Depth of water table in a Picea sitchensis fertilization experimient on blanket peat.

Abstract

Depth to water table was measured at weekly intervals over a one year period in each plot of a N/P factorial, Sitka spruce (Picea sitchensis (Bong.) Carr.) fertilization experiment on deep peat in western Ireland. The relatively rapid adjustment of water table levels to changing precipitation patterns suggested that no extreme deficits occurred in the peat during the growing season. While tree growth was increased by both N and P fertilizers, depth to water table was significantly increased only in the phosphate-treated plots. These plots showed consistent water table depression, particularly during May and June when weekly rainfall levels were at a minimum. The greatest depression was recorded at the lowest level of added phosphate. This curvilinear response, which may reflect a complex evapotranspiration effect of components of the tree stand, persisted late in the growth season when the linear response had disappeared. It is difficult to evaluate the long term effects of tree growth on this peat. Information is needed on the relationship between peat moisture content and water table depth and on the optimum moisture conditions for tree growth on this site.