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The biological stability of organic materials predicts their performance when used as either a soil improver or as an ingredient in growing media. CO 2 release in a static measurement and O 2 consumption rate (OUR) were compared for seven groups of growing media components. The ratio between CO 2 release and OUR was matrix-specific. This ratio was highest for plant fibers high in C:N and with a high risk of N immobilization, intermediate for wood fiber and woody composts, and lowest for peat and other compost types. The effect of variable test conditions in the OUR setup was assessed for plant fibers, where addition of mineral N and/or nitrification inhibitor had no effect on the OUR measurements. Testing at 30 °C instead of 20 °C resulted in higher OUR values as expected, but did not change the effect of mineral N dose. A strong increase in the CO 2 flux was measured when plant fibers were mixed with mineral fertilizer; in contrast, addition of mineral N or fertilizer before or during the OUR test had no effect. The present experimental setup did not allow for differentiation between a higher CO 2 release as a result of increased microbial respiration after adding mineral N versus an underestimation of stability due to N limitation in the dynamic OUR setup. Results indicate that type of material, C:N ratio and risk of N immobilization all appear to affect the OUR results. The OUR criteria may therefore require clear differentiation based on the different materials used in horticultural substrates., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

In the attempt to close nutrient cycles, organic fertilizers and soil improvers are getting interest as renewable P sources for crops. However, both the P availability of these compounds for crops and the underlying mechanisms are not fully understood. In this study composts (n = 8), biochars (n = 5), animal manure and processed animal manure (n = 13), digestates and processed digestates (n = 15) and blends of digestates with compost/animal manure/mineral fertilizers (n = 15) were analyzed for chemical composition, organic matter stability and P use efficiency (PUE). Biodegradability (=holocellulose/lignin ratio) proved to be a good indicator for organic matter stability and can successfully replace time-consuming incubation experiments in standard analyses of organic fertilizers. The PUE of digestates, struvites, animal manure products and blends of digestate with compost/animal manure/mineral fertilizers was determined by the NH 4 + -N, Mg and Fe content of the organic fertilizers. The PUE can be predicted by PUE = 61.34 + 8.59*NH 4 + -N/P + 42.25*Mg/P - 8.09*Fe/P (R 2  = 0.71). As increasing amounts of NH 4 + -N and Mg stimulate the formation of soluble struvite crystals, increasing PUE is explained by an increasing amount of P as struvite. The PUE of biochars and composts was determined by the Ca/P and Al content of the organic fertilizers. Here, PUE can be predicted by PUE = 88.87-1.07*Ca/P + 6.08*Al/P (R 2  = 0.93). As increasing amounts of Ca stimulate the formation of highly stable apatite crystals, increasing PUE is explained by an increasing amount of P in the form of apatite., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Previous research has demonstrated that composts (COM) and woody residues from nature management (MR) are potential peat replacers for growing media, but their compositions are highly variable. Our goal is to make growing media more sustainable by optimizing the selection of local and sustainable alternatives for peat. Different batches of COM and MR were incubated to assess the microbial activity based on (1) the N drawdown risk, (2) the C mineralization and (3) the inoculation efficiency of a commercially available biocontrol fungus. The various batches were characterized based on biochemical, chemical (pH, available and total nutrients) and microbiological biomass analysis. COM and MR were scored based on chemical or stability characteristics to assess their suitability to replace peat, lime and fertilizers in growing media. This score allowed for a clear differentiation between the materials; MR received higher scores on average than COM. Five composts were further tested for the effect of storage after blending with an acidic MR, acidification with elemental S, or removal of the finer fraction. One batch of chopped soft rush was acidified with elemental S. Blending and acidification were the most effective treatments as they resulted in a clear increase of the suitability score., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Sustainable peat alternatives, such as composts and management residues, are considered to have beneficial microbiological characteristics compared to peat-based substrates. Studies comparing microbiological characteristics of these three types of biomass are, however, lacking. This study examined if and how microbiological characteristics of subtypes of composts and management residues differ from peat-based substrates, and how feedstock and (bio) chemical characteristics drive these characteristics. In addition, microbiome characteristics were evaluated that may contribute to plant growth and health. These characteristics include: genera associated with known beneficial or harmful microorganisms, microbial diversity, functional diversity/activity, microbial biomass, fungal to bacterial ratio and inoculation efficiency with the biocontrol fungus Trichoderma harzianum. Bacterial and fungal communities were studied using 16S rRNA and ITS2 gene metabarcoding, community-level physiological profiling (Biolog EcoPlates) and PLFA analysis. Inoculation with T. harzianum was assessed using qPCR. Samples of feedstock-based subtypes of composts and peat-based substrates showed similar microbial community compositions, while subtypes based on management residues were more variable in their microbial community composition. For management residues, a classification based on pH and hemicellulose content may be relevant for bacterial and fungal communities, respectively. Green composts, vegetable, fruit and garden composts and woody composts show the most potential to enhance plant growth or to suppress pathogens for non-acidophilic plants, while grass clippings, chopped heath and woody fractions of compost show the most potential for blends for calcifuge plants. Fungal biomass was a suitable predictor for inoculation efficiency of composts and management residues. [ABSTRACT FROM AUTHOR]

