Korla fragrant pear is the main pear variety and one of the most famous fruits in Southern Xinjiang. The use of protective nets in fruit tree production is increasing; however, the cultivation of Korla fragrant pear in Xinjiang has yet to be developed. Therefore, we used the ground and underground microclimate anti-hail network and open-air conditions to determine the fruit quality and measure tree growth-related indicators. Additionally, we subsequently recorded the average yield of fragrant pear fruits to evaluate their economic value under the anti-hail net and open-air environments. Furthermore, we performed a correlation analysis to explore the correlation between environmental factors and fruit quality and growth under the two conditions. We found that the anti-hail net cover provided a conducive environment for the vegetative and reproductive growth of trees. Under similar fruit quality conditions, the average yield was markedly higher under the anti-hail net environment than under the open-air environment. Furthermore, the economic benefit under the anti-hail net was higher for all factors, except for the average facility cost during the previous year, than that under the open-air condition.
Korla fragrant pear (Pyrus bretschneideri Rehd) is a unique variety in the Rosaceae family that is mainly produced in the fruit tree belt around the Tarim Basin in Xinjiang, China. The pear is famous worldwide because of its thin skin, delicate flesh, juiciness, and high sugar content (Gao et al., 2005). In addition, the production of the Korla fragrant pear in Xinjiang has increased because of its economic benefits. Therefore, the korla pear fruit industry has become an important contributing factor in the local economy (Chen et al., 2020).
However, extreme weather, such as hail, has caused significant economic losses in apple and pear production, thus limiting the development of the fruit industry in Xinjiang (Shen and Gao, 2021). Additionally, the extreme light intensity experienced in the summer in Xinjiang may burn bark tissue (Szyma’nska et al., 2017) and cause fruit sunburn, leading to economic losses. However, protective nets (also known as anti-hail nets or shading nets) have been widely used in fruit tree production globally (Manja and Aoun, 2019). The anti-hail net is a mesh made of high-density polyethylene material to improve flexibility and reduce mechanical damage (Castellano et al., 2010). Previous studies mainly focused on the effects of net color and the level of net cover on the yield and quality of pears. The protective nets can cover the whole tree, thereby preventing damage from birds, fruit bats, insects, and wind (Chouinard et al., 2017). However, semi-covered protective nets are usually set at the top of the tree, leaving sufficient space for growth and preventing hail damage to fruits and trees (Mupambi et al., 2018). Previous studies have shown that the protective net cover increases light scattering (Nissim-Levi et al., 2008) and reduces light intensity and fruit burn (Lu, 2014). Furthermore, protective nets create an excellent microclimate by maintaining conducive relative humidity, soil and air temperatures, light intensity, and soil water content for fruit trees (Vera et al., 2019). In addition, tree protection and improvement of fruit quality and yield by protective nets have been well-documented by previous studies (Bosco et al., 2020; Girona and Behboudian, 2012). However, previous studies of anti-hail networks have mainly focused on apples; therefore, studies of pear fruits remain limited. With the introduction of technology, anti-hail networks have been used for Korla fragrant pear production in Southern Xinjiang.
The experiment was performed during a high incidence of hail disasters in Xinjiang. Factors such as microclimate and fruit tree growth and quality were used to compare the differences in various indicators of the Korla fragrant pear in the anti-hail net and open-air environments. The indicators were subsequently used to determine the effect of anti-hail net establishment on fruit quality, tree growth, and economic benefits.
This study was performed at the Korla fragrant pear demonstration orchard (40.55 °N, 81.02 °E) of the second battalion of the ninth regiment of the Xinjiang Production and Construction Corps of China from June to Sept. 2021. The orchard covers 10 ha. The anti-hail net with a 3- to 5-year service life span was erected on 3 ha of the orchard. The primary cultivation method used during this study had inter- and in-row spacing of 4 and 1.5 m (Fig. 1), respectively. The Korla fragrant pear trees were used as the primary variety, and the Dangshansu pear trees were used as pollinators. All management practices were in accordance with commercial production standards, except for the areas covered by the anti-hail net.
