风障对茶园的减风增温效果及对茶树冠层叶片含水率影响

    Effects of windbreaks on wind-decrease, temperature-increase and moisture content of tea leaves in tea garden

    • 摘要: 为解决冬季茶园风寒冻害问题,于2008年1月在安徽农业大学茶场建立塑料薄膜风障,测定风障对茶园的减风增温作用及其对茶树冠层叶片含水率的影响。风障的高度为2.0 m,以5×7网格点测定2.8、2.0 m风障高和1.2 m茶树冠层高度3个层次的风速,以4×4网格点测定地表温度、茶树冠层叶片含水率。结果表明,2.8 m高度,风障上方的风速比环境风速增加30%左右,下风方向的减风作用随风速增大而减小,距离风障7 m区域是风速减弱最强的区域,环境风速2.6 m/s时中轴线风速减小13.5%,环境风速1.0 m/s时的减小幅度达40.0%,在15 m位置基本恢复环境风速。风障高度(2.0 m)最大减风距离出现的位置介于距离风障7~10 m之间。由于薄膜风障不透风,在冠层高度(1.2 m)形成约2倍风障高度宽的准静风区。风障的有效减风作用区域大约相当于风障高度的7.5倍。风障的保温作用与日照条件关系密切,日照较强则可提高保护区的温度,夜间与阴天保温作用较不明显。大风作用下,茶树叶片含水率呈一定程度下降,下降幅度与风速正相关,风速大区域含水率下降幅度也大。在风障有效保护区域,大风结束后叶片含水率可较迅速地恢复,风障有效保护区域外的叶片含水率降幅较小,但恢复较慢。综合减风、增温及叶片含水率恢复情况,薄膜风障对于减轻冬季大风降温的危害具有较好的作用。

       

      Abstract: To solve the freezing of tea farm in winter, a field experiment was conducted in the experimental tea garden at Anhui Agricultural University in January 2008. The windbreaks which were 2.0 meters height and 20 meters long, plastic films were established in the tea garden, and the wind, air temperature and moisture content of tea leaf were measured. The wind speeds in three height levels, 2.8, 2.0 (windbreaks height), and 1.2 m (tea tree canopy height), were measured according to a 5×7 grid. And the surface temperature, moisture content of tea leaves canopy were measured according to a 4×4 grid. The collected data were used to analyze the effects of windbreaks. Results indicated that windbreaks blocking airflow and causing wind velocity had a large change in difference positions. The top of windbreak was faster than environment air velocity. The growth rate of wind velocity on the height of 2.8 m was about 30%. The effect of wind load in the leeward reduced with rising of wind velocity. The leeward area, 7 m distance to the windbreaks, had the slowest wind velocity. Wind velocity of medial axis reduced 13.5% when air velocity reached to 2.6 m/s, and the amplitude decreased to 40% when the air velocity was 1.0 m/s. The wind velocity recovery distance was about 15 m. At the wind barrier height (2.0 m), the most effective area to reduce wind speed was between 7 and 10 m downwind to the wind barrier. There was a para-calm region about double height of the windbreaks on the crown of tea (1.2 m height). The windbreaks sphere action on 1.2 m height was about 7.5 times of the windbreaks height. The windbreaks warming was controlled by the solar power. The warming effect was obviously in sunny day, but it was faint at night and cloudy. Moisture contents of tea leaves were decreased because of the gale and the rates of descent which was pertaining with the wind speed, the greater wind speeds, the faster moisture content decreased. The moisture contents of tea leaves declined smaller in the protected areas of the windbreaks, but the recovery was rapidly. The plastic film windbreaks have an effective for reduce the harm by winter wind and low temperature.

       

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