Abstract: Based on the daily observation data and experiment data in Gucheng experimental station of Chinese Academy of Meteorological Sciences,the spatial and temporal variation of soil moisture in irrigated farmland was analyzed.The results showed that soil moisture changed as one year cycle.Soil moisture in the depth 0-50cm fluctuated significantly,which could reflect soil moisture condition in 0-200cm soil layer,as soil moisture below 60cm changed little.So soil moisture monitoring should concentrate to the depth 0-50cm.Multi-point repeat measurements were needed because the relevance of soil moisture became less with the distance of two sample points extending.Soil moisture in 0-10cm surface layer could reflect accurately soil moisture condition to some extent,so it was suitable to use microwave remote sensing below 5 GHz frequency.

Key words: Irrigated farmland, Irrigated farmland, Soil moisture, Spatial and temporal variation, Automatic monitoring, Microwave remote sensing