During the study period, the weather was overcast, with light rain on 12, 13, 19, 21, and 31 July, 12, 14, 27, and 28 Aug., and 1 and 12 Sept. According to field observations, there was small-particle hail on 13, 19, and 31 July and 28 Aug.
According to previous meteorological reports, June to September is a period when a high incidence of hail disasters occurs (Shen and Gao, 2021). Therefore, the study was performed from 21 June to 12 Sept. by measuring the relevant microclimate data every 20 d. During this study, the Korla fragrant pear in an open-air environment was used as the control. Temperature, humidity, and light intensity of each measurement stage were measured at 0800, 1200, and 1800 hr local time using a DJL-18 temperature, humidity, and illumination meter (Zhejiang Tuopu Agricultural Science and Technology Co., Ltd., Zhejiang, China). The surface (20 and 40 cm) soil temperature was measured using a geothermometer (Brannan, San Francisco, CA). All parameters, except the soil moisture content, were measured from three randomly selected trees. Soil samples were collected from depths of 10, 20, 30, 40, 50, and 60 cm at 0800, 1200, and 1800 hr to determine the water content. Representative sunny and rainy days were selected, and all other indices except the soil moisture content were measured at 1-h intervals from 0800 to 1800 hr.
During the last period of the microclimate measurements, the length and diameter of spring, summer, and autumn Korla fragrant pear tree shoots and the taper of the branches in the open-air and anti-hail net environments were measured. The soil and plant analyzer development (SPAD) values of 30 leaves were measured at three locations, with each using a TYS-A chlorophyll meter (Zhejiang Tuopu Instrument Co., Ltd.) according to the methods of Ji et al. (2020). Additionally, 60 leaves were randomly collected to measure the leaf type index and water content.
Thirty pear fruits were randomly picked from each of the two environments on 25 Sept. The single fruit weight was measured using an electronic balance (Thermo Fisher Scientific, Waltham, MA). The fruit length and width were measured using an electronic vernier caliper (Mitutoyo Instruments, Kawasaki, Japan). The fruit hardness was measured using a hardness tester (Mitutoyo Instruments). The content of fruit soluble solids was measured using a digital refractometer PAL-1 (ATAGO Co., Ltd, Tokyo, Japan). The freezing method (Wang et al., 2013) was used to determine the fruit cell and peel wax contents (Zheng et al., 2019). A hand-held colorimeter CR410 (Konica Minolta Holdings, Inc., Tokyo, Japan) was used to measure the degree of skin color.
After the completion of fruit collection from the orchard, the yield and purchase price of the year were determined through market research under the anti-hail net and open-air environments to evaluate the overall economic benefit and the cost per unit area under the anti-hail network.
Data processing and view rendering were performed using Excel 365 (Microsoft Corporation, Redmond, WA) and Prism 8 (GraphPad, San Diego, CA) software.
Anti-hail nets have a positive effect on agricultural production (Bai et al., 2010). Previous studies have shown that anti-hail nets alleviate abiotic stress and reduce extreme weather effects (Liu et al., 2011). However, irrespective of the widespread use of various anti-hail nets worldwide, their use in Xinjiang is still low. Previous studies have reported that anti-hail nets can reduce economic losses caused by extreme weather (Aldrich et al., 2010). However, few studies have reported the effects of anti-hail nets on tree growth, fruit quality, yield, and economic benefits. Therefore, in the current study, we evaluated the microclimate, fruit growth, fruit quality, yield, and economic benefits of the anti-hail net and open-air environments from June to Sept. 2021, which is a period with a high incidence of extreme weather, such as hailstorms, in Xinjiang.
