Due to the environmental impact of using peat, there is social and political pressure to develop more sustainable growing media for horticulture. One possible option is a lignocellulosic fibrous material made from pulpwood residues after the hemicellulose has been removed in a non-chemical process for use as animal feed. The remaining substances are renewable organic materials that are less easily decomposed and may immobilize nitrogen to a lesser degree in plant production in comparison with ordinary wood fibre.

Plant and soil researchers at the Norwegian University of Life Sciences (NMBU) will use this material in close collaboration with industry partners to develop substrates that can replace peat in professional horticulture. They will determine the physical, chemical and biological properties in terms of stability and support of healthy plant production and consider the use of different additives such as biochar, seaweed etc. to develop strategies for reduced chemical pest control.

Preliminary results show that the wood fibre has the same pH as peat but contains less nutrients and has a very low cation exchange capacity (CEC). The wood fibre requires different watering regime than peat. The preliminary research results indicate that there are some compounds presents, which inhibit the germination and growth of the cucumber, possibly due to the production process.

Further, the environmental and economic sustainability of the production and usage of the new potting medium will be assessed through a life cycle assessment approach. To highlight the transdisciplinary nature of the project, the PeatFree research team will facilitate communication among project partners and throughout the greenhouse industry.  

This work investigates the potential of bamboo as a growing medium for soilless plant cultivation by evaluating its physical, chemical, and biological properties. Three different fractions of bamboo obtained by hammer milling were analyzed to determine their suitability, either as a pure medium or in combination with other materials.

Physical properties were determined by analyzing continuous water retention curve and hydration efficiency tests. Basic chemical properties pH and EC were measured. Finally, biological stability was assessed via CO₂ emission measurement in controlled environment.

This multi-aspect characterization using innovative methods revealed the strengths and weaknesses as well as possible improvements that could be made with a view to using bamboo as a growing media constituent.

A key component of the German climate change mitigation strategy is the rewetting of peatlands and their use for paludiculture. On raised bogs in Northern Germany Sphagnum farming is of special interest, in Southern Germany with a high proportion of fens, the focus is on plant species as Carex, Phalaris, Phragmites and Typha. Previous research revealed that the raw biomass is not suitable as a growing media constituent, due to high nitrogen immobilization and contamination with germinable seeds. Composting with the addition of ammonium sulfate or urea, as it is common practice for softwood bark, does reduce both problems, but causes high emissions of reactive N compounds to the atmosphere. Thus, it was tested, if composting is possible with the addition of nitrate N.

For the current research biomass of Carex, Phalaris, Phragmites and Typha was collected in late winter. The air-dried material was chopped and composted in composting boxes (1.8 m³). Calcium nitrate was added based on the actual amount of mineral N in the compost material and a short-term incubation experiment. The progress of the composting process was monitored by measuring the temperature as well as oxygen and carbon dioxide concentration in the heaps. At the end, chemical and biological properties of the composted materials were analyzed, and pot trials with basil were performed.

In principal, the composted materials are well suited as growing medium constituents. However, there are some weak points and pitfalls. First is the dosage of N quantities to counteract N immobilization. In the current research, it was too high, which led to N mineralization in the maturing phase. Second, the addition of high amount of Calcium during composting, partly caused Sulphur deficiency on basil. Pros and cons and further prospects of composted paludiculture biomass as growing medium constituent are discussed.

A very important chemical task in growing media is to adjust stability for fertilized N. The utilization of green waste composts is highly valued in growing media due to their role in the circular economy. However, the amount of green waste composts used in growing media industry is rather low, mainly due to the heterogeneity of raw materials, potential risk of salt stress and not at least problems with N stability. For obtaining substrate composts with a maximum positive effect on N stability we added clay before composting of green wastes in order to facilitate (i) an extensive formation of stable clay mineral-organic associations (chemical stabilization) and (ii) reduced accessibility of the organic matter for microorganisms by covering them with clay-mineral-platelets (physical separation). Both effects of clay minerals are the basis for the protection of plant organic matter and necromass of microorganisms against microbial degradation. Upon addition of clay to green wastes before composting in amounts adjusting 40 kg clay /m³ substrate compost, low amounts of water dispersable clay were observed for the substrate composts. Here clay minerals are stable associated with compost compounds, which resulted from the decomposition of plant biomass and the build-up of microbial biomass. From separation of density fractions it was derived that a high share of mineral-organic associations with a low C/N ratio formed, suggesting a significant role of mineral-organic associations on the total N balance of composts. The coating of poorly degradable organic compounds in mature composts with clay-platelets can be an important mechanism for preventing further N-consumption by microbial degradation in the cultivation period. The experiments show that clay amendments can be an important measure for improving cultivation safety in peat-reduced and peat-free growing media. Clay additions can increase the quality of composts and hereby improve their suitability for growing media industry.