Long-term effects on soil-water chemistry of wood-ash and nitrogen application in a conifer forest

Wood-ash application to forest land has been proposed as a means to compensate for increased nutrient removal at high harvest intensity. A study-plot experiment was established on a mineral soil site in Sweden to study how this measure affects soil-water chemistry. In 1995, ten treatments were applied. Here we present results from years nine to seventeen after application for eight of the treatments: control, 3×10³, 6×10³ and 9×10³ kg ha^-1 of self-hardened and crushed wood ash (WA), 150 kg N ha^-1 supplied as ammonium nitrate, 3×10³ kg WA and 150 kg N ha-1 applied simultaneously, 3×10³ kg WA with 150 kg N ha^-1 applied one month before the ash, and 3×10³ kg ha^-1 of pelleted ash. Soil-water samples were collected from a depth of 50 cm. Treatment effects (<i>p</i><0.05) were detected in the electrical conductivity, pH and concentrations of K⁺, Mg²⁺, Ca²⁺, Al, SO₄^2--S and B. Elevation of K⁺ and SO₄^2--S concentrations tended to cease towards the end of the study period. Effects were generally more pronounced with increasing ash dosage. No difference between the treatment 150 kg N ha^-1 and control was detected. Despite the high solubility of the ash, effects on the soil-water chemistry could still be detected nine to seventeen years after application.

Effects of whole-tree harvest on soil-water chemistry at five conifer sites in Sweden

Logging residues, such as tops and branches, can provide a useful biofuel for large-scale energy production. However, increasing the harvest intensity may affect the soil nutrient stores and water quality. Here, effects on soil-water chemistry after stem-only and whole-tree harvesting were investigated using data from five experimental sites in Sweden, representing medium- to high-fertility sites. They were located in recharge areas on mineral soil and harvested between the years 1995 and 2001. Soil-water samples had previously been collected from below the main part of the root zone in study plots subjected to stem-only or whole-tree harvest. Soil-water chemistry data from the five sites were jointly analyzed by ANOVA using seasonal mean concentrations from the first six seasons after clear-cutting. The concentrations of NO3–-N, K+, and Mg2+were significantly different (p < 0.05) between the two harvest regimes, indicating lower levels after whole-tree harvest than after stem-only harvest. No significant differences were detected for electrical conductivity, pH, or the concentrations of NH4+-N, Al, Ca2+, SO42–-S, and Cl–. Measurements at one site suggested that the logging residues left on the ground increased the influx of Cl–to the soil. Simple budget calculations indicated that the nutrient export by logging-residue harvest was greater than the export by leaching during the regeneration phase.