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Improve Fertility Programs with Plant Tissue Analysis

Darren Hefty of Ag PhD takes a plant tissue sample.

Well-known agronomists Brian and Darren Hefty are our guest bloggers for this post. Through radio and television programs and during workshops, the Heftys help educate farmers and provide information to help farmers improve their profitability. In this blog post, Brian and Darren discuss how to make plant tissue analysis useful and how it can help improve your fertility program. 

Plant tissue analysis can be helpful in developing a fertility program, but in order to maximize its use, it’s important to know how to use the test results after you receive them.

It’s better to find out you have a deficiency through a plant tissue analysis than by observing it in your fields. Here’s an example of a severe potassium deficiency. Notice how the yellowing starts at the outside and moves toward the center of the leaf.

How to do a Plant Analysis

If you haven’t utilized plant tissue analyses before, it’s pretty simple to pull one from a field and to understand the subsequent test results. For details on how to pull samples from your specific crop, this document from Midwest Laboratories provides good information on how and when to sample. A number of labs in the United States perform plant tissue analysis; we use Midwest Laboratories in Omaha, Neb., for our samples.

Here’s an Example

In Field A, the phosphorus reading was 0.42 percent. By itself, this number means nothing, but the lab gives the reading a rating of “S,” which means sufficient. Then I look at the norm, which is 0.38 percent, and realize my 0.42 percent rating is just fine. I have reason for concern with the potassium level, though. The reading is 1.63 percent, but the norm provided by the lab is 2.20 percent, which rated my sample as “D” or deficient.

What Actions Should We Take?

One option is to foliar-feed some nutrients into the plants. This approach seems reasonable because products such as Sure-K™ provide highly available potassium. However, the test was taken on August 3, so the plants already have pods and are fully canopied. Therefore, driving a sprayer through the field would be difficult and it also may be too late to fix the problem. Another challenge is that the test is only a snapshot of the nutrient situation on that particular day. If we had taken a sample every week for 10 weeks, we likely would have seen a trend of low potassium levels. This data would have provided better background to make a decision regarding fertilizer application. With only one test, it’s difficult to know if potassium levels are always low or if a good rain is the simple solution.

The second option is to take your medicine, especially if the only plant tissue analysis was taken late in the growing season. Think of a plant tissue analysis as your report card. In the example provided here, the report card tells us the fertility plan for this crop was insufficient in available potassium, and the best long-term fix is to change the fertility program. We would either need to apply more potassium, use a more available source of potassium or potentially supplement our program with a foliar potassium during the reproductive (flowering) stages.

Where to Begin

To get a good read on how your fertility program is working, take a field or two and pull a plant tissue analysis each week throughout the growing season. Pick two spots: a good spot and a lower-yielding spot. Mark the spots with either a GPS tool or with something as simple as a flag. Pull samples for 10 weeks and chart the results.

I will almost guarantee the results will completely change the focus of your fertility program, as it did for us. You won’t necessarily spend more money on fertilizer, but you will likely spend the same dollars more wisely to achieve better yields, and ultimately see a better return on your investment.

Here’s an Ag PhD video with more information on plant tissue analysis, and feel free to contact us with questions.

Have you done plant tissue sampling on your farm? Did your fertility program change as a result of the test findings? Let us know. We welcome your comments and want to do all we can to help you Be Ready for the future.

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