植株高大的目标作物对防护林防风效应影响的风洞模拟试验

防护林对降低风害，促进农作物稳产高产具有重要作用，但目前防护林配置研究仅注意到防护林本身，忽视了果树等植株高大作物对风速的影响。该文选取1种果树（枣树），3种疏透度林带（30.12%、25.01%和20.92%），在3种风速下（8、10、和14 m/s）进行风洞模拟，研究种植枣树等植株高大目标作物时，防护林风场特征及防风效应。结果表明：不同风速和林带疏透度下，枣树对林带前后流场均具有显著影响，特别是林带后近地面风速削减程度较大。1）随风速增大，无枣树林带防风效应减小，有枣树林带变化较小，但增量增大，在8、10、和14m/s风速下分别增大16.40%、23.65%和29.05%；2）疏透度为30.12%时，有枣树林带综合防风效应最佳。随疏透度减小，无枣树林带防风效应增大，有枣树林带变化较小，但增量减小，在3种疏透度下分别增加22.72%、15.22%和1.28%。因此总结认为在集约化和精准农业要求下，进行枣树等植株高大作物防护林带配置时，应考虑目标作物的防风效应，如此可减少防护林面积，显著提高目标作物的经济效益。

Wind tunnel simulation for contribution of tall target jujube to protective effect of shelterbelt

Abstract: Shelterbelt plays an important role in promoting a stable and high yield of crops by reducing wind speed. However, it is often ignored that plants such as tall fruiters have an impact on wind speed during shelterbelt configuration. In this study, we examined 3 shelterbelt models which were the jujube tree models with a height of 1.5 cm and different degrees of porosity (30.12%, 25.01% and 20.92%) and a shelterbelt average height of 7 cm. These models were used for wind tunnel simulation under different wind speeds (8, 10 and 14 m/s) to evaluate the effects of tall fruiters on the wind field and the protective effects of the shelterbelt. The results showed that jujube exerted a notable effect on the wind field and demonstrated the protective effect of shelterbelt, particularly by reducing wind speed in the ground layer in all the test conditions. The protective effect continued to increase with the increase in the number of jujubes. Therefore, we conclude that it is very important to pay attention to the type of crop (particularly tall fruiters) when studying the configuration of the shelterbelt. Under the same porosity condition, with the increase of wind speed, the protective effect of the shelterbelt with no jujubes reduced; however, there was not much difference observed for the shelterbelt with jujubes. In addition, the increase amplitude of protective effect exerted by the jujube increased with the increase of wind speed; the protective effect increased by 16.01%, 23.65% and 29.05% in wind fields under 8, 10 and 14 m/s wind speed, respectively. Because every plant had a range of wind resistance, the protective effect of the jujube shelterbelt did not decrease with the increase of wind speed. Under the same wind speed, with the decreasing porosity of the shelterbelt, the protective effect of the shelterbelt with no jujube increased; however, there was not much difference observed for the shelterbelt with jujubes. The increase amplitude of protective effect exerted by the jujube decreased with the decrease of porosity; the protective effect increased by 22.72%, 15.22% and 1.28% with the porosity of 30.12%, 25.01% and 20.92%, respectively. Because jujube compensated for the decreasing porosity, the shelterbelt with jujube did not decrease in its protective effects with the decrease in porosity. But porosity decreasing made the protective effect of shelterbelt increase and that of jujube decrease, so the contribution of jujube was smaller and smaller. We found that a porosity of 30.12% was optimal for the shelterbelt with jujubes, which demonstrated the maximum protective effect at this degree of porosity. In addition, we found that a smaller degree of porosity may create turbulence, which harmed the plants, increased the areas of shelterbelt and decreased the areas for plants, and was used rarely in real life. For example, in South Xinjiang, if the shelterbelt spacing was increased from 10 to 20 times of the shelterbelt average height, it would increase the plant area by 0.54%. If the jujube produced an annual 20 thousand yuan per 667 m2, 756 million yuan per year would be obtained for 7 million 667 m2 jujube in South Xinjiang. Therefore, if completely considering the protective effect of plants, it can decrease the shelterbelt areas and increase crop areas, and promote the economic effect of crops.