Evaluation of a sewage sludge based compost for the production of container tree seedlings

Abstract

The effect of a sewage sludge based compost as a substrate component on the growth and nutrient status of two containerised tree seedlings (Pinus pinea L. and Pinus pinaster Ait.) was evaluated. Compost was mixed with a sphagnum peat at rates of 25, 50, 75 and 100% by volume and no additional fertilisation was applied. A control treatment consisting of 100% sphagnum peat and 3.5 g.L⁻¹ of a controlled release fertiliser was used. Seedling and harvesting were carried out in March and October 1997, respectively. Plant growth increased with increasing doses of compost up to 50%. In fact, an increase of the total dry weight, plant height and diameter of the colar was observed. On the contrary, additions of compost greater than 75% led to a growth reduction. Despite this fact, plant growth in all compost treatments was always lower than in control treatment with fertilisation. The growth reduction that occurred in the 75% and, mainly, in the 100% compost treatments is likely a consequence of water stress since the available water (v.v⁻¹) of these substrates (13% and 5%, respectively) was quite low. The 50% compost treatment seems to supply all P, Ca, Mg, Cu, Zn and Mn needed for satisfactory plant growth. In addition, compost shows a liming effect, that is important when the basic substrate is acid.