Mitsumasa Anan

Quantification of soil surface evaporation under micro-scale advection in drip-irrigated fields

The objective of this study is to quantify soil surface evaporation under micro-scale advection in drip-irrigated fields. A numerical model for estimating soil surface evaporation under micro-scale advection, assuming drip-irrigated fields, is introduced. Results indicate that the soil surface evaporation changes spatially. Soil surface evaporation at the upwind edge of wet soil portions adjacent to dry soil portions increased abruptly. On the other hand, soil surface evaporation at the upwind edge of dry soil portions adjacent to wet soil portions decreased, and condensation was observed. These phenomena were considered to be due to airflows between differing climates. To verify the accuracy of the model, an experiment using a wind tunnel was conducted. The simulated soil surface evaporation results from the model were consistent with the experimental data. The numerical model introduced here is an effective way to quantify soil surface evaporation under micro-advective conditions.

Effects of the micro-scale advection on the soil water movement in micro-irrigated fields

The objective of this study was to explore the soil water dynamics under micro-advective conditions. A numerical model was introduced to estimate the airflow turbulence generated by the crop canopy. The vapor pressure and air temperature in the vicinity of the soil surface were estimated from the wind velocity predicted by this model. The energy budget on the soil surface was estimated using wind velocity, vapor pressure, and air temperature simulated by numerical models. The soil water content and temperature were predicted using the simulation model describing the water and heat transfer in soil. Using the energy budget, the accuracy of this model was experimentally verified using a wind tunnel. Spatial changes of the soil water content simulated by this model were reproduced by the experiment. This indicated that the numerical model for estimating the soil water movement under micro-scale advection considering the crop body was satisfactory.

Spatial-uniform application method of methane fermentation digested slurry with irrigation water in the rice paddy field

Promoting biomass utilization, the objectives of this study were to clarify the spatial distribution of nitrogen, one of the most important fertilizer components in the methane fermentation digested slurry (i.e., the digested slurry), and to establish an effective method to apply spatial-uniformly digested slurry with irrigation water in the rice paddy field. A numerical model describing the unsteady two-dimensional flow and solution transport of paddy irrigation water was introduced. The accuracy of this model was verified with a field observation. The tendencies of the TN simulated in inlet and outlet portions had good agreement with the measured data and the accuracy of the numerical model could be verified. Using the numerical model, scenario analyses were conducted to determine the method for spatial-uniform application of the digested slurry with irrigation water. The simulated results indicated that drainage of the surface water and trenches at the soil surface were effective for spatial-uniform application of the digested slurry with irrigation water in the rice paddy fields. The effect of the trenches was maximized when the surface water of the rice paddy field was drained adequately.

Evaluation of water intake rate using the diffusive tank model in the low-lying paddy area

The subject of this study is water management in low-lying paddy fields. The objective of this study is to quantify the water requirement, and estimate an appropriate volume and facilitate management of irrigation water in areas where it is difficult to estimate the flow rate continuously. A field observation was conducted at a 14-ha study site located in the Kuwabara area, Fukuoka City, southwest of Japan, to evaluate water management conditions in the command area of the reservoir. This site near the reservoir was selected, because it was impossible to understand the water supply situation in the entire command area. The farmers in this region have been unable to retain sufficient irrigation water. The observation results indicate that the water depth fluctuates widely in every irrigation canal. The canals are frequently empty because rotational irrigation is conducted by water managers; this makes quantifying the flow rate in the irrigation canal very difficult. To quantify the water requirement, an improved tank model was introduced. The accuracy of the model was examined by comparing the observed and calculated ponding depths at a paddy field. The simulation results agreed with the observed data. Using this model, water management for the reduction of water managers’ labor was simulated. Simulation results indicated that rotational irrigation effectively reduces labor and saves irrigation water.

Quantification of the crop stem flow in the sprinkler irrigated field

In sprinkler irrigated fields, irrigation water is intercepted by crop leaves. This water can be separated into several categories depending on its movement. In this study, the categories are defined as crop stem flow water, leaf storage water, and drop water to the soil. Crop stem flow water is especially effective for crop growth because it reaches the soil surface near the root zone. The objective of this study is to develop a method for quantifying crop stem flow water. Field observation is conducted to observe the movement of irrigation water droplets and to quantify the varying amounts of crop stem flow water, leaf storage water, and drop water to the soil. The measurement of the amount of leaf storage water indicates that droplet movement on the leaf changes constantly. To quantify three components of irrigated water, considering the continuous change of droplet movement on the leaf surface, a simulation model is developed. The simulated amounts of crop stem flow water, leaf storage water, drop water to the soil successfully reproduce the observed result, and model accuracy can be verified.

Water Quality Monitoring at Lowland Creek Area by GIS and Improvement Trials Using Fallow Paddy Fields

Lowland area at seacoast of the Arikake Bay in Japan is famous for rotational use of creek water for rice production. About 40 years ago, almost whole area was covered with rice paddy in summer season. For the purpose of regulating the rice production, about 40 % of rice fields have been used for upland crop production. In addition to the changes of agricultural style, the inflow of the contaminated drainage water has been increased by the development of urbanization. To keep the sustainable agriculture in this area, it is requested to establish the regional control system to keep the creek water clean. The objective of this study is to evaluate the effect of the rice paddy, upland crop, and greenhouse cultivations on the water quality. First, the effects of water management, fertilizer management, crop management on the nitrogen and phosphate loads to creek water were studied experimentally at the study site about 10 ha. Water purification functions of rice paddy were evaluated quantitatively. From this result, it was advocated to prepare water ponded fallow fields through out the year for cleaning creek water. Additionally, the effectiveness for water purification by some vegetables planted in the fallow paddy are introduced. Second, daily changes of creek water qualities were monitored with the automatic sampler at the end of creek networks. Using the data, the relationships between land use condition and water quality along the main creek were simulated with the support of GIS.

Effect of Paddy Irrigation Water on Recharging Groundwater

Paddy irrigation water is well known as big contributor of groundwater recharge. During the irrigation season, large amount of water is kept in groundwater and some parts of it flow out to the main river directly or indirectly. The objective of this study is quantifying the effect of the paddy irrigation water on the groundwater recharge, and evaluating of the influence of the land use condition on the groundwater recharge. A comprehensive simulation model of groundwater flow in alluvial plain along Chikugo River, which is located in southwest in Japan, has been established by coupling GIS technique with traditional Finite Differential Model (FDM). In this study, relationships of groundwater level change and land use change were investigated. Using GIS, the fundamental data related to groundwater flow and land use conditions are input at every nodal point as database. A GIS based surface water simulation was carried out and spatial and temporal groundwater infiltration quantity is obtained and provided for groundwater flow simulation. Groundwater flows was calculated by adopting the Successive Over Relaxation (SOR) technique. The simulated result is consistent with the observed data, and the simulation model introduced in this study is fairly satisfactory. The result indicates that the paddy irrigation condition affects on the groundwater recharge. The simulation model introduced here is effective for quantification the groundwater recharge, considering the land use condition.