Impact of a woody biochar on properties of a sandy loam soil and spring barley during a two-year field experiment

Biochar is often proposed to increase soil quality and crop yield, while sequestering carbon. Despite the growing number of studies in temperate regions, the claimed positive effects are still unsure for northwestern European soils. Moreover, there is a need to upscale results from lab and pot studies in these soil types to field experiments. The objectives of this study were therefore to investigate the effect of biochar application to a temperate agricultural soil on soil chemical, physical and biological properties, and on crop growth and nutrient uptake under field circumstances. A field trial, located in Merelbeke (Belgium), was established in October 2011 and monitored until August 2013. The biochar applied was produced from a mixture of hard- and softwood at 480 °C. The biochar dose was 0 (control) or 20 t ha−1 (on dry weight basis). Over two years, biochar addition to soil did not affect soil chemical properties, except for organic carbon content and C:N ratios. Effects on bulk density, porosity and soil water retention curves were non-consistent over time, possibly due to interaction with tillage operations. Biochar increased soil water content in 2012, although mostly not significantly. However, in 2013, when soil water content was overall lower compared to 2012, it was not affected by biochar addition. Soil temperature, as measured at a soil depth interval of 8–20 cm, was not changed by biochar addition. Furthermore, biochar addition to soil did only slightly influence soil microbiological community structure during the first year after biochar application, as only certain bacterial biomarker PLFAs were significantly affected by biochar addition, but no fungal biomarker PLFAs. Hence, it was not surprising that biochar addition did not affect crop yield, N or P uptake during the first two years after biochar application.