Dynamics of soil potassium under prominent cropping systems of Nellore district, Andhra Pradesh, India

In the present investigation five prominent cropping systems of Nellore district of Andhra Pradesh viz., paddy-paddy, fallowblackgram, fallow-bengalgram, fallow-paddy and groundnut-paddy were selected to study dynamics of soil potassium. The highest mean available K was recorded under groundnut-paddy cropping sequence (249.36 mg kg⁻¹) in surface soils, while in sub-surface soils under fallow blackgram cropping sequence (164.48 mg kg⁻¹). Highest mean water-soluble K was found under paddy-paddy cropping sequence both in surface (33.67 mg kg⁻¹) and sub-surface soils (23.87 mg kg⁻¹). Highest mean exchangeable K was recorded under groundnut-paddy cropping sequence (230.20 mg kg⁻¹) in surface soils, while in sub-surface soils under fallow-blackgram cropping sequence (152.96 mg kg⁻¹). Highest mean non-exchangeable K was found under groundnut-paddy cropping sequence at both surface (642.70 mg kg⁻¹) and sub-surface soils (668.54 mg kg⁻¹). Highest mean lattice K and total K were observed under paddy-paddy cropping sequence at both surface (30044.48 and 30572 mg kg⁻¹, respectively) and sub-surface soils (18671.76 and 19158 mg kg⁻¹, respectively). The forms of potassium were positivelycorrelated among themselves indicating dynamic equilibrium among different forms K in soils under prominent cropping systems of Nellore district.