The Soil Potassium-Supplying Capacities Measured by Resin Methods

The soil sustainability in crop production depends on the size of the indigenous sources of plant nutrients in soils. This research studied the relationships between the soil-potassium supplying capacities and plant-potassium uptake and the nutrient balance of potassium in soils. Soil samples were collected from various sites in Wisconsin, USA, and West Java and Lampung, Indonesia. The soil samples were planted with a sorghum-sudan grass cross called Sudax. A solution containing Ca, Mg, N, and S, but without K or trace elements (1/5 strength of Hoagland solution) was used to provide the initial nutrients during the seeding in silica sand and the additional nutrients during the growth period in soils. Sudax were harvested after a five-week growing period, after which the potassium in plant tissues was determined. The soil-potassium-supplying capacities were measured using Resin Methods before and after cropping. The results showed that plant-potassium uptake was well-correlated with soil-potassium-supplying capacities measured by the Resin Methods. The nutrient balance of potassium was not observed, with the plant potassium uptake being greater than the changes in the potassium-supplying capacities of soils.