Biography

Education: 

PhD in Soil Science from Norwegian University of Life Sciences (NMBU) in 2016

Areas of expertise:

- Fish sludge as organic fertiliser

- Plant-available phosphorus in organic waste

- Characterisation of inorganic phosphorus compounds

- Soil analysis (phosphorus)

- Organic farming

 

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Abstract

Closing nutrient cycles by bio-based fertilizer products (BFPs) can improve the environmental sustainability of food systems and facilitate a more circular economy. Although the theoretical potential for nutrient recycling has been explored in detail, BFPs still seldom replace mineral fertilizer products in practice. The aim of the present study was to explore the critical enabling and limiting factors for the use of BFPs as seen from the perspective of farmers, suppliers, and civil society. To this aim, qualitative interviews were conducted with seven conventional grain farmers, six suppliers of BFPs, and five representatives of civil society, limited to environmental non-governmental organizations. The presented results illustrate a mismatch between demand and supply. On the one hand, the interviewed farmers were only interested in using BFPs if they are practical to use, balanced with respect to nutrient contents, and potentially provide the same earnings as mineral fertilizers. Positive effects for soil quality were an important driver for many of the farmers. On the other hand, the suppliers of BFPs were generally not able to offer products that fulfilled the farmers’ demands without economic losses, and they emphasized that they have faced several regulatory challenges. Representatives of regional civil society organizations expressed concern that new technical solutions could cause new environmental challenges, and that BFPs could enable further intensification of livestock production. The central-level representatives from the same NGOs, however, were positive about that BFPs can solve environmental problems. Policy instruments will be needed to increase the adoption of PFPs. Fostering BFPs’ that contribute to a sustainable agriculture is important to consider when formulating these polices.

Abstract

The aim of this study was to contribute to development of organic fertiliser products based on fish sludge (i.e. feed residues and faeces) from farmed smolt. Four dried fish sludge products, one liquid digestate after anaerobic digestion and one dried digestate were collected at Norwegian smolt hatcheries in 2019 and 2020. Their quality as fertilisers was studied by chemical analyses, two 2-year field experiments with spring cereals and soil incubation combined with a first-order kinetics N release model. Cadmium (Cd) and zinc (Zn) concentrations were below European Union maximum limits for organic fertilisers in all products except one (liquid digestate). Relevant organic pollutants (PCB7, PBDE7, PCDD/F + DL-PCB) were analysed for the first time and detected in all fish sludge products. Nutrient composition was unbalanced, with low nitrogen/phosphorus (N/P) ratio and low potassium (K) content relative to crop requirements. Nitrogen concentration in the dried fish sludge products varied (27–70 g N kg-1 dry matter), even when treated by the same technology but sampled at different locations and/or times. In the dried fish sludge products, N was mainly present as recalcitrant organic N, resulting in lower grain yield than with mineral N fertiliser. Digestate showed equally good N fertilisation effect as mineral N fertiliser, but drying reduced N quality. Soil incubation in combination with modelling is a relatively cheap tool that can give a good indication of N quality in fish sludge products with unknown fertilisation effects. Carbon/N ratio in dried fish sludge can also be used as an indicator of N quality.

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Abstract

Prediction of the relative phosphorus (P) fertiliser value of bio-based fertiliser products is agronomically important, but previous attempts to develop prediction models have often failed due to the high chemical complexity of bio-based fertilisers and the limited number of products included in analyses. In this study, regression models for prediction were developed using independently produced data from 10 different studies on crop growth responses to P applied with bio-based fertiliser products, resulting in a dataset with 69 products. The 69 fertiliser products were organised into four sub-groups, based on the inorganic P compounds most likely to be present in each product. Within each product group, multiple regression was conducted using mineral fertiliser equivalents (MFE) as response variable and three potential explanatory variables derived from chemical analysis, all reflecting inorganic P binding in the fertiliser products: i) NaHCO3-soluble P, ii) molar ratio of calcium (Ca):P and iii) molar ratio of aluminium+iron (Al+Fe):P. The best regression model fit was achieved for sewage sludges with Al-/Fe-bound P (n = 20; R2 = 79.2%), followed by sewage sludges with Ca-bound P (n = 11; R2 = 71.1%); fertiliser products with Ca-bound P (n = 29; R2 = 58.2%); and thermally treated sewage sludge products (n=9;R2=44.9%). Even though external factors influencing P fertiliser values (e.g. fertiliser shape, application form, soil characteristics) differed between the underlying studies and were not considered, the suggested prediction models provide potential for more efficient P recycling in practice.

