Yellow corn and soil nitrogen
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Following the past couple of weeks of variable rainfall, many corn fields are showing light yellow areas. Where rainfall was heavy the soil has been compacted and the surface crusted. Some of the yellow areas are associated with lower areas in fields where nitrogen was lost by leaching and denitrification. In addition, the soil compaction and crusting is contributing to oxygen deficiency that makes it difficult for the roots to function properly in taking up water and nutrients. Opening up the soil by cultivation or by knifing in nitrogen will help aerate the soil and stimulate microbial activity to mineralize nitrogen and other nutrients and improve root growth.
Some of the nitrogen that was leached downward may still be in the soil profile where corn roots will eventually be able to access it. Results of the presidedress soil nitrate tests are presented in Table 1. Some of these samples were taken prior to the rainy spell, so the levels may have changed some. Twelve percent of the samples contain enough nitrogen so that additional N is required (> 25 ppm). In five percent of the samples the available nitrogen level is very low.