Potential of slurry from intensive dairy cattle farms for paulownia and populus trees, as organic fertilizer: I. effect on production

Intensive dairy cattle breeding have 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 forest production systems. These effluents can provide a good alternative to mineral fertilizers, not only from an economic perspective, but also from the point of view of soil fertility resilience. In the present study, the effect of increasing doses of slurry on tree growth was evaluated in clones of paulownia and populus, as they are genotypes that have a high efficiency in the mobilization of soil nutrients and in the capture of co2 from the atmosphere, as well as high biomass calorific value. To this end, a demonstration field was installed, 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 populus. 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, either with or without inoculation prior to transplantation, with mycorrhizal arbuscular fungi and plant growth-promoting bacteria. Results evidenced a positive effect of the slurry application, both in the diameter at breast height and in total stand height, showing its fertilizing potential which should later be assessed on the ability to constitute an alternative or, simply, a complement to mineral fertilization