The 2024 Growing Season and Late Season Tissue Testing

While things started off a little bumpy, the growing season of 2024 for much the Great Lakes region has been better than normal. Some areas have had excess rain and others would like a little more, but on average the rain has been fairly timely. As a result, crop performance is looking good to excellent. The plant tissue samples from row crops that we have seen support this. We are often asked by growers and advisors, “What are you seeing on other samples coming into the?” The answer is that most samples are reporting at normal to high ranges across all nutrients. The common patterns of deficiencies and excesses resulting from drought stresses or excess moisture are very rare this year. This has many questioning the nutrient status of their crops later into the growing season to see if there is enough fuel left in the tank to finish out these crops that right now look to have fantastic yield potential. However, as plant tissue samples are collected later in the growing season, the test results need to be evaluated with a cautious eye.

As plants transition from vegetative growth stages to reproductive stages, the nutrient content of the plant leaves will change, most noticeably nitrogen and potassium. These nutrients are mobile in plants, so as the plant starts transitioning to grain-fill, they may be translocated from the leaf to the grain resulting in low tissue test ratings that may not necessarily indicate a yield-reducing nutrient deficiency.

Another common trend in plant tissue nutrient levels is an increase in micronutrient concentrations as the plants approach physiological maturity. This is a result of carbohydrates and other carbon-based molecules being translocated from the leaf tissues to the grain effectively reducing the biomass of the leaf. The micronutrients (iron, manganese, zinc, and copper) are immobile in the plant tissue, so they remain in the leaf that has a lower mass and are now present at a higher concentration. The micronutrients may be rated as high or very high, however, this is not necessarily an indicator of excessive fertility or potential toxicity.

While plant tissue testing can be a very effective tool for fine-tuning a fertility program, be careful not to make drastic decisions based on late-season plant tissue test results alone. A continued favorable weather pattern and late-season disease control are going to be critical in finishing out this season.