Availability and mobility of nutrients in acid forest soil treated with fast and slow-release nutrients

The effects of slow and fast-release fertilizers (P, K, Mg) on the movement and availability of nutrients in acid forest soil were studied. Fast-release superphosphate, potassium chloride and magnesium sulphate and slow-release apatite (P) and biotite (K, Mg) were applied alone or together with urea or urea+limestone. The nutrient content in the organic horizon was determined one growing season and three growing seasons after the application, and in the mineral layer after one growing season. The movement of nutrient ions in the organic horizon was studied by an ion exchange resin bag method during a 5-month period following application. The fast-release salts immediately increased the soluble P and exchangeable K and Mg contents in the organic and mineral soils and in the resin bags. After three growing seasons the effect of K application in the organic layer was non-detectable and that of P had clearly diminished. Apatite gradually increased soluble P content in the organic layer, but biotite had only a minor effect on the K and Mg contents. The nutrients from the fast-release fertilizers had clearly become available and mobile in the year of application and were thus susceptible to leaching. The rate of nutrient release from apatite and biotite is slower and the added nutrients are retained in the organic horizon. Slow-release compounds, like apatite and biotite, might be potential fertilizers for counteracting acidic deposition and subsequent nutrient losses.