The author examined and compared various windbreak nets for the purposes of net selection of optimum density, effective net quality (string scale, width and number), weave system, material etc., and of exhibition of good data for an extension service of nets. To make clear the physical characteristics of nets, the horizontal pattern, vertical profile and isopleth of wind speed, a relation between net density and wind speed and so on were obtained. The results were mainly as follows:
(1) According to the horizontal pattern of the wind speed at the height of 10 cm (Fig. 2), the relative wind speed (u_r) decreases fast and violently with the increase of the density (D=100-porosity) (%), however, u_r recovers faster. Because of the windbreak net made of wide string (Wide-screen-1206), wind speed is recovered particularly fast by the large scale of turbulence and strong turbulent intensity.
(2) On the horizontal pattern of u_r (Fig. 3), the appearance level of the increase to sharp-decrease variation at the immediately leeward of the windbreak net becomes higher with the increment of D, e.g., at 20cm for Cheese cloth-110 net and 25cm for Russell-18G net.
On the vertical profile of u_r (Fig. 4), the heights except at 2cm at the windward and the heights of 5 to 20cm up to 1m leeward have an almost same value. The region of rapid increase of u_r above the windbreak net in a leeward moves to a higher region with the increment of the leeward distance. The profile shows a linear variation at the 7m leeward.
(3) Characteristic isopleths of representative net on weak and strong winds and their appearance regions were shown in Fig. 5. The isopleth is denser with the increase of D.
(4) There are minimum wind speed regions at the level of close floor (2cm) in the case closed under the net, and at the middle level of the net at 150cm lee in the case opened under the net. The wind speed at the strong wind speed region is larger in the case closed under the net than in the case opened. The strong area moves to an upper and more leeward area with the increment of D. It is necessary to shut the area under the net at 5% of net height or lower.
(5) The u_r values at the areas of smallest and largest wind speeds respectively decrease and increase with the increment of D. Both relations are expressed by linear equations. The appearance regions of minimum and maximum wind speeds respectively move to closer net area at 2cm height, and upper and more leeward area of the net with the increment of D.
(6) The ratio u₁/u_-1 diminishes rather linearly with the increase of D (u_-1, u₁ and u₇ are the wind speeds at the distances of 1m windward, 1m leeward and 7m leeward). The ratio u₇/u_-1 enlarges gradually between 0 to 50% of D and rapidly over 50%, and becomes negative at 100%. The ratio u₇/u_-1 takes a minimum at an area of 50 to 55% and increases at both larger and smaller values of D. The ratios for Wide-screen net deviate from a normal line because of the different quality of the net and large turbulent intensity.
(7) In order to obtain a wider protected area below the relative wind speed of 50% at the middle height (1m) of windbreak net for purpose of crop protection, it is suitable to use the net of fine mesh and 60 to 65% densities at least 50%. It is better to utilize Cheese cloth-100 or a little denser nets and Russell-12G or 15G nets, and is necessary to change to a finer string for Wide-screen net.

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The purpose of this paper was to investigate the effect of mulching by black polyethylene film (0.04mm thick) with planting holes (5.5cm diameter) and by soybean canopy on the microclimate near the row surface.
Four experimental plots were designed as follow: No. 1 plot was not planted and not mulched, No. 2 plot was planted and not mulched, No. 3 plot was not planted and mulched, and No. 4 plot was planted and mulched. Medium maturing soybean, named ‘Ohsodefuri’, was used in this experiment. The observation was performed from April to August in 1979.
1) Sum of the latent and sensible heat fluxes on the row surface of the mulched plot (No. 3) at night was remarkably increased by about 3.7 times that of unmulched plot (No. 1).
When the plant cover was still small (June 4), it did not much affect the soil heat flux regardless of mulched or not. But, on July 26 (LAI, No. 2: 2.56, No. 4: 3.92) the vegetation lessened the ratio of soil heat flux to the daily amount of total net radiation, and these values were 3-4% both in mulching and unmulching.
2) The plant canopy and film mulching controlled the rising of maximum temperature and the falling of minimum temperature, namely they lessened the diurnal range of soil temperature. Their effects could be called the buffer action.
3) Mulching effect on soil temperature can be also showed by the ratio of diurnal range of temperature (daily range in treated plot/that in the not-treated one). The effect of film mulching (daily range of No. 3/that of No. 1) was reduced with the increase of daily insolation amount. When the amount came to 486cal cm^-2day^-1 the mulching effect disappeared.
4) When transmissivities of solar radiation (above 40%) or the thickness of growth were same, the ratio of diurnal range of soil temperature in mulched plot (No. 4/No. 3) was greater than that of unmulched plot (No. 2/No. 1). This shows the difference in effects of soybean canopy between the case of mulching and not mulching. The ratio of No. 4/No. 1, which indicates the total effect of plant canopy and film mulching, was less than that of only plant plots (No. 4/No. 3) in early season.

