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　＜　0.001)　and　lowered　extractable　N　in　the　rhizosphere　(p　＜　0.05).　N1B　treatment　produced　the　greatest　increase　in　ammonia-oxidizing　bacteria　(AOB)　amoA　gene　copies,　presumably　because　the　combined　amendment　raised　soil　pH,　which　favored　AOB　access　to　NH4+.　Nitrifier　sequences　were　selected　after　blasting　with　reported　nitrifiers　in　NCBI　(similarity　＞=　97%).　Nitrosospira　dominated　AOB　communities　during　the　plant　seedling　stage;　however,　during　the　mature　stage,　Nitrosomonas　dominated　over　Nitrosospira　and　the　nitrite-oxidizing　bacteria　(NOB)　community　became　diverse.　Redundancy　analysis　indicated　that　nitrifying　community　composition　was　affected　by　multiple　soil　properties,　including　N　availability　(i.e.,　exchangeable　NH4+　and　NO3-)　and　soil　chemistry　(i.e.,　pH,　dissolved　organic　C,　and　exchangeable　base　cations).　Our　research　suggests　a　positive　application　of　combining　biochar　with　urea　in　improving　N　bioavailability　and　promoting　plant　growth　in　the　acidic　soil.