Nutrient Contribution of Litterfall in a Short Rotation Plantation of Pure or Mixed Plots of Populus alba L. and Robinia pseudoacacia L.

This study aims to quantify the potential contribution of nutrients derived from leaf litter in a short rotation coppice plantation which includes monocultures of the species Populus alba (PA) and Robina pseudoacacia (RP) as well as a mixture of 50PA:50RP, in the middle of the rotation. The P. alba monoculture was that which provided the most leaf litter (3.37 mg ha−1 yr−1), followed by the 50PA:50RP mixture (2.82 mg ha−1 yr−1) and finally the R. pseudoacacia monoculture (2.55 mg ha−1 yr−1). In addition to producing more litterfall, leaves were shed later in the P. alba monoculture later (December) than in the R. pseudoacacia monoculture (October) or the mix (throughout the fall). In terms of macronutrient supply per hectare, the contributions derived from leaf litter were higher for K, P and Mg in the case of P. alba and for N in R. pseudoacacia, the mix presenting the highest Ca content and intermediate concentrations for the rest of the nutrients. In addition, other factors such as C:N or N:MO ratios, as well as the specific characteristics of the soil, can have an important impact on the final contribution of these inputs. The carbon contribution derived from leaf fall was higher in the P. alba monoculture (1.5 mg ha−1 yr−1), intermediate in the mixed plot (1.3 mg ha−1 yr−1) and slightly lower for the R. pseudoacacia monoculture (1.3 mg ha−1 yr−1). Given these different strategies of monocultures with regard to the dynamism of the main nutrients, species mixing would appear to be suitable option to achieve a potential reduction in mineral fertilization in these plantations.