Nutrient extraction is related to stem diameter distribution, tissue concentration, and yield in an annually harvested Salix coppice

Abstract

In plantations, nutrient extraction is likely to be higher with shorter rotations. This is because thinner stems have a higher proportion of nutrient-rich bark, and sapwood contains more nutrients than hardwood. Annual willow plantations may extract even more nutrients than long rotation forests. In short rotation forest systems, the diameter of the harvested stems may affect the amount of nutrients exported with the wood. The present study investigated the effect of stem diameter distribution on nutrient extraction and nutrient use efficiency (UE). Two Salix clones were planted at low or high densities, and irrigated or left rainfed. Stems were harvested annually, and three years after planting, N, P, K, and Ca concentrations in small, medium, and big stems were determined, as well as the proportion of each stem diameter class at harvest. N extraction was the highest, followed by Ca, K, and P extraction. Nutrient extraction and nitrogen use efficiency were influenced by the proportion of small, medium, and big stems. The clones showed differences in nutrient concentration and stem diameter distribution, and irrigation increased the proportion of large stems and nitrogen concentration. Although the NUE and PUE were not linearly related to yield, they were related to the distribution of stem diameter and nutrient concentration. Higher yield resulted in higher CaUE and KUE, but the extraction of these nutrients during harvest was fine-tuned by stem diameter distribution and tissue concentration. This highlights the significance of stem diameter distribution in assessing the nutrient costs of wood production for bioenergy.