Top 3 Causes of Yellow Wheat
Cristie Preston, Ph.D.
Agriculture has always been an integral part of Dr. Cristie Preston’s life. She grew up in southwest Virginia and had interest in crop and animal agriculture since an early age. Once she began college, she initially chose to study animal science but switched to soil science. Dr. Preston attributes her decision partly to an influential professor who told her, “You can’t understand animals until you understand what they eat.” She received a Bachelor of Science degree in animal science and a Master of Science degree in crop and soil environmental science from Virginia Tech. Dr. Preston holds a Ph.D. in agronomy, focusing on soil fertility from Kansas State University. While completing her advanced degrees, Dr. Preston conducted more than six years of field and lab research. Dr. Preston has experience in laboratory research measuring volatility loss from urea-based fertilizers. Her field research has focused on phosphorus availability and the interactions with tillage and placement. She also has extensive experience in working with large data sets and analysis. Her main priority is helping growers to identify yield-limiting factors and fix those issues as cost efficiently as possible.
It is likely that most farmers have experienced yellowing – chlorosis – in wheat at some point in their years of production. Regardless of whether it is winter wheat or spring wheat, there are several factors that can cause yellowing and may negatively impact yield if not corrected.
Here are eKonomics’ top three causes of yellowing in wheat.
The first most common cause of yellowing is nitrogen deficiency. Early season nitrogen deficiency is common due to low soil temperatures in later winter/early spring that decrease the amount of nitrogen being mineralized from soil organic matter. Other causes include insufficient fall fertilizer rates, delay of application, nitrogen losses as nitrate due to leaching, denitrification losses in saturated soils, and heavy crop residue listed here by Kansas State. Nitrogen deficiency symptoms of wheat are characterized by yellowing of lower leaves since nitrogen is mobile within the plant. Not to be confused with nitrogen deficiency, potassium deficiency can also cause yellowing in the lower leaves. It will take a soil sample to really tell the difference. However, in early spring, nitrogen deficiency has a higher probability of causing your wheat to be yellow. If this nitrogen deficiency is not corrected, wheat yield can be negatively affected.
The second most common cause of yellow wheat is sulfur deficiency. It might be difficult to differentiate between nitrogen and sulfur deficiency at first, but with sulfur deficiency the yellowing occurs in the young/upper leaves as the plant grows. Since sulfur is not easily mobilized within the plant, newer growth will show deficiency symptoms. Sulfur deficiency can occur for similar reasons as nitrogen. Low soil temperatures decreasing mineralization, losses as sulfate due to heavy rainfall, and overall low application rates just to name a few. Sulfur is essential for two amino acids and if sulfur is limited, additional nitrogen applications will not correct the deficiency (Liebig’s Law of the Minimum). Check out this story on using tissue concentrations to determine if sulfur is deficient by looking at the nitrogen to sulfur ratios.
The third top reason for yellow wheat is due to weather. Weather can have a significant effect on wheat depending on growth stage. Dry soil, waterlogging, and shallow planting can all affect root development and cause yellowing. Cold temperatures during the tillering stage before the plant joints can lead to entire fields having a yellow tint. Once the wheat further matures and enters the jointing stage, however, freeze injury can lead yield decreases.
Several honorable mentions for why your wheat is yellow include disease pressure and iron deficiency. These two potential issues will also need to be addressed if identified.
Nitrogen and sulfur deficiencies are by far the easiest issues to fix if a farmer is experiencing yellow wheat. Check out How should a farmer sample for diagnostic purposes to learn how to take soil and tissue samples to identify the cause of your yellowing wheat.