No Effect Level of Co-Composted Biochar on Plant Growth and Soil Properties in a Greenhouse Experiment

It is claimed that the addition of biochar to soil improves C sequestration, soil fertility and plant growth, especially when combined with organic fertilizers such as compost. However, little is known about agricultural effects of small amounts of composted biochar. This greenhouse study was carried out to examine effects of co-composted biochar on oat (Avena sativa L.) yield in both sandy and loamy soil. The aim of this study was to test whether biochar effects can be observed at very low biochar concentrations. To test a variety of application amounts below 3 Mg biochar ha −1 , we co-composted five different biochar concentrations (0, 3, 5, 10 kg Mg −1 compost). The biochar-containing compost was applied at five application rates (10, 50, 100, 150, 250 Mg ha −1 20 cm −1 ). Effects of compost addition on plant growth, Total Organic Carbon, Ntot, pH and soluble nutrients outweighed the effects of the minimal biochar amounts in the composted substrates so that a no effect level of biochar of at least 3 Mg ha −1 could be estimated.