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（一）温度条件

(1) temperature condition

塑料薄膜具有保温性。覆盖薄膜后，大棚内的浊度将随着外界气温的升高而升高，随着外界气温下降而下降。并存在着明显的季节变化和较大的昼夜温差。越是低温期温差越大。一般在寒季大棚内日 增温可达3－6℃，阴天或夜间增温能力仅1－2℃。春暖时节棚内和露地的温差逐渐加大，增温可达6－15℃。外界气温升高时，棚肉增温相对加大，最高可达20℃以上，因此大棚内存在着高温及冰冻危害，需进行人工调整。在高温季节棚内可产生50℃以上的高温。进行全棚通风，棚外覆盖草帘或搭成＂凉棚＂，可比露地气温低1－2℃。冬季晴天时，夜间最低温度可比露地高1－3℃，阴天时几科与露地相同。因此大棚的主要生产季节为春、夏、秋季。通过保温及通风降温可使棚温保持在15－30℃的生长适温。

Plastic film has heat preservation property. After covering the film, the turbidity in the greenhouse will rise with the increase of the outside temperature, and decrease with the decrease of the outside temperature. And there is obvious seasonal variation and larger diurnal temperature difference. The longer the temperature is, the greater the temperature difference. Generally, the daily warming in the cold season greenhouse can reach 3-6 degrees, and the ability to increase the temperature at cloudy or nighttime is only 1-2 degrees. The spring season and in the greenhouse temperature gradually increased, increasing temperature can reach 6 to 15 DEG C. When the outside temperature rises, the temperature of the shed meat increases relatively, and the temperature can reach above 20. Therefore, the greenhouse has the harm of high temperature and freezing, so it needs manual adjustment. In the season of high temperature shed can generate high temperature above 50 DEG C. The whole roof ventilation, shed covered straws or a "shelter", can be 1 than that of the low temperature of - 2 DEG C. In winter sunny, minimum night temperature can be higher than that of 1 C, almost the same in cloudy days. Therefore, the main production seasons are spring, summer and autumn. The temperature of the shed can be kept at the temperature of 15-30 DEG C by heat preservation and ventilation.

（二）光照条件

(two) illumination conditions

新的塑料薄膜透光率可达80－90％，但在使用期间由于灰尘污染、吸附水滴、薄膜老化等原因、而使透光率减少10－30％。大棚内的光照条件受季节、天气状况、覆盖方式（棚形结构、方位、规模大小等）、薄膜种类及使用新旧程度情况的不同等，而产生很大差异。大棚越高大，棚内垂直方向的辐射照度差异越大，棚内上层及地面的辐照度相差达20－30％。在冬春季节以东西延长的大棚光照条件较好、它比南北延长的大棚光照条件为好，局部光照条件所差无几。但东西延长的大棚南北两侧辐照度可差达10－20％。 不同棚型结构对棚内受光的影响很大，双层薄膜覆盖虽然保温性能较好，但受光条件可比单层薄膜盖的棚减少一半左右。 此外，连栋大棚及采用不同的建棚材料等对受光也产生很大的影响（表4-2-3）。从表中可看出，以单栋钢材及硬塑结构的大棚受光较好，只比露地减少透光率28％。连栋棚受光条件较差。因此建棚采用的材料在能承受一定的荷载时，应尽量选用轻型材料并简化结构，既不能影响受光，又要保护坚固，经济实用。 表4-2-3 不同棚型结构的受光量 大棚类型透光量勒克斯（万）透光率（％） 单栋钢材结构 单栋竹木结构 单栋硬塑结构 连栋钢筋水泥 露地对照  薄膜在覆盖期间由于灰尘污染而会大大降低透光率，新薄膜使用两天后，灰尘污染可使透光率降低14.5%。10天后会降低25％，半月后降低28％以下。一般情况下，因尘染可使透光率降低10－20％。严重污染时，棚内受光量只有7％，而造成不能使用的程度。一般薄膜又易吸附水蒸气，在薄膜上凝聚成水滴，使薄膜的透光率减少10－30％。因此，防止薄膜污染，防止凝聚水滴是重要的措施。再者薄膜在使用期间，由于高温、低温和受太阳光紫外线的影响，使薄膜＂老化＂。薄膜老化后透光率降低20－40％，甚至失去使用价值。因此大棚覆盖的薄膜，应选用耐温防老化、除尘无滴的长寿膜，以增强棚内受光、增温、延长使用期。

The new plastic film transmittance up to 80-90%, but during use due to dust pollution, water adsorption, aging and other reasons, the film transmittance decreased 1030%. The light conditions in greenhouse are greatly different from season, weather condition, coverage mode (canopy structure, orientation, size, etc.), film type and the degree of using new and old. In the tall, radiant intensity difference in vertical direction is shed, shed upper and ground irradiance is about 20% - 30%. To what extend in the winter season in a better light conditions, than the north and South extension greenhouse light conditions as well, local illumination conditions are almost the same. But what extension of the north and south sides of greenhouse irradiance was up to 10 - 20%. Different roof structure on the shed by the light of the great influence, double film covering although good insulation properties, but light conditions than the monolayer film cover shed reduced by about half. In addition, the multi span greenhouses with different shedconstruction materials and also have a great effect on the light (table 4-2-3). As can be seen from the table, with single steel and hard plastic structure of greenhouse better exposure, only 28% lighter than the open field transmittance. Multi span shed by light conditions. Therefore, when the material used in the building shed can bear a certain load, the light material should be selected as much as possible, and the structure can be simplified. The utility model can not affect the light absorption, but also has the advantages of firmness, economy and practicability. Table 4-2-3 shed different type structure light greenhouse type light quantity lux (million) transmission rate (%) Dan Dong steel single bamboo single hard plastic multi span reinforced concrete structure in the control period due to dust pollution in the film coverage and will greatly reduce the transmission rate, the new film after two days of use, the dust pollution can make light to reduce the rate of 14.5%. 10 days later, it will be lowered by 25% and 28% below the half moon. Generally, because of dust, the transmittance can be reduced by 10 - 20%. Serious pollution, the light is only 7%, which is not the extent of use. Generally, the film is easy to absorb water vapor, and condenses into water droplets on the film to reduce the transmittance of the film by 10 - 30%. Therefore, to prevent membrane pollution and prevent condensation of water droplets is an important measure. Moreover, when the film is used, the film is aging because of the influence of high temperature, low temperature and ultraviolet ray of sunlight". The film transmittance decrease by 20-40% after aging, even lose value. So the greenhouse films should be used in high temperature aging, no dust drop long film, in order to enhance the light, temperature, prolong the time.