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Use of nutrients recycled from societal waste streams in agriculture is part of the circular economy, and in line with organic farming principles. Nevertheless, diverse contaminants in waste streams create doubts among organic farmers about potential risks for soil health. Here, we gather the current knowledge on contaminant levels in waste streams and recycled nutrient sources, and discuss associated risks. For potentially toxic elements (PTEs), the input of zinc (Zn) and copper (Cu) from mineral feed supplements remains of concern, while concentrations of PTEs in many waste streams have decreased substantially in Europe. The same applies to organic contaminants, although new chemical groups such as flame retardants are of emerging concern and globally contamination levels differ strongly. Compared to inorganic fertilizers, application of organic fertilizers derived from human or animal feces is associated with an increased risk for environmental dissemination of antibiotic resistance. The risk depends on the quality of the organic fertilizers, which varies between geographical regions, but farmland application of sewage sludge appears to be a safe practice as shown by some studies (e.g. from Sweden). Microplastic concentrations in agricultural soils show a wide spread and our understanding of its toxicity is limited, hampering a sound risk assessment. Methods for assessing public health risks for organic contaminants must include emerging contaminants and potential interactions of multiple compounds. Evidence from long-term field experiments suggests that soils may be more resilient and capable to degrade or stabilize pollutants than often assumed. In view of the need to source nutrients for expanding areas under organic farming, we discuss inputs originating from conventional farms vs. non-agricultural (i.e. societal) inputs. Closing nutrient cycles between agriculture and society is feasible in many cases, without being compromised by contaminants, and should be

This study aimed to improve the phosphorus (P) use efficiency of various biowastes. To achieve this, we proposed the combination of placement and the acidification of biowastes for the development of P-efficient biobased fertilizers. Seven biowastes were used as P-fertilizers, including two meat and bone meals (MBM), two solid fractions of biogas digestate (BGF), and three sewage sludges (SS). Two acidification approaches were evaluated: pre-treatment with sulfuric acid (73.5 g sulfuric acid per kg fresh weight) and co-application with ammonium sulfate (15 mg N per kg soil). The treated materials were placed close to winter wheat (Triticum aestivum cv. Benchmark) seeds in a 42-day pot experiment in a growth chamber. The P use efficiency was compared to the corresponding untreated material homogeneously mixed or similarly placed in the soil. A 33P indirect labeling method was used to differentiate P uptake from soil and fertilizer. The negative control showed a shoot dry matter of 0.42 g ( ± 0.05) and a total P uptake of 0.62 ( ± 0.06) mg per plant. The placement of acidified sewage sludge did not show significant differences in shoot dry matter and P uptake compared to the negative control. On the other hand, the placement of acidified MBM significantly increased plant growth (MBM I: 2.93 ± 0.46; MBM II: 1.78 ± 0.09 g) and P uptake (MBM I: 7.38 ± 1.10; MBM II: 6.21 ± 0.53 mg) compared to the untreated MBM placed and the negative control. Similarly, the placement of acidified BGF showed promising results, with a 3-fold increase in P uptake from the fertilizer compared to untreated BGF mixed with the soil (7.74 ± 1.47 vs. 2.71 ± 0.26 mg). Therefore, our results demonstrate that the placement of acidified MBM and BGF can increase the P use efficiency of these biowastes and may provide a basis for formulating P-efficient biobased fertilizers using these materials.

