The effects of lime on the liberation of potassium in a number of Iowa soils were studied in a series of experiments and the results obtained are summarized as follows:

1. Analyses of 12 high-lime soils showed that all of the soils contained relatively large amounts of total potassium, carbonates and total nitrogen.

2. The available potassium content of 11 of the 12 high-lime soils was insufficient for maximum plant growth according to the Aspergillus niger test. This low content of available potassium was correlated with the high carbonate content.

3. The exchange complex of an acid Tama silt loam was completely saturated by applications of 6 tons of calcium carbonate per acre in greenhouse experiments and 6 months after treatment the amounts of exchangeable and available potassium were decreased.

4. Calcium carbonate, calcium chloride and calcium hydroxide replaced potassium and increased the available potassium in the soil exchange complex in acid Tama silt loam and to a smaller extent in basic Webster silty clay loam, calcium chloride being the most effective. Calcium sulfate had little or no effect on the exchangeable and available potassium.

5. The availability of potassium in high-lime soils was lower in inoculated than in uninoculated soils and the decrease in availability was greater in soils treated with calcium carbonate than in the untreated soils.

6. It is suggested that a decreased hydrolysis of primary potassium-bearing minerals and the formation of insoluble potassium complexes and possibly also a reduction in available potassium by microorganic activity may be responsible, in part at least, for the decreased availability of potassium in these soils.