Three characteristics are considered key for optimal use of composts in growing media: maturity, pH and organic matter content. Maturation is a critical step in the processing of composts contributing to compost quality. Blending of composts with chopped heath biomass, sieving out the larger fraction of composts and acidification of composts by adding elemental sulfur may be used either to increase organic matter content or to reduce pH for a better fit in growing media. While several studies have shown the effectiveness of these treatments to improve the use of composts in growing media, the effect of these treatments on the compost microbiome has merely been assessed before. In the present study, five immature composts were allowed to mature, and were subsequently acidified, blended or sieved. Bacterial and fungal communities of the composts were characterized and quantified using 16S rRNA and ITS2 gene metabarcoding and phospholipid fatty acid analysis. Metabolic biodiversity and activity were analyzed using Biolog EcoPlates. Compost batch was shown to be more important than maturation or optimization treatments to determine the compost microbiome. Compost maturation increased microbial diversity and favored beneficial microorganisms, which may be positive for the use of composts in growing media. Blending of composts increased microbial diversity, metabolic diversity, and metabolic activity, which may have a positive effect in growing media. Blending may be used to modify the microbiome to a certain degree in order to optimize microbiological characteristics. Acidification caused a decrease in bacterial diversity and microbial activity, which may be negative for the use in growing media, although the changes are limited. Sieving had limited effect on the microbiome of composts. Because of the limited effect on the microbiome, sieving of composts may be used flexible to improve (bio)chemical characteristics. This is the first study to assess the effects of maturation and optimization treatments to either increase organic matter content or lower pH in composts on the compost microbiome. [ABSTRACT FROM AUTHOR]

The question was tackled on how the green waste compost industry can optimally apply the available biomass resources for producing both bioenergy by combustion of the woody fraction, and high quality soil improvers as renewable sources of carbon and nutrients. Compost trials with removal of woody biomass before or after composting were run at 9 compost facilities during 3 seasons to include seasonal variability of feedstock. The project focused on the changes in feedstock and the effect on the end product characteristics (both compost and recovered woody biomass) of this woody biomass removal. The season of collection during the year clearly affected the biochemical and chemical characteristics of feedstock, woody biomass and compost. On one hand the effect of removal of the woody fraction before composting did not significantly affect compost quality when compared to the scenario where the woody biomass was sieved from the compost at the end of the composting process. On the other hand, quality of the woody biomass was not strongly affected by extraction before or after composting. The holocellulose:lignin ratio was used in this study as an indicator for (a) the decomposition potential of the feedstock mixture and (b) to assess the stability of the composts at the end of the process. Higher microbial activity in green waste composts (indicated by higher oxygen consumption) and thus a lower compost stability resulted in higher N immobilization in the compost. Removal of woody biomass from the green waste before composting did not negatively affect the compost quality when more intensive composting was applied. The effect of removal of the woody fraction on the characteristics of the green waste feedstock and the extracted woody biomass is depending on the season of collection. [ABSTRACT FROM AUTHOR]

