On-farm use of recycled liquid ammonium sulphate in Southwest Germany using a participatory approach

Nutr Cycl Agroecosyst https://doi.org/10.1007/s10705-023-10329-2 ORIGINAL ARTICLE On‑farm use of recycled liquid ammonium sulphate in Southwest Germany using a participatory approach Benedikt Müller · Jens Hartung · Moritz von Cossel · Iris Lewandowski Torsten Müller · Andrea Bauerle · Received: 27 April 2023 / Accepted: 10 November 2023 © The Author(s) 2023 Abstract For political and environmental reasons, there is an urgent need for alternatives to energyintensive synthetic fertilizers. One solution is the targeted recycling of nutrients within agriculture. In this study, liquid ammonium sulphate (LAS) as a recycling product derived from digestate treatment was compared to calcium ammonium nitrate, manure and original digestates in an on-farm experiment using a participatory approach. Based on regular meetings with the farmers involved, a flexible experimental design was developed which integrated the fertilization legislation and the farmers’ operational structures already in place, such as crop rotation, available application techniques and manure management demands. The aim was to achieve both implementation practicability and acceptance of the study results Supplementary Information The online version contains supplementary material available at https://doi. org/10.1007/s10705-023-10329-2. B. Müller (*) · M. von Cossel · I. Lewandowski · A. Bauerle Biobased Resources in the Bioeconomy, Institute of Crop Science, University of Hohenheim, Stuttgart, Germany e-mail: J. Hartung Biostatistics, Institute of Crop Science, University of Hohenheim, Stuttgart, Germany T. Müller Fertilization and Soil Matter Dynamics, Institute of Crop Science, University of Hohenheim, Stuttgart, Germany by the farmers. Results from the year 2020 showed that LAS applied with three-jet nozzles in barley and wheat had significantly lower yields than the other fertilizers. Applied with a slurry tanker trailing shoe applicator in 2021, LAS had comparable yields to the other fertilizers in maize (51.2 t ha−1) and comparable yields to digestate in rapeseed (4.4 t h a−1). Application techniques that minimize environmental impacts and lower the LAS pH could potentially increase the effectiveness of the fertilizer. We recommend that farmers use this fertilizer not as a single solution but as a mineral compensatory fertilizer in addition to organic fertilizers following local fertilizer legislation. In this case, LAS could potentially substitute calcium ammonium nitrate (CAN). Keywords On-farm · Participatory research · Ammonium sulphate solution · Recycled fertilizer · Nitrogen fertilizer replacement value Introduction High livestock densities can cause regional accumulations of slurry and farmyard manure, leading to drastic nitrogen (N) and phosphorus (P) surpluses in agricultural soils in the region (Svanbäck et al. 2019). Transporting this organic fertilizer to distant areas with a need for these nutrients is not lucrative due to the high water content, especially considering current soaring energy costs (European Vol.: (0123456789) 13 Nutr Cycl Agroecosyst Commission 2022a, b). Even in areas with high livestock densities, additional mineral fertilizers are often used to fulfill plant needs, as the nutrient ratio in manure is suboptimal. Mineral fertilizers have a poor climate balance and a high price volatility for farmers (Hasler 2017; Schnitkey et al. 2023). Therefore, regional production of mineral fertilizers from existing material flows such as biomass, manure, and digestate could help reduce imported fertilizers and make regional farming systems more resilient. The European Innovation Partnership (EIP) “Agriplus Hohenlohe” (EIP‐AGRI 212018) is an example of a case study that addresses this issue in the Hohenlohe region (south-west Germany) and aims to increase the efficiency of arable farming through improved nutrient management. By building a nutrient recycling plant on an industrial scale, manure from local farmers is processed into mineral fertilizers after being used for biogas production (European Commission 2023). These fertilizers can be used specifically in arable farming to close nutrient cycles. One of the products of the nutrient recycling plant is the mineral fertilizer liquid ammonium sulfate (LAS). Studies with LAS were conducted in the form of pot/greenhouse (Sigurnjak et al. 2016, 2019) and onstation field experiments (Vaneeckhaute et al. 2013b, 2014; Mokry 2013; Sigurnjak et al. 2016, 2019). All studies found the fertilizing performance of LAS to be satisfactory. Even though it is important to test non-conventional fertilizers in real agricultural systems for their effect on yield (Sigurnjak et al. 2016), to our knowledge, no on-farm field experiments have yet been performed. The owner of the nutrient recycling plant and some neighboring farmers as potential users of the products asked the University of Hohenheim to test LAS and suggest ways to implement it into their farming practices. In initial meetings, it became clear that the trials should take place on the farmers’ own land and that this should be done as a participatory investigation to target the outcomes of the study specifically to the farmers’ needs. Studies conducted with a participatory approach have found that a close collaboration between farmers and scientists supports innovations in agriculture, increases innovation acceptability when farmers are in control of the experimental process, and produces more relevant technologies and greater economic impacts, especially when participation starts early in the Vol:. (1234567890) 13 research process (Bellon et al. 2002; Johnson et al. 2003; Padel et al 2015). Mokry (2013) conducted an on-station field experiment from 2009 to 2012 in the same region and indicated that a star wheel application technique is optimal for LAS. However, the fact that farmers can only use this technology for LAS makes it too expensive to acquire. They would rather use their existing technology. In addition, the star wheel technique takes a relatively long time to apply fertilizer, which increases the variable costs for the farmers. The objectives of this study were to implement knowledge from on-station field experiments in onfarm best practice, to compare established fertilizing strategies with recycled LAS, and to investigate whether recycled LAS could substitute the commonly used mineral fertilizer calcium ammonium nitrate (CAN) in the future. The following research questions were derived: 1. How can scientific methods be successfully applied to a fertilizer experiment in an on-farm setting and scale? 2. What is the most suitable application technology for LAS in farming practice? 3. Can the recycling fertilizer LAS serve as a substitute for CAN in common fertilizing regimes? Materials and methods Location and climate A two-year (2020–2021) field experiment was conducted in the Hohenlohe district in the HeilbronnFranken region at an altitude of 300 to 348 m. Compared to (...truncated)