We’ve all been there—applying fertilizer with high hopes and a solid plan, only to see underwhelming results in the field. You check the soil tests, the rates, the timing… but the return on investment just isn’t there. So, what’s going on?
The soil is actually the worst place to store nutrients. Especially when we’re talking about phosphorus (P) and potassium (K).
Why P & K Get Locked Up in the Soil
Phosphorus and potassium are notorious for binding to the soil’s exchange sites. Once they’re there, they don’t move easily back into the soil water solution—the only place where plants can take them up.
One book Kurt read last year said it straight: we’re only about 10% efficient with phosphorus. That means for every dollar you spend on P fertilizer; you’re only getting about ten cents worth into the plant.
So… What’s the Fix?
If you’ve got a drip irrigation system, here’s the good news: you can do better.
Instead of relying on big, one-time applications of fertilizer into the soil, you can deliver nutrients directly through the water—right into that soil solution where the plant needs them.
Small, targeted doses through fertigation (especially with phosphorus and potassium) can dramatically increase efficiency and uptake. It’s not just about putting it out there—it’s about putting it where the plant can use it.
Rethinking Your Fertilizer Budget
We’re already seeing this shift in action. More and more growers are replacing soil-applied fertilizer with PPM applications in the irrigation water.
Here’s where we think that’s headed:
- Phosphorus & Potassium: Up to 80% of these nutrients should be applied through the water.
- Nitrogen: Somewhere around 50–60% is a good target, depending on your crop and timing.
It’s not one-size-fits-all, but this is the general direction we’re moving as the data comes in.
Why You’ve Seen Mixed Results in the Past
Ever apply fertilizer and see no response? You’re not alone. But new testing methods are showing us why: we weren’t accounting for nutrient interactions or availability.
Some nutrients simply weren’t making it to the plant in the first place—or were being overpowered by other elements in the soil water.
One More Big Idea: Plants Don’t Choose Their Nutrients
This might surprise you: plants can’t choose what nutrients they take up.
They absorb nutrients via mass flow, and that includes whatever anions (like nitrate, sulfate) and cations (like potassium, sodium, calcium, magnesium) are most prevalent in the soil water. If sodium is winning the competition over potassium? The plant gets sodium—even if it’s not what it needs.
So our job isn’t just to apply nutrients—it’s to balance the whole soil solution so the right ones are available in the right ratios.
The Bottom Line
We can’t keep treating the soil like a bank account where we deposit nutrients and expect them to be there when the plant needs them. It doesn’t work that way—especially for phosphorus and potassium.
Instead, we need to treat soil water as the delivery mechanism and balance as the key. Through drip irrigation and strategic fertigation, we can get more value out of every fertilizer dollar—and give our crops exactly what they need, when they need it.
Ready to rework your fertility game plan? Let’s talk about getting more nutrients into your crop—and fewer tied up in your soil.
