Synergistic use of peat and charred material in growing media–an option to reduce the pressure on peatlands?

Peat is used as a high quality substrate for growing media in horticulture. However, unsustainable peat extraction damages peatland ecosystems, which disappeared to a large extent in Central and South Europe. Furthermore, disturbed peatlands are becoming a source of greenhouse gases due to drainage and excavation. This study is the result of a workshop within the EU COST Action TD1107 (Biochar as option for sustainable resource management), held in Tartu (Estonia) in 2015. The view of stakeholders were consulted on new biochar-based growing media and to what extent peat may be replaced in growing media by new compounds like carbonaceous materials from thermochemical conversion. First positive results from laboratory and greenhouse experiments have been reported with biochar content in growing media ranging up to 50%. Various companies have already started to use biochar as an additive in their growing media formulations. Biochar might play a more important role in replacing peat in growing media, when biochar is available, meets the quality requirements, and their use is economically feasible. © 2017 The Author(s) Published by VGTU Press and Informa UK Limited, [trading as Taylor & Francis Group]

Synergistic use of peat and charred material in growing media – an option to reduce the pressure on peatlands?

Peat is used as a high quality substrate for growing media in horticulture. However, unsustainable peat extraction damages peatland ecosystems, which disappeared to a large extent in Central and South Europe. Furthermore, disturbed peatlands are becoming a source of greenhouse gases due to drainage and excavation. This study is the result of a workshop within the EU COST Action TD1107 (Biochar as option for sustainable resource management), held in Tartu (Estonia) in 2015. The view of stakeholders were consulted on new biochar-based growing media and to what extent peat may be replaced in growing media by new compounds like carbonaceous materials from thermochemical conversion. First positive results from laboratory and greenhouse experiments have been reported with biochar content in growing media ranging up to 50%. Various companies have already started to use biochar as an additive in their growing media formulations. Biochar might play a more important role in replacing peat in growing media, when biochar is available, meets the quality requirements, and their use is economically feasible.Peer reviewe

Biochars in soils : towards the required level of scientific understanding

Key priorities in biochar research for future guidance of sustainable policy development have been identified by expert assessment within the COST Action TD1107. The current level of scientific understanding (LOSU) regarding the consequences of biochar application to soil were explored. Five broad thematic areas of biochar research were addressed: soil biodiversity and ecotoxicology, soil organic matter and greenhouse gas (GHG) emissions, soil physical properties, nutrient cycles and crop production, and soil remediation. The highest future research priorities regarding biochar's effects in soils were: functional redundancy within soil microbial communities, bioavailability of biochar's contaminants to soil biota, soil organic matter stability, GHG emissions, soil formation, soil hydrology, nutrient cycling due to microbial priming as well as altered rhizosphere ecology, and soil pH buffering capacity. Methodological and other constraints to achieve the required LOSU are discussed and options for efficient progress of biochar research and sustainable application to soil are presented.Peer reviewe

Critical review of chemical properties of biochar as a component of growing media

The objective of this review is to critically asses the chemical characterization of biochar when it is used as a component in growing media and indicate the recommend parameters which could improve its use as component of growing media. In some earlier work on biochar little attempt was made to characterize the biochar and plant growth trials were done on an empirical basis. However, even recently, in growing trials biochar is chemically characterized only for pH, electrical conductivity (EC) and total macro and micronutrients. Only limited papers have presented available (extractable) nutrients. This is surprising since biochar can contain significant amounts of extractable nutrients and adjusting for this would be in our opinion important as it is unclear whether positive or negative response of plants is due to these or due to intrinsic properties of biochar such as specific surface area or nutrients. The methods used for pH and EC determination however have been numerous, from saturation paste extract, press extract, pour through method, various water extracts (1:1.5, 1:5, 1:10, 1:100, 2:1) and some on weight/volume and some on volume/volume ratio. Obviously, these methods will give different values especially regarding EC. In general, pH adjustment of peat by biochar has been suggested. However, it misses the point that peat, woodfibre and coir not only need pH adjustment but also require adequate levels of Ca and Mg, the uptake which can be exacerbated by high levels of K present in most biochars. Regarding available nutrients again there is a plethora of tests used, mostly water extraction often done on the same extract as for pH and EC. However, it has been shown that the CAT extractable method is closely related to plant uptake of N and P in peat/biochar media probably because it takes into account the strong buffering ability of biochar. In any case it is important to know precisely the available nutrient content in biochar for nutrient management as biochar can be a significant source of nutrients (often depending on feedstock and processing conditions). Only few papers have considered this response. It has been also shown recently that different fractions of biochar can contain different levels of macronutrients, and this has hardly been taken into account. We will show that biochar addition at low rates can reduce the EC in fertilized peat composted greenwaste (CGW) and spent mushroom compost. The reduction in EC was related to the specific surface area of the biochar. Very preliminary results also showed that addition of biochar can improve the seedling vitality index in “phytotoxic” composted green waste

