Every year, across Wisconsin and the Midwest, thousands of plant tissue samples are pulled from corn and soybean fields. They are bagged, labeled and shipped to the lab, and then a report comes back with results. And too often, that is where the story ends.
Plant tissue testing is not just about measuring nutrients. It is about making decisions.
It is about understanding why one part of your field thrives while another struggles. It is about figuring out whether that pale-green corn is starving for nitrogen or experiencing something entirely different.
Too often, we sample without a clear purpose. We collect data without a decision tied to it. Instead, ask these four main questions to get the most out of your results this year:
1. Why am I testing plant tissue?
Some of the questions you may want to answer with a plant tissue test are:
- Am I dealing with a nutrient deficiency or toxicity?
- Do tissue levels explain what I am seeing in the field? Tissue sampling to check a specific problem (color, normal compared to abnormal, uneven growth, past low- or high-yield area) is useful in troubleshooting. Sometimes it is not a nutrient issue.
- What is the crop’s nutrient status at key growth stages?
- Are nutrients affecting each other? Plant tissue can help troubleshoot complex nutrient interactions. Nutrient interactions matter. For instance, high magnesium can affect potassium and calcium uptake. Samples help you learn more about essential plant nutrients.
- Can I use plant tissue for on-farm research? Plant tissue testing is one tool used to evaluate different fertilizer rates. For example, half of the field received one nitrogen rate, while the other had a different amount. Use soil and tissue results from each rate.
Before tissue sampling, write down the goal you have. If the test will not influence a decision, reconsider taking it.
2. How and when do I test plant tissue?
Plant tissue results are based on a specific crop, at a certain growth stage and plant part (see table below). Work with your testing lab or agronomist and follow the plant tissue sampling guidelines for the crops you grow.
| Crop | Growth Stage | Plant Part Sampled | # of Plants |
|---|---|---|---|
| Alfalfa | Bud to 1st flower | Top 6″ | 30-40 |
| Alfalfa | Harvest | Whole plant | 15-20 |
| Corn | 12″ tall | Whole plant | 10-15 |
| Corn | Pre-tassel | Leaf below whorl | 15-20 |
| Corn | Harvest | Ensiled / chopped | 10-15 |
| Soybean | Prior to or at first flowering | 4th petiole & leaflet or 4th petiole only | 20-25 |
| Wheat | Tillering | Newest fully developed leaf | 30-40 |
| Wheat | Prior to heading | Newest fully developed leaf | 30-40 |
Keep in mind that plant tissue samples should be kept cool and dropped off at a laboratory for analysis within 24 hours of collection to keep sample integrity.
3. How do I interpret plant tissue results?
Test results are interpreted against research-based sufficiency ranges. The lab report will show whether a nutrient concentration is “low,” “sufficient” or “high” compared to those established ranges. The plant tissue sufficiency ranges are calibrated for a specific crop, at a certain growth stage and plant part.
A common misconception is that plant tissue nutrient status is related to soil nutrient availability. Instead, the results provide nutrient levels at the time of sampling.
Keep in mind, weather swings like saturated soil or dry spells can limit nutrient uptake even when soil levels are adequate. A “low” plant tissue result may not be a true deficiency, but a weather-induced deficiency during drought.
4. What do I do next?
Like any test, plant tissue testing has limitations. Because of timing, it is common to get plant tissue test results back and nothing can be done for the current crop.
Plant tissue reports do not include fertilizer recommendations. The good news is you can use plant tissue results with recent soil results to make fertility changes for the field next year.
Nutrient Application Guidelines for Field, Vegetable and Fruit Crops in Wisconsin says that micronutrients should only be applied when all the following are met:
- Soil test is low.
- Visual deficiency symptoms are verified with plant tissue results.
- The crop has a high nutrient demand (see chart below).
| Boron | Copper | Manganese | Molybdenum | Zinc | Sulfur |
|---|---|---|---|---|---|
| High | Medium | Low | Medium | Low | Medium |
| High | Medium | Low | Medium | Low | High |
| Low | Medium | Medium | Low | High | Medium |
| Low | Medium | Medium | Low | High | High |
| Low | Medium | High | Low | Low | Medium |
| Low | Medium | High | Low | Low | -no data- |
| Low | Low | High | Medium | Medium | High |
| Low | Medium | High | Low | Low | Medium |
Plant tissue analysis complements soil testing and is another tool in your toolbelt. Asking better questions can turn tissue testing from data into an advantage. That is where real value lies.
Need to go deeper?
Watch the video below to learn more about how to fine tune your crop nutrients with plant tissue samples.
