The water potential of a medium for plant tissue culture may affect the growth and development of the plantlets in vitro.
The purpose of the present paper is to give the water potential values of liquid media in a tabular form or by equations, which are influenced by the composition of the liquid culture medium.
The osmolality of the following four kinds of aqueous solutions were measured separately by using an osmometer. Namely, (1) the basic component solution containing inorganic salts, and vitamins and other micro organic substances, (2) the sucrose solution, (3) the mannitol solution, and (4) the sorbitol solution.
The osmolality of each solution was converted into the water potential value, using the following equation:
φ_w=4.6153×(273.16+t)×ρ_w×ln(55.509/(55.509+a)) where φ_w is the water potential [bar], t the temperature [°C], ρ_w the density of water at t°C [g/cm³], and a the molality [mol/kg] (The osmolality is equal to the molality because the solution can be considered as the ideal dilute solution).
The results can be summarized as follows:
(1) The water potentials due to the basic component of the widely used culture media were measured and the result is shown in Table 1.
(2) The following equation was obtained to estimate the water potential of a liquid medium, φ_w.
φ_w=φ_b-0.78C_s-1.47r_m-1.45r_s
where φ_b is the water potential due to the basic component (see Table 1) [bar], C_s the sucrose concentration (w/v) [%], r_m the mannitol concentration (w/v) [%], and r_s the sorbitol concentration (w/v) [%].

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This paper intends to obtain the detailed map of number of days with snowcover based on mesh-square technique and to apply it for land use planning for barley cultivation in the Hokuriku District.
Statistical relationships were established between the snowcover properties and topographical land features for selected locations in the Hokuriku District. The third degree orographic mesh data was used to determine the topographical parameters which, in tern, were related to number of days with snowcover. The detailed geographical distribution of number of days with snowcover was then estimated from these relationships with the orographic mesh data as inputs. The results were applied for land use planning for barley cultivation.
Important results obtained were as follows:
1) Number of days with snowcover (Sd) on average was given by
S_d=62+2.153√H_m+0.032(R_{e, r1})²+0.145K+0.270(L_r15)
-1.053√P_{60, r15}-0.007H_{a, r10}-0.013K_{s, r3} (r=0.96)
Sd on five- and twenty-year return periods were respectively
S_{d, 5}=72+2.166√H_m+0.028(R_{e, r1})²+0.150K+0.295(L_r15)
-2.757ln(P_{60, r15})-0.008H_{a, r10}-0.016K_{s, r3} (r=0.95)
S_{d, 20}=73+6.850ln(H_m)+0.370(R_{e, r1})²+0.136K+0.218(L_r15)
-0.013K_{s, r1}-0.015K_{s, r3} (r=0.94)
where each predictor variable is indicated in Table 1.
2) Errors of estimate with above regression equations were within about 10% of the observed values for most sample stations (Fig. 3). The regressions underestimated by more than 10% for the adjacent regions of a mountain range over the elevation of about 2, 000 meters in the central Japan where especially heavy snowfall occurs. On the other hand, overestimates were obtained for those stations in island and peninsula regions where oceanic influence on climate may exist. Such deficiency suggests the necessity of introducing factors based on a larger geographical scale if more accurate estimates are required.
3) Multiple regression equations (Eq. 2 through 4) provided distribution of number of days with snowcover (a part of which is mapped in Fig. 4) for all the mesh points of about 1km² grid for the Hokuriku District.
4) This information, together with the effect of snowcover on barley yield (Fig. 5), revealed the areas suitable for barley cultivation on much smaller spatial scale than before (Fig. 6).
We therefore conclude that the multiple regression analysis used in this study with topographical parameters as inputs is a useful tool for agricultural land use planning.