Comprehensive evaluation and development of Irish compost and digestate standards for heavy metals, stability and phytotoxicity

Abstract: Recent EU circular economy, bioeconomy policies and the New Green Deal promote the recycling of organic wastes into soil improvers and fertilisers, thereby reducing the use of mineral fertilisers. This has renewed interest in the use of compost and digestate as fertilisers. At the same time, the Russian invasion of Ukraine has strengthened the demand for sustainable domestic fertilisers to guarantee the security of supply. It is now more important than ever that quality standards in Ireland are fit for the purpose of aiding the sustainable local production of fertilisers. Quality standards for compost and digestate ensure and protect the environment. This study collated the results of the analysis of Irish compost and digestate samples and made comparisons of the Irish data to databases, reports and standards from other countries, including the EU Fertiliser Products Regulation 2019/1009. This paper, therefore, provides comprehensive information on heavy metal, stability and phytotoxicity standards from a number of European and other countries. In addition, it includes actual data on these parameters from Ireland and a few European countries. From this collation and comparison process, we propose to update the heavy metals and stability limits in the Irish compost standard (IS 441) and heavy metals and stability limits in a new digestate standard (whole, liquid and fibre). Our methodology and collated data can be used as templates for countries, especially in Europe, which have not developed their own standards. Having an updated compost quality standard supports the development of a circular economy while still respecting the precautionary principle of avoiding pollution when compost and digestate are used on the soil.</p

Biochar type, ratio, and nutrient levels in growing media affects seedling production and plant performance

Biochar can be used as an alternative component in growing media, positively affecting plant growth/yield, but also media properties. In the present study, two commercial grade biochars (BFW-forest wood; and BTS-fresh wood screening), mainly wood-based materials, were used at 7.5% and 15% (v/v), adding nutrient in two levels (100% and 150% standard fertilizer level-Fert). Biochar affected growing media properties, with increases on pH and changes on the nutrient content levels. Biochar BFW enhanced the emergence of seeds in comparison to the control. Increased fertilizer levels benefited plant yield in BFW and BTS at 7.5%, but not at 15%. Leaf stomatal conductance was reduced at 150% fertilized biochars (BFW + Fert and BTS + Fert) at 7.5%, while total chlorophylls increased at BTS + Fert at 7.5% and 15%. The addition of biochars decreased the antioxidant activity in the plant. Lipid peroxidation in lettuce was increased in most cases with the presence of biochars (BFW, BTS) and 150% fertilization, activating antioxidant (superoxide oxidase and peroxidase) enzymatic metabolisms. The addition of Biochars in the growing media increased the content of nutrients in seedlings, as plants could absorb more available nutrients. Biochar of beech, spruce, and pine species (BFW) at 7.5% was more promising for substituting peat to produce lettuce seedlings. However, examining different species (tomato, leek, impatiens, and geranium) with BFW at 7.5%, the results were not common, and each species needs to be evaluated further

Chemical characterization of biochar and assessment of the nutrient dynamics by means of preliminary plant growth tests

Biochar can be produced from several organic sources with varying nutrients and metal concentrations. Four commercial grade biochars were evaluated as peat substitute. Biochars were characterised for plant nutrients and for biological stability. The results showed that there were negligible quantities of N and P and generally high levels of K and high biological stability. When these materials were mixed with peat at 10, 25 and 50% and nutrients were added to bring them to the same level of nutrients as in fertilized peat, it was found that biochar mixtures considerably reduced the levels of calcium chloride/DTPA (CAT) extractable N (including nitrate), P, and electrical conductivity- greater extent with higher rates of biochar addition except for K. The pH and K levels were increased with biochar addition. The drop in EC has important implications regarding the use of other materials used to dilute peat, for example, composted green waste, the rate of dilution is limited due to high EC and biochar addition gives the potential for higher peat dilution of these materials. Nitrate and phosphorus are very vulnerable to leaching of these nutrients in the environment in peat substrates and the binding of these by biochar has implication for leaching and nutrient application strategy. Root development using Cress test and tomato plant height and biomass using containers, were in some cases better than peat indicating that biochar could be used to dilute peat e.g. for seedling production where root development and rapid growth are very important. Application of biochars resulted in a marked reduction of N (and P) in the plant. There were significant correlation between CAT extractable N and P and corresponding plant concentration, indicating the standard growing media test, CAT, would be suitable for assessing the nutrient status of peat biochar mixes