Experimental studies were conducted on the characteristic mechanism of soil moisture decrease during irrigation cycles at four tangerine orange orchards in Wakayama Prefecture. In these series of experiments, glass filter block electric resistance soil moisture meters (glass filter block electrodes) were used for measuring soil moisture changes.
The results were;
(1) A process of vertical soil moisture decrease characteristic to the root zone soil layer was clearly seen during the irrigation cycles. Soil moisture in the top layer (0-10 cm) rapidly decreased to C. M. E.(pF 3.0) in several days, but on the contrary, the rate of moisture loss was very slow in sublayers (20-30 cm) until a certain higher moisture tension gradient was attained between the top layer and sublayer. After a certain higher moisture tension gradient has been attained, the rate of moisture decrease was rather rapid in spite of the sparse distribution of roots in the soil layers. This process can be fully explained by the upward movement of soil moisture from the sublayer to the upper layers (0-20 cm) by taking into consideration the soil moisture extraction pattern and vertical root distribution. The estimated upward movement was 15-20, 10-15 and 7-9 percent of the total water consumed for the various types of soil profile of L-C (loam-clay), L-L (loam-loam) and L-G (loam-gravel soil), respectively.
(2) The process of horizontal soil moisture decrease at the root zone was also discussed. About twice as much water was lost at “between the trees” or “under the edge of tree crown” position which are exposed to sun light when compared with the “under a tree” position.
(3) More than 90 percent of the total root (root surface area in cm²) was found within a depth of 20 cm layer at the farm plots investigated.
(4) Time of irrigation and quantity of irrigation water were also discussed in relation with soil moisture extraction pattern in accordance with the types of soil profile. It was found that the critical soil moisture at the irrigation time was C. M. E.(pF 2.7-3.0) in terms of average moisture content in the profile. This mode of thinking is supported by the fact that (a) change in soil moisture is observed only within 40 cm soil layer, (b) upward capillary movement of soil moisture is particularly observed (in L-C and L-L type soil profile), and (c) almost all roots are distributed within 20 cm of the surface soil layer.

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Data on soil moisture decrease at four experimental farm plots in the tangerine orange orchards in Wakayama Prefecture were analyzed in order to estimate the quantity of water consumed. It was confirmed that the quantity of water consumed (ET) is controlled by the soil moisture level, besides climatological conditions. Every year in July and August, daily ET decreases from 7-8 mm just after supplying irrigation water to about 2 mm after 8-9 days. Therefore, ET cannot be estimated without considering soil moisture level in the root zone.
Calculated ET values of these farm plots during whole irrigation period (July-September) were presented. The peak of monthly mean ET value was 4.8 mm/ day for the four experimental farm plots and this appeared in August. Monthly mean ET value was related to pan evaporation (E₀), and calculation of α_ET (= ET/E₀) revealed that α_ET showed larger values in the months of August and September than in July.
The influence of soil moisture level on fruit diameter increment was also discussed. Soil moisture level at depths of 20 cm and 10 cm influenced the fruit growth of young trees and old trees, respectively. The critical soil moisture level for normal growth of fruits of both young and old trees when indicated as the average soil moisture level within the root zone was found to be pF 2.7.
Effects of irrigation appeared directly as (a) increase of the fruit diameter, (b) increase in production and (c) improved quality of fruits. The over-all effect of irrigation was 14-20%.

