Influence on plant growth of carbon sources, pyrolysis- and HTC-biochar, as additives to carbon-poor-soils

Worldwide, the low and decreasing carbon-content of agricultural soils is an obstacle to sustainable plant production. Just as peoples thousands of years ago initiated “Terra Preta”, an anthropogenic fertile tropical soil, investigations have started to imitate this phenomenon using different sources of biochar carbonisates, through pyrolysis of wooden biomass and hydrothermal carbonization (HTC) of different resources.Durable carbonisates can be produced by using side chain and waste products -e.g. digestates, sewage sludge, plant biomass, and biological waste among others- through the HTC process. These products can increase soil carbon and soil fertility. Soil C-content has an impact on plant growth, and influences soil microorganism communities. Soil C-content is a major factor influencing the water-holding and ion-exchange-capacity of soils, influencing water and nutrient supply to plants. CO2-sequestration through durable carbonisates could increase the C-content of agricultural soils. Cultivation of degraded and C-poor soils with carbonisates could therefore increase soil fertility and plant productivity.Here we show the results of pot experiments testing the effect of adding HTC-biochar, pyrolyse-biochar and a mixture of both, to soil, on maize growth. The three treatments promoted the shoot and root growth of maize seedlings, e.g. between 20 and 50% higher shoot dry matter of 40 days old plants. The strongest effect on shoot growth and on the root system was caused by the mixture. The results suggest that durable carbonisates from waste may increase the growth and resource efficiency of maize.Future agricultural and horticultural production systems have to fulfil the demand for being high yielding, sustainable, and resource efficient, including reduction of carbon emissions. Efficient carbon (C, CO2) utilization with durable carbonisates from waste products could be a key for a future sustainable bioeconomy