Abstract

The aim of this study was to contribute to closing global phosphorus (P) cycles by investigating and explaining the effect of fish sludge (feed residues and faeces of farmed fish) and manure solids as P fertiliser. Phosphorus quality in 14 filtered and/or dried, composted, separated or pyrolysed products based on fish sludge or cattle or swine manure was studied by sequential chemical fractionation and in two two-year growth trials, a pot experiment with barley (Hordeum vulgare) and a field experiment with spring wheat (Triticum aestivum). In fish sludge, P was mainly solubilised in the HCl fraction (66 ± 10%), commonly being associated with slowly soluble calcium phosphates, and mean relative agronomic efficiency (RAE) of fish sludge products during the first year of the pot experiment was only 47 ± 24%. Low immediate P availability was not compensated for during the second year. Thus efforts are needed to optimise the P effects if fish sludge is to be transformed from a waste into a valuable fertiliser. In manure solids, P was mainly soluble in H2O and 0.5 M NaHCO3 (72 ± 14%), commonly being associated with plant-available P, and mean RAE during the first year of the pot experiment was 77 ± 19%. Biochars based on fish sludge or manure had low concentrations of soluble P and low P fertilisation effects, confirming that treatment processes other than pyrolysis should be chosen for P-rich waste resources to allow efficient P recycling. The field experiment supported the results of the pot experiment, but provided little additional information.

Abstract

Fosfor i husdyrgjødsel blir i dag dårlig utnyttet, og det er vanlig at fosfor akkumuleres i jorden i områder med høy husdyrtetthet. Det har blitt utviklet en rekke ulike behandlingsteknologier som gjør det mulig å transportere fosfor i husdyrgjødsel fra husdyrtette områder til områder med behov for fosforgjødsel. Denne rapporten er en gjennomgang av litteraturen på de viktigste behandlingsteknologiene og deres effekt på gjødselvirkningen av fosforet i produktene.

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Abstract

The aim of this study was to contribute to the development of pelleted compound recycling fertilizerswith favourable handling and spreading characteristics and balanced nutrient ratios by combiningnitrogen (N)- and phosphorus (P)-rich waste resources (meat bone meal, fish sludge or food waste)with potassium (K)-rich bottom wood ash. Pelleted compound recycling fertilizers with gooddurability and low dusting tendency were produced by roll-pelleting preheated waste resources at asuitable moisture content. However, the nutrient ratios in the final products were insufficientlybalanced, with too low N concentrations relative to P and K to meet crop demands. In a bioassayusing barley ( Hordeum vulgare) and a nutrient-deficient sand/peat mixture, the relative agronomiceffectiveness (RAE) of pelleted compound recycling fertilizers and reference recycling fertilizers was22–42% of that of mineral compound fertilizer. Growth limitation was due to reduced N availability(mineral fertilizer equivalent - MFE = 35–57%) or reduced P availability (MFE = 20–115%), with thegreatest P fertilizer value obtained for digestate based on dairy manure and fish sludge. Availability ofK in bottom wood ash was masked by the experimental soil.

Abstract

Application of fish sludge as fertiliser to agricultural land can contribute to closing nutrient cycles in fish farming. The effect of different treatment technologies on the nitrogen fertilisation effects of fish sludge was studied by a bioassay with barley (Hordeum vulgare), an incubation and a field experiment. Dried fish sludge resulted in relative agronomic efficiency of 50–80% compared with mineral fertiliser. The anaerobic digestate based on fish sludge (20 vol%) and dairy manure did not increase nitrogen uptake in barley. Increasing the ratio of fish sludge in the digestate increased the fertilisation effect, but requires optimisation of the biogas process. A simple logistics analysis conducted for a case hatchery showed that on-site drying and co-digestion of fish sludge in a central biogas plant can be regarded as equal in terms of costs. Norway can become an exporter of fish sludge-based recycling fertilisers if current regulations are modified to facilitate nutrient recycling.

