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Use Smart Soil Sampling This Fall
By Scott Banks - Crop Specialist, Kemptville OMAF

Fall is usually a good time to take a few soil samples. Having the results this fall and winter will help you plan for next year’s crops to maximize your fertilizer $ investment. A soil test will give you a good idea what are your actual levels of available plant nutrients. Applying fertilizer will pay if your nutrient levels are in the low to medium range. On high or excessive fertility levels, applying un-needed fertilizer can influence the availability of other plant nutrients. For example, excess Phosphorus can induce Zinc deficiency and excess potassium can induce magnesium deficiency in corn. So getting the right balance of fertility and pH is also important.

The smart part of taking soil sampling is dependent on how representative the soil sample is of the "area "or "zone" within your fields. Things to consider when deciding what defines each sampling area or zone are the past field history of such things as previous fertilizer applications including manure spreading patterns, previous crops and yields, topography, slope, tillage practices, etc. A soil sample should represent no more than 25 acres and should be taken once every three years and more often on sandy soils. Each sample should have 2 to 3 cores taken per acre. Fertilizer recommendations in Ontario for Phosphorus (P), Potassium (K) and Lime are based on samples taken at a depth of 6 inches. This represents the depth where plant roots are taking up the majority of the nutrients. Soil below this "plow layer" tend to be lower in fertility. Deeper soil samples will give a false reading, resulting inaccurate recommendations. In a reduced or no-till system, nutrients tend to concentrate closer the soil surface. You should still sample to the six inch depth to determine your P & K requirements. To determining soil pH, a separate sample taken of the top 2 inches in acid soils will be useful.

There are now 6 accredited Soil Test Labs in Ontario: Accutest Laboratories in Nepean, Agri-Food Laboratories in Guelph, A & L Canada Laboratories in London, Stratford Agri Analysis Inc. in Stratford, Soil & Nutrient Lab, University of Guelph and new to the list is Brookside Laboratories, Inc. New Knoxville, Ohio. Each lab has met the Ontario Ministry of Agriculture and Food (OMAF)'s standards for soil testing and will also provide OMAF recommended fertilizer rates, if you request them. OMAF recommended rates are based on research to produce the highest economic yields when accompanied by good or above average management.

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