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Peat replacement by compost in growing media can increase the sustainability of soilless cultivation. Compost, when mixed into growing media, is a source of fiber, i.e., a rooting medium, as well as an important source of nitrogen (N), phosphorus (P) and potassium (K). Physical properties as well as nutrient levels in growing media are known to affect plant growth and health. Therefore we monitored the evolution of nutrient release in compost-amended growing media for strawberry in greenhouse culture with drip fertigation for a double cropping system of cv. Elsanta, i.e., autumn culture with continued culture in spring. Compost amended and other alternative growing media for strawberry production were tested during four years of trials at full-scale level in a professional greenhouse growing system, in order to optimize the new cropping system with alternative substrates. Compost amended substrates contained 20–100% (v/v) compost, with different compost types tested. We assessed effects on yield and nutrients, i.e. nutrient availability in the substrate, uptake in the plants, and losses with the drainage water, as well as effect on diseases and pests (infection by powdery mildew (Podosphaera aphanis), aphids (Chaetosiphon fragefolii), and the anthracnose pathogen (Colletotrichum acutatum)). Adding compost to growing media has potential to increase the sustainability of soilless strawberry culture. Results show that growing strawberries on alternative substrates is feasible, but the substrate mixtures containing compost required adjusted fertigation due to nutrients supplied by the compost. This study revealed that strawberry plants made highly efficient use of the P and K in the compost when P and K input by fertigation was reduced, and that compost addition results in reduced export and potential losses of nutrients with the drain water and spent growing media. In general, the compost-amended substrates with lower N fertigation performed well as a growing medium during the autumn culture, but in the continued spring culture, these substrates needed an adapted fertigation regime for N, P and K. The N supply by the tested composts during the autumn culture allowed for significant reductions in N supplied by fertigation, i.e., 50% reduction when 100% (v/v) compost was used, and 10% reduction when 20% (v/v) compost was used. Degree of infection with powdery mildew and aphids was strongly positively correlated with the N status of the crop, pointing at the risks of high N supply for the crop. At the end of the autumn culture, no significant positive or negative effect of the compost treatments on the latent survival of C. acutatum on the strawberry leaves was found.

We investigated the potential of C-rich byproducts to replace wood chips as bulking agent (BA) during composting. The impact of these alternatives on the composting process and on compost stability and characteristics was assessed. Three BA (chopped heath biomass and spent growth media used in strawberry and tomato cultivation) were used for processing leek residues in windrow composting. All BA resulted in stable composts with an organic matter (OM) content suitable for use as soil amendment. Using chopped heath biomass led to high pile temperatures and OM degradation and a nutrient-poor compost with high C/P ratio appropriate for increasing soil organic carbon content in P-rich soils. Spent substrates can replace wood chips, however, due to their dense structure and lower biodegradation potential, adding a more coarse BA is required. Generally, the nutrient content of the composts with growth media was higher than the composts with wood chips and chopped heath biomass.

Farmers have to combine several measures to balance carbon contents in the top soil to preserve soil quality but potentially increasing the risk for N and P losses by leaching. We studied the effect of a combination of several measures on topsoil C content, nutrient leaching and soil quality in a multi-year field trial. Soil quality was defined as the result of the interaction between chemical, physical and biological soil characteristics, and included an assessment of disease suppressiveness as well. Initially, the soil had a suboptimal C content (i.e. 0.81%). Soil organic carbon (SOC) levels were maintained and slightly increased by applying slurry and good agricultural practices such as the use of cover crops and the incorporation of cereal straw (on average +0.04 percentage point). Only with a yearly extra plant-based farm compost amendment SOC levels were substantially increased after a period of four years (on average +0.17 percentage point). This application of 8.3 Mg C ha−1 also improved chemical, physical and biological soil quality. Our research demonstrates that farmers can use compost, for at least 4 years, on top of cattle or pig slurry application to soils with suboptimal C levels to increase C content in the top soil, without inducing higher N and P leaching. Repeated compost application increased the microbial biomass (measured by means of PLFA) and disease suppressiveness against Botrytis cinerea on lettuce. There was no effect on the abundance of the plant-parasitic nematode Pratylenchus penetrans in the soil, nor on disease severity caused by Dickeya solani, Streptomyces scabies and Rhizoctonia solani after a potato cropping. Differences between tillage practices were most obvious in the 0–10 cm soil layer as non-inversion tillage (compared to ploughing) resulted in an increase in SOC, Total N, hot-water extractable C and P, plant-available P and K, aggregate stability, earthworm abundance and bacterial and fungal populations in this layer.