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Abstract

Minable rock phosphate is a finite resource. Replacing mineral phosphorus (P) fertilizer with P-rich secondary resources is one way to manage P more efficiently, but the importance of physicochemical and microbial soil processes induced by secondary resources for plant P uptake is still poorly understood. Using radioactive-labeling techniques, the fertilization effects of dairy manure, fish sludge, meat bone meal, and wood ash were studied as P uptake by barley after 44 days and compared with those of water-soluble mineral P (MinP) and an unfertilized control (NoP) in a pot experiment with an agricultural soil containing little available P at two soil pH levels, approximately pH 5.3 (unlimed soil) and pH 6.2 (limed soil). In a parallel incubation experiment, the effects of the secondary resources on physicochemical and microbial soil processes were studied. The results showed that the relative agronomic efficiency compared with MinP decreased in the order: manure ≥fish sludge ≥wood ash ≥meat bone meal. The solubility of inorganic P in secondary resources was the main driver for P uptake by barley (Hordeum vulgare). The effects of secondary resources on physicochemical and microbial soil processes were of little overall importance. Application of organic carbon with manure resulted in microbial P immobilization and decreased uptake by barley of P derived from the soil. On both soils, P uptake by barley was best explained by a positive linear relationship with the H2O + NaHCO3-soluble inorganic P fraction in fertilizers or by a linear negative relationship with the HCl-soluble inorganic P fraction in fertilizers.

Abstract

This study examined the P fertilization effects of 11 sewage sludges obtained from sewage treated with Al and/or Fe salts to remove P by a pot experiment with ryegrass (Lolium multiflorum) and a nutrient-deficient sand−peat mixture. Also it investigated whether fertilization effects could be predicted by chemical sludge characteristics and/or by P extraction. The mineral fertilizer equivalent (MFE) value varied significantly but was low for all sludges. MFE was best predicted by a negative correlation with ox-Al and ox-Fe in sludge, or by a positive correlation with P extracted with 2% citric acid. Ox-Al had a greater negative impact on MFE than ox-Fe, indicating that Fe salts are preferable as a coagulant when aiming to increase the plant availability of P in sludge. The results also indicate that sludge liming after chemical wastewater treatment with Al and/or Fe salts increases the P fertilization effect.

Abstract

Mineable rock phosphate is a limited resource. Replacing mineral phosphorus (P) fertiliser with P-rich secondary resources is one way to manage P more efficiently. The Norwegian potential to replace mineral P fertiliser with total P in secondary resources was analysed here using substance flow analysis. The results obtained were integrated with data on P plant-availability in secondary resources and showed that, theoretically, plant-available P in manure alone could fulfil the Norwegian demand for P fertiliser. However, P in manure is inefficiently utilised due to the geographical segregation of animal husbandry and arable farming, which contributes to considerable P over-application to agricultural soil. In Norway, agriculture and aquaculture drive P consumption and losses at similar levels, and the amount of P in fish excrement and feed losses from off-shore aquaculture pens (fish sludge) is of the same order of magnitude as P in manure. Fish sludge is currently not collected or utilised, but lost to coastal marine waters. All other secondary resources represent relatively small amounts of P, but may still be important regionally. Political incentives are thus needed in current regulations to efficiently close P cycles. To achieve P recycling in practice, it is essential to know the relative agronomic efficiency (RAE) of secondary P products compared with mineral fertiliser. Nine secondary P products were analysed here: Two biomass ashes, meat bone meal, fish sludge, catering waste, two food waste-based digestate products, dairy manure and chicken manure. The RAE of these secondary products studied in a bioassay with ryegrass (Lolium multiflorum) varied widely, partly depending on soil pH. Fertilisation effects were mainly attributable to the solubility of the inorganic P species contained in the secondary products. Combining sequential chemical fractionation and non-destructive speciation methods revealed that P was mainly present as calcium phosphates of differing solubility. Further analysis showed that microbial and physicochemical soil processes induced by the secondary P products studied were of little overall importance for total P uptake in barley (Hordeum vulgare). Based on the results obtained, two chemical extraction methods for predicting the RAE of secondary products with unknown fertilisation effects are suggested: At soil pH <6.5, RAE should be predicted by the fraction of inorganic P in the secondary product (% of total P) that is extractable in H2O. At soil pH >6.5, RAE should be predicted by the fraction of inorganic P (% of total P) that is extractable in 0.5 M NaHCO3 (Olsen P).

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Abstract

N-rich waste resources have potentially good effects if applied as fertiliser to spring cereals. P fertilisation effects of meat and bone meal are strongly determined by soil pH, whereas P in bottom wood ash seems to have almost the same availability as easily soluble P in mineral fertilisers. K fertilisation effects were hidden by the soils ability to provide plants with plant available K.