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

Nutrient cycling in a short rotation forest system can be manipulated to give sustainable biomass production and land use. Internal factors, such as species, litter source and initial chemical composition, 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 using leaf litter of three species (Eucalyptus botryoides, E. globulus, and E. ovata) from two sources (trees without irrigation and trees irrigated with meatworks effluent) under a short rotation forest regime in New Zealand. The species had significant effects on the litter decomposition and nutrient release while litter source mainly influenced nutrient release. The litter dry weight loss for the three species after the 12-month period were E. globulus (84%)>E. botryoides (55%)>E. ovata (41%). Similar trends were found for the release of six nutrients (N, P, K, Ca, Mg and Mn). Litter from trees without irrigation released these nutrients slower than did litter from trees irrigated with meatworks effluent. For nitrogen, this was 28.9% and 49.2%, respectively, of the original total amount released after 12 months, and for phosphorus 10.4% and 42.4%. Potassium was consistent in being released most rapidly (from 67 to 93% of the total after 12 months) from all litter types. Phosphorus, magnesium, and nitrogen accumulated more than their initial amount in some litter types. The initial contents of acid detergent fibre (cellulose and lignin) and magnesium of leaf litter, and their ratios with other nutrients (e.g. lignin/N and cellulose/Mg) were key factors influencing litter decomposition and nutrient release. The effects of these internal factors should be considered when managing litter in plantation forests to give sustainable biomass production.