Every time that I walk a field, I’m reminded why I love agronomy: The information is all around us. Corn has no pretenses. Soybeans are not coy. Every problem has its symptoms. The soil and plants are veritably waiting to give us information, if only we listen.
This isn’t to say that agronomy isn’t complex though. It is. The dynamics between a plant and the soil that it grows in can be downright mind-boggling. Soil that tests as nitrogen sufficient can send forth corn that is yellower than a sunflower; soil that is boron deficient can yield the greenest and prettiest corn you ever did see. Our crops may have loads of information to offer us, but answers are quite another story. For answers, that’s where we turn to science, and a little art, and a little old fashioned, Sherlock-Holmes-type deduction.
Consider our yellow corn above. A soil sample tells us that the nitrogen is there, but the appearance of the corn tells us that it most certainly is not. How can this be? The answer is that there is a difference—sometimes a shocking difference—between what nutrients exist in the soil and what nutrients the soil makes available and what nutrients a plant growing in the soil actually uses. Just because nitrogen is there doesn’t mean that the plant is using it (or using it properly). Or, as is often the case with potassium, just because the potassium is there, doesn’t mean that the soil is giving it up.
Regardless of the complexity of plants and soil, they both willingly yield the information necessary to make sense of that complexity. Though they present puzzles, they also present the information to solve those puzzles. Like well-done mystery movies, all the clues to whodunit are there for the crafty sleuth.
How to be a crafty sleuth: take soil samples (you, friends, are already doing this,) which tell you what exists in your soil, and take tissue samples, which tell you what your plants are using. The intersection of these two pieces of information is rich with insight. You will know how well your plants are using nutrients and how well your soil is providing.
For those of you new to tissue sampling, and for those of you in need of a refresher, careful sampling and careful note taking are key:
- Be sure to sample the newest growth on your plants. On corn, this is the newest collared leaf. On soybeans, this is the uppermost trifoliate. On alfalfa, this is the top six inches.
- You will need to provide a softball sized amount of leaves for the sample.
- The sample should represent less than 40 acres.
- Pay attention to the time of day, the weather conditions, and soil conditions when you take your sample. Write these details down. Having this information will help you answer some questions when your sample results are returned to you.
- Once you have your sample, put it in a bag, and send it to the lab.
One giant note of caution here: Never use tissue sample results as the lone source of information on which you base your decisions. When used in conjunction with a soil sample, the tissue sample can illuminate issues and needs in your fields. Since false information is common in a tissue sample report, however, using it alone is a bad idea.
Let’s return to our yellow corn again: The soil sample says that the nitrogen is there, but the appearance of the plant suggests otherwise. You send in a tissue sample and sure enough, it reports that your corn plant is nitrogen deficient. So which is right, the soil sample or the tissue sample? Both, but if we have to call a winner, then it’s the soil sample. In this case, the corn plants are stressed, which is causing them to hoard nitrogen rather than use it. They are essentially stress eating, mowing through Kit Kats but using none of that energy to do anything more productive than sit on the couch and watch the History Channel. The nitrogen is there, but the plant is using it incorrectly, essentially causing its own deficiency.
Had a grower made a decision based only on the tissue sample, that grower would have mistakenly wasted time and money on an unnecessary nitrogen application.
Perhaps you’re asking now why a tissue sample is worth it if it’s going to provide information that is basically incorrect? It’s a fair question. The answer is that the information it provides, when compared with information from other sources, gives you incredible insight into the life and operations of your crops. Sure it might take a little investigation, but with some thought, tissue samples can provide key information about the dynamics between soil and plant and lend you a critical understanding of windows of nutrient demand when you can make a significant impact on your crops.
Information that will lead you to happier plants and better economy is hanging off the leaves of your plants for your taking. So take it. Take a softball sized amount, in fact.