Evaluation of a microplate spectrophotometer for soil organic carbon determination in south central Idaho

Determination of soil organic carbon (SOC) is highly desirable for assessing fertility and carbon sequestration; however, numerous methods of determination warrant study of method agreement. Recently, a novel method was developed following dichromate oxidation using a microplate spectrophotometer. This novel method was compared with (i) total C by dry combustion - soil inorganic carbon (DCw/o pretreatment - Pcal); (ii) traditional Walkley-Black titration (WBTIT) and (iii) loss on ignition (LOI360°C) in calcareous soils of south central Idaho (n=75) in conjunction with North American Proficiency Testing program soils (n=10). A two-way ANOVA was fit with soils as a blocking factor to identify any difference between methods, means were separated using Tukey’s HSD (α=0.05). Additional comparisons were made for all soils (n=85) and for soils in the lower 75th percentile of SOC determined by WBTIT (n=56) using regression analysis. Only the WBTIT and LOI360°C methods were statistically equival...