Application of compost in spruce forests: effects on soil respiration, basal respiration and microbial biomass

Compost from separated organic household waste contains considerable amount of nutrients such as N, P, K, Mg and Ca and may be used for amelioration of degraded forest soils. Our objective was to assess the effect of compost application on soil respiration, soil basal respiration and soil microbial biomass of two mature Norway spruce plantations in Lower Saxony, Germany. The plantations are growing in a silty soil at Solling (SL) and in a sandy soil at Unterluss (UL). We applied 6.3 kg m(-2) of mature compost from separated organic household waste to the soil surface in late summer 1997. We measured soil respiration from control and compost treated soils monthly from September 1997 to April 1998 and biweekly from May 1998 to December 1999. Application of compost significantly (p < 0.05) increased soil respiration rates from 5.1 to 6.3 Mg C ha(-1) yr(-1) (SL) and from 4,2 to 7.0 Mg C ha(-1) yr(-1) (UL) in 1998, The effect of compost on soil respiration rates was weaker at both sites in 1999. Soil respiration rates increased from 5.0 to 6.0 Mg C ha(-1) yr(-1) (p = 0.06) in SL and from 4.0 to 5.8 Mg C ha(-1) yr(-1) (p < 0.05) in UL. Twenty-one months after the application of compost, the basal respiration at 22 degreesC and microbial biomass C were measured from the sieved O-horizons >2 and <2 mm and from the mineral soils from 0 to 5, 5 to 10 and 10 to 20 cm depth. Basal respiration rates of the compost plots decreased in the O-horizon by 1-44% and increased with one exception in the mineral soils by 2-29%. However, the effect of compost application was significantly (p < 0.05) different only in the O-horizons <2 mm of SL. Microbial biomass C significantly (p < 0.05) increased in the mineral soils by 22% (SL, 0-5 cm depth) and 50% (UL, 0-5 and 10-20 cm depth). Basal respiration rates and microbial biomass C showed the same pattern and were positively correlated in the control plots (r(2) = 0.96) and the compost plots (r(2) = 0.96). This study suggests that surface application of compost may promote microbial activity in the mineral soil of spruce plantations. (C) 2002 Elsevier Science B.V. All rights reserved.