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Rain infiltration and lateral soil moisture diffusive movement after infiltration under spray irrigation condition were discussed on the basis of data obtained from field measurements in experimental plots in tangerine orange orchards in Wakayama Prefecture.
The infiltration profile characteristic to spray irrigation indicated that moisture content profile during infiltration extended smoothly downward while retaining approximately the “Field Capacity” moisture content the entire depth. In this process, saturate zone was not formed at all, which differs entirely from ponded water infiltration. The data obtained suggested that rain infiltration mechanisms can be explained rather well by the theoretical procedures presented by Rubin and Steinhardt (1963-4) and Philip (1956) because rain infiltration is influenced less by localized heterogeneous conditions of the field soil.
The permissible intake rate was 12-15 and 8-10 mm/hr for loamy and clay loamy soils, respectively. However, field measurements revealed that the intake rate was affected considerably by soil management.
Disturbed distribution of spraying water due to leaf interception was sufficiently normalized owing to the remarkable lateral moisture diffusive movement after infiltration in both of the flat and sloping land.
Therefore, appropriate sprinkler spacing and spraying pattern efficiency can be easily estimated from the data obtained from spraying tests on bare land. The authors proposed the following concept of Ep (pattern efficiency) by taking into consideration the lateral moisture diffusion phenomenon:
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As was discussed in the third paper of the authors, complex phenomena observed in orchard spray irrigation can be approximately predicted from spraying tests on bare land. Therefore, at first, the authors conducted on bare land various spraying tests, such as one sprinkler spraying test, four sprinklers spraying test with rectangular spacing, etc. under various climatological conditions. Then, the results obtained were applied to spraying tests in the orchards.
The results are summarized as follows;
(1) Spraying efficiency E_a (water application efficiency in spray irrigation) had a linear relation with pan evaporation E_o with ri (spraying intensity) as the parameter. Maximum water loss due to adherence to leaves was estimated as 5 per cent.
(2) The effects of wind on the disturbance of the spraying pattern such as on the radius of the pattern's center and the mechanism of occurrence of localized dense spraying depth were discussed. Appropriate sprinkler spacing and spraying pattern efficiency when they are influenced by wind were also discussed.
(3) The appropriate sprinkler spacing and pattern efficiency were presented as a function of the grade of wind velocity using the concept of Ep (spraying pattern efficiency), which has already been discussed in the third paper.
(4) The characteristics of spraying in orchards were discussed. Irrigation efficiency (E_f) in case of four sprinkler spraying was between 70-86%, and E_f of multiple overlapping spraying in an actual orchard irrigation increased 4-5% and became 74-90%, as a function of climatological conditions.

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Almost all Orange orchards in Japan are situated on sloping land. Spray irrigation is most suitable for such sloping lands. However, spraying characteristics on steep slopes have not been fully studied as yet.
Therefore, the authors conducted several spraying tests on steep slope of 33° and also on slope of 14°, to find out various correlated facts. The results were as follows;
(1) Loci of water jet from the nozzles of sprinkler was discussed. The relation between the appropriate inclination of the sprinkler rotation axis to the lower slope and angle of slope for obtaining uniform spraying distribution, was also analyzed.
(2) Spraying pattern efficiencies (E_p) and appropriate sprinkler spacing on sloping land were compared to those of flat land to find out the correction coefficients between them. E_p and spacing on sloping land can be easily calculated for various topographical and wind conditions with use of these coefficients.

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In irrigation planning, determining the soil moisture precisely is of major importance. There are many difficulties in moisture determination but the use of neutron soil-moisture meter seems most promising for practical use.
In this paper, therefore, the authors studied especially the sphere of measurement and the accuracy of neutron soil-moisture meter.
Generally, the depression of density of radial rays is proportional to soil thickness dl and if the original density is taken as N_o, density at distance l as N and depression coefficient as μl,
N=N₀ exp(-μ_ll)
Based on this theory, the depression of counts of moisture-depth-counting rate can be approximated to an exponential curve. Consequently, the sphere of measurement can be treated in connection with the accuracy (count ratio to standard) of neutron soil-moisture meter (Table 1).
The results found in this approximation are:
1. Between 90-95% accuracy, surface probe has a sphere of measurement of about 20cm depth (radius).
2. Between 90-95% accuracy, depth probe has a sphere of measurement of about 30cm radius.
As the sphere of measurement is rather large, the soil-moisture content of variable depth can be measured quickly.
It was therefore found that the neutron sod-moisture meter is especially suitable for application to continuous field irrigation.

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As mentioned in the preceding paper, the sphere of measurement of neutron soil-moisture meter increases with decreace in soil-moisture. Consequently, error in measurement results when a neutron soil-moisture meter is used foil-calculation of consumptive soil moisture.
Therefore, in this paper, the authors investigated the possibility of varying the sphere of measurement.
In order to enlarge the sphere of measurement of the surface probe, a part of the probe was laid under the ground. The relation between buried depth and increased counts was approximately linear and the effect of increasing was about 30-40%(Table 2).
On the other hand, in order to have a smaller sphere, iron plates were laid under the probe. The effect of decreasing was about 20-30%.
With regard to the depth probe, a new probe in which Cd was fixed was prepared to shield thermal neutron flux. By varying the width of the slit of the Cd shield, which was fixed around the counter, it was possible to change the sphere of measurement about 50%(Table 4).
Consequently, it was proved that the optimum sphere to be used can be chosen within these limits irrespective of soil moisture.

