Relationships between the Soil Exchangeable Potassium and Growth Responses of some Vegetable Crops to Potassium Fertilizer

Abstract

Pot experiments were carried out to clarify the effect of K fertilizer on the growth of some vegetable crops in the volcanic ash soils with different levels of exchangeable K.
1. On the soil with 94ppm exchangeable K, growth of spinach, lettuce, turnip and cucumber plants not receiving K fertilizer seemed to be inferior to those supplied with K, already from the cotyledon stage. In radish, carrot and snap beans, the increase of growth due to K supply did not become apparent until the mid-stage of growth. Howewer, at the harvest time, K application resulted in a marked increase in yield of all species investigated.
2. On the soil with 255ppm exchangeable K, K application resulted in a noticeable increase in yield of spinach and cucumber. With lettuce and carrot there was a slight increase in yield due to K fertilizer.
3. On the soil with 472ppm exchangeable K, there was no increase in yield due to K supply, with the exception of spinach.
4. These results suggested that the exchangeable K level, below which yield increase due to K application would be expected, might be higher for vegetable crops on volcanic ash soils than that reported by other investigators. It seemed that the critical level of exchangeable K described above might be different by the plant species.