Studies on Soil Potassium

Summary The immediate Q/I relation of K in a soil relates the amount of labile K present to its chemical potential, measured relative to the chemical potential of (Ca+Mg) in the same soil. The present work shows that the form of the Q/I relation is almost unchanged either by large additions of K, up to 3750 kg K 2 O/ha, and the fixation of up to 1900 kg K 2 O/ha or by the depletion of the soil of both labile and some fixed K, equivalent to 5–20 years cropping. Release is shown to occur from a pool of non‐labile K, at a rate which decreases as the non‐labile pool is exhausted. The resulting increase in cation exchange capacity is greater than the amount of K released. Not all the K which is exchangeable to M NH 4 OAc solution is in exchange equilibrium with the soil solution.