中文摘要：

利用土壤的介电特性测量土壤含水量是一种快速、简便、可靠的方法.根据频域反射（FDR）法测量原理,电磁波在土壤中的传播频率可用来测试土壤的介电常数,从而得到土壤容积含水率,设计出了一种基于FDR原理的自动灌溉系统,介绍了FDR测量原理,阐述了自动灌溉系统的软硬件构成,土壤水分传感器测得的土壤水分含量信息,经信号处理,输出为0～5V电压信号,经A/D转换送至AT89S52单片机进行判断处理,根据输出数值的大小控制电磁阀的通断时间,从而实现自动灌溉和节水灌溉的目的.试验表明：该系统工作稳定,控制准确,反应灵敏,满足自动灌溉要求.

英文摘要：

It is a rapid,simple and reliable method to measure soil moisture content using dielectric property of soil.Based on the lrinciple of frequency domain reflectometu（FDR）,the soil dielectric constant can be tested by the travel frequency of electromagnetic waves in soil,and the soil volumetric water content will be obtained.A set of an automatic irrigation system is designed based on FDR.The theory of FDR is briefly introduced,the hardware and software components of the automatic irrigation system are explained.The soil water content information measured by the soil moisture sensor converts to 0 ～5 V voltage signal by signal processing,after analog to digital （A/D） conversion,sent to single chip AT89S52,control on-off time of solenoid valve according to output value to realize automatic irrigation and water-saving irrigation.Experiment shows that this system is stable,accurate and sensitive,satisfies the requirements of automatic irrigation.