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Seven Tips To Better Fall Soil Tests

You wouldn’t fill your truck with gas without checking the gauge to see how much fuel is already in the tank. No matter which philosophy of soil testing you choose, knowing what’s in your soil is a cornerstone of field management.


There are many reasons to test your soil in the fall instead of waiting for spring. Fall fertilizer prices may be lower, it may be too wet next spring to get a reliable sample and sampling in the fall will free up time in the busy spring season.

So when should you sample? Patrick Mooleki, crop eevelopment specialist with Saskatchewan Agriculture’s Ag Knowledge Centre, says “the cooler it is, the better.” As the temperature drops, microorganisms in the soil become less active. Wait as long as you can, while still leaving time to get your test results and apply fertilizer (if you plan a fall application) before the soil freezes.


If you’re doing traditional sampling — combining random samples to represent your entire field —consider your soil’s history. For example, Mooleki says if you have a field that was previously

seeded half to lentils and half to canola, “you should always treat these areas as separate fields.”

Edgar Hammermeister, Alameda farmer, field services manager for Western Ag Labs and self-confessed “soil geek,” echoes that thought. “Fields used to be smaller,” he says. “It’s important to have an

idea of what’s gone on.”

Any kind of past disturbance may have impacted the soil in a small area. Samples taken from that spot and mixed in with the rest will distort overall results. Hammermeister recommends digging back in your memory to locate disturbances from oilfield activity, old yard sites, or even old fence lines. The fences may be long gone, but the impacts of soil blowing against the fence can survive for decades. Hammermeister says that even past discing can impact today’s nutrients. Years of throwing soil in the same direction with every pass may have created a distorting “wave of soil quality.”


The standard recommendation for traditional sampling is to choose 15 to 20 sample sites per field. Mooleki recommends gathering as many samples as you can to ensure that your entire field is well represented.

Looking at last year’s yield maps is one way to assess fertility and choose representative sites, but Hammermeister warns against solely relying on these maps, simply because they don’t provide enough information. Two areas may have had the same low yield for completely different reasons. Hammermeister sees soil testing as the ultimate proof when it comes to yield problems: “You need groundtruthing to verify what’s causing the limitation.”


When you go out to take your sample, Mooleki suggests packing along a cooler filled with ice to keep your sample cool until you ship it to the lab. Setting the sample on the dashboard or in the back of the truck can give it a chance to warm up, causing the microorganisms to become more active. Then, Mooleki says, “all of a sudden, boom! There are high levels of nitrogen.” If this happens, recommended application rates will be lower than you really need.

Darryl Armitage, an agrologist with Farmers Edge at Camrose, Alta., says “if it’s frozen, keep it frozen,” and “keep it from warming and cooling.”


As if the excess moisture in 2011 hasn’t caused enough stress, anyone in a flood zone will have yet another challenge when it comes to soil analysis. If you fertilized last fall, those nutrients still being available. As Armitage points out, “Mother Nature may have done something with them in the meantime.”

Western Ag Labs investigated the impacts of excess moisture in south-east Saskatchewan with some mid-summer soil testing. Hammermeister says “there’s a lot of variability.”

In those fields that were so wet that “the sprayer was still getting stuck in July,” Western Ag Labs found that soil was low in nitrogen and sulphur due to leaching and denitrification. Denitrification losses are variable and hard to predict. In fact, up to half of the nitrogen applied can be lost when a field is flooded.

In fields that were a bit less wet, but overwhelmed by weeds in the wet spring, Western Ag Labs found that the weeds used up nutrients. If the weeds were controlled early, their nutrients should be available for 2012. But if they were allowed to grow more than a few weeks, there will be slower rate of release of nutrients next year.

Western Ag Lab also tested fields that were unseeded, but kept relatively weed-free. They generally found a decent nutrient supply in these fields.

The main lesson is that the effects from excess moisture, especially standing water, can vary widely. Based on what he’s seen in Alberta, Armitage says that when it comes to nutrients, “drought would be a little more predictable than wet-dry wet-dry.” In flooded areas, you may want to consider taking more samples than usual, to be sure that you have a picture of exactly what the water has done to your fields.

Where it’s still wet, sampling will be more difficult than usual. In these cases, Armitage says, “wait until it’s frozen and take a sample at that point.”


Hammermeister refers to small areas with high nutrient density as “hot spots,” that aren’t representative of the whole field.

One type of hot spot to watch for is sulphate salt. White flecking on the ground surface can indicate excess sulphur in a small area. These white flecks vary in size, but are generally about the width of half of the end of a pen, and Hammermeister says they “tend to look like course ground pepper” (although they’re white, rather than black).

Other hot spots are caused by history. Hammermeister says, “If I come to a yard and there’s a barn on the yard site, I don’t sample close to the barn.” In bygone eras when stone boats were generally used to move manure, spreading was usually done relatively close to the yard. These areas may still have high levels of nutrients not representative of the rest of the field.


These tips are fairly standard, but different testing labs have different protocols, and some companies, like Western Ag Labs, use different sampling techniques altogether. Always make sure to call the lab for specific information before you head out to collect your samples.

More and more, farmers are seeing fertilizer is an investment, rather than an expense. Hammermeister believes soil testing is key to using the right mix of nutrients to get the return on investment you’re looking for. While farmers are at the mercy of a lot of different variables, as Hammermeister says, “nutrients are one thing farmers can control and influence.”



Years of throwing soil in the same direction with every pass may have created a distorting wave of soil quality

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