By Darren Hefty
I bet you’ve heard Brian and me talk about plant tissue analysis a number of times, and perhaps you’ve even pulled a test or two from somewhere on your farm. The question then becomes “What do I do with the test results once I have them?”
If you haven’t seen a plant tissue analysis before, it’s pretty simple to pull one from a field and to understand the results once you have them back. For details on how to pull a sample from your specific crop, visit http://www.agphd.com/images/sampling_guide_for_plant_tissue.pdf. There are quite a few labs around the country that do plant tissue analysis (often the same lab where you send your soil samples), but I personally like the way Midwest Labs in Omaha does it. Here’s an example:
In Field A, the Phosphorus reading was 0.42%. That really means nothing to me, but the lab gives it a rating of “S” which means sufficient. Then I look at the Norm, which is 0.38%, and realize my 0.42% rating is just fine. I have reason for concern with the Potassium level, though. The reading was 1.63%, but the norm is 2.20% and the lab calls it “D” or deficient. So what do you do when your test result tells you this?
Option A – You could try to foliar feed some nutrients into the plant. This seems realistic, and there are products like Sure-K that could deliver some highly available Potassium to your plants. The challenge in this case is that the test was pulled August 3rd, and the plants already have pods on them and are fully canopied. Driving a sprayer through the field is tough, and it may be too late to fix the problem. Plus, you’re looking at one tissue test that only gives you a snapshot of the nutrient situation that day. If you took a sample every week for 10 weeks, and they showed a trend of low to deficient Potassium levels, that would be better data to make a fertilizer application decision on. With only one test, it’s hard to know if the Potassium levels are always low or this is a one-time deal that may correct itself next week with a good rain.
Option B – Take your medicine. I view plant tissue analysis as the report card of the farmer. In this case, the report card is telling you that the fertility plan used for this crop was insufficient in available Potassium. The best long-term fix is to change your fertility program. Either apply more Potassium, use a more available source of Potassium, or potentially supplement your program with a foliar Potassium right around the reproductive stages (flowering).
The trick with soybeans is they don’t tend to show nutrient deficiencies until the plants are putting on pods and filling them (in other words, in a period of high nutrient demand). With corn and wheat, the nutrient deficiencies tend to show up much earlier in the season.
If you’d like to get a good read on how you’re doing with your fertility program on your farm, I’d suggest taking a field or two and pulling plant tissue analysis each week throughout this growing season. Pick a good spot in the field and a lower yielding spot. Mark them with a GPS tool like a FarmPad (www.farmlogic.com) or with a low-tech tool like a flag. Pull samples each week for 10 weeks and chart the results. I will almost guarantee this will completely change the focus of your fertility program, as it did for Brian and me. This didn’t mean spending more on fertilizer for us. It meant spending the same dollars more wisely to get a better return on investment and ultimately better yields.
For more information on plant tissue analysis, check out the Ag PhD channel on YouTube.