Preliminary Studies On Marginal Effect In Wide-span Plastic Covered Tunnel Greenhouse

With the development of modern facility agriculture, the large-sized facility is an imperative trend. The wide-span plastic covered tunnel greenhouse is becoming the new favorite of gardening facility. This study observed environmental factors especially marginal environmental factors, and the Conditions for growing of crops which in the marginal and center area grows; analyzed the change of marginal environmental factors and the effects to the crops in autumn-winter and early-spring. By analyzing the data of soil temperature, air temperature, illumination, air speed in the east, we found out the boundary point of marginal soil temperature and characteristics of the various environmental factors, provided basic theory for the studying of wide-span plastic covered tunnel greenhouse marginal effect and improving land utilization rate and Performance-to-price ratio in deed. The concrete results are as follows:1. Results of marginal soil temperature:The soil temperature boundary points of east side were various at different observing period, the distance from soil temperature boundary point of southeast side to east in the wide-span plastic covered tunnel greenhouse was 705cm in the middle ten-day of November 2008,the marginal effect had been existed.The number of soil temperature boundary point was 3,the distance to east was 295cm in the middle ten-day and the last ten-day of December,2008.the soil temperature boundary point of southeast side to east base of the plastic covered tunnel greenhouse was 295cm in the middle ten days of February, 2009, there were the same border area with the middle ten-day of November, 2008. And the point existed in the second cultivation line in the last ten-days of March, 2009, the marginal effect reduced. The soil temperature boundary points of southeast side were various at different times in a day: the farthest soil temperature boundary point appeared in 08:00-10:00, the nearest boundary point appeared in 16:00-18:00, which keeps the same steps with the maximum and minimum values of soil temperature. The distance between farthest soil temperature boundary point and the nearest boundary point was 545cm, which shows that the temperature between day and night was high in soil temperature. The soil temperature boundary point of center in the east were various at different observing period: The marginal effect had been existed from the middle ten-day of November to the first ten- day of December, 2008, the soil temperature boundary point was the number of 6 or 7. The soil temperature boundary point was 2 ,the distance to east was 160cm in the last ten-day of December,2008.Later the soil temperature boundary point began to depart the east. The soil temperature boundary point was 7,the distance to east was 705cm in the first ten-day of February,2009.The middle ten-day or the last ten-day of March, 2009, the soil temperature boundary point was 100cm to east, the marginal effect did not exist. The soil temperature boundary points in center of the east were various at different period of a day: the farthest soil temperature boundary point appeared in 02:00-06:00 and the distance was 507cm to the east, the nearest boundary point appeared in 12:00-18:00 and the distance was 100cm to east, which in this period marginal effect did not exist. The temperature boundary point away from the east. So attention should be paid to the effects of marginal soil temperature to crops.The changes of soil temperature boundary point of northeast was: the boundary point was 7, it was 705cm to the east in the middle of ten-day of November to the first ten-day of December, 2008, and there were six lines of crops growed in the low area. As long as the change of climate, the soil boundary point changed. All in all, the crops which growed in the area would be affected by marginal effect in a long time.The change of soil temperature boundary points in east side were similar. It had levelled at around 3 by the last ten days of March, 2009; scenarios in the centre and north were the same; maximum and minimum values appeared in the south were lagged one period compared with the centre and north.2. Results of marginal air temperatureThe daily change trend of marginal air temperature in the east side was similar with the same height outside. The air temperature was high at noon, and it was lower in morning and night.The change trend was muted and stable in cloudy,it was middle partï¹¥south partï¹¥north part;In sunny,outside and the northeast of plastic shelter was the highest level, and the highest appeared at 12:00,whith the center and north of the east side.In 06:00,the air temperature attained the lowest,and later the air temperature began to rise.From nightfall to 08:00 of next day, the air temperature of center in the east was higher than the north and south,and the situation was opposite from 08:00 to 16:00. The change of air temperature with the measuring point was relatively complex affected by radiation, so it's very difficult to determine the boundary point.3. Results of illuminationThe daily change of marginal illumination was a single peak curve in east side of the wide-span plastic covered tunnel greenhouse, and the maximum value appeared at about 12:00. There were similar trends in and out of wide-span plastic covered tunnel greenhouse. When the solar height is big, the illumination enhanced, when the solar height is small, the illumination reduced, and the change of illumination in the plastic covered tunnel greenhouse was flat.Then, the daily change of marginal illumination of east at the wide-span plastic covered tunnel greenhouse was affected by the times of a day .4. Results of marginal cropThe growth vigor of the middle cucumber was better than marginal, this can be found from plant height, stem diameter and LAI, which indicated that the influence of marginal effect to crop was quite distinct.the cucumber's vigor was better than the south and north, which grow in middle of the east side. The stem was thinner than the south and center of the north, and the growth rate was bigger ,so the crops was more hairchested which growed in the center of the east.5. Result of air speed researchThe change of air speed was very small when had no wind. The overall tendency assumes: in 11:00 around air speed was bigger than in the morning and night. In level distribution, it was small in the central spot and edge is relatively bigger. In the vertical direction, air speed overall change tendency was that the air speed increased along with the temperature difference caused by heights.The distributing rule of air speed in the north and south direction: the air speed was similar in the south and the middle, and it was bigger in the north than in the south and middle. The distributing rule of air speed in the east and west direction: the air speed in the middle was smaller than in the east and west, the east air speed was bigger. The distributing rule of air speed in horizontal direction level: there was little change in north-south direction, east-west direction was half V-shaped distribution.