Abstract
This experiment aimed to establish a method for diagnosing potassium deficiency in ‘Delaware’ grape using petiole extract. It is considered that potassium concentration in petiole extract could be used for diagnosis of potassium deficiency in ‘Delaware’ grape, because there was a significant positive correlation between potassium concentration in the petiole extract and potassium content in leaves. When potassium concentration in the petiole extract which was measured by a simple reflection photometer system at the flowering stage was found to be lower than 2,400 ppm, potassium deficiency would definitely occur at a later stage, even if none of the symptoms were observed at that time. However, it is suggested that potassium deficiency could be avoided by the application of potassium after diagnosis.
