Do Your Crops Get three Square Meals?

An adequate, well-balanced fertility program will ensure your crops are healthy.

By Paul Hermans

Looking at historical yield gains for both corn and soybeans across North America is exciting.

Over the past 25 years, corn yields have increased by about 50 bushels per acre, and soybeans have increased by approximately 15 bushels.

But are we feeding this crop adequately to maintain these high yields?

Why are yields on the rise?

A lot of this is attributed to genetic yield gain and the management practices growers are utilizing during specific stages of crop development to minimize stresses on plants. This allows for continuous water and nutrient uptake and the conversion to sugars, protein, and starch to make more yield.

The question we should be asking ourselves is, “Are we feeding the crop enough nutrients to sustain this continual yield growth today and in the future?”

To answer this, we need to look at what the corn and soybean crop needs to make a bushel of grain for each crop.

For this article, I am going to focus on phosphorus and potassium. Similar principles would apply to other crop nutrients.

Phosphorus is a primary nutrient. It aids in photosynthesis and cell division, which is critical for crop development. It is taken up for enhanced root development and can be instrumental in the initial stages of development of a crop. As well, phosphorous helps with crop maturity of plants.

Potassium is instrumental for water regulation and controls the stomates in a plant. It also aids with stalk quality (formation of lignin and cellulose), and can help later in the season with improved lodging resistance. It assists with disease and insect resistance (think about soybean aphids that usually attack low-K soil test areas). Industry experts would refer to it as the “Power of Potash.”

A 2015 survey conducted by the International Plant Nutrition Institute showed samples that tested below the critical levels for phosphorus and potassium ranged from 31 to 38 per cent for phosphorus and nine to 65 per cent for potassium for various states. Critical levels are defined as the level below which a profitable yield response would be expected in the year of application. Simply put, if you apply fertilizer, you will get a positive return on the investment that covers the initial cost and provides a return above that.

This intrigued me, so I decided to investigate what soil test levels would be like for Ontario.

All soil lab companies keep historical data sets. For Ontario, I recently talked with Chris Meier, Business Development and Key Account Manager for A&L Canada Laboratories based in London. Chris pulled a five-year history of data for Ontario, looking at soil test levels for phosphorous and potassium.

On the phosphorus front, 70 per cent of samples were in the very low, too low, and medium categories, with the split almost equal among the three levels.

Looking at potassium, two per cent were in the very low range, 13 per cent in the low range and 50 per cent in the medium range.

Chris commented that “generally speaking, we are seeing a downward trend in soil test levels. Some of it can be attributed to higher fertilizer costs, as growers look at only applying crop (nutrient) removal. The challenge is that we are attaining consistently higher yields, with improved genetics and cropping practices, which is potentially taking out more nutrients than once thought.”

If we look at crop removal rates, OMAFRA would suggest the following for corn and soybean removal rates per bushel.

One can simply do the math to see crop removal rates comparing yields from today and yields from 25+ years ago to see that we need to ensure we are feeding our crop to maintain high yield levels.

In my area, soybean yields were up five to 10 bushels and corn 20 to 30 bushels in 2023 compared to the prior year – and as much as 10 to 15 for soybeans and 30 to 40 for corn over a five to 10-year period.

This alone is a huge jump in one year that results in more crop removal.

The best way to determine crop needs is through a solid soil test program. Ideally, this is done either on a grid basis or, better yet, by soil management zones.

Utilizing precision agriculture with yield maps, a crop removal variable rate script can be utilized. Soils can be built up to optimum levels and then maintained using simple crop removal rates.

The ideal program would be to utilize variable rate prescriptions. As we all know, fields have variability and yields vary across a small area in a field. With today’s economy, variable rate fertility programs are a no-brainer.

If you know me, I am an analytical type of person. Show me the money on replicated studies and I have an easier time buying into a specific principle.

I will refer to some recent research done in Southern Ontario to show the value of increasing soil fertility levels.

Dr. Dave Hooker and others in Southern Ontario conducted research work on this exact principle. In his research work, they drew down fertility levels in part of a plot and made sure optimum levels were applied in the other part of the experimental plot. In the portion of the plot that had below optimal soil test levels, they applied fertilizer.

In essence, they were looking at what effect applying soil fertilizer would have on low fertility fields, to show the yield response to applying optimal levels of fertilizer.

For optimum soil test levels, they aimed for phosphorus at 20 ppm or higher and potassium at 120 ppm or higher.

Summarizing the work, they found about a four to six-bushel gain in soybeans, and 10 to 13 for corn.

These types of yield gains can be used to factor in the economics of applying fertilizer at sustainable rates to maintain and/or increase long-term yield goals.

The analogy that you always need three square meals a day holds true when we compare the crop to humans.

You never want your crops to have a bad day.

An adequate, well-balanced fertility program will ensure your crops are healthy, giving you the best yield potential year in and year out.

As the old saying goes, you will pay the price today or later. My vote is to pay the price now by getting fertility in check for long-term yield gains rather than losing yield down the road.

Good luck this winter. Look over yield maps from 2023 as you design optimum fertility plans for the 2024 cropping season. BF