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.