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

Abstract

Abstract 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.