The recent activities developed under the solution “Blending of raw and treated organic materials to produce organic fertilizers (NPC)” aimed to evaluate a broad range of manure-based materials (manures, slurries, and the treated slurries) to assess their potential to be blend and allow the production of a crop-tailored fertilizer, with N:P:K ratios similar to those present in commercially available products.
Seven manures and slurries, representative of the main Portuguese livestock systems, were analysed, in terms of their physicochemical characteristics (pH, OM, EC, macro- and micronutrients content), the potential of N mineralization, and plant available P. Three treatments were applied to the slurries: solid-liquid separation, acidification and combined acidification and solid-liquid separation. By calculating their N:P:K ratios, it was possible to evaluate their potential to be blended, and respond to the crop needs, using two different approaches: i) at a farm scale, where a single animal species manure, and the products of their treatment, are available, and ii) at a central-plant approach, where manures from different species are available to be processed and blended, to produce a material with the desired N:P:K ratios. We believe that the application of these materials, regardless of the need to be complemented by mineral fertilizers, will be an efficient way to promote their use and ensure closing the N P and C nutrients loops.
Currently, the first scenario is being tested through the blending of pig slurry, cattle slurry and poultry manure, complemented with two sources of N, urea and ammonium sulphate, and two sources of P, superphosphate and orthophosphoric acid. Considering the results from the previous study, the pig slurry solid fraction can be used without mineral P supplementation, as it was observed that its N:P ratio of 0.5 was interesting as a fertilizer. Currently, an incubation trial to follow the N and P dynamics and to assess the greenhouse gases emissions, as well as a leaching trial are in progress, to evaluate the performance of some of the designed blends. With the results from these experiments, the interaction of the blends with plants, in pot trials, will then be assessed.
Text Prepared by Joana Prado, Paula Alvarenga and David Fangueiro