地膜覆盖棉花、玉米、大豆生育盛期的降温效应

Effects of plastic film covering on dropping ground temperature at the full-growing stages of cotton, maize and soybean

1999～ 2 0 0 1年的试验结果表明地膜覆盖在夏季作物旺盛生长期 (棉花 :开花 -吐絮、玉米 :抽雄穗 -乳熟、大豆 :开花 -结荚 ) 3种覆盖作物的叶面积均比对照作物大 ,其叶面积系数分别为 :棉花 :3.9/ 3.1、玉米 :3.3/ 2 .7、大豆 :4.0 / 3.2。进入作物群体中的光照度 ( I)主要与叶面积系数 ( F)有关 ,而叶面积系数又直接影响消光系数 ( k)的大小。农田覆盖地膜后 ,其在作物生育前期的增温保湿作用 ,使其作物生育速度加快 ,到作物旺盛生长期因其枝叶茂盛 ,叶面积系数增大 ,消光系数减小 ,白天冠层上部叶片截留的太阳总辐射多 ,致使最终进入作物群体中下部的光能减少。白天覆盖地虽然蒸发量减少 ,但因其作物枝叶茂盛 ,蒸腾量则增大 ,农田消耗于蒸散 ( LEC)的能量增多 ,导致加热土壤 ( B项 )的能量减少。覆盖作物地的土壤温度较对照地低 ,其中又以白天地面最高温度降温最为明显 ,棉花、玉米、大豆等 3种作物降温幅度分别为 3.1℃、2 .7℃和 2 .5℃。地膜覆盖在作物旺盛生长期的降温效应 ,可减轻夏季高温对作物的危害 ,夏季白天当温度超过光合作用适宜温度 ( 2 0～ 2 5℃ )以上时 ,呼吸作用消耗的有机物质增加 ,作物生长缓慢 ,而覆盖作物地因其温度较对照地低 ,光合强度大 ,生长活力增强 。

A extensive application of plastic film covered in crop cultivation brought about an international “white revolution” in 1970's.A lot of researches on using of plastic film in cropping have reported nowadays, and the effects of plastic film covering on production increase and water saving have studied in the ways of temp-increase and soil moisture preservation at the early growing stage of crops. The studies were conducted at the full-grown stage of crops in order to discover the effects of plastic film covering on growing rate and production increase and provide a theoretical base for more applications of plastic film. Three-year's researching work began in 1999 on college farm of Hubei Agricultural College in Jingzhou city, Hubei province. Cotton, maize and soybean sowed in 20 April, which was the optimum sowing period in this test area. Contrast design was used in the test with two plots of 100m2 (a film-covering treatment and a contral) and four replications each crop. The test materials were emian15, xiyu3 and edou4. Daily observations of soil temp and growth status of each crop were gained through the whole stages from sowing date to ripeness date, and light intensity of the canopy, outer active layer and soil around root were observed for 5 times per day at full growing stage. Three year's test observations showed that in summer the leaf area of film covering treatments were bigger than the controls when covering plastic film at full-growing stages, to which cotton from blooming to boll opening,maize from heading stage to milking stage and soybean from blooming to milky stage. The LAI of cotton, maize and soybean was 3.9/3.1, 3.3/2.7 and 4.0/3.2 respectively. According to Beer formula( I=I 0·e -KF), light intensity in the crop colony was meanly relative to LAI, but LAI influences the extinction coefficients. Covering plastic film in the field speeded up the growth of field crop for its effects of temp-increase and soil moisture preservation at the earlier growth stage, but at the full-growing stage increased LAI, decreased extinction coefficients for the excessive amount of global radiation held back by the canopy and the lessened solar energy entered lower layer of the crop colony. In addition, according to the heat equilibrium theory:R=PBLEc, evaporation of covering field is reduced but the transpiration is increased for its flourishing branches and leaves, which lead to more energy dissipating and less energy heating the soil. The two reasons above resulted in the lower soil temp of the film covering treatments than the controls. Temperature decreased most when soil temp got the highest level in daytime, and the decrease extents were 3.1℃, 2.7℃ and 2.5℃ for cotton, maize and soybean respectively. Effects of temp-decrease on crops by covering plastic film at the full growing stage could lighten the harm of high temp to crops in summer. According to the theory about three basic temp points of photosynthesis and respiration, when temp exceed the optimum temp of photosynthesis (20～25℃) in the summer days,the respiration consumption of organic matters is increased, and the growth of crops became slow. Film-covering patterns had lower ground temp and higher productivity for a better growth vitality and bigger photosynthesis intensity than non-covering ones in this study. The temp-decreasing effect of film covering at full growing stage will renew the production-increasing theory of film covering, raise the applied value of plastic film covering, and corrected the lopsided conclusion on film covering, which explain the productivity increase merely owe to temp-increasing effect at the early stage of crop, meanwhile,and provide a meteorological basis for more extended application of plastic film covering.