Preliminary Studies On Marginal Effect In Sunlight Greenhouse

Because of good economy and wide adaptability, sunlight greenhouse still would be the developmental mainstream of facilities agriculture in china in future. Recent years, most of studies on sunlight greenhouse were concentrated on structure optimization and practical application. The studies on environmental factors were still not systemic and comprehensive, especially on marginal environmental factors. During main growth stage of eggplant from winter to spring ,the experiment regularly observed marginal light and temperature factors in the east, west, south and north side of sunlight greenhouse, and observed the growth vigor of marginal and middle crop, then analyzed the change of marginal environmental factors in sunlight greenhouse in winter and autumn; the article proposed the concept of sunlight greenhouse marginal effect ,by analyzing the data of soil temperature in different parts, the experiment found out the boundary point of marginal soil temperature, we could provide theoretical basis for studying sunlight greenhouse marginal effect and improving land utilization rate, the concrete results were as follows:1. Results of marginal soil temperature:The soil temperature boundary points of south side were various at different observing period: the distance from soil temperature boundary point of south side to south base angle in greenhouse was 105cm in the last ten-day of November 2007, the marginal effect had been existed. In the coldest January 2008, the number of soil temperature boundary point was 18, the distance to south base angle was 270cm, for greenhouse of 10m span, the exist of marginal effect was indispensable. In the last ten-day of March 2008, the distance from soil temperature boundary point of south side to south base angle was 45cm, the distance from cultivation area to south base angle was 60cm, the marginal effect had not been existed. The soil temperature boundary points of south side were also various at different period of one day: the distance from the farthest soil temperature boundary point to south base angle was 285cm, the distance from the nearest soil temperature boundary point to south base angle was 150cm, the time they appeared was uniform with maximum and minimum value of soil temperature. The distance from the nearest soil temperature boundary point to the farthest soil temperature boundary point was 135cm; this shown that the diurnal temperature of south soil temperature was high.The soil temperature boundary point of west and east side were various at different observing period: the distance from soil temperature boundary point of east side to east wall of greenhouse was 210cm, the distance from soil temperature boundary point of west side to west wall was 150cm in the last ten-day of November 2007; In the cold January 2008, the distance from soil temperature boundary point of east side to east wall of greenhouse was 420cm, the distance from soil temperature boundary point of west side to west wall was 390cm; in the last ten-day of March 2008, the distance from soil temperature boundary point of east side to east wall of greenhouse was 120cm, the distance from soil temperature boundary point of west side to west wall was 90cm. For the distance from cultivation area to west and east wall were all 100cm, in the east side of greenhouse, the influence of variable and low temperature on crop still had, but in the west, had not the influence The soil temperature boundary point of west and east side were also various at different period of one day: the time which the farthest boundary point of west and east soil temperature appeared were all 15:00-17:00,the distance to east wall was 270cm, to west wall was 240cm; the time which the nearest boundary point of east soil temperature appeared was 9:00-11:00, the distance to west and east wall were all 150cm; the time which the nearest boundary point of west soil temperature appeared was remained 12 hours, this shown that the daily change of west soil temperature boundary point was smaller and more stable than east.The change of north soil temperature was very complex; it could not obtain definite soil temperature boundary point, unlike south, east and west marginal soil temperature. The change of north marginal soil temperature following the measuring point was that measuring point temperature nearing the north wall was high, with the increasing of distance, temperature dropped in early spring and late autumn; in the coldest January 2008, from No.1 measuring point to middle, the north marginal soil temperature was continuous increase with a little amplitude, it shown that the heat storage dropped sharply under continuous snowy and cloudy day.The vertical change of marginal soil temperature in sunlight greenhouse: the difference was relatively large among each measuring point in south side, however, the difference was small in north side. The result of vertical change of south marginal soil temperature shown that boundary point of south marginal soil temperature is No.4 measuring point, the distance to south base angle is 140cm on December 30th 2007.It was uniform with the boundary point on December 28th 2007.The change trend were fundamentally uniform among each measuring point in west and east side, Compared with soil temperature of different measuring point in different depth, change amplitude of east was relatively large, of west was very small.Daily change of marginal soil temperature in different parts and different depth: the change amplitude of marginal soil temperature was 5cm>10 cm>20cm, that is, the daily change of measuring point which closed to the surface of soil was large, with the increasing of the depth, the daily change was small. Meanwhile, the time which maximum and minimum soil temperature appeared was relatively lagged with the depth increased.2. Results of marginal air temperatureThe daily change trend of marginal air temperature of 2/3 plant height in north and south side was uniform with the same height outside, just gentler than outside at night. The south air temperature was higher than north in most of daytime, but it was opposite at night. The daily change trend of marginal air temperature in west and east side was uniform with the same height outside; the west air temperature was higher than east in most of the day, and the west soil temperature reached the maximum value of the day.The change of air temperature with the measuring point was relatively complex because affected by radiation, so its boundary point can not be determined.3. Results of marginal illuminationThe daily change of marginal illumination was single peak curve in each side of sunlight greenhouse, and their maximum value appeared at pre and post noon. The illumination outside was strongest ,the north was weakest; compared with west and east side, before 13:00,the illumination of west was bigger than east, but after that time, west was smaller than east; compared with middle part and south side, the illumination of south was a little stronger than the middle.The change trend of illumination following the measuring point of sunny and cloudy day was completely same in different part of greenhouse: with the distance to south base angle increased, at first the illumination was stably invariant then was descendant. With the distance to west and east wall increased, the illumination was ascending. The illumination of north was constant.4. Results of marginal crop The growth vigor of the middle eggplant was better than marginal; this can be found from plant height, stem diameter and transmittance of plant. It indicated that the influence of marginal effect to crop was quite distinct.The relationship between transpiration rate, stomata conductance and photosynthetically active radiation of different parts eggplants in greenhouse were linear correlation; transpiration rate and stomata conductance were all ascending with the increasing of photosynthetically active radiation in the range of 0～1400μmol·m-2·s-1.The measurement on the response of net photosynthesis to photosynthetically active radiation of eggplant in different parts of greenhouse shown that the range of light saturation point was about 1 370～1 600μmol·m-2·s-1, the range of light compensation point was about 50.974～93.604μmol·m-2·s-1,and the value of south were all the biggest, the value of north were all the smallest.