Deficient or unbalanced nutrient status can limit tree growth in peatland forests. Assessment of nutrient status and need of fertilization for forest vitality has traditionally been made by analysing needle samples collected during winter. A new method has been developed at the Finnish Forest Research Institute (Metla), in which foliar colour measurement can be used to assess the nutrient status of Scots pine.
An ocular estimation of nutrient deficiency based on needle colour is quicker and cheaper to perform in the field than chemical analysis. However, ocular inspection of colours is subjective, because colour vision is a personal characteristic and colour resolution will depend on the prevailing lighting conditions. Although foliar colours are considered to be significant indicators of nutrient deficiency, the connection between colour and nutrient concentrations has not been sufficiently studied. In this Metla research, needle colour was measured using a chromameter and nutrient concentrations were analyzed. The results were used to assess whether the method of measuring needle colour is suitable for estimating nutritional status of Scots pine.
The results showed that needle colour is a fairly good indicator of simultaneous deficiency of phosphorus and potassium. The colour of needle tips was a better indicator of the deficiency than that of the needle butt. The hue of the needles, especially their tips, was yellower when the needles suffered from potassium deficiency. However, on the basis of needle colour, deficiencies of nitrogen and boron were not successfully detected in the study. In addition to nutrient deficiencies, other factors, such as drought, can also cause change to foliar colours in needles.
Needle samples for a nutritional analysis must be collected during the winter season. Further studies will be performed to determine whether nutritional status can be reliably inspected already during autumn, when forest planning is done.
The needle samples studied were collected from peatland forests in the area of the Forest Management Association of Kalajoki.
Publication: Hytönen, J. & Wall, A. 2006. Foliar colour as indicator of nutrient status of Scots pine (Pinus sylvestris L.) on peatlands. Forest Ecology and Management 237 (1-3): 156-163.