The effect of water and nutrient availability on the productivity of Norway spruce in northern and southern Sweden

Abstract

Results from two yield optimisation experiments in young stands of Norway spruce in northern and south-eastern Sweden are presented after 10 and 9 years' treatment, respectively. The aim of the experiments was to demonstrate the potential yield of Norway spruce, under given climatic conditions and non-limiting soil water, by optimising the nutritional status of the stands, at the same time as leaching of nutrients to the groundwater was avoided. A complete mix of nutrients was supplied either once a year or daily during the growing season, in combination with irrigation. On the basis of repeated foliar analysis and predicted growth response the proportions and amounts of nutrients applied were adjusted annually. After 10 years' treatment at the northern site, fertilisation had increased the annual stem volume production from 3 m3 ha-1 a-1 in unfertilised stands to 14 m3 ha-1 a-1. Although site quality initially was high at the southern site, nutrient optimisation increased annual stem volume yield from 12 in control stands to 29 m3 ha-1 a-1 in irrigated-fertilised stands. Water had a positive effect on stem growth in southern experiment, but no effect in the north. In all stands in which the availability of nutrients and soil water was optimised by combined fertilisation and irrigation, the yield of stemwood was similar to or surpassed the best yields obtained by conventional silvicultural means.