The agricultural sector is a major user of water resources.In the world, agricultural uses about seventy percent of water resources.In Japan, they use about sixty five percent of water resources.Until recently Japan has focused on the development of new water resources such as irrigation water and water reservoirs to secure water for agriculture.But it has not focused on developments of water-saving technologies for agriculture.Our project is leading Japan on the development of water-saving systems for agriculture with the focus on development innovative technologies for site-specific irrigation management to meet the need of plant growth by using a precise control technique for water resources in the rooting zone, following by high efficiency uses of agricultural water.This system will be particularly applicable in arid lands suffering from drought require water-saving agriculture technologies.This study is aiming at the implementation of a limit water-saving cultivation approach by using irrigation water to the limit level of plant growth while maintaining plant productivity.The key point is only wetting the rooting zone while keeping other areas completely dry to increase water use efficiency.A water retention area was formed around the rooting zone during the growing period and we used precise control of subsurface capillary flow to meet the small reduction in water potential around the rooting zone when plant absorbs water.We call it precision irrigation approach which enable water supply with correct amount at correct time and correct location.Tomato was selected for the precision irrigation experiment conducted in a climate controlled environment (phytotron) located in the campus of Tokyo University of Agriculture and Technology from December 25, 2014 to March 31, 2015.The soil used in the experiment was red clay which was dried in the oven with 105℃ for 24 hours and then grinded and sieved pass through 1mm sieves.The tomato was sowed from seeds in the soil with a quantified water supply management.The water supply point was a fibrous medium with 1.5cm× 1.5cm in size equipped in the tip of a plastic pipette buried at the planting point in the soil.A soil moisture sensor (decagon EC-5) was set in the water supply point (the same with planting point) to measure the soil moisture at five minutes interval.Two decagon sensors were set at 10 cm from the water supply point at horizontal and vertical direction, separately.These sensors measured the assumed boundary moisture of the water retention area.Another two decagon sensors were set at the bounty of soil container (50cm×50cm×50cm) to monitor the soil moisture in the dry area.After water supply, the soil moisture response was apparently observed at each point.The timing of water supply was determined at the "wilting point" of the planting point and the amount was determined based on the tomato growing stage and soil moisture data.The irrigation time and frequency was recorded and will be used to model the infiltration process by transfer function.As a result, the total height change of the tomato was 42 cm with 13.8 L total amount of water supply.Three tomatoes were harvested in the end of the experiment.A 25cm diameter water retention area was formed while other area was dry and the roofing zone was concentrated in the wetting area.We confirmed the existing of water retention area in dry soil where plant can grow.This indicated the possibility to use precise irrigation approach by maintaining water retention area in dry land to increase water use efficiency.