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By Lee Beers, CCA, Assistant Professor, Agricultural and Natural Resources Extension Educator, Ohio State University Extension, Trumbull County
Q: Last year I noticed some discoloration in my corn crop. I suspect a nutrient deficiency was the cause, but how can I tell which nutrient was lacking?
A: Some nutrient deficiencies are rather easy to spot due to their unique symptoms, but others are more difficult to diagnose. Nitrogen deficiency of corn results in a pale green color that can be relatively uniform throughout the field or follow a pattern like when one anhydrous row unit is plugged. Pale green may also indicate a lack of sulfur, but since sulfur is not as mobile in the plant as nitrogen, you may see yellowing in the younger leaves first. Phosphorus deficiency can result in a purpling of the plant tissues, most seen in corn seedlings in cold soils. Yellowing of older leaves at the base of the corn plant followed by a browning at the leaf margins may indicate a lack of potassium. Iowa State University has a great visual guide on nutrient deficiencies you can find here: https://crops.extension.iastate.edu/files/article/nutrientdeficiency.pdf. Unless you have a trained eye, and the plants show textbook symptoms it can be difficult to pinpoint the exact deficiency, if one exists. Your best tool to diagnose suspected nutrient deficiencies will be a tissue test. Tissue testing will tell you exactly what nutrients are in your plant, including micronutrients. Many soil testing labs also offer tissue testing.
Q: I soil sample all my fields, and my phosphorus and potassium levels are adequate. Could I still have a nutrient deficiency?
A: Yes. Nutrient uptake requires moisture and an active root system. Purple corn seedlings are a perfect example of this. The seedlings do not have a fully developed root system to take up phosphorus despite excess nutrients being available in the soil. Once the root system grows, it will be able to uptake the phosphorus. Dry soils also limit the ability of the plant to take up nutrients. Depending on where you are in Ohio, you had too little water or too much during the 2022 growing season. Here in Trumbull County, we were drier than most parts of the state. It was not too difficult to find sulfur deficiency on our sandier soils, but once it rained, the plants were about to take up the mineralized nutrients. In wet years, planting into wet soils may lead to smeared seed furrows, sidewall compaction, and lack of oxygen getting to the root zone. All of these can limit nutrient uptake even with adequate soil test levels.
Q: I am hearing more and more about micronutrients, and how they can boost yield. Should I consider adding micronutrients to my fertilizer program?
A: Micronutrients include boron, zinc, manganese, iron, copper, molybdenum, and chlorine. Plants do not need large quantities of these nutrients, and most Ohio soils have adequate levels for crop growth. There are a few scenarios in Ohio where you should scout for deficiencies. Boron deficiency has been found alfalfa grown in sandy soils with low organic matter. Micronutrient availability in muck soils can vary based on soil pH. Low pH muck soils may lead to copper deficiencies while high pH may lead to a lack of manganese. The addition of zinc to starter fertilizers has become a common practice, but unless you have low soil test zinc and high pH soils (>6.5) it may not be needed. Many soil testing labs include some micronutrients as part of their standard lab analysis, and it can be a valuable tool to monitor your levels if you have the above conditions. Again, most Ohio soils have adequate levels of micronutrients and the addition of these to your fertilizer program should be done only to address specific problems. Micronutrient trials conducted by Ohio State University showed that there is no consistent yield response with micronutrient fertilization.
Q: I don’t want to repeat my mistakes from last year, what strategies can I use to prevent nutrient deficiencies this year?
A: Soil testing is the foundation for successful nutrient management. Make sure you have current soil test results from the last 3 to 4 years. If you can afford it, and have access to variable rate fertilizer application, grid sampling may be a good investment due to high fertilizer prices. Grid sampling will provide detailed information about your fields that you can use to isolate areas that are below, or near the critical nutrient levels. Soil test levels below the critical level may limit yield, but not necessarily show deficiency symptoms. The critical levels for corn, soybean, wheat, and alfalfa are published in the Tri-State Fertilizer Recommendations. This publication was updated in 2020 and can be purchased at most OSU Extension offices or you can download a free PDF copy at https://go.osu.edu/trumbullfert. Applying nutrients based on your soil tests will prevent most nutrient deficiency issues. Also pay attention to your soil. Mudding in corn at planting or heavy compaction can also limit nutrient uptake. If nutrient deficiencies do appear this year, identifying it correctly early may allow for a rescue fertilizer application. This means scouting your fields on a regular basis, and consulting with your local Extension Educator or CCA if you suspect an issue. Don’t forget to pray for rain, just not too much.
