EFFECTS OF DRYING AND TIME OF INCUBATION ON THE COMPOSITION OF DISPLACED SOIL SOLUTION

Abstract

Soil solution compositional analysis is widely used to evaluate plant growth response and environmental fates of chemicals, but little is known regarding the influence of sample storage techniques on the composition of displaced soil solution. We conducted this research to determine the effects of time of incubation (storage at room temperature) on soil solution composition of Ultisol Ap and B horizons that had been maintained field-moist or had been air-dried and rewet. We analyzed soil solutions displaced immediately after soil sampling or over a 32-day period of incubation for pH, electrical conductivity, dissolved organic carbon, and total concentrations of SO4, Cl, NO3, Ca, Mg, K, Na, Si, and Al. Soil solution composition was frequently influenced by the interaction of sample treatment (field-moist versus air-dried and rewet) and time of incubation. The effects of sample storage were most pronounced in A horizon samples, where higher organic C and microbial activity resulted in greater variation in soil solution composition in comparison to soil solutions from B horizons. It is difficult to identify any one combination of sample treatment and time of incubation which most closely corresponds to the composition of soil solution obtained immediately after sampling. Samples stored field-moist and displaced after 2 or 4 days of incubation, however, seemed to result in the most consistent composition for the bulk of components determined. The variation in soil solution composition anticipated as a result of sample storage should be recognized and carefully dealt with when soil solution composition is used as a diagnostic measure.