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Effects of different long-term fertilizer treatments on soil autotrophic azotobacter (a) and soil nitrogenase activities (b). MF: Chemical fertilizer alone; RF: Rice straw residue and chemical fertilizer; OM: 30% organic manure and 70% chemical fertilizer; CK: Unfertilized as a control. Error bars were represented standard error of mean. Different lowercase letters were indicated significantly different at p<0.05 level. The same as below.
