Weak exchange resins add nutrients with minimal direct impact on other soil elements - A new method for small scale fertilization studies

Traditional soil nutrient addition experiments have yielded great insights into the controls on ecosystem processes. However, experimental nutrient manipulations are often confounded by the addition of multiple nutrients in a single treatment. Here we report a new method using weak exchange resin beads to add single nutrients to soil. This is particularly useful for phosphorus (P) addition, because other P fertilizers contain base cations that can themselves effect soil processes. To test this method, we loaded weak exchange resin beads with either nitrogen (N) or P. Mesh bags of beads placed on the soil surface increased extractable pools of soil N and P over a 60-70 day period, with little influence on other elements or pH. The increases were similar across four tropical soils ranging from Inceptisols to Oxisols. Resin beads mixed into soil increased readily available pools of P, but not N, after the same time period. These data suggest that weak exchange resins offer a method for single element manipulations. This will be useful in assessments of how microbes, roots and soil fauna respond to changes in nutrient availability.