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Traditionally two types of equations for representing frost-pillars have been used: One type is based on considering heat conduction through the pillars, while the other is considering only the effect of long wave radiation at the surface of the frost-pillars. The former is inappropriate for describing short pillars of frost, while the shortcoming of latter is inadequate description of the long frost-pillars.
Unifying above two equations, we intended to derive one that could apply to both long and short frost-pillars. In this study, we have taken into consideration the heat balances that occur at both the pillars' surface and base, and from the viewpoint of unifying both, have derived the following equation:
dl/dt=A₃l+A₄/A₂l+k_i
where
A₁=-θ_a(h+4ε_lσT_a³+L_ih_va′)+ε_lR_n0+L_ih_vζρ_as
A₂=h+4ε_lR_n0/T₀+4ε₁σT_a³+L_ih_va′
A₃=A₁h′_va′+A₀A₂
A₄=k_i(A₁/Lρ_iα+A₀)
A₀=h′_v(a′θ_a-ζρ_as)-q_s0/Lρ_iα
k_i=αk_i+(1-α)k_a
where dl/dt; growing velocity of frost columns, θ_a, T_a; air temperature (°C), (°K), h; heat-transfer coefficient, ε_l; emissivity of long wave radiation from surface of frost columns, σ; Stefan-Bolzmann constant, L_i; latent heat of ice sublimation, h_v; transfer coefficient of water vapor, a′; dρ/dT, R_n0; net radiation of black body at 0°C, ζ; (1-ζ)=relative humidity of air, ρ_as; density of water vapor saturation at a given temperature, T₀; 0°C (°K), h′_v; h_v/ρ_i⋅ρ_i; density of ice, q_s0; heat flux from ground, L; latent heat of water freezing, k_i; heat conductivity of ice, and k_a; heat conductivity of air between columns of ice.
The existing two equations can be obtained as approximations by simplifying given conditions of our equation.
The calculated values obtained by our equation correspond values of both short and long frost-pillars.

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The amounts of the daytime and nighttime transpiration of greenhouse cucumber crops in hydroponic culture and of the evaporation from the gravel pots were determined by measuring the nutrient solution uptake and the increase in fresh weight of the crop.
The experiments were conducted during the period from October 11 to December 7 in 1980 for the mature cucumber crops.
The solution uptake expressed as the decrease in level of the solution in a solution storage tank was measured using an accurate level meter with micro-processor controlled pulse motor.
Average daytime evapotranspiration was 0.74l/plant/day. During the daytime, 34% of the transmitted solar radiation was converted into latent heat by evaporation, on average.
A stepwise multiple regression analysis showed that daytime evapotranspiration can well be expressed by a linear equation of solar radiation and average daytime saturation deficit of the air.
During the night, average transpiration was 0.10l/plant/nighttime and average evaporation from the gravel pots was 0.08l/plant/nighttime; the average evapotranspiration being 0.18l/plant/nighttime. For this evapotranspiration, about 10-20% of the total nighttime heat input for the greenhouse heating was consumed.

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In the previous paper, the author investigated on windbreak nets and relatively compared with vertical and horizontal profiles of wind speed formed by various single-windbreak nets in a wind tunnel (Maki, 1982). In this paper, an experiment was carried out in the wind tunnel using four representative windbreak nets and the relations among the net density, decreasing rate of wind speed, minimum and maximum wind speeds and so on were obtained.
The results were mainly as follows:
(1) In the case of successive windbreak nets at every 13H times (distance expressed as a multiple of the net height, H=15.0cm), the effect of decreasing wind speed was accumulated up to the third net at 30 to 40% of density (D) and to the second net at about 50%, and the accumulation of decreasing wind speed was not recognized at about 75%. The relative efficiency of windbreak goes down in successive net number.
(2) The effect of decreasing wind speed at about 10m/s (200rpm of fan rotation number) is higher than those at about 4m/s (80rpm) and 25m/s (500rpm).
(3) The spreading windbreak nets in a region of paddy rice cultivation in Hokkaido are vinylone cheese cloth (CC-110) and polyethylene russell (PE-9G) ones, however, the effectiveness of the former is higher than that of the latter. As the relative minimum wind speed is about 40% around 2H for CC-110 and the effective area below 50% is by about 10H in the open field, it is considered that CC-100 is more reasonable than CC-110 for the purpose of spread of effective area.
(4) According to the results of experiment in the wind tunnel and of observation in the open field, the effective distance of settled successive nets seems to be 35 to 45H for CC-110 and 40 to 45H for CC-100. It is necessary to select the variety of net on the basis of limiting wind speed to crop protection. The net interval is 35 to 45H in the cases of 40 to 80% of D, i.e., for 2m-high windbreak net of CC-100 or CC-110, about 80m at the paddy rice field.
(5) The minimum wind speed (u_ri) decreases with the increase of D. The u_ri value deteriorates with the increment of successive net number at the lower D for CC-200 and PE-9G, on the contrary at the higher D for PE-18G, vice versa. At the middle D for CC-110, u_ri decreases up to the 2nd net, but recovers slightly at the 3rd net. The distance of appearance point of u_ri in the leeward side diminished with the enlargement of D.
(6) The maximum wind speed (u_ra), and the distance (x axis) and height (z axis) of the appearance point of u_ra increase linearly in proportion to D. The wind speed and the distance of x direction decrease in the order of the 1st, 2nd and 3rd successive nets, on the other hand, the height of z direction enlarges.
(7) The wind speed ratio (u₁/u_-1) decreases, u₂/u₁ decreases below about 50% of D and increases over that, and u₃/u₂ increases, with the increment of D. The variation of wind speed ratios at 200rpm is more moderate than that at 80rpm. Although the order of u₁/u_-1 is the same as that of D at the 1st net, u₃/u₂ is the opposite at the third. Notations are same as in Fig. 8.

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