Fertilizer potential of slurry from intensive dairy cattle farms in Intensive production forestry systems

Intensive dairy cattle breeding has a relevant social and economic impact in Portugal, particularly in the northern region. This activity generates a high flow of livestock effluents (slurry), rich in important nutrients for plant growth, which can be introduced into intensive production forestry systems. These effluents can provide a good alternative to mineral fertilizers, not only from an economic perspective but, particularly, from the point of view of environmental protection. In the present study, the effect of increasing doses of slurry on tree growth, either with or without mycorrhizal arbuscular fungi (AMF) and plant growthpromoting bacteria (PGPB) inoculation, was evaluated in clones of Paulownia CoT2 and Populus i214, as they are genotypes that have a high efficiency in the mobilization of soil nutrients (namely N) and in the capture of CO2 from the atmosphere, as well as high biomass calorific value. For this purpose, a demonstration field trial was installed, occupying an area of 14,607 m2 , where the trees were planted with the compasses of: 2.5 x 1.5 m and 2.5 x 0.75 m, respectively for Paulownia and for Poplar. Prior to transplantation to the field, some plants were inoculated with AMF and PGPB. In the field, the following treatments were performed: T0 - no fertilization, either mineral or organic; T1 - amount of slurry equivalent to 85 kg of N ha-1; T2 - amount of slurry equivalent to 170 kg of N ha-1; T3 - amount of slurry equivalent to 340 kg of N ha-1, both with and without inoculation. Results revealed a significant and positive effect of the slurry application, both in the diameter at breast height (DBH) and total stand height (TH), showing its high fertilizing potential, and, on the other hand, there was no increased contamination by nitrates and by pathogenic microorganism in the leachates for the experimental doses of slurry. Therefore, we can conclude that, under the experimental conditions, the slurry resulting from the intensive exploitation of cattle constitutes an alternative to exclusively mineral fertilization in intensive production forestry systems, either by increasing the production of biomass or by the absence of contamination of aquifers by nitrates and pathogens.