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试验测定了在纱布罩盖下塑料薄膜作为烟草苗床土表复盖物的效果。威斯康辛地区烟草育苗于4月20日开始播种,一般在6月初开始移栽,当地4月20日的平均气温为8℃,而6月10日平均气温为18℃。由于这个地区在此时季中的气温迅速升高及强烈的光照,若使用塑料薄膜来罩盖苗床会使罩内发生高温,而造成土壤迅速失水干燥和热伤烟苗。因此,塑料薄膜用作苗床罩盖物已被证明失败了。而塑料薄膜用作在正常纱布罩盖下的土壤表面复盖物,显示了效果。苗床在播种后,立即在土表复盖2密耳(0.005厘米)厚的塑料薄膜,一直保持到烟苗的生长进入五叶期。与无塑料薄膜复盖物对比,在薄膜下的适宜环境条件使烟苗出得更快更多;如下表所示:
The test determined the effect of the plastic film under the cover of the gauze as a cover of the soil surface of the tobacco seedbed. Tobacco nurseries in Wisconsin began sowing on April 20 and generally begin transplanting in early June, with the average temperature of 8 ° C on April 20 and 18 ° C on June 10. Due to the rapid temperature rise and strong light in the area during this time of year, the use of plastic film to cover the seedbed will cause high temperatures in the cover, causing the soil to quickly dehydrate, dry and burn tobacco seedlings. Therefore, the use of plastic film as seedbed cover has proven unsuccessful. The plastic film is used as a cover on the soil surface under the normal gauze cover, showing the effect. The seedbed immediately sowed and covered with 2 mil (0.005 cm) thick plastic film on the soil surface until the growth of tobacco seedlings entered the five-leaf stage. In contrast to the plastic-free film coverings, the tobacco leaves developed faster and more under suitable environmental conditions under the film, as shown in the following table: