Plant nutrient deficiency symptoms: where, when, and what to look for

Crop nutrient deficiencies are a major cause of yields not reaching the genetic potential of the seed you planted. Discerning crop-nutrient deficiencies in a timely manner may allow for corrective actions or at the least inform you of spatially defined nutrient problems in your field that may be addressed prior to the next crop cycle.

Knowing where, when, and how these nutrient deficiencies may be caused will help refine your search for symptomology. Visual observation of symptoms is just one tool that can be used along with soil and tissue testing to help you focus on problem areas.

There are soil and environmental factors that might define situations where a close look at plant symptomology is warranted. Let's have a look at some common situations that might be correlated with potential nutrient deficiencies. Soil pH, Soil-water status, plant stage, and weather can all be important in defining potential problems.

Soil pH controls plant availability of several essential nutrients especially the micronutrients Fe, Mn, B, Cu, and Zn all of which are more available at lower soil pH values

Nutrient mobility within the plant also helps interpretation of deficiency symptoms. If a nutrient is mobile within a plant (N, P, K, Mg) the deficiency symptoms will appear in lower leaves as the nutrients mobilize to the growing points and newer tissue. Somewhat mobile nutrients (S, Fe, Mn, Cu, Zn) typically show over a wider area of growth and immobile nutrients (Ca, B) express deficiencies at the growing point.

The most commonly seen nutrient deficiencies are nitrogen, phosphorus, potassium, sulfur, and magnesium. On occasion zinc, boron and copper deficiencies occur. Iron deficiencies are regionally very important in the high-pH soils of the Western Corn Belt, particularly for soybeans See Understanding and Managing IDC in Soybean, Bill Backhaus . Calcium (secondary) and the remaining micronutrients not mentioned are rarely in short supply but may occur in very specific soil situations such as organic soils, or extremely high or low pH soils. Micronutrient deficiencies may often be corrected with foliar applications of specially formulations that improve plant uptake.

Nitrogen deficiencies can result from too little nitrogen fertilizer, slowed, or impaired mineralization and often denitrification in wet spots. N deficiencies express on the lower leaves and are characterized by a yellow color that starts at the leaf tip and moves down the midvein towards the stem. Once these symptoms show some damage has been done but timely additions of N can be economically effective.

Sulfur is plant available as sulfate, which is negatively charged. In humid regions sulfur may leach to subsoils and not be available for young shallow root systems. Sulfur deficiencies have been increasing as fossil fuel power plants are taken off line or have emissions scrubbed. In cool soils where significant fertilizer nitrogen has been added there may not be enough mineralization to release sufficient sulfur thus warranting the use of preplant S applications.

Phosphorous is most available at pH 6.0 to 7.0. Soil pH levels higher or lower can result in phosphorus deficiencies. Poorly developed or injured root systems in young crops, especially in cold conditions may lead to phosphorous deficiencies. Purple colors on older leaves is symptomatic but some corn hybrids exhibit these color even when P nutrition is adequate. Plants often grow out of these symptoms when temperatures warm.

Potassium deficiencies are unusual in young plants but may express after a month or two starting as necrosis or death along the leaf margins of older leaves. Since K is mobile in plants the upper leaves may look fine. Potassium deficiencies may show up in plants growing in weathered soils that have clay minerals that trap and potassium especially in dry conditions.

Knowing where, when, and how to look for nutrient deficiency symptomology will help you address crop needs this season and next.

Coming next week: Spring nutrient considerations and fertilizer placement