We investigated the use of biochar (10% on a dry weight basis) to improve the composting process and/or the compost quality by adding it to either the feedstock mixture or the mature compost. The addition of biochar to the feedstocks was essayed in a full scale trial using a mixture of green waste and the organic fraction of municipal solid waste. Addition of biochar to mature compost was performed in a medium scale experiment. The use of biochar, even in small amounts, changed the composting process and the properties of the end products. However these effects depended on the time of application. We observed a faster decomposition in the bio-oxidative phase and lower greenhouse gas emissions when biochar was added at the beginning of the composting process, and a reduction in readily available P when biochar was applied during compost storage. Biochar as a means to increase the C content of the compost was only effective during compost storage. The P fertilizer replacement value of the compost with and without biochar was tested in a plant trial with annual ryegrass. While there was a clear effect on readily available P concentrations in the compost, adding biochar to the feedstock or the compost did not affect the P fertilizer replacement value. [ABSTRACT FROM AUTHOR]

Judicious management of organic matter supply and tillage practice is crucial for sustaining soil quality in horticulture. We have studied whether N fertilization of vegetable crops should be adapted in the short term when soil management changes to include compost application and reduced tillage as soil quality improving factors. The experimental setup was a multiyear field trial on a sandy loam soil with a vegetable crop rotation. Soil tillage in spring was either conventional (moldboard plough) or reduced, non-inversion tillage (with a specially designed chisel plough). Starting in 2008, farm compost was applied each autumn at three rates: 0, 15 and 45 Mg per hectare. The three-year crop rotation (2009–2011) consisted of broccoli ( Brassica oleracea , var. Italica Group), carrots ( Daucus carota ) and leek ( Allium porrum ). Small but significant differences in N dynamics were found between treatments. Broccoli had a higher N uptake and biomass production under reduced compared to conventional tillage. In accordance with this, the apparent net N mineralization tended to be higher for reduced tillage compared to conventional tillage. In contrast, for leek, N uptake did not differ between tillage practices despite a higher apparent net N mineralization under conventional tillage. A tendency for a higher biomass production under conventional tillage was in line with a tendency for a higher amount of residual soil mineral N that might have increased the risk of N losses. In the carrot crop, a higher amount of mineral N under conventional tillage did not increase root yield. Compost application maintained soil organic matter content and did not result in a higher amount of residual soil mineral N. Only in the carrot growing season, compost application increased soil mineral N content to a limited extent. The small short-term changes in overall N availability observed between treatments do not necessitate changes in N fertilization strategy or additional precautions regarding residual soil mineral N. [ABSTRACT FROM AUTHOR]

The aim of the current study was to create a high quality growing medium blend that replaces 70 vol% peat with 40 vol% woody green compost and 30 vol% bark compost and organic fertilizers (i.e., blood meal and chitin), all locally sourced. A range of "woody composts", i.e., green composts based on feedstock selection with mainly woody material from tree prunings, were produced for this purpose at green compost facilities. First, the woody composts were characterized chemically and biologically, including their microbial biomass and net N release. In comparison with regular green composts or vegetable, fruit and garden (VFG) waste composts, woody composts are more suitable for use in growing media due to their lower pH, EC and inorganic C content; however, the woody compost had a low N mineralization rate. Three types of composts supported a higher microbial biomass than wood fiber or bark compost. The additional mineral N release after 100 days for compost mixed with blood meal was tested for different VFG and green composts. A significantly higher additional net N release was measured for composts with higher initial mineral N concentrations (317 mg Nmin/L) as well as VFG composts (417 mg Nmin/L) than for green composts with a lower initial mineral N concentration (148 mg Nmin/L). In a last step, woody compost, bark compost, wood fiber, coir and peat were mixed in different ratios, resulting in six blends ranging from 100% peat-free to 100% peat. Two batches of woody compost were compared, and the blends were mixed with blood meal or chitin. A strong effect of both the organic fertilizer and the blend composition on the mineral N release was observed, with a clear link between the microbial biomass and the net N release. There was a significant negative correlation between the net change in microbial biomass and the net N release (R = −0.85), which implies that a larger increase in microbial biomass during incubation with the organic fertilizer resulted in less N mineralization. The blends containing woody compost scored better for nitrification activity, as the NH4-N concentrations were lower in these than for the blends without woody compost. For the peat blends, no effect on the microbial biomass was observed after addition of organic fertilizers; mineral N did increase, however. Woody composts have the potential to be used in high vol% in growing media blends, but the blends still need further optimization when supplemented with organic fertilizers. [ABSTRACT FROM AUTHOR]

