| With the reference of the outdoor, functions of the single- covered plastic shed and double- covered plastic shed were compared, in Teaching Garden of Vegetable, Hunan Agricultural University. Also, the cultivated effects of the two kinds of greenhouses were compared by the cultivation of cucumbers and tomatoes. The primary testing result was showed as follows.1. The character of the variations of the temperature inside the simple -covered shed and the double-covered plastic shed1.1 From Dongzhi to Chunfen , The current of air temperature variations inside the simple-covered and double-covered plastic sheds presented rise. The each average air temperature in a period of ten days in Dongzhi was 6.1℃, 8.1℃ respectively ,and in Chunfen was 19.2℃, 20.2℃ respectively. In each period of ten days , the average air temperature increased by degrees of 2℃, The average air temperature in a period of ten days inside the simple-covered plastic sheds was higher 2~3℃ than outside ,and The average air temperature in a period of ten days inside the double-covered plastic sheds was higher 4~5℃ than outside. There were obvious effects for increasing the amount of covered layer.1.2 From winter to spring , the difference in temperature inside the simple-covered or double-covered plastic shed was higher than outside , inside the simple-covered plastic shed was 9~19℃,inside the double-covered which was 10~20℃,and the outside was 6~18℃.the extremely lowest temperature inside the simple-covered and double-covered plastic sheds was respectively 1℃, 3.5 ℃,higher 2℃, 4.5℃ respectively than the outside .1.3 The variation of temperature inside the different-covered plastic shed on the different weather conditions roughly took on the shape of a Sine, and the variation range of temperature in sunny day was greater than that in cloudy day and rainy day. The highest air temperature appeared at 14:00 probably, and the lowest air temperature appeared 6:00 probably.1.4 About the vertical variation of air temperature inside the sheds, it increased withthe increasing of height in day, but on the contrary ,it descended in the evening.1.5 The horizontal variation of air temperature inside the different-covered plastic shed , in the morning ,was that the east side was higher than the west side, but in the afternoon, the results were opposite. The south side air temperature was higher than the north in the whole day, but the variation of air temperature was not obvious. 2 The variation of the ground temperature inside the simple-covered plastic shed and the double-covered plastic shed.2.1 From Dongzhi to Chunfen , the current of the ground temperature variations inside the simple-covered shed and the double-covered plastic shed presented rise as a whole. The solar term average ground temperature in Dongzhi was 8.5 °C , 8.TC respectively ,and in Chunfen was 21.4DC> 21.7°C respectively. The solar term average air temperature inside the simple-covered plastic shed was higher 2~4°C than outside ,and inside the double-covered plastic sheds was higher 3~5°C than outside. The variation of ground temperature was synchronous with air temperature.2.2 The ground temperature inside the sheds all decreased in turn that the sunny days was higher than the cloudy days and the cloudy days was higher than the rainy days. There were obvious differences between the outside and the simple-covered plastic shed or the double-covered plastic shed. It was obviously favorable that increased the amount of covered layers.3. The variation of the relative humidity inside the simple-covered plastic shed and the double-covered plastic shed.3.1 The relative humidity variation inside the single-covered plastic shed showed straightly decrease trend in winter and spring, and the highest relative humidity inside sheds appeared on January, which were 90.8°/^ 91.3% respectively . The relative humidity inside the double-covered plastic shed was higher than the simple-covered plastic shed in some sort.3.2. The diurnal variation of the relative humidity inside sheds was reduced gradually along with the increasing of air temperature in day time, while it was raised along with the decreasing of air temperature in the evening.3.3 The variation of the relative humidity in the different-covered plastic shed underthe different weather conditions took on a single valley curve, and the variation range in sunny days was obviously greater than in cloudy days or in rainy days, and the outside was obviously greater than the inside.3.4 The vertical variation inside the different-covered plastic shed was reduced along with the increasing of height in the day, while it was raised along with the increasing of the height in the evening.3.5 About the horizontal variation of the relative humidity inside the different-covered plastic shed, the eastside was higher than the west ,but it was small along the south side to the north side.4. The variation of illumination inside the different-covered plastic shed.4.1 The seasonal variation of illumination in the different-covered plastic shed showed gradual increase trend from winter to spring. The illumination outside the shed was the greatest, and then inside the single-covered plastic shed, finally inside the double-covered plastic shed.4.2 The diurnal variation of the illumination inside the different-covered plastic shed were consistent with the outside, showed a shape of single peak, that is to say that in the morning and the dusk was weak, while it was far stronger at noon..4.3 About the variation of illumination in the different-covered plastic shed under different weather condition, it in sunny day was greater than that in cloudy day and rainy day, the outside was greater than inside.4.4 The horizontal variation of illumination in the different-covered plastic shed was reduced gradually from east to west in the morning, while it was raised in the afternoon.5. The highness of tomato plant had increased with the increase of covered layer, but the change of sickness and the spread degree of tomato or cucumber plant was opposite to the highness. The fruit shape and the single fruit weight of cucumber and tomato inside the different-covered plastic shed did not take on distinct difference.6. The velocity of the crop photosynthesis inside double-covered plastic shed in sunny day showed a shape of double peak, the minimum PR appeared at 12:30 probably; The velocity of the crop photosynthesis inside double-covered plastic shed in cloudy day showed a shape of single peak, the maximum PR appeared at about 12:30.The velocity ofthe crop photosynthesis inside plastic shed decreased along with the increasing of covered layer.7. The premature trait of cucumber in the double-covered plastic shed were the earlier 7 days than in the single-covered plastic shed, and 18 days than the outside. And the early output increased 25.7% and 33.4% respectively, the total output increased 4.9%and 4.8% respectively. The economic benefit that planted cucumbers and tomatoes in the double-covered plastic shed was better than that planted cucumbers or tomatoes in the single-covered plastic shed.
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