Recycling of municipal waste products, such as composted household waste and sewage sludge, is beneficial in many respects, especially to establish a sustainable circular economy of nutrients, reduce the loss of valuable nutrients and reduce need for mineral fertilizers in crop production. However, these types of products may also contain various xenobiotics such as heavy metals and organic pollutants, which may compromise soil fertility. Further, the microplastic content in some waste product is an emerging concern. Studies on how these products impact on soil fertility are consequently very important. Earthworms perform a number of soil services and are therefore very important for soil fertility in many parts of the world. Additionally, earthworms may be susceptible to soil pollution, as they live most of most their lives buried in the soil, ingest soil and pass it through their gut. Earthworms are therefore often used as model organisms in ecotoxicology studies. In this study we use the endogeic earthworm species Aporrectodea caliginosa. We designed an experiment with the purpose of comparing the effects of long-term fertilization with NPK, cattle manure, composted household waste (at normal and accelerated level) and sewage sludge (at normal and accelerated level) on body volume, burrowing behaviour and reproduction of A. caliginosa. Additionally, we included an experiment where we spiked with high amounts of two different kinds of microplastic (polyethylene (PE)) and polymethylmethacrylat (PMMA)), evaluating the same parameters. We found no significant effects of the plastic treatments on earthworm fitness, but saw indications that earthworms may be able to detect and avoid plastic particles at high concentrations in the soil. We found significant differences on earthworm fitness in the soil screening experiment, but these effects were not related to pollution level in the soil. Mostly, the earthworms in the treatments considered potentially problematic (i.e.

Data on the dynamics and fate of phosphorus (P) under low soil-test P (STP) conditions is essential for the development of cropping strategies with a high P use efficiency. This study examined the effects of long-term (20 years) mineral and organic fertiliser P applications on a P-depleted sandy loam soil in Denmark. The cycling of P was examined by use of P budgets (inputs-offtake), chemical P extractions, 33P isotopic exchange kinetics (IEK), and solution 31P nuclear magnetic resonance (NMR) spectroscopy on NaOH-EDTA extracts. Recovery of applied P in the topsoil was smaller for animal slurry P compared with mineral fertiliser P. The budgets suggest deeper soil layers play an important role for the cycling of P. Resin-extractable P (2 to 17 mg kg−1), Olsen-P (7 to 16 mg kg−1) and E1min (1 to 6 mg kg−1) were correlated with the P budgets. Between 63 and 77% of total inorganic P was not exchangeable in a period of three months (E>3months), with the lowest value observed in no-P treatment N1K1. The data show that a redistribution of exchangeable P had taken place under the influence of a strongly negative P budget. Microbial P (6 to 18 mg kg−1) increased under animal slurry inputs compared with mineral fertiliser applications (p < 0.05). All soils were dominated by phosphomonoesters and orthophosphate (98 to 99% of the NMR signal). Concentrations of orthophosphate (86 to 135 mg kg−1) varied significantly between treatments (p < 0.01), whereas forms of organic P remained largely unchanged. The results demonstrate that P applications increased the amount of P that is potentially available for plants, irrespective of input form. Nevertheless, most P applied in excess of crop uptake resulted in an increase of the amount of P that is slowly exchangeable. Under low soil test P conditions such as in the current trial, fertiliser P applied in e

Organic farming systems need to replace nutrients exported via farm products, especially phosphorus (P) which may otherwise become depleted in soil in the long term. In Europe, EU regulations for organic production are shaping the farming systems with respect to inputs of nutrients. Permitted off-farm P sources include conventional animal manure, composted or anaerobically digested organic residues, rock phosphate, and some animal residues such as meat and bone meal. The recent proposed revision of EU regulations for organic production (2014) puts less emphasis on closing nutrient cycles and instead aims at minimizing off-farm inputs, to reduce the risk of importing contaminants. This development, which has received little attention from the organic sector so far, is explained here. The paper further explores the regulatory conditions that govern the P supply to organic agriculture in six European countries: Austria, Denmark, Germany, Great Britain, Norway, and Switzerland. Organic farmers are subject to substantial variation in standards arising from the interpretation of EU regulations into national laws, restrictions imposed by private actors such as retailers, and private standards which may be stricter than EU regulations. In several countries, the majority of organic farmers are certified by private, stricter standards. We propose that EU regulations and private standards for organic production should not limit the use of recycled fertilizers in organic farming systems, as long as means are taken to ensure the quality and safety of these inputs. Awareness of the need to close nutrient cycles may contribute to adapting regulations and private standards to support recycling of nutrients from society to organic agriculture. A better definition of the term “natural substance” in organic regulations is required.