This paper reports the results on the agronomic performance of organic amendments in the EU 7th FP project "FERTIPLUS—reducing mineral fertilizers and agro-chemicals by recycling treated organic waste as compost and bio-char". Four case studies on field-scale application of biochar, compost and biochar-blended compost were established and studied for three consecutive years in four distinct cropping systems and under different agro-climatic conditions in Europe. These included the following sites: olive groves in Murcia (Spain), greenhouse grown tomatoes in Almeria (Spain), an arable crop rotation in Oost-Vlaanderen (Merelbeke, Belgium), and three vineyards in Friuli Venezia Giulia (Italy). A slow pyrolysis oak biochar was applied, either alone or in combination with organic residues: compost from olive wastes in Murcia (Spain), sheep manure in Almeria (Spain), and compost from biowaste and green waste in Belgium and Italy. The agronomical benefits were evaluated based on different aspects of soil fertility (soil total organic carbon (TOC), pH, nutrient cycling and microbial activity) and crop nutritional status and productivity. All amendments were effective in increasing soil organic C in all the field trials. On average, the increase with respect to the control was about 11% for compost, 20% for biochar-blended compost, and 36% for biochar. The amendments also raised the pH by 0.15–0.50 units in acidic soils. Only biochar had a negligible fertilization effect. On the contrary, compost and biochar-blended compost were effective in enhancing soil fertility by increasing nutrient cycling (25% mean increase in extractable organic C and 44% increase in extractable N), element availability (26% increase in available K), and soil microbial activity (26% increase in soil respiration and 2–4 fold enhancement of denitrifying activity). In general, the tested amendments did not show any negative effect on crop yield and quality. Furthermore, in vineyards and greenhouse grown tomatoes cropping systems, compost and biochar-blended compost were also effective in enhancing key crop quality parameters (9% increase in grape must acidity and 16% increase in weight, 9% increase in diameter and 8% increase in hardness of tomato fruits) important for the quality and marketability of the crops. The overall results of the project suggest that the application of a mixture of biochar and compost can benefit crops. Therefore, biochar-blended compost can support and maintain soil fertility. [ABSTRACT FROM AUTHOR]

Separating dairy cattle slurry in a liquid and solid fraction (SF) is gaining more interest, since it enables a more targeted use of both fractions. However, the valorization of the SF is limited on P-rich soils, due to its high P content, and the export or use as bedding material requires sanitation. Therefore, we investigated the influence of composting or ensiling the SF, whether or not mixed with bulking agents, on the product quality in terms of fertilizer value, sanitation and stability. Ensiling can be considered as a controlled storage method for conserving C and nutrients. Soil amendment with co-ensiled SF resulted in a higher N mineralization and crop growth compared to amendment of co-composted SF. Co-composting SF with structure-rich feedstock materials optimized the composting process and sanitation when compared with composting pure SF and did not increase the risk for extreme-heat-resistant spores of thermophilic aerobic spore-forming bacteria (X-TAS). Further, the composts contained more P per unit of fresh weight than the silages, beneficial for the export of the composted SF. The oxygen uptake rate was found to be less powerful to determine the stability of fresh, composted and ensiled SF. [ABSTRACT FROM AUTHOR]

Highlights: [•] Long-term field experiment studying the effect of repeated farm compost amendment. [•] Chemical, biological and physical properties were integrated into a soil quality index. [•] Farm compost increased soil quality and crop yields. [•] Causal relationship between soil quality and crop production. [•] SOC was pointed out as the most important indicator influencing crop production. [Copyright &y& Elsevier]