Effects of soil incorporation depth of Biodiesel Co Product (BCP) additions on N leaching losses and on genes involved in soil nitrogen cycling in an acidic Chinese tea soil

Effectiveness of Biodiesel Co Product (BCP) in decreasing N leaching from an acidic soil (pH 3.7), effects on greenhouse gas emissions and N functional genes following surface application (0-6 cm depth) and complete mixing (0-18 cm depth) of 1.5 mg BCP-C g-1 soil was investigated in a 35 day laboratory lysimeter experiment. The BCP additions significantly decreased AOA and AOB amoA gene copy numbers, especially from the surface BCP application. Both methods therefore inhibited nitrification and decreased N leaching. Microbial biomass N and C significantly increased following both types of BCP incorporation, particularly with surface mixing. BCP increased nifH genes with both applications. Surface application of BCP produced higher emission rates of N2O and CO2 than complete mixing. Based upon (nirS+nirK)/nosZ ratios, more N2O emissions, caused by denitrification, came from the surface application than complete mixing, in support of the gaseous measurement of N2O. However, complete mixing was more effective than surface BCP application in decreasing N leaching: 2.14% of 15 32 N fertilizer in the leachate from complete mixing, compared to 51% following surface application, and 68% without BCP addition. These findings demonstrate that complete mixing was more effective than surface BCP application in decreasing N leaching and gaseous losses. We conclude that BCP is an effective and biologically safe method to prevent nitrate leaching in this acidic Chinese soil.