Evaluate Your Fertility Program
This is the time of year when a grower is able to evaluate his fertility program by taking plant tissue tests. What can you address if you come across deficiencies? Of the tissue test results I’ve looked at over the years, Nitrogen and Zinc seem to be the most prevalent nutrients showing deficiency. Phosphorus, Potassium, Sulfur, and sometimes Boron may show up as deficient as well.
Testing for N will be important in 2011, due to the wet spring increasing the possibility that N has been lost due to denitrificaton or leaching. Early season N deficiency appears in the plant as overall yellowing. Later in the season the yellowing will show up on the lower, older leaves of the plant, starting at the leaf-tip and proceeding down the midrib. At this point in the season, it is still early enough to address the N problem; Nitrogen uptake in corn does not really take off until V8. You can mitigate by side-dressing anhydrous or liquid 28%. Spreading dry urea is not recommended due to the chance of fertilizer injury, though, the lack of N will reduce yields much more than the burn so only utilize this method as the option of last choice.
Zinc deficiency is another typical problem in our region due to our higher pH soils or the lower organic matter soils outside the valley. Every single sample I took last year showed Zn deficiency, even on fields that had an in-furrow treatment at planting. This year we had growers adjust their rates and put test strips out at planting of 1qt/acre and 2 qt/acre. A Zn deficiency typically shows up from the V2 through the V8 growth stages. The visual symptoms are light-green or yellow areas between the veins of the leaves, normally the lower leaves. A 9% chelated EDTA Zn source should be used and can be tank mixed with glyphosate.
The soil test for Sulfur is one of the most unreliable tests we have in soils. Fact checking your soil levels by tissue testing is a good way to double check your fields. Sulfur deficiency looks very similar to Nitrogen deficiency, but the difference can be seen because S is not plant mobile, so yellowing will be seen at the top of the plant versus the bottom of the plant with Nitrogen.
Boron is another nutrient that has gotten some press lately. While very seldom an issue in corn, it can show up from time to time on a tissue test. Normally it will only show up on low-organic matter, sandy type soils. There is a narrow window between sufficiency and toxicity so you should not apply B unless a problem has been clearly identified. 1lb/acre of soluble boron should be enough to correct a deficiency.
The thing to remember with tissue testing is that you are testing the levels in the plant at a particular moment in time. At this point in the season, plants are taking up great volumes of nutrients and these levels can change quite a bit this time of year. Multiple sample dates are recommended to ensure you didn’t check the plant at the wrong time of uptake, showing an artificially low level
Take the time to look at plant nutrition through tissue testing.