Light intensity is the most important factor determining the growth, development, quality, and yield of fruit trees (do Amarante et al., 2011). Previous studies have shown that drought, high air temperature, high light intensity, and many other environmental stresses affect photosynthesis (Kuai et al., 2008). Generally, soil and air temperature changes are correlated with light intensity; however, previous studies have shown that increases in the microclimate soil and air temperature are caused by a reduction in light intensity after covering trees with the anti-hail net (Su et al., 2011). The anti-hail net used during this experiment was made of high-density polyethylene, and the pores in its structure had reflective and scattering effects on light (Shahak et al., 2008). Therefore, the light intensity of the anti-hail network environment was generally lower than that of the open-air environment, particularly on sunny days. Other studies have shown that covering trees with hail nets can improve light intensity utilization efficiency and reduce sunburn (Lu, 2014). In the current study, the damage caused by excessive light intensity on Korla fragrant pear trees was reduced by using hail suppression nets, and the photosynthetic efficiency was effectively improved. During this study, a comparison between the long-term microclimate data (Fig. 2) and the all-day microclimate data (Fig. 5) indicated that when the light intensity was weak for a certain period, the difference in light intensity between the two environments was not significant. However, the stronger the light intensity was at a time point, the greater the difference in light intensity between the two environments, which was consistent with the findings of previous studies. When the shoots and leaves of fruit trees in different environments were compared, the taper of spring shoots in the anti-hail net environment was considerably larger than that in the open-air environment, and other leaf-related indicators in the anti-hail net environment were higher than those in the open-air environment. The anti-hail net promoted tree growth, which was consistent with the results of previous studies.
Temperature affects physiological processes in plants (Brakke and Allen, 1995) and is the most basic factor affecting plant life activities (Jia et al., 2016). Previous studies have shown that the effect of the anti-hail nets on soil and air temperature is not significant (Liu et al., 2011). However, a study showed that the air temperatures on sunny and cloudy days under anti-hail nets with different apertures were higher than those in an open-air environment. In the current study, the anti-hail net environment somewhat improved the microclimate temperature. Furthermore, it was found that the difference in soil temperatures of the two environments increased with the increasing soil depth in the long term. When soil temperature was measured during a single day, the dynamic trend of soil temperature changed with changes in depth and differed between the two environments.
Water is an environmental factor important for plant growth and development. Previous studies have shown that the soil and air water contents affect plant physiological activities (Vera et al., 2019). Other studies have shown that using an anti-hail net can improve water use efficiency (Girona and Behboudian, 2012). In this study, there were differences in water-related indicators of the two environments. For example, with increasing depth, the soil moisture content was higher in the anti-hail net environment than in the open-air environment. However, there was a general increase in the soil moisture content in the two environments with increasing depth. When comparing the relative humidity, the anti-hail net environment had a better water retention effect because of higher relative humidity than that in the open-air environment during most periods, thereby indicating the positive effect of hail suppression network on small environments.
Studies of the application of anti-hail nets have mainly focused on apples. Related studies have shown that anti-hail nets can optimize the orchard environment (Bosco et al., 2020). In addition, it was found that the anti-hail net environment improved the growth of fruit trees compared with that of the open-air environment (Bai et al., 2010). This experiment was conducted from June to September, which is a period with a high probability of hail and Korla fragrant pear fruit enlargement and ripening. Therefore, all data collections and analyses were performed during the same period. We obtained the measurement data over the course of 20 d. We also recorded the time and frequency of hail in the experimental area from June to September. Furthermore, we analyzed the correlation between environmental factors and fruit quality and growth. We found that the growth of Korla fragrant pear trees in the anti-hail net environment was better than that in the open-air environment. Moreover, the marketable yield in the anti-hail net environment was markedly higher than that in the open-air environment because of fruit drop and damage caused by hail in the latter, leading to unmarketable fruits, and also because the fruit with damaged peel was harvested. Therefore, we found that the anti-hail net could optimize tree growth, which was consistent with the results of previous studies of apples. In the present study, pear fruit peel indices in the two environments were different, but there was no significant difference in other indicators, consistent with the results of previous studies.
We found that covering fruit trees with anti-hail nets can change various environmental factors to varying degrees, thereby promoting vegetative and reproductive growth. In addition, during the harvest period, although there was little difference in fruit quality, the fruit yield under the anti-hail net environment was improved, subsequently increasing the economic benefits.