Abstract:

The soil temperature in the eastern foothills of the Helan mountain, where wine grapes are buried in layers of soil during winter and spring, is important for grape growth and annual yields. Therefore, the variation law of soil temperature in buried soil layers for different soil types has been analyzed to provide a reference for scientific management of planting sites. In the winter to spring of 2021/2022 and 2022/2023, four buried soil layers with different soil types were selected at the eastern foot of Helan mountain, site 1(F1): heavy stone and sandy soil; Site 2(F2): 40% stony soil and 60% sandy soil; Site 3(F3): light lime soil; Site 4(F4): fine sandy soil, and the soil temperature at 10cm (T1), 20cm (T2), 30cm (T3) and 40cm (T4) from the surface soil was monitored in real time, to analyze the characteristics of soil temperature changes of buried soil layer in winter (December to February of the next year) and spring (March to the excavation). The results showed that: (1) in winter, the daily mean soil temperature and the daily minimum soil temperature fluctuated in line with the trend of the air temperature, and the fluctuations decreased as the soil depth increases. The maximum difference in average temperature and average minimum temperature of buried soil layers at the same depth at test site 1 to 3 were 1.2℃ and 2.2℃, respectively. The temperature of the buried soil layer in F4 was lower than that at the other test sites. With the increase of buried soil depth, the average soil temperature and the minimum soil temperature increased by 0.2−1.3℃ and 0.9−2.2℃ per 10cm. (2) The starting date of the lowest 5 days of buried soil temperature for each test appeared within 1d after the cooling process. The occurrence time of the daily minimum soil temperature in the buried soil layer was gradually delayed as the depth of buried layer increased, and the duration of the low temperature was extended. (3) In spring, the average daily soil temperature decreased gradually with increasing depth, and decreased by 0.1−1.2℃ every 10cm. The accumulated temperature of ≥10℃ increased with time in a single linear relationship, the accumulated temperature of T1 and T2, T3 and T4 had little difference, with a daily growth rate of 13.1−14.4℃ and 12.2−13.7℃, the average accumulated temperature difference of T1/T2 and T3/T4 was 25.4−33.8℃·d. Based on the soil temperature index of Cabernet Sauvignon germination, the ≥10℃ accumulated temperature of germination start date from T2 to T4 was 277.9−307.6℃·d. (4) The relationship equation between ≥10℃ active accumulated soil temperature and ≥10℃ air accumulated temperature was established for buried soil T1/T2 and T3/T4 in test site F1−F3. It can be seen that the equations show the change trend of one variable equation, and the fitting effect was good, the efficiency coefficients of models were above 0.95, and the average absolute error was below 22.4℃·d. In conclusion, the risk of overwintering freeze damage to grape branches is small in different types of soil layers buried during winter, and the temperature of the buried layer increases with depth, with a gradual decrease in fluctuation. The temperature of fine sandy soil is slightly lower than that of other soil types. The ≥10℃ active accumulated temperature index of grape soil germination starting date and the linear relationship model between air accumulated temperature and buried soil accumulated temperature in spring can provide reference for spring excavation.

Key words: Wine grape, Buried soil layer, Soil temperature, Temperature characteristic analysis