Study on the protective effect of cold-proof and wintering measures on Tunisia soft-seed pomegranate

Abstract：【Objective】Using Tunisia soft-seed pomegranates as experimental materials, we performed 21 treatments, involving 7 physical protection measures at 3 soil thickness. The temperature and humidity changes around the Tunisia soft-seed pomegranate trees under various physical measures were measured, and the heat preservation effects of different measures were studied. Freezing damage of Tunisia soft-seed pomegranate trees at different ages was studied and freezing damage grade formulated. Moreover, the different freezing damage levels were analyzed, and the patterns of freezing damage were examined. Eventually, the anti-freezing cultivation modes were summarized so as to provide guidance for production practice.【Methods】Seven physical protection measures under three soil cover thickness were adopted in the experiment, with a total of 21 treatments, in which all of Tunisia soft-seed pomegranate trees were entirely covered with soil. There were 3 creeping cultivated Tunisia soft-seed pomegranate seedings under each treatment, and the seedlings planted in the open field without any protection measures were used as the control group. The daily minimum temperature, daily temperature varia-tion range, daily maximum temperature, daily mean temperature and air relative humidity around the trees were compared and analyzed. The daily variation of temperature around the trees treated with different cold-proof measures was compared when the extreme minimum temperature (December 31) occurred. 3-year-old Tunisia soft-seed pomegranate were utilized as the experimental materials. Five coldproof measures were set in the cold sheds of Company 20 and 2 cold-proof measures in the cold shed of Company 19 and freezing damage on pomegranate trees in the following spring was recorded so as to screen the suitable cold-proof and overwintering measures.【Results】The winter temperature in southern Xinjiang was relatively low, and the cold-proof effect of the traditional soil bury method was not satisfactory. The Tunisia soft-seed pomegranate trees still suffered severe freezing damage, and the frozen parts were mainly the root necks and branches. The older the trees were, the lighter the freezing damage was. Through this experiment, it was found that the seven physical protection measures could effectively increase the daily average temperature around the Tunisia soft-seed pomegranate trees, reduce the daily maximum temperature, daily temperature variation amplitude, and the temperature difference, and greatly increase the relative humidity in the tree microenvironment, which was close to 100% . The thicker the covering soil was, the gentler the daily temperature change was, and the smaller the temperature difference between the tree microenvironments under different covering materials. Covering with soil cold-proof layer effectively reduced the temperature fluctuation in the tree microenvironment with time, thereby increasing the micro-domain temperature and reducing the daily range. Among the seven physical protection measures, the cold-proof measures with straw curtain + covering soil, straw curtain + steel rebar holder + covering soil, and straw curtain + plastic film + covering soil had better effects in safe overwintering of the pomegranate trees and markedly increased the daily average temperature and daily minimum temperature around the pomegranate trees. In the field freezing damage investigation experiment, the Tunisia soft- seed pomegranate trees covered by straw curtain + plastic flim + covering soil 15 cm cold-proof measures had the lightest overall freezing damage (freezing damage index around 8.3). The best physical protection measure among the different covering methods in the cold sheds was straw curtain + arched shed, in which none of the Tunisia soft-seed pomegranate seedlings were frozen, and the physical protection measures that were more effective were felt (freezing damage index 11.0) and soil cover (freezing damage index 17.3). Burying Tunisia soft- seed pomegranate seedlings under the soil to overwinter in the cold sheds reduced the degree of freezing and drought, which was a more effective physical protection measure.【Conclusion】The winter climate of Xinjiang is very cold. Even with the traditional cold-proof measure of soil cover, Tunisia soft-seed pomegranate still suffered severe freezing damage. It is necessary to take other physical protection measures combined with soil covering to avoid freezing damage. The freezing damage in trees of Tunisia soft-seed pomegranates covered with straw curtain + plastic film + soil covering 15 cm was the lightest (frost damage index 8.3% ), which could be popularized and applied. The cultivation in cold sheds alone does not have a good anti-freezing and drought- resistant effect on Tunisia soft- seed pomegranate trees, and the construction of small arches in cold sheds and the covering of grass curtains on them improves the safe overwintering of softseeded pomegranate trees.