Open access publications in the SLU publication database

In a 60-year-old mixed coniferous stand dominated by Norway spruce on a sandy-silty till, the effects on soil chemistry, field vegetation and stem growth of applying two different ash products were studied during 1995-2002. Eight field plots (30x30 m) were established in early summer 1995, 56 km VNV Sundsvall in Central Sweden on forest land belonging to SCA Skog. One year later, in June 1996, 3 tonnes of pelleted bark ash (A) from a pulp mill factory (Ortviken near Sundsvall) were applied per hectare on four of these plots. During the production of these ash pellets, 8-10 % of tall oil was added.The other four plots were control plots (K). In July 1996, six more plots were established, in connection to the other eight plots. Two of these new plots were control plots (C), the other four plots were treated with granules (AS) of bark ask (from the pulp mill at Östrand, north of Sundsvall) and sewage sludge from the sewage-treatment plant Fillan in Sundsvall. Two different doses of these granules were used; two plots received 300 kg per plot or 3.3 tonnes ha-1 (AS3) and two plots received 900 kg per plot or 10 tonnes ha-1 (AS9).

The field vegetation in treatment A and K was inventoried one year before treatment, and one and five years after treatment. In the other treatments (C, AS3 and AS9) the field vegetation was inventoried only one and five years after treatment. Growth measurements (diameter at breast height and height of the trees) were made in connection to the treatments in June-July 1996 and six years later in May 2002. Soil samplings (humus layer, 0-5 cm below humus layer) were performed six years after the treatments. The soil samples were analyzed on pH, electrical conductivity, organic matter, organic carbon and total nitrogen.

Six years after the treatments, considerable more ash pellets than ash granules were found on or in the humus layer. Apparently the ash granules disintegrated faster than the ash pellets. The effects on soil chemistry, six years after treatment, were also more apparent on plots treated with ash granules than on plots treated with ash pellets. The effects of ash pellets on soil chemistry, field vegetation and stem growth were insignificant, except a tendency of a higher pH in the humus layer.

Significantly higher pH values in the humus layer and the upper 5 cm of the mineral soil were observed six years after the AS treatment. An apparent dose effect on the pH values was also observed with this treatment. A clear tendency of raised electrical conductivities in the humus layer and the upper 5 cm of the mineral soil were also noticed. There were also tendencies that the AS9 treatment affected soil bulk density and organic carbon content. However, the occurrence of different vascular plants or the stem growth were not affected by the AS treatments.