Source: Central Valley Ag
“Sign, sign, everywhere a sign … Do this, don't do that, can't you read the sign?” - Five Man Electrical Band
There is no doubt that in the last 20 years we have come a long way in reading what our fields tell us. 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 read the signs that our fields give us. These signs, or to be truthful, our willingness to read the signs have unlocked a lot of yield for us in these last 20 years as we have seen the US average corn yield go from 140 to 170+. There is another area of our fields that we have the ability to read that most growers have been ignoring, and needs to be taken more seriously, that is plant tissue testing.
When it comes to any testing that we do in our fields, we are taking a “picture” of what is happening at that moment in time. In the case of soil sampling in the fall, we know that there are nutrients in the residue that will not show up on a soil test, but it is part of the process. The same is true with plant tissue testing. Plant nutrient levels change based on plant maturity, the part of the plant sampled, the hybrid, and even the weather. So we need to look at plant tissue testing from the aspect that it really has two areas of value; monitoring the health of the plant, or diagnosing a problem within the plant.
The diagnostic side is treated much like going to the doctor. I am only going to go if I am sick, and I want answers right now. So we test, try to figure out what is wrong, and what, if any medicine is going to make it better. All too often we only think of plant tissue sampling as a tool in this regard. We go take tissue samples if the crop has poor color, is weak, or is struggling. And then we look to that single test for answers and action. But, much like our own health, the doctor’s visit when ill should not make up all of the health care plan. And that is where the monitoring side comes in.
Sampling earlier in the season identifies deficiencies in time to “take action” if needed, to help reach yield goals and manage economic risks. It is a bit like an annual checkup. Our universities and labs have standard values for crops at every growing stage. If you indicate that your plant is at growth stage X, then they will compare the values of your plant with the known standard and advise how far out of bounds that we are. It could be that something in the soil is depleted or in excess. However, it often has to do with weather and rainfall, and the nutrients that are available in the soil because of those two factors have a lot of influence on nutrient availability and uptake.
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 on for upcoming growing seasons.
It is important to remember there is a difference between soil and plant deficiencies. If you are only tissue testing or twice per year, it can be a good idea to take a soil 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.
Knowing where and when to sample can be a daunting task. Being off a couple of leaves from the ones you are supposed to take, or telling the lab that the plant is at the wrong growth stage can have a tremendous influence on your results. Relying on your Agronomist or Crop Scout to take tissue samples with you or for you is a good policy to go with if you are uncomfortable or nervous about inadvertently skewing your results. Once you receive your test results back, work with your doctor, I mean agronomist, to understand the results and compare them to the proper data sets. Remember, plants are like people in that they are each a bit different. What is “normal” for one hybrid may be very different than what is normal for another. Finally, don’t 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, it just means we need a tweak here or an adjustment there. Some problems are solved by time; others may require a shot, I mean an application of a Macro or Micronutrient to boost health. Tissue, and for that matter soil testing is a very inexpensive way to monitor our crops and help ensure yield potential.