Maintaining and increasing soil quality and fertility in a sustainable way is an important challenge for modern agriculture. The burgeoning bioeconomy is likely to put further pressure on soil resources unless they are managed carefully. Compost has the potential to be an effective soil improver because of its multiple beneficial effects on soil quality. Additionally, it fits within the bioeconomy vision because it can valorize biomass from prior biomass processing or valorize biomass unsuitable for other processes. However, compost is rarely used in intensive agriculture, especially in regions with high manure surpluses. The aim of this research is to identify the barriers to on-farm composting and the application of compost in agriculture, using a mixed method approach for the case of Flanders. The significance of the 28 identified barriers is analyzed and they are categorized as market and financial, policy and institutional, scientific and technological and informational and behavioral barriers. More specifically, the shortage of woody biomass, strict regulation, considerable financial and time investment, and lack of experience and knowledge are hindering on-farm composting. The complex regulation, manure surplus, variable availability and transport of compost, and variable compost quality and composition are barriers to apply compost. In conclusion, five recommendations are suggested that could alleviate certain hindering factors and thus increase attractiveness of compost use in agriculture.

Soil quality in vegetable cropping systems is seriously threatened by intensive tillage and fertilization practices and by limited crop rotations. Inclusion of cover crops, compost application and reduced tillage may help to sustain soil quality. A three-year field trial was set up on horticultural land to explore the combined effects of compost amendment at three rates (0, 15 and 45 Mg ha−1 year−1) and tillage practices (reduced tillage versus conventional ploughing) on soil quality. Cover crop was not a factor in the experiment, but cover crops were included in the rotation for reasons of good agricultural practice. The highest compost dose supported the initial level of total organic carbon in the arable layer. The decrease in pH in the arable layer was considerably limited by compost application, irrespective of the dose applied. Reduced tillage resulted in a favorable stratification for different soil quality indicators both by placement of organic inputs near the soil surface and by a reduction of leaching of base cations and organic carbon compounds. Differences between tillage practices and compost doses were most striking in the 0–10 cm soil layer. Compost application at the highest rate enhanced organic C content by 16% compared to the content in the non-amended soil. Reduced tillage induced a 13% higher organic C content in the 0–10 cm soil layer than that in the underlying 10–30 cm layer. Combining reduced tillage and recurrent compost application resulted in a different soil microbial community structure in the 0–10 cm surface layer, as revealed by phospholipid fatty acids analysis. Total microbial biomass was 44% higher under reduced compared to conventional tillage and increased by 27% due to compost application at a rate of 45 Mg ha−1 year−1. Fungal biomass doubled in the surface layer by reduced tillage. Actinomycetes and arbuscular mycorrhizal fungi were favored by both reduced tillage and compost application. Conversion to reduced tillage allowed for sustaining crop production in this intensive vegetable cropping system. Compost application and reduced tillage counteracted soil degradation.

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.

Farm composts were produced from selected feedstocks and compared to one external farm compost and one green waste compost. Nematodes were omnipresent in the composts (on average 26 ind./g dry weight compost) and many taxa were common to all composts (i.e. Mononchoides composticola, Diploscapter coronatus, Halicephalobus gingivalis, Ditylenchus sp., Diplogaster sp., Diplogastrellus sp. and Diplogasteritus sp.) and occurred in similar proportions. Composts with a somewhat different species composition or proportion also displayed differences in the abiotic parameters, suggesting that compost maturity and status may be reflected by the nematode community. Significant differences (ANOSIM, p = 0.001) in nematode community between the farm composts and the green waste compost were found. Nevertheless, despite largely different feedstock materials and proportions, and despite clear differences in chemical properties and stability of the composts, biologically very similar composts were produced. The 11 composts of different composition were further tested in an incubation experiment to investigate their short-term effect on the existent soil nematode community and on the soil chemical properties. Therefore, the nematode community together with several abiotic parameters (pH, EC, DM, OM, Ptot, C/N, and NO3/NH4) of the used composts and the soils before and 12 weeks after compost amendment, were analyzed. All compost amendments resulted in a significant pH increase in the soil (one-way ANOVA, p