Between the V3 to V5 growth stages, corn seedlings transition from energy dependence on the seed to acquiring energy and nutrients through the roots and leaves. This is the time when corn plants can begin to show yellowing due to suboptimal growing conditions. Multiple factors can contribute to yellow corn leaves and/or uneven growth early in the growing season including cool air and soil temperatures, areas with excess moisture, soil compaction, and interactions that reduce nitrogen (N) and sulfur (S) uptake.
Cool spring temperatures can slow plant growth. Cool temperatures, saturated soils, and compaction can limit root growth and penetration into the soil. This can confound slow plant growth by limiting nutrient uptake. The mineralization and plant availability of nutrients, including N and S, is also reduced due to slower microbial activity in cool, wet soils. Heavy rainfall may also cause N and S to leach below the root zone leading to nutrient deficiency symptoms in corn.
Nitrogen (N) deficiency can result in chlorosis (leaf tissue yellowing or bleaching) and necrosis (leaf tissue death) in an inverted V shape running up the midrib (Figure 1). Nitrogen is mobile in the plant so deficiency symptoms will show on the older leaves first. There are several reasons a plant may be deficient in N (for example, restricted root growth) and it may not be that the soil is deficient in N.
Sulfur (S) is not as mobile in the plant as N and deficiency will show on newer leaves as striping and interveinal chlorosis (the veins, midrib, and leaf margin remain green; Figure 2). Because mineralization is dependent on soil microorganisms, soil temperature and moisture affect how much sulfate is available to the crop. As soils warm, increased mineralization usually occurs and plants recover from S deficiency.
Zinc (Zn)-deficient corn plants exhibits interveinal chlorosis on the upper leaves. As the deficiency intensifies, bands (or stripes) develop on either side of the midrib and the leaves may turn almost white (Figure 3). Additionally, a Zn-deficient corn plant may be stunted.
It is likely that the problem of yellow corn seedlings is more related to delayed root growth than to low levels of soil nutrients. If the yellowing is due to cool temperatures, wet soils, or inadequate sunlight, the crop will likely turn green with the return of warmer temperatures and adequate sunlight. If crop color remains poor even after a week of drying soils and good growing conditions, then it is possible that N deficiency due to leaching of N below the root zone is affecting the ability of the corn plants to recover. Nitrogen is most likely still present, but a sidedress N application may be considered to increase N availability to the root zone. Additional N application decisions should be based on original yield goals and quantities applied in the fall and spring, in combination with the potential N lost due to weather conditions since the time of application. Scouting for diseases and insect pests is especially important in weather-stressed corn fields.
For more information on nutrient deficiency symptoms and management in corn click here.