By: Ken Panchuk, PAg, Provincial Specialist Soils
Fall soil testing offers producers advantages over spring testing: having more time to get the job done, receiving the analysis on time for fall banding urea or anhydrous ammonia, and providing valuable information for planning for the next year’s crops.
By the end of September the soil is cooling, and by the end of the first week of October the soil temperature is usually below 10 C. Soil microorganisms are part of a healthy soil system that break down crop residues and soil organic matter, releasing nutrients in a form that can be used by crops. This process is called mineralization. The mineralization process is slowed considerably when the soil cools below 10 C. Therefore, soil testing in the fall when the soil has cooled will result in similar soil analysis as a spring soil test.
Benchmark sampling has become the most common method for soil sampling and is accomplished by selecting an area of a field that best represents the performance of the field based on several crops in rotation. GPS coordinates are used to return to that site for soil sampling. Then 15 to 20 cores or a furrow slice perpendicular to travel of the zero-till drill rows can provide the representative sample for lab analysis using either the Root Simulator Probe technology or conventional lab extraction process.
Getting more from your soil test can be as easy as providing as much detailed information as possible about the field, including cropping history and subsoil moisture measurements. Setting realistic yield targets is also an important step for determining the right nutrient rates. Subsoil moisture measurements can be further updated at freeze-up and again in the spring just before seeding to allow adjustments to target yields and nutrient levels just in time for seeding. Working with a crop advisor and soil test lab will provide you with the information necessary to assess nutrient management requirements.
Once nutrient requirements are determined, fall banding urea or anhydrous ammonia can also commence after the soil has cooled below 10 C. These forms of nitrogen minimize losses because they convert to ammonium, the stable form of nitrogen that stays on the soil exchange until the soil warms up in the spring.
Remember that it is always a good practice to clean and sanitize your soil probes, trucks and boots before moving to the next field, as soil can spread weed seeds and soil-borne pathogens that cause diseases such as clubroot and aphanomyces.
Soil sampling is an important step in the industry-led 4R nutrient stewardship program: the Right Source, applied at the Right Rate, at the Right Time and in the Right Place.