圆形喷灌机启闭时段对喷洒化学液均匀性的影响

圆形喷灌机采用比例法喷洒化学液，引用赫尔曼—海恩(Heermann-Hein)公式计算喷洒化学液均匀系数。喷洒化学液开始和结束时，由于配置在输水管上的喷头喷洒化学液的起始时间不同，造成了局部面积内喷洒化学液的不均匀性。该文提出了圆形喷灌机从输水管第一个喷头开始喷洒化学液至最末喷头开始喷洒化学液的间隔时间内，每个喷头喷洒时间的计算公式。计算结果表明当圆形喷灌机输水管布置喷头总数为80～200时，在首末喷头喷出化学液的时间段内，有效喷洒化学液面积约占此时段内总扇形灌溉面积的1/2。为提高喷洒化学液的均匀性，提出了圆形喷灌机喷洒化学液的正确操作步骤。

Effect of start/stop time on uniformity of chemigation for center pivot

Center pivot systems usually use proportional method for chemigation. The uniformity coefficient of chemical applied can be calculated using the modified formula of Heermann and Hein. When chemigation starts or stops, the chemical applied by the sprinklers along the lateral is not uniform, which will result in a bad uniformity in the chemical application area. A new mathematical equation, for calculating the amount of net water applied by each sprinkler between the time interval of the first sprinkler and the last one beginning to apply chemical, is proposed in this paper. By using the developed equation, a derived result indicated that as the total number of the sprinklers along the lateral ranges from 80 to 200, the effective chemical area is about one half of the total fan-shaped irrigated area during the time interval. In order to improve the chemigation uniformity, a proper procedure of operating the center pivot is presented.