Last week, I went out on a farm call to diagnose some milo that had turned purple. The grower suspected that a chemical had caused the unusual coloring, but in fact, purple is a symptom of a phosphorus deficiency. His soil is dense clay, and with all the rain, it became too wet for the roots to spread well enough for sufficient nutrient uptake, causing the deficiency.
There are two particular strokes of luck in this situation: 1) purple plants makes it pretty clear what the problem is, and 2) phosphorus deficiencies show up early in crops.
You don’t always get this lucky with nutrient deficiencies. They can be difficult to diagnose with a visual inspection because many different deficiencies present similarly: zinc and sulfur deficiencies are almost impossible to distinguish, and though nitrogen deficiency presents with a characteristic inverted V, sometimes potassium deficiencies look like that too. More problematic than this is that in most cases, by the time your crops are showing signs of a deficiency, you’ve already suffered some yield loss.
This is why tissue sampling is so very important to your operation. While a visual inspection might not be able to tell us if it’s a zinc or sulfur deficiency streaking your corn leaves with yellow, a tissue sample will yield a clear answer. If you use tissue samples proactively as a preventive measure against deficiencies, you will be able to catch any issue before it affects your yield.
Likely, you developed your nutrient plan for this growing season last November or December, and you were probably betting on a dry year. We’re a long way from last November or December though, and the year has been surprisingly wet. The difference between our plans and the reality of this year necessitate some reevaluation of our nutrient plan because rain does some funny things to soil. As it changes our soil, it changes too the availability of nutrients. Perhaps the heavy rains have washed the topsoil from a hillside exposing the subsoil in your field and causing a zinc deficiency. Perhaps the saturation of your clay soil has inhibited root spread and caused a phosphorus deficiency as happened with the purple milo. Whatever might have happened, a tissue sample will let you know what your plants are actually receiving and guide you through any amendments you would make to your nutrient plan yet this season.
As always, I’m certain that concern about the cost of sampling is lurking somewhere in your mind. As with most things that I talk about in this series, the upfront cost is very real, but will be worth every penny plus some come harvest as the information you gain from sampling will help you increase your yield. Think of tissue sampling as an investment rather than an expense: for every 60 cents you spend on a pound of nitrogen now, you could reasonably expect to earn about $3 come October.
By the time this article is published, there will still be time to sample if you haven’t done so already. In fact, there will be quite a bit of time still to sample and make amendments on milo and soybean crops. For those of you considering sampling corn though, move fast. Corn plants determine their ear size in V6—your plants are likely already in V8, but sampling now and correcting any deficiencies can still greatly affect your yield as we can yet affect grain fill. Acting quickly with corn will also keep the door open for ground-based application. Very soon, the corn will be tall enough to require aerial application which would, of course, increase the cost of correcting any deficiencies revealed by your sample.
If you’re yet a little dubious about the need for tissue sampling, let me offer one last little nudge: the rain that we’ve received lately brought with it the promise of a yield bump. But realizing that promise requires that we adjust our nutrient plan to match. Tissue sampling will guide you through this adjustment and ensure that you apply exactly and only what your plants require. It’s a valuable activity in any given year, but has particular benefits for us this year as we enjoy an unexpected water surplus.