K acquisition from vermiculite by sweet potato also improves K nutrition in neighboring plants

Intensive agriculture requires substantial external potassium (K) application to meet crop K requirements. Recent research has revealed that sweet potato (Ipomoea batatas), a crop with high K requirements, could acquire sufficient K from a mixture of Andosol and vermiculite without the need for additional fertilization. However, the specific K component in growth medium being utilized is still unclear. We evaluated K acquisition by sweet potato grown in either Andosol or vermiculite, comparing it with soybean, barley and water spinach (Ipomoea aquatica). Additionally, soybeans were grown in vermiculite together with sweet potato to assess the rhizosphere effect of sweet potato. Changes in K component in growth medium after plant growth were examined to identify the specific fraction responsible for these changes. Only sweet potato and water spinach, both from the genus Ipomoea, exhibited normal growth in vermiculite-only medium without K application by promoting the release of K from slowly available (fixed interlayer K) pools, which is unavailable to other crop species. K mapping image analysis confirmed that sweet potato roots accumulated more K than other species, even during 7 days of growth. In the mixed-culture system, the presence of sweet potato enhanced K availability in vermiculite to soybean (Glycine max), enhancing K and biomass accumulation of soybean. Our results reveal that sweet potato and water spinach exhibit efficient K acquisition from vermiculite, especially from slowly available K pool. Besides, sweet potato enhances K availability to neighboring plants through rhizosphere acidification.