Response of a Scots pine (Pinus sylvestris) stand to application of phosphorus, potassium, magnesium and lime: 2. Soil solution composition.

In 1985-88, a 25-yr-old Scots pine forest in Netherlands was limed (5 levels) and fertilized with P, K and Mg in a factorial design. This paper discusses the influence of P, K and Mg addition (as one treatment) and liming, on solute concentrations at depths of 30 cm, i.e. in the root zone (monitored September 1989 - April 1992) and 100-150 cm, i.e. below the root zone (April 1991). Liming increased NO3 concentrations at both depths. At 30 cm this effect of liming gradually vanished during the study period, concurrently with declining soil solution pH, while an increasing effect of PKMg on NO3 developed. Probably it took several years for nitrifying microflora to adapt to improved nutrient availability, while the effect of liming was instantaneous. These data show that besides liming, fertilization may increase NO3 leaching. NH4 was not affected by any treatment. Applied K and Mg compounds were easily soluble, and their soil solution concentrations were increased at both depths in PKMg-amended plots. Probably slow-release fertilizers would allow for a more efficient incorporation of K and Mg into the system's biomass. Reducing effects of liming on soluble Al were weak (30 cm) or absent (100-150 cm). Al at 30 cm did not reach concentrations known to be harmful to Scots pine, but Ca:Al ratios were critical in unlimed plots. No evidence was found for enhanced cation leaching caused by increased formation of nitric acid in limed plots.