Studies On The Function And The Planting-effect Of A Single-covered And A Double-covered Plastic Shed In Changsha

The plastic shed is a predominant type of protected cultivation in south. The characteristic of the variation of microclimate inside the single-covered and the double-covered plastic shed were studied in Changsha, and their functions and planting-effect were compared. In order to provide a scientific basis for application of proper covering layer and taking workable measures to control, in Changsha, and getting high productivity, good quality and high efficiency in vegetable. The results are as follows:1. Law of variation of temperature inside the single-covered and the double-covered in Changsha.1.1 The seasonal variation of temperature inside the single-covered and the double-covered showed gradual increase trend, in winter and summer. The lowest temperature appeared on the first ten day of January, the lowest air temperature in the double-covered plastic shed, which was 4.2 ℃,increased respectively2.7℃, 4.1℃, compared with the single-covered plastic shed and outside. The highest temperature appeared on the third ten day of March, the highest air temperature in the double-covered plastic shed, which was 30.6℃, increased respectively2. 2℃, 4. 4 C,compared with the single-covered plastic shed and outside.1. 2 The variation of temperature inside the single-covered and the double-covered plastic shed in different weather roughly took on the shape of a Sine, and the variation of temperature in sunny day was greater than that of cloudy and rainy day. The highest air temperature was at about 14:00, in sunny, the mean highest air temperature in the double-covered plastic shed, which was 27. 9℃, increased respectively2. 8℃, 10. 7 ℃, compared with the single-covered plastic shed and outside; the highest soil temperature was at about 16:00; The lowest temperature was at about 6:00 in the early morning. Their diurnal variation took on a single curve peak in the morning, while decreased gradually in the evening.1. 3 In the day, the vertical variation inside the single-covered and the double-covered plastic shed increased along with the increase of height, while in the evening decreased along with the increase of height. Their horizontal variation, in the morning, was that the east side was high while the west side was low, in the afternoon the results were opposite. From south to north, the variation of air temperature was not obvious because the distance was too long.2. Law of variation of intensity of illumination inside the single-covered and the double-covered in Changsha.2.1 The seasonal variation of intensity of illumination in the single-covered and the double-covered plastic shed showed gradual increase trend from winter to summer, the illumination inside the single-covered plastic shed was far stronger than that of the double-covered plastic shed.2. 2 The variation of intensity of illumination in the single-covered and the double-covered plastic shed under different weather took on a single peak curve, and the variation of illumination in sunny day was far greater than that in cloudy day and rainy day, the outside was greater than inside. The maximum of illumination was at about 14:00. Their diurnal variation of intensity of illumination was weak in the morning and the dusk, while it was strong at noon.2.3 The horizontal variation of intensity of illumination in the single-covered and the double-covered was reduced gradually in the morning from east to west, while it was raised in the afternoon.3. Law of variation of relative humidity inside the single-covered and the double-covered in Changsha.3.1 Relative humidity inside in the single-covered and the double-covered plastic shed showed straightly decrease trend in winter and summer. The highest relative humidity inside appeared on December, the relative humidity inside the double-covered plastic shed, which was 95%, increased respectively by 5%, 12% compared with the single-covered plastic shed and outside.3. 2 Variation of the relative humidity inside the single-covered and the double-covered plastic shed under different weather took...