The use of compost and biochar to increase soil organic carbon content without increasing nutrient leaching

Carbon addition to the soil is beneficial for a wide range of chemical, physical and biological soil properties. However, the restricted use of organic fertilizers related to the nitrate directive constrains the built-up of stable soil organic carbon (SOC). Both compost and biochar have high contents of stable carbon and can be incorporated in the soil to improve soil quality. Therefore, two long term experiments (BOPACT and BIOCHAR) were established on nearby fields at ILVO to investigate if SOC, overall soil quality and crop yield can be increased by adding compost, biochar or biochar/compost blends to the soil without increasing N leaching. BOPACT (started in spring 2010) has a strip split plot design with three factors and four replications. The factors are 1) slurry application (cattle vs pig slurry), 2) tillage practices (ploughing vs non-inversion tillage), and 3) compost application (0 vs 2 ton C/ha.year). BIOCHAR (started in spring 2011) has a completely randomized design with four replicates comparing the application of a woody biochar (Romchar) with a control treatment. In the fall of 2012, the application of another woody biochar (Refoak650) was included in the experiment. Our results indicated that for both compost and biochar (Romchar) application the change in SOC content was significantly (p<0.05) higher compared to no amendment after three and one year, respectively. Moreover, both amendments did not increase the risk for N leaching in fall. As the experiments are still ongoing, we will continue to monitor the SOC evolution, nutrient dynamics and crop growth.