Soil characteristics of raised sphagnum bog in relation to intensively grown deciduous species

Abstract

Peat bulk density, water content, and pH were studied on a raised bog in central Sweden with particular attention to the demand of the crops. Volume defined samples of the 0–30 cm soil layers were taken during 1981 and 1982 in order to find out seasonal patterns and between‐treatment variations of the soil characteristics. Four plots with different liming, fertilization, and irrigation regimes were included in the investigation. Two willow plots (Salix viminalis and S. dasyclados) and one plot with Alnus incana were all irrigated‐fertilized by drip tubes during the growing season while an unplanted reference plot was not. Large variations in the studied soil properties occurred within all the plots at any time, to a great extent depending on variations in the mixture of Eriophorum and Sphagnum in the peat. Peat bulk density tended to be higher in the irrigated‐fertilized plots than in the reference plot and averaged about 70 and 63 g . dm⁻³, respectively. Water content increased rapidly with depth in the irrigated plots and the pores were filled with water to about 90% at 6 cm depth. Seasonal fluctuations were small. The reference plot contained less water than the irrigated ones and the water content increased almost linearly with increased depth in this plot. The seasonal fluctuations were large, with the lowest water content in late summer. A somewhat higher degree of humification and a higher water‐holding capacity was found in the soil of irrigated‐fertilized plots than in the reference. Microbiological activity, decomposition rate of litter, and recycling of nutrients should be high and favourable under these circumstances resulting in increased soil fertility. The soil also contained enough air in the pores to allow good root growth. Liming increased pH in the 0–30 cm soil layer and irrigated‐fertilized plots showed a faster increase of pH than the reference plot. However, the pH profiles obtained were concluded to be non‐optimal for the root growth of willow but satisfactory for grey alder. The use of KCI solution instead of distilled water in pH measurements resulted in lower pH values but also in smaller seasonal fluctuations. The difference was smaller near the soil surface than further down in the peat, indicating a higher base saturation in upper soil layers than in lower.