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The thermal performance of a solar heating greenhouse designed for a hydroponic system was studied. The system was constructed with an air-water heat exchanger and heat storage tanks that were combined with hydroponic water beds.
The heat exchanger had been designed for a moderate heat source. To achieve a reasonable price and a compact heat exchanger, the heat transfer surface is made of a polyethylene film shaped into a bag; many poly-bags are installed into a casing in parallel and close to each other. The heat transfer is accomplished as follows: Water flows down inside the bags in a thin layer, and air flows outside the bags.
The water tanks to store solar heat were separated into two parts with a polyethylene film. The upper parts were filled with hydroponic water used for the plant growth bed, and the lower parts were filled with fresh water. The fresh water was circulated into the heat exchanger to recover the solar heat inside the greenhouse and to release the heat for heating.
The system was designed in 3.6m×9.0m greenhouse equipped with an interior curtain. The total heat transfer surface in the heat exchanger was 28m² and the heat transfer rate was 16kcal/m²h°C. The two water tanks (6m long, 0.6m wide and 0.5m deep) were installed and filled with 0.8m³ of hydroponic water and 2.8m³ of fresh water. The tanks were buried 0.35m deep under the ground to keep favorable working conditions. A 2.08kW electric water heater was installed into the tank for auxiliary heating.
Cucumbers were grown and the data were collected through seventy days from Jan. 5 in 1983.
The averaged minimum air temperature inside the greenhouse was maintained at 11.4°C, the solar heat storage efficiency was 0.18 and solar heat provided 77% of the total heat for heating through seventy days.
The solar heat storage efficiency depended on outside insolation. When outside insolation was less than 1000kcal/m² day, the solar heat storage efficiency was zero, and was 0.32 when outside insolation was over 3000kcal/m² day. The highest COP of the system (the heat released from the heat storage tank/the energy consumption to store and release the solar heat) was 6.6 and the averaged COP was 4.1. The COP was also in proportion to outside insolation. In the days when the COP was over 4.1, the heating was achieved with only the solar heat storage.
The hydroponic water temperature was maintained at 24-15°C by the heat from the fresh water, high enough to grow cucumbers. Therefore, it was not necessary to apply another heat source to heat the hydroponic water.
The cucumbers grew well and the system appeared to be able to supply 77% of heating energy from solar heat. It would be necessary for further research to optimize carbon dioxide and humidity levels without deteriorating the capability of solar heating for practical use.

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In recent years, energy saving in greenhouse cultivation has been an objective of many researches. One of measures for energy saving is an accurate control of a room temperature to avoid excessive heating. To achieve such an accurate control with small heaters used in greenhouses, it is necessary to repeat firing and extinguishing with short time intervals.
It has been said that the heat efficiency of the hot water boiler drops with the decrease of the heating load factor due to the increase of the heat loss from the boiler surface. Little is known, however, on the effect of the frequency of the intermittent firing on the heat efficiency, or on the difference of the heat efficiencies between intermittent firing and continuous firing. The objective of this study is to evaluate the heat efficiency at the intermittent firing.
First of all, we evaluated the heat loss caused by the unburned carbon particles, carbonhydrates and imperfect combustion at the start and end of burning and results were compared with those at the continuous combustion. The measurements showed that the unburned carbon particles appeared only at the start of firing and the period of the appearance was less than 1 second. This means that the effect of unburned carbon particles on the heat loss is negligibly small, if the heater burns for more than 1 minute. The heat loss due to unburned carbonhydrates and imperfect combustion which was estimated from their maximum concentrations during combustion was less than 0.5% and was also negligibly small, if the heater burns at the appropriate air ratio. These results show that firing or extinguishing brings about only a negligible heat loss.
After long period of the intermittent firing had been conducted, the heat efficiency at the continuous combustion dropped only 4-5% from the initial value for a type of the hot-air heater easily accumulating soot. It dropped less than 1% from the initial value for a type of the hot-air heater hardly accumulating soot. These results show that the effect of long term intermittent firing on the heat efficiency is less than the value so far estimated without measurements. One of the reasons of this phenomena may be that most part of the heat generated by the heater is exchanged on the surface of the combustion chamber where the soot accumulates hardly.

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For energy saving and producing high quality crops, development of the accurate control method for the greenhouse air temperature has been desired. Accurate control should be achieved by frequent repetition of heater firing in the case of small scale greenhouses which are common in Japan. It has been said, however, that heat efficiency decreases at the intermittent firing and consequently it should be avoided.
Heat efficiency of a heater during the intermittent firing is affected not only by heat loss due to imperfect combustion and unburned carbon but also by the change of conditions referent to the heat transfer. In the previous report (Ohara and Naito, 1986), heat loss due to imperfect combustion and unburned carbon has been shown to be negligible. In this report heat efficiencies affected also by the change of heat transfer conditions were studied. Experiments were conducted using a hot-water boiler and two types of hot-air heater.
The results showed that heat efficiency of the boiler (kerosene combustion type) at the continuous circulation of low temperature water increased as the period of firing became shorter, while heat efficiency at the intermittent circulation of high temperature water decreased due to the increase of heat loss from the boiler surface.
The heat efficiency of the hot air heater (LPG combustion type) was little affected by the intermittent firing. In this case, cool air was supplied to prevent the body exposed to the flame from the high temperature corrosion, which resulted in high heat loss after the extinguishment. If the heat stored at the heater body is collected and utilized for the greenhouse heating, the heat efficiency may be increased. The heat efficiency of the hot-air heater (heavy oil combustion type) at the intermittent firing increased by 4% compared with the efficiency measured during the continuous firing. At the firing heat loss due to the exhaust gas was decreased by the increased heat transfer to the lower temperature surface and at the extinguishment most of the heat stored in the body was collected and utilized.
From these results, it has become clear that frequent firing for the accurate room temperature control does not decrease heat efficiency and it even increases heat efficiency in some cases.

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