Nutrient Tie-Up and Overload - West Coast Nut

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Nutrient Tie-Up and Overload

Overapplying Nutrients and Soil Amendments is a Common Grower Mistake

By Rich Kreps | CCA, SSp, Contributing Writer
Published: November 23, 2020 • 718 views

Make a plan to balance nutrients throughout the season to keep a steady supply of nutrients to match tree demand.

I have some food for thought. It actually has to do with food for trees…eventually. I’ve mentioned many times in my articles to make sure you are trying to balance your nutrition. That becomes abundantly harder when we overapply specific nutrients. I was trying to help my wife bake a loaf of banana nut bread and it wouldn’t rise. I’m a mad scientist in the kitchen as well as in the field. But in the kitchen, I try to emulate Emeril Lagasse. “A pinch of this, dash of that, splash of those and BAM! Kick it up a notch!”

But in baking, much like in soils, recipes should be followed. Our banana nut bread still didn’t rise. After sleuthing to find what I’m sure I botched in the recipe, we realized I had added the two cups of sugar… after she had already added the same two cups of sugar. Not only did it not rise, it caramelized nicely into a delicious albeit not very nutritious molten batter. Unfortunately, it is my humble opinion we do the same with overapplying nutrients and amendments in our soils.

 

Uptake and Applications

Let’s look at Nitrogen. Many of my new clients have nutrient budgets that have stayed the same for years. Two hundred units of N. Two hundred and fifty units of N. Three hundred units of N. Often times, it seems it is more in relation to the hopeful yield and not the expected yield based on what Mother Nature and the trees show us early on.

In correlation, there needs to be a balance with the other nutrients. It would be great if we could get 10% of our N levels in our P uptake, 80% of our N levels in K uptake, 100% of our N levels in Ca uptake, etc. Of course, those numbers can be tweaked a bit based on soil types, yields and tissue levels, but a plan should be in place. It is not what you put “on” your trees that’s as important as what you get “into” your trees. Let’s break this down further.

Suppose you are a 200 unit of N farmer. At 10%, you need 20 units of P. Now if you apply 10 gal 10-34-0 at 11 pounds per gallon, that would seem like a little more that 37 pounds of P. But remember, that’s measured as P2O5, so multiply that number by .44. That gives you 16.4 units of P. Not enough. And if you apply that in the spring when it takes 60 days for the polyphosphate form in that fertilizer (70% polyphosphate) to break down at those temperatures, it is too late to get it into those springtime energy-deficient trees when they need it.

When we realize this in May and shoot on 12 gallons 0-20-0, we add another 11-plus unit of P all at once. A tree can’t take in 50% of the P it needs in one fertigation event. As the soil dries down and rewets, that extra P combines with extra calcium in the ground and forms plaster. We just lost two nutrients we need throughout the season and wonder why our soils seal up in summer. Now, just for giggles, change your N inputs to 250 or 300. How much extra would you need to apply to make it balanced? Then calculate the efficiency factors of inferior or less clean nutrition products.

Let’s take another nutrient: Calcium. In a very insoluble form such as gypsum (2g per liter at 72 degrees F), we can over-apply that very quickly. And that solubility is in the lab and not on your soil with your well water. At 23% Ca, a 2-ton application is 920 pounds of Ca. If you need 100% of your N demand in Ca, that’s 200 pounds. You just applied an extra 720 pounds, and not in a soluble form. Take this a step further. Let’s say you have 2000 ppm Ca in your soil based on your test. That’s 4000 pounds per 6 inches of soil or 16,000 pounds in 2 feet. And that’s not the absolute number, that’s just what came off in the current acetate extraction test.

I postulate, Ca is not the issue; rather, its soluble Ca that matters. It has to be soluble to both get into a tree and kick sodium off the soil colloid. Now add that extra Polyphosphate in the wet, cold spring and tie more of it up.

Now look at sulfate of potash (SOP). SOP is only 7% soluble. A good form of it will be as high as 50% K, so a 400-pound application will be 200 pounds of K. Again, it is measured by two K ions as K2O, so multiply your fertilizer number by .83. That comes out to 166 pounds. That’s pretty close to the 80% of the 200-unit N applications and would fit. But if only 7% is soluble, that’s 11.6 soluble pounds.

We usually apply it in the fall. If that’s when mother nature starts to bring the rain, how much of that soluble K gets leached out of the ground before we actually need it? K is almost the same size and charge as sodium. Isn’t that what we are usually trying to leach out in the winter? Putting most of it out when it doesn’t match the nutrient uptake of the tree doesn’t make much sense to me. And at a time when we are going to lose a bunch of it below the active feeder root zone is again confusing.

 

Next Steps

Now what? Make a plan. Plan to balance your nutrients. Have your CCA do your calculations and devise your formulations. Plan on spoon-feeding your crop when it matches the nutrient demand curves: early N and P after root stores are used up. Follow it with a little Ca. Flow into late spring with N and Ca, and add your K as nutrient demand increases. Add a little more P so the tree can make energy. Plan to go upstairs as well as down. Many micronutrients absorb well foliarly.

You can also add a soil application of one nutrient that may be antagonistic to another nutrient that you are applying in a spray. Keep a constant supply of nutrients in the water in ratios that match demand. Have a recipe and follow it. Test and retest. Verify with tissues. Keep those trees happy. If you have any questions or feel the need to debate this, I’d love to hear the comments. Email me at rkrepsCCA@gmail.com. Remember, a little sugar goes a long way! A good recipe will make those yields very sweet.