Battle for the Belt: Season 3, Episode 20: Corn and Zinc Deficiency in Grain

Season 3, Episode 20 of Battle for the Belt is now available: https://www.youtube.com/watch?v=Z83cKAHQD5M

In Episode 20, we hear from Dr. Jim Ippolito, Rattan Lal Endowed Professor of Soil Health & Soil Fertility at Ohio State University. Dr. Ippolito discusses one of the more overlooked, but important aspects of corn production: zinc deficiency in grain.

Soils throughout the United States, including Ohio, often meet the accepted threshold of zinc concentration (1.5 parts per million). Despite adequate soil zinc levels, the grain harvested often fails to meet the necessary nutritional standards set by the FDA. Concentrations of zinc present in corn grain harvested in Ohio are typically about half what is considered adequate for human and animal consumption and health. This is why many cereals you purchase from the grocery store are “fortified with zinc”. The naturally occurring levels present in the grain are simply not high enough.

Dr. Ippolito explains that the current fertilizer recommendations may not reflect the realities of plant uptake and nutrient availability. His ongoing research aims to test whether increasing zinc fertilizer rates can boost zinc concentrations in corn grain. The current project is a foundational step before expanding the work to a broader field-scale trial.

The discussion also covers visible nutrient deficiency symptoms to look for in corn. For example, potassium deficiency appears as chlorosis or necrosis at the leaf margins on older, lower leaves (Figure 1). Potassium does not notably interact with zinc. Nitrogen deficiency typically presents as a V-shaped yellowing starting at the leaf tip and following the midrib inward (Figure 2). While nitrogen deficiency is well understood on its own, its interaction with zinc can be unpredictable. Sometimes synergistic, sometimes not, the effects can vary by region, soil type, landscape position, and even continent.

This episode offers important takeaways on the role of micronutrients in crop production, how they may affect resulting food quality, and highlights the potential need for a more refined focus on fertility management, particularly as it refers to zinc.

Field and Crop Update

Across the three locations, planting dates one through five, have progressed to the reproductive stages. The first two planting dates at each location are at the R5 growth stage, or “beginning seed”. At this stage, developing seeds must be at least 1/8 inch long at one of the four uppermost nodes on the main stem.

The plant is now focused on seed development, requiring lots of water and nutrients from the rest of the plant. The nutrients are redistributed to the seed, with half of the nitrogen (N), phosphorus (P), and potassium (K) coming from the vegetative parts, and the other half coming from N fixation and nutrient uptake from the roots.

By R5.5, the plant typically reaches its maximum height, node number, and overall leaf area. Nitrogen fixation has reached its maximum and begins to slow, while the seed will continue to accumulate dry weight. These plants will soon progress to R6 “full seed”.

Corn is similar in development to soybean, with all but the fifth and final planting date reaching the reproductive stages. Further details on growth stages and weather information for the past week can be identified in Table 1 below.

Table 1. Precipitation, soil temperature, average air temperature, and cumulative GDDs at the Western Agricultural Research Station, the Northwest Agricultural Research Station, and Wooster Campus. Weather data retrieved from: https://weather.cfaes.osu.edu/.