Taking fertility back to the basics for better nutrition

This is the first of five columns that will look at building yield efficiently.

I continue to get calls from farmers with questions regarding fertilizers.

Some of them are what I consider basic questions that I assume most producers would know, but then we all know what assume will do. So I thought I would go back to the basics, so to speak, with a series of columns discussing fertility.

In my career I have had the opportunity to work with some great minds in the fertility world — or more specifically, the fertility world as it relates to Western Canada. These include the team I worked with during my time with Westco Fertilizers, including John Harapiak, Rigas Karamanos, Norm Flore, Lyle Cowel and Tom Jensen. These men could take complex issues and dynamics that are our soils and boil them down into concepts that farmers are able to put to work on their farms.

Over this series of columns, I will try to take some of what I learned from these experts and 40-plus years in the field and communicate it to you so that you can better understand the fertility end of your farming business.

I see a lot of information being thrown your way: some factual, some based on speculation and some that is science fiction. What I hope to be able to do is give you some background information so that you can reasonably decide on which pile to file the information.

First, some laws.

The first law of understanding fertility is Liebig’s law of the minimum. This concept is a principle developed in agricultural science by Carl Sprengel about 1828 and later popularized by Justus von Liebig. It states that a plant’s growth will be limited by the most limiting of the essential plant factors or nutrients. For the most part, this law remains relevant today, almost 200 years after it was first proposed.

So, what does this mean?

You have probably seen this concept described as staves on a barrel of varying lengths, where the yield is limited by the shortest nutrient supply and can be increased only by lengthening that limiting stave. Over my years of scouting in the field, I have become a firm believer in this concept.

I have solved many issues and problem areas in fields, including wheat, barley, peas, canola, alfalfa and other crops, by using tissue and soil sampling as my primary diagnostic tools. I lengthened the shortest staves. However, in these situations, there has already been some top-end yield loss for that year.

The second law is the law of diminishing returns, which says that yield will increase as an input is added to a crop. However, as each incremental units of fertilizer are added, there will be a point where the additional output of crop gained from one additional unit of fertilizer will be smaller than the additional output of production from the previous increase in fertilizer.

At some point, there may also reach a point where the output actually begins to decrease because too much fertilizer can become deleterious to production.

There is a cost to each unit of fertilizer, so there will be a point, before the point where yields are starting to decline, where the economics turn and the cost of applying another unit of fertilizer will, while still increasing yield, show no economic yield. This point is called the maximum economic yield.

The bottom line is that there is an end-point to the amounts of fertilizer you can apply and still get a reasonable return on the investment. This is governed by a number of factors, including crop types (canola versus soybeans, for example), crop varieties or hybrids, crop prices, fertilizer prices, weather (including rainfall) and your unique soil.

The third law is based on 4R nutrient stewardship, which states that for each nutrient, there is a right source, a right rate, a right time, and a right place to apply that will result in maximum economic returns and minimum environmental impact.

These four decisions will be unique for each farming situation and may vary from field to field. However, being able to use them correctly will improve yields, lower costs and lower the losses of nutrients from your field.

Let’s look at the nutrients you deal with annually on your farm.

The mineral elements are the ones we think about most often. They are divided into three different categories, classified by the quantity used by the plant. However, this does not mean that a primary nutrient is necessarily more important for plant growth; only that more of it is required.

  • Primary: nitrogen (N), phosphorus (P) and potassium (K). Because the plant uses a larger quantity of the primary nutrients, we see deficiencies of these nutrients showing up more frequently.
  • Secondary: calcium (Ca), magnesium (Mg) and sulfur (S). The crop uses more secondary nutrients than micronutrients, but less than the primary nutrients. We rarely see deficiencies in calcium and don’t often see magnesium deficiencies, but sulfur deficiencies have become more common as we started growing crops with high sulfur demands, as well as the reduced sulfur dioxide emissions from power plants.
  • Micronutrients: boron (B), chloride (Cl), copper (Cu), iron (FE), manganese (Mn), molybdenum (Mo), nickel (Ni) and zinc (Zn). Micronutrients are used in smaller amounts, but we do see deficiencies occurring from year-to-year. Because micronutrients are found in such small amounts in the soil, tissue testing in conjunction with soil testing can be a solid practice to help detect deficiencies. Also, because many of the nutrient’s availability is affected by soil pH, presence of the nutrient in the soil does not mean it’s getting to the plant.

Except for potassium, these nutrients must be mineralized from organic matter, and mineralization occurs at different rates every year and is driven by various environmental factors.

There are four additional nutrients that can be classified as essential in some crops but are rarely deficient in most soils: sodium (Na), cobalt (Co), vanadium (V) and silicon (Si).

So let’s dig in and examine these nutrients, what they do in the plant, how they get there and other things that are handy to understand as it relates to your crop. Over the next few columns, I will try and discuss the individual nutrients in more detail and relate them to the three laws described above.

Thom Weir PAg. is an agrologist with Farmer’s Edge. He can be reached by emailing thom.weir@farmersedge.ca.

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