Evaluation of hot KCl extraction as an index of mineralizable N: Ammonium and ultraviolet absorption measurements

Abstract

Hot KCl extraction was examined as a possible nitrogen (N) soil test. The focus of this study was the influence of the method for determining N in the extracted solution. The study was conducted on a diverse set of Fraser Valley soils of British Columbia, using aerobic incubation as a reference for potential N mineralization rate. The pattern of nitrate and ammonium accumulation over time differed, possibly reflecting differences in organic matter composition, and affecting the interpretation of the results . Results from anaerobic incubation, a simple, alternative method, differed sufficiently from aerobic incubation to warrant caution in using it to estimate mineralization. The MgO steam distillation method was subject to interference in hot KCl extracts; a flow injection system involving room temperature volatilization and diffusion was proposed as a better alternative. Some soils had significant ammonium present before hot KCl extraction, requiring correction. These adjustments, though increasing laboratory requirements, improved the correlation of hot KCl ammonium with aerobically mineralized N. Simple measurements (steam distillation with strong NaOH and ultraviolet absorbance) of organic N extracted by hot KCl were good alternatives for estimating potential N mineralization. Further examination of extraction conditions and measurement variables are required to optimize these methods. Key words: Mineralized soil N, incubation N, soil N test, MgO-steam-distillable N, sodium-hydroxide-distillable N, flow injection analysis, ultraviolet absorbance