By Darren Hefty
Are you sufficiently alarmed? I am, just by reading that title. Can you turn a plant tissue test result into a fertilizer application that will make your farm money consistently? Before you can do that, you really have to understand your soils.
Example 1: Your soil is borderline low in copper but great in everything else. Surprise, surprise – your plant tissue test comes back a little low in copper even though you are getting perfect weather this year. Will a foliar application of copper make a difference? Odds of success are pretty high in this scenario.
Example 2: Your soil is dramatically low in copper. Now your plant tissue test results say you’re super low in copper. Will a foliar app make a big difference? It should, but a single application of a micronutrient isn’t going to get you maximum yield. In this case, multiple foliar applications or a good soil application early in the season is what it will likely take to achieve top yields.
Example 3: Your soil is borderline low in copper and very low in phosphorus. Your plant tissue test says you need both phosphorus and copper but you only apply copper because that’s what you’re doing everywhere else. Will you get a good return on this application? I’d be very surprised if it helped at all since a primary nutrient, phosphorus, was more likely the yield limiting factor.
All these scenarios are pretty obvious, but when you pull plant tissue tests through the year on a weekly basis you will begin to see patterns show up on your farm. If a micronutrient is trending low all season, you probably need to address it with both your soil applied fertility program and your foliar apps. The big ones like N, P, K, Ca, Mg, and sulfur really need to be in good shape coming out of your soil program or you’re in trouble before you even start. The only way to really know this is to take good soil samples across your farm. If you KNOW there is plenty of nitrogen in the soil, but your first couple of tissue tests say you are a little low, it’s very possible you’ll hit that N soon, and additional applications aren’t necessary. On the other hand, if you were trying to get by with relatively low levels of soil N, and tissue test after tissue test comes back low to deficient on N, you’ve got to get more nitrogen out there.
Can plant tissue tests help? Absolutely. I believe they’ve saved our farm a ton of money on fertilizer we would’ve applied incorrectly, and they have helped shift our program to things that make us money. Just don’t get too carried away applying things in-season if you don’t know what’s in the soil that will come available with some rain or just bigger roots. Also, we don’t have an exact formula for turning tissue tests into fertilizer recommendations. Our suggestion is to use the data for this year’s foliar and next year’s soil applications. Try some things out. Monitor your results closely, and keep working to build your soil, your yields, and your profits for both the short-term and the long-term.