Eucalypt litter decomposition and nutrient release under a short rotation forest regime and effluent irrigation treatments in New Zealand: I. External effects

Nutrient cycling in a short rotation forest system can be manipulated to give sustainable biomass production and land use. External factors, such as irrigation of meatworks effluent and age of plantation, could play some special role when managing litter in plantation forests to provide biomass sustainably for use as a fuel. These factors were examined for their effects on eucalypt leaf litter decomposition and nutrient release under 1, 2 and 3-year-old short rotation forest plantations grown in New Zealand. Both factors had significant effects on the rate of decomposition and nutrient release. Effluent irrigation significantly increased litter decomposition (from 46 to 62%) and nutrient release under 1-year-old stands, made no significant difference under 2-year-old stands (decomposition: 68 and 66%) and retarded the process under 3-year-old stands (decomposition: from 75 to 42%). In stands without irrigation, the decomposition and nutrient release occurred least under 1-year-old stands compared with 2- and 3-year-old stands. Conversely, in stands irrigated with effluent, the decomposition and nutrient release occurred least under 3-year-old stands. Phosphorus, magnesium, and nitrogen accumulated more than their initial amount in the litter, particularly under 3-year-old stands irrigated with effluent. The effects of these external factors should be considered when managing litter in plantation forests to give sustainable biomass production.