Since early August, farmers and consultants have been reporting what they believed were potassium (K) deficiency symptoms in soybean leaves located in the middle or upper canopy. This is not surprising in fields or portions of fields with soil-test values in the very low or low K interpretation categories. Moreover, K deficiency symptoms could develop at these growth stages with drought conditions, even in fields with adequate soil-test K levels. Sometimes symptoms occur in late summer with rainfall events after a dry period. Potassium deficiency symptoms are very common and well known at early growth stages, but due to poorly understood reasons, in the last couple of decades deficiency symptoms in upper leaves at middle to late reproductive stages also have become common.
Iowa State University
Mallarino, Antonio, "Soybean Potassium Deficiency Symptoms During Early and Late Growing Stages" (2018). Integrated Crop Management News. 2506.
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