Plant Tissue Analysis and Precautions During a Drought

Plant tissue analysis can be a useful tool for improving crop nutrition and yield. The diagnostic nature of tissue analysis can be a benefit and a shortcoming. It can quickly guide us towards corrective action in problem areas, but it is still a reactive technique that cannot replace a proactive soil sampling plan and fertility program. Additionally, this year’s dry conditions will affect the outcome of your results. Proceed with caution because your results could be more indicative of a drought than anything else.

Collecting and Submitting Samples

First, consider the growth stage of the crop and the goals of your program. Follow the instructions of the lab where samples will be analyzed because results and interpretation are sensitive to timing and can be regionally specific. In a diagnostic scenario with trouble spots, collect 10 to 20 samples each from the troubled area and the normal area of the field. In a uniform field, create a composite sample by collecting from 10 areas of the field. This technique strives to find the crops “hidden hunger.” The reliability of this approach is mixed since timing and environmental factors are critical.

Most labs will provide paper sample bags if requested. Avoid plastic bags and don’t freeze samples. Keep them dry and cool until submission. Testing labs provide submission forms that need to be completed for the most accurate interpretations. Consider submitting new complimentary soil samples.

Commonly Recommended Sample Timing. Follow specific instructions from your testing lab.

Crop

Corn

Soybean

Alfalfa

Growth Stage

<12” tall

Pre-tassel

Tassel

(most common)

Before R2

Bud to 1^st flower

Sample

Whole plant above ground

First whole leaf below whorl

Ear Leaf or first leaf below ear

Newest full trifoliate

Cut top 6”

Interpretation of Results

Testing labs will indicate sufficient levels and most provide a likelihood of crop response to fertilizer in their reports. They do an excellent job of making the results easy to understand. Remember that variables and reliability still depend on several factors:

The most important thing to remember about tissue analysis is that it needs the context of soil sample information, your fertility plan, growth stage timing and environmental conditions. The gap between a soil test and a well-timed tissue test is nutrient uptake.
Lack of moisture from drought, sample timing, or soil type can increase or decrease results. Nutrients taken up from the soil can increase concentration in the plant when moisture decreases. Or nutrients can become unavailable for uptake from the soil; in which case we see test results decrease. Potassium uptake from the soil is very sensitive to drought. The uptake process needs water, so deficiency symptoms will be common in a dry year even in fields with adequate soil tests and fertility plans.
Some nutrients are more reliably measured with a tissue test. For example, phosphorous and potassium have lots of research behind them, increasing reliability. Some universities do not even promote sampling for micronutrients because of a lack of meaningful results. Additionally, mobile nutrients such as nitrogen or sulfur are more susceptible to seasonal variations. These seasonal variations exist with all nutrients to some degree.

Overall, the lack of moisture in 2023 may not allow tissue analysis to appropriately represent crop and field conditions. A shortage of nutrients in the crop could be the result of an underdeveloped root structure, or just a general lack of opportunity for the plant to pick up the nutrients that are in the soil. Water makes everything work!