Kozue Yuge

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.

Heat Environment Affected by Different Land Surface Conditions

Study of heat environment and evaporation affected by different surface condition. Observation and simulation of bare, grass and paddy field were performed, which results were compared. The observation was conducted at an experimental farmland. The simulations model used in the study includes numerical model of temperature, wind and humidity distributions in atmospheric boundary layer and soil temperature change. Crop resistance model was adopted to analyze heat energy exchange on surface layer. Using the model, simulations were conducted for 6 fine days in 6 different months using meteorological data measured at other experimental stations. The results show different thermal behavior of the three surface conditions. Temperature order from the highest are bare, grass and paddy; and evaporation order from the highest are paddy, grass and bare.

The desalinization effects by the cleaning crop with Na+ absorption ability

This paper includes discussions on the improvement of salinity problems at newly reclaimed fields from the sea. The object of this research is to quantify the amount of desalinization by the plant’s absorption abilities. A big reclamation project for agricultural production is going on at Isahaya Bay, Nagasaki prefecture in Japan. To improve salinity problems at initial stage of reclamation, desalinization by the plants were investigated. First, the native halophyte plants such as Shichimensou (Suaeda japonica Makno), Hamamatsuna (Suaeda maritima LINN. Dumort), Shiokugu (Carex scabrifolia Steud.) and Yoshi (Phragmites communis Trin.) living around the reclaimed land in Japan were investigated on Na+ and K+ absorption potentials. Second, the crop’s Na+ absorption abilities were investigated. Spinach, turnip, radish and some kinds of grass were grown up by some concentrations of saline irrigation water and Na+ absorptions were examined. Finally, in order to examine the effect on the Na+ cleaning, the above plants were grown in the reclaimed land soil. The desalinization by irrigation such as the leaching is effective and easy if we could use much water. But the absorption of Na+ by the crops can remove the salinity from the root area certainly though the amount of adsorption is not so much.

Evaluation of Evapotranspiration by Using Numerical Model and Remotely Sensed Surface Temperature Data

Evapotranspiration (ET) involves a complex set of processes which are influenced by the local conditions. These conditions are characterized by meteorological and ground surface condition. ET for large area with different land covers were estimated by evaluating the energy balance components for each land use, using a numerical model of the energy balance which includes differential equations of wind velocity, specific air humidity, potential air temperature, soil temperature and soil moisture. Remotely observed surface temperatures were used to modify the parameters used within the model. The inputs for this numerical model are direct and diffused solar radiation, solar elevation, long wave radiation, surface temperature, ground moisture, crop transpiration resistance, leaf area index, crop canopy architecture, wind velocity, air temperature and relative humidity. The extinction of solar radiation intensity as it passes the land cover canopy is estimated by treating the plant canopy as a single ‘big leaf’. As for the upper boundary of this system, constant values of wind velocity, potential air temperature, and specific humidity were used at the height of 100 m above ground. The total daily latent heat of every land use for paddy field, bare soil and forest are 12.5 MJ.m-2d-1, 11.2 MJ.m-2d-1 and 15 MJ.m-2d-1. These values are equal to 5, 4.5 and 6 mm of water.

Effects of Plastic-Film Mulching on Discharge Rate of NO3-N from Chemical Fertilizer Inputted Fields

The lysimeter experiments were conducted to examine the effects of plastic-film mulching on the discharge rate of nitrate nitrogen (NO3-N) from the chemical fertilizer inputted fields. Two lysimeters filled with sandy loam were kept in the different mulching conditions. One of which was mulched partially only the part of ridge and another one was mulched fully including the furrow with black plastic film. Chemical fertilizer was plowed into the soil equally to the two lysimeters before the application of mulch. After transplanting broccoli, the amount of subsurface drainage discharge and the NO3-N concentrations of drainage water were measured everyday. The large rate of NO3-N discharge occurred mainly during a heavy rainfall for all treatments. The effect of mulching on the reduction of NO3-N discharge rate was higher for the sole-mulch treatment. This result showed that some types of mulching would be effective for an appropriate fertilizer management for which the amount of fertilizer applied will be reduced.

Irrigation Scheduling to Control the Capillary Saltish Water Movement at Crop Fields Newly Reclaimed from the Sea

A substantial big reclamation project for agricultural production is currently taking place at Isahaya Bay, Nagasaki prefecture located in the southwest of Japan. To improve the soil physical properties, a large amount of gypsum was added to the original heavy clay soil. Also, leaching was conducted for several months using a sprinkler. Following these treatments, crops were planted, but saltish clay soils near the drainage pipes buried below 70cm from the soil surface are still probable to damage the crop growth. In this report, some trials to control the salt damages in crop production are introduced. First, the soil’s physical improvement processes from the first stage of reclamation to the present stage are introduced. Second, experimental and numerical studies on the soil water movement and salt movement in the cropped fields are stated. Third, the optimal irrigation scheduling to suppress the upward flow of saltish water in the draught condition is discussed.