Soybeans throughout the county are beginning to look better. Development has been slowed and many fields have areas (sometimes large areas) with a light green or yellowish tint to the beans. What is causing this yellowing? One possibility is:
Too much water/waterlogged roots
In some fields, the pale green to yellow leaves are the result of very wet soil conditions. Soybeans are a legume (like alfalfa) and do not like wet feet (roots)! This problem is commonly seen in low areas of the field or on poorly drained soils where water tends to stay for a prolonged period of time. When digging up plants in wet areas of the field you will find poorly developed or weaker root systems when compared to a healthy plant.
Soil water content is critical not only to supply the water needs of the plant, but to also dissolve nutrients and make them available to the plant. A poorly developed root system can limit nutrient uptake causing what is likely a temporary nutrient deficiency.
Temporary nutrient deficiencies can be observed when excess water in the soil depletes oxygen and builds up carbon dioxide levels. Although oxygen is needed by roots to grow and take up nutrients, high carbon dioxide levels are toxic and limit root growth and activity.
With better weather conditions plants will usually (sometimes slowly) grow through this phase.
Soybean nutrient deficiencies will be discussed in a different post.