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As the center pivot irrigation system requires high fertigation uniformity, a kind of proportional fertilizing device was adopted in order to make the injection flux of fertilizer solution stable. A fertilizer injection device with plunger pump was designed. Based on the orifice size and installation location of injection check valve, and power frequency of plunger pump, field experiments on a center pivot irrigation system with fertilizer injection device were carried out to evaluate fertigation uniformity. The results indicated that when the center pivot irrigation system stopped and the plunger pump worked with power frequency of 50Hz, the Christiansen uniformity coefficient CU and variation coefficient CV of fertigation ranged from 99.00% to 99.65% and from 0.46% to 1.37% respectively under the combination of three orifice diameters and three installation locations. The maximum CU could be obtained by using the injection check valve with the orifice diameter of 2.5mm and the installation positioned at the horizontal inlet pipe. And when the center pivot irrigation system ran, the Heermann-Hein uniformity coefficient of fertigation C*UH with single line catchcans ranged from 88.77% to 90.66%, which indicated that the center pivot irrigation system can obtain high fertigation uniformity with the fertilizer injection device. In addition, the fertigation uniformity was compared with plunger pump working at power frequency and nonpower frequency of 46Hz. It was found that the average electrical conductivity of fertilizer solution had a significant positive correlation with the power frequency. Thus, changing the power frequency of plunger pump can provide an effective way to achieve high uniformity of variable rate fertigation for the center pivot irrigation system.