With reports of high yielding crops across the Prairies, fall soil tests are a good way to see how much nutrient reserves are left. It might not be much. Or, if yields were variable, some areas may have more than you think.
The key with soil tests is to be consistent. If you usually test in the fall, continue testing in the fall, and sample in similar locations in the field. (If you have GPS marked coordinates, you can sample the same places each time.) Then when you get the results, concentrate on the trends — are reserves going up or down over time? Use the trend line to reassess fertilizer rates.
When to sample: Take fall 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 close representation of nutrient levels at seeding next spring. The cooler the better when sampling, but you want to make sure you can still get the probe down 24”. Submit samples for 0-6” and 6-24”.
Fall soil tests give growers time to process samples and get results and recommendations. That way growers can develop a fertilizer program for this fall or next spring, and have more time to order fertilizer, to take advantage of typically lower fall fertilizer prices, and to spread the workload out over two seasons.