Sampling infiltration water in a sandy soil is still a challenging task due to high variation in water content with small suction changes. A Suction Controlled Flux Sampler (SCFS) consisting of an Automated Vacuum System (AVS) and a Sampling Filter Device (SFD) has been developed to collect infiltration water effectively without disturbing the infiltration stream line. The SCFS was applied to sandy soils where the risk of fertilizer leaching was high. In this study, we monitored the fertilizer leaching in an unsaturated sandy field during rainy season, while evaluating the sampling performance of the SCFS for infiltration water sampling. The water-collecting efficiency of the SCFS was excellent when the filter suction was controlled at 0 to 51 cm. Lower suction was preferred because the sandy soil showed large drainage with relatively small suction change. This was achieved by employing a buffer container to moderate the suction. The SCFS directly collected the infiltration water effectively for several months in sandy field and resulted Water-Collecting Efficiency (WCE) varied from 92 to 115 % under various infiltration conditions, which was recorded during the focused 50 days. The WCEs were affected by rainfall intensity as well as antecedent rainfall, which gave better WCE. The results obtained from the SCFS and several sensors demonstrated that the amount of leached water was kept low as long as irrigation was applied according to the cultivation manual. However, an unexpected heavy rainfall caused fertilizer leaching. Fertilizer leaching trend was effectively monitored by several sensors in the soils, while detail components were analyzed after collected by using the SCFS. Direct access to infiltration water enabled us to examine the infiltration process and the detailed variation of the discharged anions. The sensor-equipped monitoring system together with the SCFS is beneficial for the precise management of fertilizer and irrigation.