The potential for large-scale implementation of biochar in the agricultural sector : a quantitative study on plant growth in light soils and a qualitative study on the agricultural sector’s perception on biochar

Abstract: Agricultural activities are collectively one of the largest contributors to accumulation of greenhouse gasses (GHG). At the same time, agriculture is at a risk to be affected extensively by climate change. Concurrently, in conventional agriculture GHG emissions have become inevitable to maintain efficiency. Therefore, to maintain agricultural production, systems change will be paramount. Biochar is regarded a carbon dioxide removal (CDR) technology according to the IPCC and has been observed to contribute to agricultural production. However, for biochar to be adopted in Swedish agriculture benefits need to be derived. At present, most research have been conducted in tropical regions and therefore more research is needed in temperate regions. At the same time, introducing new practices in agriculture require agricultural actors’ perception, not in the least farmers, on the intended new practice. Reading the literature on biochar, a knowledge gap was identified regarding the contemporary discussion on biochar in the Swedish agricultural sector. From these views it was decided to conduct a transdisciplinary study, including one quantitative and one qualitative part, on the potential for large-scale implementation of biochar in the agricultural sector in Sweden. The quantitative part was conducted as a pot trial and aimed at studying how different biochar concentrations (BC): 0 ton/ha (reference soil), 10 ton/ha, 20 ton/ha, 30 ton/ha and 50 ton/ha, might influence soil properties and plant growth. Soil used in the study was sandy loam. Studies on the effect of biochar on soil properties showed that (I) bulk density decreased significantly with increasing BC (p-value < 0.001), (II) compact density slightly decreased with increasing biochar (p-value < 0.001) where the greatest difference was between BC of 20 and 30 ton/ha, (III) porosity did not show a significant difference (p-value > 0.05) and (IV) neither did water holding capacity (WHC) (p-value > 0.05). The same went for (V) pH and (VI) conductivity showing no distinctive difference between treatments. The study on plant growth was divided into two parts. One part was treatments with just the different BC mixtures and the other were the different BC with added NPK (equal amount of NPK in all pots), sown with spring barley. Results from the germination rate (GR) test showed that increasing amount of BC delayed GR, for both treatments with and without NPK. However, all treatments had reached at least 90% GR on the eighth day after sowing (DAS, thus the last day of counting). According to the results from plant height, in treatments without NPK plant height significantly decreased with increasing BC. In treatments with NPK, the relationship was the opposite even though not as distinct. In reference soils and BC of 10 ton/ha, both with and without NPK, there was not a significant difference in plant height. At the same time, reference soil, BC of 10 ton/ha and BC of 20 ton/ha with NPK developed more tillers than BC of 30 and 50 ton/ha. Furthermore, spring barley in treatments with BC of 20, 30 and 50 ton/ha without NPK did not develop ears by the eighth DAS, whereas reference soil and BC of 10 ton/ha did. Spring barley in treatments with NPK did all develop ears and the number of ears increased significantly with higher BC. However, considering that spring barley with lower BC developed more tillers, there is a possibility that these plants would have a greater number of ears if given more time to develop. Fresh and dry weight also showed a significant decrease with increasing BC, firmly for treatments without NPK. Treatments with NPK diverged in the dry weight test showing that there was no significant difference between treatments. The qualitative part aimed to gain deeper knowledge on the contemporary discussion on biochar of farmers, farmer’s counsellors and biochar producers and entrepreneurs. This study was conducted through semi-structured interviews. Parameters studied were the actors’ attitude towards biochar, their view on biochar as an integrated part of agricultural systems, the role of biochar in an agricultural system. Furthermore, the aim was to identify ideas for sustainable biochar production and application systems and incentives, practically and economically, for large-scale implementation of biochar. From the interviews it was indicated that the general attitude towards biochar implementation is positive, but respondents also stressed the importance of creating a biochar system with high regards to environment and economy to ensure a long-term sustainability of both production and application. Questions regarding economic aspects were viewed upon as mostly challenging considering biochar being an expensive product and that more research is required to understand in what context biochar is mostly preferrable. Respondents mentioned contexts of light and poor soils, in production systems of speciality crops, and in animal production systems. To ensure resource efficiency respondents stressed the possibility to connect biochar with e.g., energy production and use biomasses that does not already have a primary value and thus promote research for the possibility to use societal waste products.