No such thing as a free lunch when it comes to crop nutrition

Yields can suffer if soils are deficient in any crop nutrient

When I worked as a plant pathologist for Alberta Agriculture in the 1970s, I was surprised to find only 10 per cent of Prairie farmers have ever had their soil tested for crop nutrients.

How could they grow a cereal or canola crop without knowing what plant nutrients — nitrogen (N), phosphate (P), potassium (K) or sulphur (S) — were present in the soil and in what available amounts? Even fewer farmers had a concept of soil organic matter content and pH levels. In those days, the provincial average yield for wheat was around 22 to 25 bushels an acre, Argentine canola was in the low 20s and I remember Polish canola at 16 bushels an acre on average.

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How much of the present crop yields are due to plant breeding or an understanding of balancing crop nutrient inputs? Do not let plant breeders make you believe they were the prime cause of the doubling and more of crop yields per acre for both wheat and canola, the principal field crops.

Plant breeders have brought us disease resistance such as blackleg and clubroot resistance in canola and smut, bunt and fusarium head blight resistance in wheat. However, don’t forget the contribution of effective herbicides, insecticides and fungicides. Plant breeding has given us better crop standability, shatter resistance and an ability to utilize higher rates of crop nutrients (fertilizers), resulting in improved yields and required quality.

With all of these breeding inputs over the last 50 years, we now have better yielding and better-quality crops necessary for the food market. I won’t talk about peas, beans, sunflowers, flax, barley, soybeans, lentils, oats, mustard or other Prairie crops, since the same broad principles apply to all Prairie grain crops.

Despite all of these advances in Prairie crop breeding and crop production technology and equipment, it still boils down to optimizing each and every crop’s nutritional requirements and getting an expected profitable return.

Balanced availability of crop nutrients

Many farmers will tell you that they expect, on average, around 70 bushels of canola per acre and around 100 bushels of hard red spring wheat. This is true for the wetter areas of the Prairies and the irrigation areas. In the drier Prairie areas, the major limitation is just water, the overriding plant nutrient. Limited water, limited yield.

Provided that farmers are fully aware of the annual average rainfall in their areas, they can adjust their balanced fertilizer inputs to water (rainfall) availability.

If you are farming in southeastern Saskatchewan in an average year, you will be fully aware the rainfall limitations in your area will allow you to grow around 50 bushels of wheat and 30-35 bushels of canola. If you farm in the Lacombe or Edmonton area of Alberta, your higher rainfall expectation allows you to aim for that 100-bushel wheat crop and the 70-plus-bushel canola crop.

All of these yields, Prairie-wide, are fully dependant on balanced crop nutrient availability. The words “fertile soils” are a misnomer, since what you really mean is the balanced availability of crop nutrients to achieve your yield or goal objective.

All too often in the past, I would visit research sites to look at wheat plot demonstrations where the plots would receive 100, 200 and 300 pounds of available nitrogen per acre. There was no mention of phosphate, sulphur or potassium. Naturally, the 200- and 300-pound nitrogen crop input plots would lodge badly, stay green and oftentimes failed to mature. Nitrogen was the only answer in those days. To mention balanced macronutrients to the researcher, I got a bland stare with no mention of needed micronutrients, especially for the high-nitrogen plots. Micronutrients were looked upon as heresy or given ridicule.

What these researchers failed to comprehend was the nutrient depletion of both macro and micronutrients by crop removal. What was even more confusing was crop research on station cropland, which unlike regular farmland had little or no uniform crop removal, further contributing to erroneous yield results — nutrient depletion was not a major factor at the research station cropland compared with regularly cropped farmland.

Nonetheless, wherever you farm on the Prairies, whether it be conventional or organic farming, you must perform soil testing on your cropland at least every few years to find out your soil nutrient availability, or just plain depletion of specific crop-needed nutrients.

Remember, if you step up your nitrogen inputs based on your soil test, with a knowledge of your soil organic matter (nitrogen release) you can save on nitrogen. For your target yield, you need to keep the nitrogen in balance with the need and availability of phosphate, potassium and sulphur as well as one or more micronutrients that may be deficient to attain, say, your target yield of 60 bushels of wheat or 35 bushels of canola.

There is no free lunch in any agricultural crop production. If any crop nutrient is deficient in your soil, your expected yield suffers substantially, whether it be zinc or potash or any other essential nutrient shortage.

Miracles involving soil nutrients do not occur in agricultural soils and no one source of nutrient is better than the other if both result in crop availability. When you see advertisements that say you only need half as much nitrogen if you use this product, it’s factually untrue.

For example, if you target a 60-bushel crop of wheat at, say, 12 per cent protein, you must have in the growing season just over 100 pounds of nitrogen either from added fertilizer, soil residual or expected release from your soil organic matter.

You must also have about 50 pounds of phosphate, 90 pounds of potassium and 12 pounds of sulphur per acre at available and minimal levels. You assume at a soil pH above five that calcium and magnesium are okay. Micronutrients such as boron, copper and zinc you have been told by a soil test are fine. Any of these nutrients, macro or micro, in deficiency, will have a major impact on your expected yield.

A similar nutrient package is needed for a 35-bushel crop of canola with about the same amounts of nitrogen, phosphate and potassium, but you need to double the amount of sulphur.

If, by chance, you are in a good rainfall area in any of the Prairie provinces and you decide to double the aforementioned crop yields of 60 for wheat and 35 for canola, you have to almost double your nutrients for grain production, with a little less for the straw (crop residue).

Remember, if your level of boron, copper and zinc was adequate for a 60-bushel crop of wheat or a 35-bushel crop of canola, you may have to step up your micronutrient input either in furrow or as a foliar spray to obtain this higher yield. Every nutrient, whether macro or micro, is essential to attain goal yield objectives of any crop, and soil testing gives you the accurate answer to reach this expected yield.

Do not skimp on needed crop nutrients if your soil test tells you what’s deficient in your cropland nutrient bank. Think, if you have a crop failure in any given year due to severe drought, hailstorm or flooding, most of those nutrient inputs will still be in your cropland with perhaps some loss of nitrogen or sulphur. You did not lose your fertilizer inputs, they were not removed by the intended crop that unfortunate year.

About the author


Dr. Ieuan Evans is a forensic plant pathologist based in Edmonton, Alta. He can be reached at [email protected]



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