For proper irrigation planning, a non-destructive and non-penetrating method of measuring water content of plants and soils is needed. Near-infrared (NIR) reflectance technology is designed to provide rapid, non-destructive, and accurate measurements of water inside materials. A total of 40 reflectance spectra (1550–1950 nm) from different plant and soil samples were measured in the laboratory using an inexpensive hand-held sensor. The result of drying experiments showed that there were close relationships between spectrum parameters of the water percentage of leaves and soil. The result of log-linear model and linear regression analysis showed significant effects to spectrum parameters based on the water percentage of leaves and soil respectively. The result of our study confirmed that the absorption of NIR light by samples’ water was highest around 1940 nm and lowest at around 1650 nm. It is suggested that the simple index using single wavelength (1940 nm) can be used for universal index to estimate the water content of leaves. The ANCOVA analysis showed significant differences of regression among soil types in Japan. This result suggests that different calibration models for the water percentage of the soil is needed for each soil type. These results reveal that an inexpensive hand-held NIR sensor can be applied to measure water status of living plants in the field.

  In the Sengari reservoir which supplies domestic water to Kobe City, Japan, total phosphorus (TP) concentration remains higher than the prescribed environmental standard value. Since 88% of the reservoir basin is forested and 10% occupied by paddy fields, the study sites were set in a group of paddy fields with 7 plots and a forested area of 111 ha. Field observation was conducted to estimate TP loads emitted from the paddy fields and the forested watershed, measuring TP concentration and discharge in an agricultural drainage canal as well as in a mountain stream. Water samples were collected once a week during the irrigation season (from May to mid-September) and intensively collected during floods both in the irrigation and non-irrigation seasons. Data loggers were operated to record water depths with an interval of 10 minutes, to determine the discharges with relevant hydraulic methods. As a result of hydrological analysis, we found that less frequent heavy rainfall events cause significant intensification of TP loads both from the paddy fields and from the forested watershed. Based on our observation, half of the annual TP loads both from the paddy fields and the forested area were estimated to be produced in a few percentage points of time, which correspond to around 10 days. In addition, the amount of TP load from the paddy fields during the non-irrigation season was found to be almost the same as that during the irrigation season.

  Japan experienced significant rainfall particularly from western Japan to the Tokai region in the Heavy Rain Event of July 2018. This caused extensive human casualties and tremendous property damage due to landslides and river flooding, particularly in Hiroshima, Okayama, and Ehime Prefectures. Agricultural facilities were no exception, with damage to farmland and hydraulic facilities. In this study we summarized the rainfall and Soil Water Index (SWI) mainly in areas where serious damage occurred in Ehime. The damage to agricultural infrastructure was also reported and the relationship between the damage and the rainfall characteristics including SWI was investigated. Furthermore, the behavior of the phreatic surface was traced using runoff analysis and saturated–unsaturated seepage flow analysis for the two irrigation tanks that were seriously damaged, and the factors related to collapse were investigated.

  Understanding snowmelt characteristics in forest areas is essential for the effective use of water resources because forests cover most of the mountainous areas in Japan. However, most previous studies investigating the snowmelt characteristics in open and forest areas have been conducted in March or later in the spring. In Japan, few studies have analyzed the energy balance of the snowmelt over an entire winter season, including the severe winter months. We selected Ishikawa Prefecture as the study area to clarify the characteristics of the energy balance for snowmelt in open and forest areas over the entire period of snow cover. The reduction of shortwave radiation by the forest was small during the severe winter months between December and February. The amount of longwave radiation was greater by approximately 25−85 MJ m^-2 day^-1 in the forest, which is significantly higher than that observed in the open area. We found that there are cases in which the energy available for snowmelt in the forest is larger than that in the open area, and that forests had no effect in terms of slowing the snowmelt during the severe winter months.

  This study is to examine the effect of a paddy field decrease on the diversion requirement for paddy area by modeling its water demand structure using the CB method in a paddy field area where urbanization has progressed in recent years. As a result, it was shown that where in case of the irrigation system with a dual-use canal, it is necessary to add the decrease of return flow from the paddy field due to the paddy area decrease to the diversion requirement as delivery water requirement.

  This study investigated and assessed the actual management of irrigation at the small-scale irrigation development site in northern area of Zambia and estimated the conveyance efficiency and the application efficiency as the basic specifications of the irrigation planning. Irrigation water is taken from the stream by the weir and directly distributed to the irrigated fields through the main earthen canal. Discharge measurements in earthen canal had been conducted at three locations, namely intake, middle stream and downstream, and the conveyance efficiency per km was calculated to be 80%/km. Regarding irrigation management, irrigation period, amount of irrigation, irrigation frequency and irrigated area for each section recorded by farmers have been assessed. Although excessive water had been irrigated by a few farmers, proper irrigation management had been done by most of farmers. In addition, evapotranspiration has been estimated by the penman method from measured meteorological data, and the application efficiency was calculated using evapotranspiration and average daily amount of irrigation. Application efficiency was estimated to be 50% from April to July when the evapotranspiration was low and 80% from August to October when the evapotranspiration was high.