2019
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Sorption could be a way to concentrate nutrients in diluted waste streams to bring more nutrients back to agriculture. However, the sorbed nutrients must be plant available. The aim of this work was to investigate how plant available nitrogen (N) added sorbed to zeolite and is compared to conventionally added N. First, 15N labelled ammonium was sorbed to a sorbent, zeolite, in an aqueous solution. Then, the fertilizer effect was compared to the ammonium fertilizer and added the conventional way, with and without zeolite. A pot experiment with two soil types (chernozem and sandy soil) and wheat as test crop was used. Results indicated that the fertilizer effect of sorbed ammonium in the first growth cycle is about 50% of ammonium added conventionally. The sorbent itself had a positive effect in sandy soil, but not in chernozem. N uptake without added N was higher in chernozem than in sandy soil and more N from fertilizer was left in the soil after the experiment in the chernozem than in the sandy soil. In conclusion, ammonium added sorbed is plant available to some extent, but less so than conventionally added ammonium.
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Biofertilizers, fertilizers made from organic residues, could replace some mineral fertilizers, reducing energy consumption and resource mining. The main treatment options are composting, anaerobic digestion, drying, pyrolysis and combustion, they can be used alone or in combination. The quality of biofertilizers depend both on the original residue and on the treatment, but in most cases not all the nutrients are immediately available to plants. It is difficult to predict how available the nutrients are, and when they will become available. The methods to assess and predict nutrient availability are reviewed. Furthermore, the effect of biofertilizers on the environment in the form of nutrient losses and greenhouse gas emissions are reviewed and compared to mineral fertilizers. There is a need to produce biofertilizers with better and more predictable qualities, and also to understand their effects over multiple seasons.
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