Nutrients and energy in proleptic branches and leaves of poplar under a short-rotation coppice

Abstract

Renewable energy is often generated from biomass, produced in short-rotation coppice (SRC) cultures. These cultures are frequently established on former agricultural land with ample availability of plant nutrients as nitrogen, phosphorous, potassium, calcium and magnesium. Nevertheless, little is known about the annual recycling of these nutrients through the leaves, as well as about the amounts that are removed at harvest. We therefore quantified soil nutrient concentrations, as well as nutrient concentrations and the gross calorific value of the proleptic branches and of the leaves of 12 poplar (Populus) genotypes in the second rotation of an operational SRC (with two-year rotations). For the produced leaf biomass, we also quantified the standing energy stock and the nutrient stock of each genotype. After four years the P, K, Ca and Mg soil concentrations had not significantly changed, while the N concentration at 30–60 cm of soil depth had significantly increased. On average, the standing aboveground woody biomass of the 12 genotypes in 2013 was 13.75 Mg ha−1 and the total leaf biomass was 3.54 Mg ha−1. This resulted in an average standing energy stock in the leaves of 64.8 GJ ha−1. Nutrient concentrations were lower in the proleptic branches as compared to the leaves, but the proleptic branches and leaf nutrient concentrations significantly varied among the genotypes.