Effects of applying biogas liquid manure on the key source-sink metabolism enzymes and grain yield of summer maize]

15000, 22500, and 30000 kg x hm(-2) of biogas liquid manure were applied to maize hybrid Zhengdan 958 to study their effects on the key source-sink metabolism enzymes and yield components of the summer maize. Compared with CK and applying nitrogen fertilizer, the application of biogas liquid manure not only increased the aboveground biomass, leaf area index (LAI) and chlorophyll content, but also enhanced the activities of nitrate reductase (NR), glutamine synthetase (GS), and sucrose phosphate synthetase (SPS) in leaves and the sucrose synthetase (SS) in grains. The yield parameters such as ear diameter, ear length, grain rows per ear, grains per row, kernels per ear, 1000-kernel mass, and grain yield per unit area were also increased significantly. Of the three test application rates, 22500 kg x hm(-2) (7500 kg x hm(-2) applied at jointing, big trumpet, and tasseling stages, respectively) had the best effects on enhancing the above mentioned enzyme activities and grain yield, with the yield reached 14006.7 kg x hm(-2) and being 40.7% higher than the control.