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In this paper, the authors measured head losses of widely used rigid PVC pipes in actual system, for the purpose of obtaining basic data for rationalizing the pipe distribution system for sprinkler irrigation, and investigated about the various hydraulic coefficients of pipes for design use, applicable formulas and so on.
The results obtained are summarized as follows:
(1) Actual values of the coefficients in hydraulic flow formulas for the 30, 50, 100 and 125 mm sprinkler and distribution pipes were respectively K_s= 0.38-0.32, C= 130-140, f= 0.026-0.020 and n= 0.009-0.008.These coefficients were found to vary with pipe sizes.
(2) There was large difference between the coefficients of sprinkler and distribution pipes and transmission pipes. Therefore the Scobey formula is applicable to the former pipes (especially in sloped land) and the Manning formula to the latter, judging from the coefficients and Reynolds numbers.
(3) Adequate design values of K_s are 0.38 for 20-30 mm, 0.36 for 35-65mm, 0.34 for 75-100mm and 0.32 for 125-150mm sprinkler and distribution pipes.
(4) Reliability of the above coefficients was verified by applying these coefficients to actual calculation, and by comparing measured and calculated pressures in sprinkler heads of two different pipe-line arrangements.
(5) In using a certain constant coefficient in a restricted range of diameters for pipes of the same material, it is reasonable to select the coefficient for pipe diameter of the longest line.

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The forms of the landownership influence the forms of the paddy field. The influences are exerted not only on each element of the paddy fields, such as road, canal, section, and so on, but on the relations between them. The influences are illustrated by four cases, that is, by Japanese paddy fields under feudallordship, landlordship, peasantry, and American paddy fields under capitalism.

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Almost of all volcanic soils in Hokkaido which are believed to have erupted in the alluvial period, have been surveid. Also, the chemical and agronomical properties of these soils have already been studied but only a few studies have been carried out on the physical properties because these soils are very complex as they are composed of pumice, scoria, ash, crystal minerals such as plagioclase and pyroxene, rock fragments and clay minerals. It is very difficult to consider these as mixtures because there is a great difference among these. Needless to say, some studies on physical properties have been carried out on some types of volcanic soils in Japan, for example, on the so-called “Kanto Loam”.
In this report, the authors classified pumice pores into four kinds and measured them volumetrically because it was considered that the pores have a large effect on physical properties.
The pumice pores were classified into (1) dead pore, (2) active pore, (3) semi-active pore and (4) secondary active pore.(1) is pore sealed in pumice and dols not have a passage to the surface, (2) is pere on the surface and water is admitted into it easily, (3) is also pore on the surface or is present in active pore but admission of water is restricted to some extent because of the narrower diameter than (2), and (4) is a dead pore but isolated from the surface or (2) or (3) by a thin membrane which breaks by a slight positive or negative pressure.
(1) The authors determined the specific gravity of pulverized pumice with Beckmann's air comparison pycnometer and the volume of the solid phase of the pumice was obtained.(2) The specific gravity of the original pumice was determined with air comparison pycnometer, and in this case dead pore and secondery active pore volumes were determined together with the solid phase.(3) The pumice used in (2) was placed in a wide mouth pycnometer together with some water. After 24 hrs., the specific gravity was determined. By this method the total volume of dead pore, semi-active pore and secondary active pore are determined together with that of the solid part.(4) After the (3) treatment, the pycnometer was placed in a vacuum desiccator for 4 hrs. under a reduced pressuire of 50 mm Hg, and the specific gravity determined. The volume of dead pore and solid phase are obtained by this.(5) Finally, the specific gravity of pumice covered with paraffin is determine and the apparent volume of pumice is obtained.
By such a method, the pores of pumice are obtained as follows:
(1) is the volume of the solid phase of pumice,
(4)-(1) is the volume of dead pore,
(5)-(3) is the volume of active pore,
(3)-(2) is the volume of semi-active pore
and (4)-(2) is the volume of secondary active pore.

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