Quantity–Intensity Relationships and Potassium Buffering Capacity of Four Ganges River Floodplain Soils

Abstract

Ganges river floodplain soil extends from Nepal through India to Bangladesh, which is a good niche for rice–rice and rice–wheat cropping systems in Asia. Application of potassium (K) fertilizer does not give any yield benefits to rice and wheat grown on most of the Ganges floodplain soils in Bangladesh. Understanding of soil K dynamics in this soil is important for the development of K management for rice–rice and rice–wheat cropping pattern in the region. Four Ganges floodplain soils, Sara clay loam, Ghior clay loam, Gopalpur silt, and Ishurdi silt loam, were evaluated for labile K (ΔK⁰), K intensity (), change in solution (ΔK), equilibrium exchangeable K (EKo), magnitude of conversion of solution K to exchangeable K (α), and potential buffering capacity of K (PBC^K). The four soils had exchangeable K [ammonium acetate (NH₄OAc extracted)] of 0.17 to 0.43 cmol kg⁻¹, with the least in Ishurdi silt loam and the most in Ghior clay loam. The greatest ΔK⁰ (−0.81 cmol kg⁻¹) was observed in Gopalpur silt, and the least (−0.25 cmol kg⁻¹) was found in Ishurdi silt loam soil. The four soils exhibited equilibrium values of 0.007 to 0.021 (mmol L⁻¹)^1/2, with the least in Ishurdi silt loam and the greatest in Gopalpur silt soil. The greatest EK₀ (0.66 cmol kg⁻¹) was observed in Ghior clay loam, and the least (0.21 cmol kg⁻¹) was in Ishurdi silt loam. Four soils were also different in the magnitude of conversion of solution K to the exchangeable K (α), being the greatest (67%) in Ghior clay loam and the least (25%) in Gopalpur silt soil. The tested soils were similar in PBC^K [36.80–39.39 cmol kg⁻¹/(mmol L⁻¹)^1/2]. The characteristics of ΔK⁰, , ΔK, EKo, α, and PBC^K in the studied soils varied with the depth. Future research is needed to calibrate the characteristics of K dynamics for soil fertility management and to predict how long a nonresponsive soil can meet crop K demand for rice–rice and rice–wheat cropping systems.

Keywords:

• Change in solution (ΔK)
• equilibrium exchangeable K
• labile K
• potassium intensity
• potential buffering capacity of K