Stop Paying for Nutrients Your Crop Can’t Use
In a high-risk year where margins are tight, commodity prices are volatile, and fertilizer costs remain high, the growers who win will not always be the ones who spend less. They will be the ones who make every fertility dollar work harder.
Too often, fertilizer decisions are made by comparing price per tonne or nutrient concentration alone. How many pounds of nitrogen am I getting? What is the cheapest source of phosphorus? Those are important questions, but they are only part of the story.
The real value of a fertilizer is determined by how efficiently your crop can use it. To understand that, we need to look beyond the analysis on the tag and pay attention to two things that often get ignored: salt index and pH. These two factors affect seed safety, nutrient availability, microbial activity, and ultimately your return on investment.
Salt Index
Every fertilizer contains salts in different concentrations. Whether it is granular, liquid, or gas, those salts influence how the fertilizer behaves in the soil. Salt index is a measurement developed to compare how strongly a fertilizer increases salt concentration in the soil solution, using sodium nitrate as the benchmark at 100.
The higher the salt index, the greater the osmotic pressure created around that fertilizer. When high salt index fertilizers are placed too close to the seed, water moves away from the seedling and toward the fertilizer. Instead of feeding the plant, the fertilizer pulls moisture away from it. This creates fertilizer burn, weaker emergence, and thinner stands. That is why seed placement matters.
Urea is a good example. 46-0-0 remains one of the most common and affordable nitrogen sources on prairie farms. But it also carries a relatively high salt index, around 75, which creates significant seed-row risk if placed in-furrow. That is why your agronomist recommends urea be side-banded rather than seed-placed.
MAP (11-52-0), on the other hand, has a much lower salt index, around 26, which makes it a safer option for starter phosphorus at reasonable rates. That lower salt load is one reason it remains a common in-furrow phosphorus source.
But salt stress does not stop at the seed. Your soil biology feels it too. High salt conditions reduce microbial activity, especially the bacteria responsible for residue breakdown, mineralization, and nutrient release. When microbial activity slows, nutrient cycling slows. That means less nitrogen released from organic matter, less phosphorus made available from soil reserves, and less efficiency from the fertilizer you already paid for.
In other words, you can spend money applying nutrients that not only stress the crop but also shut down the biology needed to make those nutrients available.
pH Matters Too
Every fertilizer interacts with soil chemistry differently. Some fertilizers create temporary acidity around the fertilizer band, while others create short-term alkaline conditions depending on the nutrient form and how it transforms in the soil.
Ammonium-based fertilizers like urea, ammonium sulfate, and anhydrous ammonia all create localized pH shifts during conversion. Over time, repeated nitrification of ammonium releases hydrogen ions and contributes to acidity in the fertilizer zone.These localized changes matter because pH controls nutrient availability.
Phosphorus is one of the best examples. Across much of the western Canadian prairies, high pH soils cause phosphorus to tie up quickly with calcium, making it less available to the crop. You may have plenty of total phosphorus in the soil, but very little that the plant can actually access.
Biology plays a major role here too.
Microbial activity helps solubilize phosphorus and move it into plant-available forms. Mycorrhizal fungi extend the root system and improve phosphorus uptake. When pH is working against the biology, the crop loses one of its best nutrient delivery systems.
Micronutrients like zinc, manganese, iron, and copper respond the same way. They may be present in the soil, but poor pH conditions reduce availability and efficiency.
Think beyond pounds applied
The goal with nutrient recommendations is not simply to replace what the last crop removed. That’s a very old school way of looking at things. The goal is to create a system where nutrients stay available, safe, and efficient. That requires both proper fertilizer management and a healthy biological environment that supports nutrient cycling.
This is where advanced soil analysis changes the conversation. Instead of asking only how much N, P, or K is needed, we need to ask how the soil will handle that fertilizer. What is the salt load around the seed? What is the pH of the system? How active is the biology? Where are nutrients being tied up or lost?
Sometimes the answer is a different fertilizer source. Sometimes it is different placement. Sometimes it is using humic products to reduce salt stress, improve nutrient retention, and support biological function. The point is that better fertility does not always mean more fertilizer. Often, it means better decisions.
Your crop does not respond to what you apply. It responds to what it can safely access. Salt index and pH help determine that.
In a high-cost fertility year, understanding both is not optional. It is good agronomy, and it is one of the best ways to protect your return on investment. Talk to your Johnston’s Regenerative Agronomist today to determine if your fertility program is helping or hindering your margins this year.
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