off. Because canola seed can keep respiring at a high rate for 4 to 6 weeks after harvest, this is a good time to check bins and make sure canola has cooled and is stable heading into winter. As the outside air cools, air cycles within the bin tend to concentrate moisture at the top of the central core. (See the image below.) This is a good place to check first when probing for temperature spikes. If you have any suspicions, take out one third of the bin and feel the canola to make sure it’s cool. Heated canola produces a distinct odor, so smell can also be a good indicator of spoilage occurring.

For a real example of grower who had 7,000 bushels of canola heat last winter, read the article on page 10 of the September 11 Canola Digest. The canola went into storage last fall dry but with high green. By March, two bins were severely damaged. About half of the canola was so badly damaged, the grower could only get $1 a bushel for it.

Check for air flow. To be effective, aeration fans need the horsepower to push the air front all the way through the mass of canola. The quick and easy way to check air flow is to climb to the top and feel for air exhausting through the vents.

Bin size matters. Canola has a higher bulk density than other grains, and canola in a tall narrow bin will create more resistance for air being pushed up through it than canola in a short wide bin with the same capacity. Does your fan have the horsepower it needs for your bin configuration?

	How air moves in the bin in fall and winter.

Bag storage is a short term solution
Growers who put canola in 10,000-bushel plastic tubes this fall to improve harvest efficiency and provide surge storage capacity will want to consider moving that canola first. Early results from the first year of a University of Manitoba research study showed that canola at less than 10% moisture can be stored in bags for 10 months without damage, while canola at 14% moisture spoiled badly in that time. Until we have more results under a wider range of conditions, we encourage caution to make sure bagged canola is safe. Here is a PDF of the study summary to date:Bag storage research summary

One problem with bags is that are not always easily accessible if regular monitoring reveals spoilage in the winter or spring. If, for example, the bag is on high ground but surrounded by soft ground and pools of spring runoff, this could prevent timely removal. Also bags in remote locations could be more susceptible to animal damage, which can let water into the bag and promote spoilage.

	Bags are loaded this fall for the second year of University of Manitoba's canola bag storage study.

Fall weed control ahead of cereals, not canola
The opportunity to spray weeds is nearly closed for this fall, especially on fields planned for canola in 2012. If you have a stretch of warm sunny days in the forecast, you might have a chance to give dandelions one last hit. Note that glyphosate needs a few warm days with several hours per day of bright sunlight as well as non-freezing conditions (day and night) to do its job well. If using residual product, be mindful what you’re seeding next spring. The best product to use at this time of year is 2,4-D, but spraying now ahead of canola won’t give it enough time to break down before seeding next spring. Do not spray 2,4-D on land planned for canola next spring. 2,4-D is suitable to clean up fields for cereals next year.

2,4-D can be applied for winter annual control as long as the nozzles are not freezing up. If you have the space, keep the sprayer in a heated shop overnight and wait until temperatures are above freezing to start spraying. Phenoxy herbicides not only control winter annuals directly by crushing stem tissues and cutting of water supplies, but also by sending a signal to resume growth when they should be entering a dormancy phase to survive the winter.

If your target is narrow-leaved hawk’s-beard, take note: This weed is not susceptible to 2,4-D at this time of year and 2,4-D can actually interfere with hawk’s -beard control next spring with glyphosate. That’s because the injury that 2,4-D causes to the plant actually protects it from the glyphosate.

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