Foliar analysis for detecting and correcting nutrient imbalances in Norway spruce

Abstract

Results are presented from the first seven years of a nutrient optimisation experiment in young stands of Norway spruce in northern Sweden. The principal aim of the experiment was to eliminate water and mineral nutrients as growth-limiting factors, at the same time as leaching to the groundwater was avoided. The approach applied was the definition of target values for the foliage concentration of each nutrient element. On the basis of repeated foliar analysis and predicted growth response the proportions and amounts of nutrients applied were adjusted annually. Imbalances in the nutrient status of the trees, induced by fertilisation as determined by foliage analysis, were successfully corrected by adjustment of the amount and composition of the fertiliser mix. Accumulation, followed by depletion, of starch in needles during summer had a pronounced effect on nutrient concentrations, thus making evaluation of nutritional status difficult. A variation in needle dry weight of up to 30% occurred during the growing season. The depletion of starch coincided with the onset of growth and was both earlier and faster in fertilised trees than in control trees. This indicates that the growth rate in non-treated stands was not limited by carbon, but rather by nutrient availability. It is recommended that for diagnostic purposes, several age-classes of foliage are sampled on a number of occasions during the season(s). If sampling is restricted to one age-class of foliage, it is recommended that one-year-old foliage is used, to reduce between-year variation and to enable sampling throughout the season. If nutrient concentrations are assessed on samples taken during the period late spring to early autumn, the carbohydrate content must be determined to allow values to be normalised. Nutrient imbalances can, however, be detected without correcting for carbohydrate reserves, by calculating the ratio between elements. Experience obtained during the first seven seasons has indicated that the nutrient quotients relative to nitrogen, based on detailed studies of plant nutrition, have been more generally valid than the concentrations regarded as optimal for Norway spruce.