A Preliminary Evaluation of Cation Exchange Resins as a Soil Test of Potassium Availability in Soils of Northern Greece with Different K Loadings

Contribution of non-exchangeable potassium on soil K availability can be significant, and in such cases, using a soil test that simulates the mechanisms of K release to the soil solution is a research objective. The purpose of the present study was to investigate whether cation resins, which are considered to function as a sink for both solution K and non-exchangeable K released to plants, could reflect accurate relationships with K availability, especially on soils that contain significant amounts of 2:1 clay minerals or for soils under intensive cropping. A greenhouse pot experiment with winter wheat was conducted on soils with different K loadings, and cation resin's performance in predicting soil available K was tested under different application techniques, in comparison with chemical extraction methods of exchangeable or non-exchangeable K. The study showed that resins buried in soil for a 9-day period predicted more accurately total K uptake by plants (r(2) = 0.69, p <= 0.001), while strong relationships were observed between them and resin-extracted K with the short-term routine extraction procedure (r(2) = 0.96, p <= 0.001). In addition, critical levels of soil K content obtained with the resin burial method at a 9-day adsorption period, as well as for the sum of 3 burial periods (27 days), were estimated at 4.6 and 19.8 mg cm(-2), respectively, indicating that a possible response on K additions would be expected. The study suggests that cation resins could be adopted as a useful tool in explaining K availability of soils within a wide range of K loading, while the resin-burial method applied in field could be combined with laboratory short-term resin routine analysis, building a common comparison base of data obtained.