Taking on Tissue Testing
Its been the hottest topic in farm publications and from yield contest winners. Tissue testing. Many individuals are touting the benefits of in season tissue testing as an essential factor in reaching the next major yield goal. But is it all that it is cracked up to be? Does this method live up to the hype? How helpful are tissue tests in improving yield? We wanted to find out some of these answers ourselves. So come along with us as we explore the world of tissue tests.
What are tissue tests? What do they show us?
Tissue tests take place during the growing season. Leaf tissue is cut from the plant and sent in to a laboratory for testing of macro and micro nutrient levels in the plant. This concept is similar to soil sampling, in that we are getting a test value returned that represents a static moment in time. Each sample represents what was going on in the field, whether it was the soil or plant at that moment. We begin to differentiate between the two when we consider that the soil test value is showing all the nutrients contained in the soil available for use, while the tissue test is showing the amount of nutrients that were taken in by the plant. This is an important point to differentiate. Just because the nutrients are in the soil does not mean that they are available to the plant. Issues with pH, water availability, or rooting depth by the plant affects its availability to uptake the nutrients in the soil.
A tissue test from the lab will often look something like this.
From this test you can see the percentage or ppm of each nutrient sampled. We also see a range of sufficient to deficient that provides us guidelines on how much of that specific nutrient a plant needs, and ultimately, if the amount contained in the sample is enough for the plants cellular and reproductive functions.
Macro and micronutrients in corn
There are 16 nutrients necessary for plant function. Nutrients in corn are grouped into two segments: macro and micro nutrients. Macro nutrients are those needed in larger quantities. Micro nutrients, while no less necessary, are needed in smaller quantities. Nitrogen, potassium, phosphorus, sulfur, calcium and magnesium are all considered macronutrients. Boron, chlorine, copper, iron, manganese, molybdenum and zinc are all considered micronutrients. Of these nutrients, all are extracted solely from the soil except sulfur. Sulfur can be extracted from the atmosphere, as well as the two necessary remaining nutrients: carbon and oxygen.
The amount of these nutrients needed by the plant depends on the specific hybrid. Each hybrid will need slightly different quantities to maintain cellular function. When we are conducting tissue tests, we are verifying that the micro and macro nutrients are within the correct ranges for optimum plant function and development.
Timing and quantity of micronutrients varies across the growing season. This principle is called elemental prominence and says that a certain point in the growing season, a specific nutrient will be in more demand by the plant than any other nutrient. This is highly related to the developmental processes of corn and which nutrients are needed to complete those functions. For instance, boron is a component used in reproduction, so will be more in demand during those times than another element.
When do you take tissue tests?
The schedule and timing for taking tissue tests depends on the growth stage of the plant. Prior to tassel, the first collared leaf from the top should be selected. After tassel, the earleaf should be selected. For each sample, 15-20 leaves should be collected. Ideally, these should be chosen from the same exact growth stage and from adjacent or nearby plants. This will give a more representative sample of what is going on with the corn at that growth stage and that location in the field.
How do we use tissue tests?
Tissue tests are really used for two main functions. First, they can be used to correct nutrient deficiencies in season as soon as results from the tests come back. This can be done through foliar nutrients or sidedressing. This method allows a grower to be very responsive to what is going on with their field. However, some experts say that by the time that the deficiency is detected, the yield impact has already been set and no benefit will come from in season application. An extremely important factor to consider is the ability for plants to take in nutrients through their leaves. Many times, after tissue testing we are applying a product foliarly. Leaves have a waxy cuticle layer for protection which makes it very difficult for plants to take in nutrients through the leaf. 10% of the leaf surface is stomata where water and gas exchange take place. Foliar applications will only be taken in through that 10%. For that most part, macro nutrients, which are needed in larger quantities, are not readily available to the plant by foliar feeding. Nearly 100% of macro nutrients should be supplied through the soil and only provide foliar macronutrients if absolutely necessary. The response for micronutrients is much more positive, since they are needed in such smaller quantities. Complete leaf coverage is a necessity for maximum uptake. The entire leaf surface should be wet. This can often be completed in conjunction with a fungicide application. While these corrective measures can help during the growing season, it is still advised that additional micronutrients be soil applied with your traditional fertility program moving forward.
The other method is to record the deficiencies seen throughout the season and use them to make fertility recommendations for the next year. This method allows for more time for reaction and to gather additional test to verify deficiency. However, if there truly were problems in season, we did not take immediate action to correct them, possibly causing further yield impact. Applying via the soil will provide a much higher nutrient uptake efficiency that via foliar feeding.
Are there any issues with tissue tests?
There are a few factors to consider when utilizing tissue tests. First, as we previously mentioned, tissue tests are a snapshot in time. They don’t tell us if those values are increasing or decreasing. It is wise to set up a weekly sampling program in order to gain as much value from this practice as possible. Find a location in the field and each week sample as close to that location as possible. Over the course of the growing season you will then be able to see which nutrients increased, decreased, or stayed relatively static.
Leaf expansion is also a factor that should be considered. During rapid growth by the plant, plant leaf area expanding rapidly can change the percentage of a nutrient in a leaf. This should be taken into consideration during those periods of rapid growth as an adjustment to returned values.
Our experience with tissue testing
Over the past couple growing seasons we’ve ventured into the world of tissue testing. We’ve used tissue tests for both in season reactive recommendations and for the next years growing season. We have seen benefits to both approaches, and we’ve seen times when applications did not return results we had planned. It is important to remember that tissue testing success depends heavily on reliability of samples as well as timing of the crop. It is likely that some of the times when we have not seen any benefit from in season application, the crop was already past the point of highest demand, or that nutrient was not elementally prominent. Several times we have seen a positive response, particularly when applying nitrogen or potassium. Additionally, using tissue test results to schedule applications of sulfur or zinc in the fall has been particularly beneficial.
Tissue sampling is not the holy grail of fertility management. This isn’t the silver bullet that fixes all our problems. It is however, a very useful tool for making both reactive and predictive management decisions. Contact us if you have any questions on tissue sampling, or how they can work on your farm.