Effect of Long-Term Manurial Application on Soil Potassium and Suitability of Different Chemical Methods for Determining Available Potassium

Continuous application of manurial treatments (P, PK and FYM) along with a basal dose of N for seven years to acidic brown hill soil of Fagu (Simla), put to a monoculture of potatoes showed that in soil HCl-K and 1 N HNO₃-K were not significantly affected by different manurial treatments. However, available K in soil increased significantly in the treatments receiving K and such increase was higher under FYM than under the K fertilizer treatment alone. Application of P alone tended to depress the available soil K. Q/I studies showed that continuous application of K fertilizer resulted in higher equilibrium activity ratio than FYM whereas labile K remained unaffected.

Warm 0.7 N H₂SO₄ and cold 3 N H₂SO₄ extractable K, which were comparable to NH₄OAc-K, were significantly correlated with yield and K uptake by tubers in pot and field experiments. However, the warm 0.7 N H₂SO₄ and cold 3 N H₂SO₄ methods have an edge over NH₄OAc method in terms of simplicity and cost.