Agronomy Agronomic Articles

Where To Stash The Potash

Seed Row or Mid Row? - Cutting Edge, Winter 2019

The term "potash" refers to a group of potassium (K+) bearing minerals and chemicals. The compound, Potassium Chloride (0-0-60), is the dominant source of potassium in the North American market.  Potash, a macronutrient essential for plant and human health, is important in several chemical reactions in the plant, including photosynthesis, protein synthesis and starch synthesis. It is also very important in helping the plant regulate moisture loss by playing a pivotal role in stomata opening and closing on the leaves.  Stomata are the small openings that allow air to enter the leaves on plants.  Healthy stomata activity in the plant will reduce wilting during heat stress periods.

Our soil tests identified potassium deficiencies in several of our fields.  This was not a surprise, since, as an industry, the majority of farms haven’t matched potash fertilizer application rates with crop removal rates.  This may be surprising to many as Saskatchewan is a major exporter of potash around the world.  So why, if Saskatchewan is so abundant in potash, would we show a shortage in our soil?  Although Saskatchewan is a major exporter, this valuable resource is found thousands of feet below the surface inaccessible to the plant’s roots.  I’ve been soil testing in the St. Brieux area for over 20 years and have seen levels of potassium decline from over 500 ppm to under 100 ppm in client’s soil tests.  This past spring, to address this deficiency, we decided to increase our potassium rates to better reflect crop removal rates.  Looking at the forecast, we decided that it would be wise to not place any additional fertilizer in the seed row to compete for moisture, so the potash was placed down the Mid Row Banders®.

1. We seeded all of our wheat on canola stubble from May 8th to May 14th into perfect moisture. The first wheat seeded came up beautifully by May 20. There was no rain all spring and by the early part of June it was extremely dry.
2. We had swathed all of our canola on an angle in 2018. In the 2019 season, after we finished swathing canola in August, the skies opened up and rain and snow fell on the swaths for over a month.

By the end of June, there were distinct patterns showing up in some of the wheat fields. Drone photos provided us with a bird’s eye view of the pattern. Plants from the dark green strips and from areas between the dark green strips were closely inspected.  There were obvious differences in plant growth.  At first glance, the symptomology of the affected wheat resembled nitrogen deficiency. The oldest leaves were pale, chlorotic and plant growth was delayed. Tissue samples were sent to a lab to help determine what exactly the issue was. The tissue tests confirmed we were dealing with a potassium deficiency.

This result was further supported by the photo below. Sulphur was applied across the entire field the fall before. This spring, the field was seeded placing phosphate in the seed row and nitrogen and potash in the mid row.  In one area of the field, the potash was moved from the mid row to the seed row as an on-farm trial.  The right side of the photo is where the potash was placed in the seed row, and the left side is where potash was placed in the mid row.

All crops require a high amount of potassium, just below that of nitrogen. However, only about 25% is exported in the seed, with the remainder staying in the straw.  Abundant rainfall in the fall of 2018 caused nutrients to leach from the canola swaths into the soil below them.  

This made adequate potassium available for the 2019 wheat growing in these strips. The plants outside of these strips experienced potassium deficiency due to low levels in the soil.

This is why we saw a deficiency in the field, but not where the canola swaths were from the previous year. We also didn’t see the deficiency as severely where the potash was placed in the seed row instead of in the mid row.

This photo shows the difference between the plants in the swath rows (wheat on left) and the affected plants between the rows (wheat on right).

If you have a potassium deficiency in your soil, apply a safe rate of potash in the seed row topping up in the mid row if needed.

Moving forward, we will be placing a safe amount of starter potash and phosphorus in the seed row of all crops, with the bulk of fertility requirements applied down the MRBs. The Mid Row Bander® Fertilizer Application System gives the flexibility to place a safe amount of starter fertilizer in the seed row, while still being able to apply the entire nutrient package the crop requires in a single-pass.

As interesting as it was to witness this in the crop this year, I hope to avoid a similar situation in the future. There are many other learning experiences ahead I’m sure!