Changes in abundance and composition of nitrifying communities in barley (Hordeum vulgare L.) rhizosphere and bulk soils over the growth period following combined biochar and urea amendment

To understand the effects of biochar and urea on soil N availability and plant growth, we conducted a pot experiment growing barley (Hordeum vulgare L.) under six treatments: control (N0), soil with 30 g kg−1 biochar (N0B), soil with 0.23 g kg−1 urea (N1), soil with 0.23 g kg−1 urea and 30 g kg−1 biochar (N1B), soil with 0.46 g kg−1 urea (N2), and soil with 0.46 g kg−1 urea and 30 g kg−1 biochar (N2B). The nitrifying community abundance and compositions in rhizosphere and bulk soils were analyzed using quantitative polymerase chain reaction (qPCR) and amplicon-based Illumina Hiseq sequencing. Adding urea with biochar (N1B) produced the greatest increase in above- and belowground plant biomass, followed by doubling the amount of urea with biochar (N2B); both treatments raised pH (p