Effects of wood ash fertilization on forest soil chemical properties.

The effects of wood ash fertilization on soil chemical properties were stud ied in three young Scots pine (Pinus sylvestris L.) plantations and a Norwa y spruce (Picea abies (L.) Karst.) plantation with different site fertility in southern Finland. The dose of 3 t ha(-1) of loose wood ash was applied to 4 replicate plots (25 x 25 m) at each experiment. Humus layer and minera l soil samples were taken before the treatment and 7 and 16 years after woo d ash application. Results showed that neutralization as well as fertilizat ion effects of wood ash on forest soil were of long duration. An ash-induce d pH increase of 0.6-1.0 pH units and exchangeable acidity (EA) decrease of 58-83% were detected in the humus layer 16 years after wood ash applicatio n. The decrease in acidity was most pronounced on the Calluna site with ini tially the lowest pH and highest EA. In the mineral soil the increase in pH was observed later than in the humus layer. After 16 years, the mineral so il pH was increased (0.2-0.3 pH units) on the Vaccinium and Myrtillus sites . A corresponding and in most cases a significant increase in the extractab le Ca and Mg concentrations was detected in both the humus layer and in the mineral soil. Wood ash significantly increased the effective cation exchan ge capacity (CEC,) and base saturation (BS) but decreased the concentration of exchangeable Al in both soil layers on all the sites. No response of N availability to wood ash application could be found.