The author continued the measurements of potential evapotranspirations of various crop§ from April, 1957 to Sept. 30, 1958 by using such portable evapotranspirometers as shown in Fig. 1, and obtained the evapotranspiration coefficients of some winter crops in 1956, and other summer crops in 1957 and 1958. The results are shown in Table 9 and 10. The following definition was made here that the evapotranspiration coefficients “M” are expressed by the potential evapotranspirations of crops in the growing season. In this case, however, that of the mix-seeded pasture of orchard grass and red clover is taken as a standard value.
As the result of experiments on the relation between soil texture and potential evapotranspiration (PE) with lysimeter, it was not considered that the potential evapotranspiration varied with the physical properties of soil. The soil tank A of the lysimeter was of clay soil and bare. The orchard and red clover were replanted in tanks B (clay), C (loam) and D (sandy) on May 9, 1958, and potential evapotranspirations were measured ; the result of which are shown in Fig. 3.
The rainfall in Dec. 1956 was 6. 5 mm, which was very little as compared with 58. 2 mm in an or-dinary year, and the winter barley was damaged considerably from a drought in the early period of growing season. The author made a survey about the yields of barley in the soil tank No. 15 and in the neighboring field which had not been irrigated. As the result, the yield of barley in the soil tank is estimated 12% larger than the non-irrigated one.
The experimental study of evapotranspiration started by the suggestion of the paper regarding the potential evapotranspiration by Dr. C. W. Thornthwaite closes with this fourth report. In order to develop the problems of evapotranspiration into the sphere of soil conservation, field irrigation and run-off, the mechanism which rainfall infiltrates, percolates and holds itself in the soil should be studied. From now on the author is going to develope his study on these lines.

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1. In case the discharge formulas of a dike sluice with a flap-gate are expressed by the water levels of Shioasobi and Kawayuki, and the same type as that with a lift-gate is adopted, the discharge coefficients are unstable. In this case the variable x which will arrange the observed coefficients in a regular change, is expressed by the function of the water level of Shioasobi, difference of water levels between Shioasobi and-Kawayuki, and hinge height of a flap-gate.
2. In case where a dike sluice is in the state of “running full”, “tranquil flow or subcritical flw”, or “critical flow”, the discharge coefficients may be expressed as the function of x with a good accuracy.
3. In cace fresh water is discharged from a dike sluice, the discharge resistance due to the difference of specific gravity will take place, as the fresh water is light as compared with the sea water. Such being the case the author proposed a practical formula by which the tide level might be converted into the water level of a fresh water lake for the drainage calculation.
4. The author expressed the discharge formula of a dike sluice with a lift gate, using the water levels of Shioasobi and Kawayuki, and also made a formula showing the classification of flows for the discharge calculation.
5. Employing the calculation diagram in the 7th report, the author derived actual values relating to the differences between the inside and outside water levels which are necessary when the dike sluice with a flap gate begins its action of drainage, and he also described some points which must be improved, regarding the dike sluice with a flap gate.
6. As the reduction of time due to a flap gate is little, the drainage calculation should be done by the tides converted into the water levels of a fresh water lake as well as the case of a lift gate.
7. Though there is an example in which about 2 hours were reduced due to the resistance of a flap gate in the case of drainage, this is, perhaps, ascribable to the inaccuracy of valuation of water pressure.
Note : Shioasobi means a pool or a channel regulating drainage water in a reclaimed area during high tide.
Kawayuki means the tidal space between a dike sluice and the sea.

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In Japan there are the greater part of the cultivated fields in the narrow-strips along the seashore. When the land sinks with the result of an earthquake, the mean sea level rises relatively to the land. In this case the sea water flows into the cultivated fields, and farming can not be engaged in the fields polluted with sea water. Such being the case how the sea water infiltrates into the land should first be investigated, and then the countermeasure against the salt damage be considered. The author made use of the differential equation for the unsteady flow in free ground water in order to clarify the circumstances of the inflow of sea water into the land. As is well known, the differential equation is nonlinear, and we must satisfy with an approximate solution of the differential equation. The author used the approximate solution, which he had already made use of in tie series of his studies of the coastal ground water. He succeeded in expressing the quantity and the velocity of inflow of sea water into the land as the function of time after the inking of land. It should be noted here that the author regards this as the problem of solving Fick's diffusion equation for sorption in a semiinfinite medium in the case where free ground water infiltrates from the sources at an infinite distance from the seashore, and the mean sea level rises abruptly and linearly respectively.

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When we intend to work heavy wagons such as tractors or bulldozers on the peat ground, we are faced with the problem of the bearing power of the ground. So, at the first stage of this research, the authors intended to investigate the bearing power of peats of different kinds, making use of loading plates of various sizes and shapes, and examined the relations among the load, the required time and the sinking degree. They investgated the penetration resistance of the cone, too. The results of the investigation were reported in Report I. From the results of the above-mentioned investigation, they could conclude as follows :
(1) The shape of the loading plate touching the ground surface dominates the sinking degree of the plate under the same intensity of the load.
(2) In the case of the constant sinking, the following formula introduced by Housel is applicable to the peat soil also. P=mx+n
where P is the intensity of load, x is the ratio of the circumferential length to the area of the plate.
On the basis of the above conclusions, this report explains the results of the experiments on the sinking amount of low-humased and medium-humased peat soils, which are unstripped and 20cm stripped of the surface, under the real static wagons.
Five bulldozers or tractors with track-shoes of different shapes and giving various pressures on the ground surface were used in the experiments. The results are summarized as follows :
As in the case of the loading plate, the intensity of the loading weight for the constant sinking is influenced by the circumferential length and the area of the ground-touching part of the machine, and is-in direct proportion to the ratio of the circumferential length to the area, and when other conditions are the same, is dominated by the shape of the ground touching part of the track-shoe.

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