Effect of sample pretreatment on extractable soil potassium

Abstract

Abstract Effect of soil sample treatment on potassium (K) release characteristics of Northern Great Plains soils was studied. Samples of agricultural soils were extracted with neutral normal ammonium acetate for K after selected pretreatment. Field‐moist sub‐soil samples with approximately 100 mg/kg extractable K release nearly double this amount after they were air on oven‐dried prior to analysis. The percentage increase in extractable K in dried soils decreased as the K level in the field‐moist soils increased. At 420 and 500 mg/kg, the extractable K content of air‐dried and oven‐dried soils, respectively, equaled the extractable K content of field‐moist samples. Above these concentrations, drying decreased extractable K. Oven‐drying (60 C) affected extractable K more severely than did air‐drying the soils. Drying and grinding the 15‐ to 30‐cm depth samples significantly increased exchangeable K compared to field‐moist samples. Rehydration of oven‐dried soils to 40% water did not affect extractable K. However, results indicated that rehydration of dried soils to 40% water, followed by freezing (‐29 C air temperature) for 15 hours, and redrying the samples to a range of 0.5 to 5% water, returned extractable K to the level which existed in the original field‐moist samples.