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

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.