Rotational upland fields with heavy clay soil in Hokuriku area often face the problem on drainage of surplus water, due to both the rich precipitation during winter and poor permeability of water in soil. We made some experiments about improvement of the soil pore structure by planting some winter crops, and its effect on drainage of water. Four experimental plots, each of which differs in planted crop or period after conversion from paddy to upland field, were set:(1) wetland rice-Italian rye grass-soybean (2) wetland rice-barley-soybean (3) wetland rice-fallowsoybean (4) wetland rice-Italian rye grass-soybean-barley-soybean. On each plot, tensiometers were set and the suctions of soil moisture were recorded. Soil survey were also conducted before sowing soybean, and some soil physical properties were measured. From these experiments, following results were obtained :
1) During autumn and winter, soil never dried more than the field capacity ; improvement of permeability in plow layer proved to be effective for rapid drainage of soil water to the ditches on the surface of the fields.
2) By planting winter crops, volume of soil macropore in plow layer increased and hydraulic conductivity raised. Especially as the first winter crop after conversion from paddy, Italian rye grass grew well and its root zone contributed to the development of remarkable macropore in plow layer.
3) At the plot No. (4) where one year and a half passed after conversion from paddy, the soil structure at plow layer highly developed. As the result, the surplus water was drained smoothly and soil dried rapidly in spring.
4) Transpiration from winter crops plays an important role in drying of the field in spring. Transpiration rate is so deeply related to the growth of the crops that drying rates of fields depend on the condition of crops.
The responses of stamatal conductance to environmental factors, such as solar radiation, on Cryptomeria Japonic a in Japan and grasses in Tibetan Plateau were examined. Also, mechanism of water storage in trees with three types of xylem structures ; namely, C. japonica (coniferous wood), Magnolia salicifolia (diffuse-porous wood), and Quercus serrata (ring-porous wood) were investigated experimentally. The effects of environment factors on stomatai conductance varied with its location. The stomatai conductance in C. Japonica forest were heavily depend on solar radiation and water vapor pressure difference between atmosphere and the leaf. In the grassland on the Tibetan Plateau, the reaction to the water vapor pressure difference was significant. The response of water uptake to transpiration differed with the relations between water storage and water potential due to pore structures.
Plant organs contain large amounts of water. An essential role of water is in maintenance of their internal enviromental conditions where cell growth and physiological functions proceed normally. Plant water stress or water deficit develops when water loss exceeds water absorption due to excessive loss of water, inadequate absorption or a combination of the two. Water stress affects plant growth, modifying morphology, physiology and biochemistry. How much of the water stress are dependent on the degree of the decrease in water potentials, on the processes in physiology, on the growth stages and on the kinds of plants. Osmotic adjustment contributes to the maintenance of turgor for keeping normal plant growth processes. Osmotic adjustment refers to a net increase in solute, as distinguished from the passive increase in the concentration caused by loss of water. We examined the degree of osmotic adjustment in the mangroves, Rhyzophora stylosa Griff, and Bruguiera gymnorrhiza (L.) Lamk., in the area from sea water along the coast to brackish water in the mouth of the river. From these examinations we found that the mangrove trees growing in sea water and brackish water areas maintained high turgor potentials due to osmotic adjustment and that the mangrove trees growing in sea water area along the coast were probably absorbing water with higher water potential than that of sea water. However, the small and young tree directly absorbing sea water could not maintain high turgor potential due to insufficient osmotic adjustmet. Therefore, we suggest that this tree would suffer from water stress under intense transpiration condition on fine day.
Water harvesting is the agriculture with the primitive irrigation which has been developed in arid region as middle East and north Africa. It is modified and arranged in Israel to the new modern arid agricultural thechnology which is called as runoff agriculture. It is expected to be the sustainable agricultural thechnology for developping contries due to low investment and unnecessity of high technoligy. In this paper it is pointed out that the water harvesting is also very important in humid region as Japan. Effective rainfall which is caught in root zone is decreased irrigation water require-ment, and the river discharge in drought period is released as groundwater from stored rain water in geological formation. The former is the rainfall caught is soil and the latter is the rainfall caught in geological formation. Both of them are caught by storage capacity in the watershed. It is concluded that Water harvesting concept is very important in irrigation plannig and water resourced develop-ment in the humid regeion.
The water table of investigated fields was high and the ground water flowed from heavy fertilized renovated grassland to non-fertilized meadow. The concentration of nitrate nitrogen in shallow ground water decreased rapidly, when it flowed into meadow. There is a possibility to reduce nitrate nitrogen concentration in ground water by locating meadow as buffer zone along streams.
Nitrate movement under simultaneous influence of hydraulic, electric and chemical gradients was investigated. A one-dimensional ion migration model was developed and compared with laboratory column experiments. Operation of subsurface drainage with an electrode was dis-cussed as an application. The ion transport equation was developed utilizing non-equilibrium thermodynamics. Onsagefs reciprocal relations were applied to reduce the number of linear phenomenological coefficients that relate flux to driving forces. Then phenomenological coefficients were ex-pressed using known or measurable physical, chemical and electrical properties of solute and porous media. Without water flow, nitrate concentration increased at the anode by 2.5 times after 100 hrs of 30 V application. Two flux rates (0.112 and 0.225 cm min * *), and three inflow concentrations (100, 500 and 1,000 ppm NO3-N) were used to evaluate nitrate transport in the column. Nitrate concentra-tion at the anode increased by 10 to 20% at the end of all experiments. However, the concentra-tion in the column was same as inflow concentration. The application of electrokinetic nitrate removal by installed subsurface drainage with on-off (no flow then flush out) operation is recommended over a continuous flow approach. The numerical model results showed very low flux rates (i.e. 2.68X 10_3cm minィ)are required for nitrate accumulation in a sand column, and the experimental results confirmed no accumulation at a flux rate of 0.112 cm min-1.
Rain, river, ground and tap water resources can be used for agriculture in Japan. Ground water is available in large quantities and low cost. Therefore, it is one of the main source of water for agriculture and horticulture. But in many horticultural area especially close to sea, the salt level of ground water varies widely. Sometimes it exceeds the acceptable maximum for sound plant growth. It is not economically and technically viable to mix ground water with fresh water for the purpose of reducing salt concentration. The author suggests that the membrane separation technology can be applied to control quality of ground water for agricul-ture. Information on precious studies related to the application of membrane technology in agricul-ture, and an general aspects were summarized in the beginning. Subsequently, practical exam-ples of applications of membrane method for desalination of ground water in horticultural filed in Japan. Advantages and disadvantages of application of membrane method in agricultural water quality control were also discussed.
In Japan, some treated water called “functional water” interest in the medical and agriculture area. These functional water are produced by the electrolysis, the high voltage electrostatic filed, the magnetic field, the explosion of ultra sound and the addition of mineral and so on. In this paper, some effects of these water for agriculture like promotion of plant growth, microorganism control, quality control of products and extension of product shelf life are reviewed by the relative papers and reports.