Today, we are more in tune with listening to what is going on around us than we were 20 years ago. This is particularly true when it comes to our fields. Whether it has been the wide adoption of soil sampling, yield monitors, or even the advent of infield sensors like moisture probes, we have come a long way in learning how to listen to the messages that our fields give us. These messages (or our willingness to listen to these messages) have unlocked a lot of yield for us in these last 20 years, as we have seen the average corn yield in the U.S. go from 140 to 170 plus bushels per acre. But for a majority of growers, I can think of another area that we could be listening to more: plant tissue testing.
When it comes to fertility testing, soil health, or any other test we do in our fields, we are taking a “picture” of what is happening at a moment in time. In the case of a soil sample that is taken in the fall, we know that there are nutrients in the residue that will not show up on that soil test, but if we take it in April, it will be a different set of results. In general, we accept this as part of the process. The same is true with plant tissue testing. Plant nutrient levels can and often do change based on plant maturity, the part of the plant sampled, the hybrid or variety, and even the weather we have in the hours and days leading up to the test.
For me, I look at plant tissue tests in one of two ways. It is either to monitor the health of the plant for a specific set of parameters, or it is to look at the health of the plant to diagnose a problem within the plant.
Today, I feel like most growers that use plant tissues are testing solely as a diagnostic tool, akin to going to the doctor. I know I only am going to go to the doctor if I am sick. When I do go, I want answers right now. I also want a course of action or medicine to cure the problem. Many growers and agronomists apply that line of thinking directly to tissue samples. We go take tissue samples if the crop has poor color, is weak, or is struggling. Then, we look to that single test for answers and action.
I challenge you to think of a different course of treatment. I know my physician would be quick to say that, while important, the doctor’s visit when ill should not make up the entire health care plan. An annual physical can help be proactive and take care of little things before they become big things. That is where the monitoring potential of plant tissue testing unlocks additional, and perhaps greater, value.
Sampling at predetermined times and intervals identifies deficiencies, excesses, issues and successes in time to “take action” if needed to help reach yield goals and manage economic risks. Again, it is a bit like an annual checkup. If you indicate that your plant is at growth stage x, then the lab of your choice will compare the values of your plant with their standards (universities and private labs have their own values, and they differ slightly from one to another) and advise how healthy the plant is or if there are indicators that raise concern. Late-season samples serve as the report card to tell us how well we did getting nutrients from the soil to where they needed to be in the plant. This report card can help identify where we need to focus for upcoming growing seasons.
It is important to remember there is a difference between soil and plant deficiencies. If you are tissue testing once or twice per year, it can be a good idea to take a soil sample and even a soil health sample at the same time and place as the tissue sample to help bring clarity to the process. Not only does it give you soil nutrient baselines at the same time but it can also reveal issues like compaction, insects, nematodes, or other variations from “healthy” soil that could be contributing to the above-ground symptoms that you would miss otherwise.
The real power in any testing, whether soil, soil health, or tissue, is in establishing a cadence. Using the same lab, sampling in the same area, and doing it at the same time each year build a pattern. Once you have a pattern, you can study it to find the answers that you are looking for. Remember, do not be discouraged by having values that are outside of target ranges. It doesn’t mean that you or your trusted advisor are doing a bad job.
Finally, remember that this is a part of tuning the machine that is your ecosystem. Just because you show a deficiency of a micronutrient or an excessive amount of something else, it doesn’t definitively mean to go spray a foliar product or cut a rate in the future. It might mean those things, but it first means to study the system and theorize on your why before you decide on your response.