Browsing by Subject "Biobased fertilizer"

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Suitability of recycled organic residues from animal husbandry and bioenergy production for use as fertilizers
(2021) Bauerle, Andrea; Lewandowski, Iris
In recent years, agriculture has been increasingly faced with the acute need to find a more sustainable practice for dealing with nutrient-rich organic side streams. For ecological and economic reasons, pressure is mounting every day to implement an improved utilisation and to close nutrient loops in agriculture to the maximum possible. Pig manure and biogas digestates are suitable as organic fertilisers because they contain essential plant nutrients. They also provide organic matter that contributes to the maintenance of soil fertility. However, their current use is often insufficient. Both residues can be used as fertilisers either directly or following treatment. This can be as simple as solid-liquid separation. A more advanced approach is the precipitation of phosphorus for conversion into phosphate fertilisers ("P-Salts"). The fertilising effect of such innovative P-Salts needs to be investigated in an agronomic context. The same applies for the integration of separated biogas digestates as organic fertilisers into different biomass production systems. The primary objective of this thesis is to establish whether recycled fertilisers from organic residues are comparable to mineral fertilisers and can serve as a suitable substitution. For this purpose, five specific objectives were defined: (1) to determine whether separated biogas digestates can complement or substitute mineral fertilisers and whether/how they affect long-term yield performance in different biomass cropping systems; (2) to ascertain which type of separated biogas digestate is suitable for which biomass production system; (3) to test the effect of two recycled P-Salts on yield and quality of different crops compared to triple superphosphate (TSP); (4) to examine whether the combination of recycled P-Salts with biochar and dried solid digestates results in interaction effects; and (5) to assess whether there are differences in the uptake efficiency of recycled and mineral fertilisers between different crop types. Thus, several experiments were carried out. The fertilising effect of separated biogas digestates on three biomass production systems (perennial grassland, intercropping of triticale and clover grass, silage maize) was investigated in multi-year field experiments in south-west Germany. P-Salt and biochar from pig manure were tested in a greenhouse study with spring barley and faba bean. In a second greenhouse study with ornamentals, the P-Salt from manure, a P-Salt from biogas digestate, and dried solid digestates were assessed. The long-term yield stability of biomass cropping systems fertilised with separated biogas digestates was clearly demonstrated under field conditions. Separated biogas digestates can substitute mineral fertiliser in perennial and intercropping systems. Solid digestates were most suitable for cropping systems with soil tillage where their incorporation into soil is possible. The intercropping of triticale and clover grass was found to be the most stable system, with constantly high biomass yields being maintained using only digestates. For maize, a combined application of digestates and mineral fertiliser proved to be the best option. The P-Salt from manure had the same or even better effects than TSP on spring barley and faba bean. In the experiment with ornamentals, the two P-Salts from manure and digestate had more or less the same effect as TSP on biomass production. These results suggest that both P-Salts have an equivalent fertilisation effect to TSP and can thus replace it as mineral fertiliser. In this thesis, it was possible to achieve competitive yield results with the tested fertilisers, provided that they are integrated in a suitable fertilising strategy. The next step is for the recycled fertilisers to be actually used in agricultural practice - a prerequisite for which being that their implementation has agronomic, practical, ecological and economic advantages. The enhanced use efficiency of N and P already available on farms is challenging but necessary to reduce dependency on both synthesised N fertilisers and imported P fertilisers. This thesis significantly contributes by providing knowledge on the fertilising effect of selected recycled fertilisers necessary for their future implementation in agriculture. Optimised nutrient management and residue treatment using advanced technologies can contribute to the further closing of nutrient cycles. The highest environmental benefits can be realised on farms with excess residues and limited agricultural land. It is therefore highly recommended that these farms improve their current practice by prioritising the implementation of appropriate measures. Sound residue management necessitates strategic planning and capital investments from farmers and companies, but is a crucial step towards the sustainable intensification of cropping systems and resilient future agriculture.