黄土高原不同降水量区旱作苹果园地水分生产力和土壤干燥化效应模拟与比较

为了揭示黄土高原旱作苹果园深层土壤干燥化对果园产量的长远影响,确定果园适宜利用年限,应用WinEPIC模型定量模拟分析了1965—2009年黄土高原半湿润区洛川、半湿润易旱区白水、半干旱区延安、半干旱易旱区静宁等不同降水量区旱作苹果园地水分生产力演变和深层土壤水分动态变化规律,并比较了其区域差异。结果表明：洛川、白水、延安和静宁果园产量均呈现出“先逐年升高达到最大值,之后随当地降雨量变化而波动性降低”趋势,45 a平均值分别为26.05、23.89、22.29和20.51 t/hm²;1~20 a生果园平均年耗水量均高于同期年降水量,导致果园深层土壤干燥化强烈,洛川1~22 a生、白水1~21 a生、延安1~18 a生、静宁1~16 a生的土壤逐月有效含水量呈明显波动性降低趋势,年均土壤干燥化速率分别为59.6、56.9、63.9和64.9 mm/a,静宁>延安>洛川>白水,此后苹果园地土壤有效含水量在较低水平上随季节降水变化波动;洛川、白水、延安和静宁苹果园地0~15 m土层土壤湿度剖面分布变化剧烈,土壤湿度逐年降低,土壤干层出现时间分别为13 a生、11 a生、7 a生和6 a生,土壤干层逐年加厚,在20 a生时均已超过11 m,21 a生以后3~15 m土层土壤湿度保持相对稳定的干燥化状态;4个试点果园水分生产力和土壤干燥化效应区域差异显著,果园土壤水分可持续利用年限为20~25 a。

Simulation and Comparison of Water Productivity and Soil Desiccation Effects of Apple Orchards in Different Rainfall Regions of the Loess Plateau

In order to investigate long-term effects of deep soil desiccation on yields of dryland apple orchards, and to determine suitable age limit of apple orchards on Loess Plateau, WinEPIC model was used to simulate water productivity and deep soil desiccation of dryland apple orchards during 1965-2009 at four sites on the Loess Plateau, which included Luochuan County of Shaanxi Province in semi-humid region, Baishui County of Shaanxi Province in semi-humid and prone-to-drought region, Yan􀆳an City of Shaanxi Province in semi-arid region, and Jingning County of Gansu Province in semi-arid and prone-to-drought region. The simu-lated results showed as follows: in Luochuan, Baishui, Yan􀆳an and Jingning, simulated yield of 1-45 years old apple orchards averaged 26.05, 23.89, 22.29 and 20.51 t/hm², respectively, and annual yield increased to a maximum at the earlier stage of growth, then followed by the tendency of decrease fluctuating with the local rainfall. In 1-20-year-old apple orchards,average annual water consumptions are higher than annual rainfalls, which resulted in desiccation in deep soil layers. In 1-22-year-old orchards of Luochuan, 1-21-year-old orchards of Baishui, 1-18-year-old orchards of Yan􀆳an and 1-16-year-old orchards of Jingning, simu-lated monthly available soil water amounts in 0-15 m soil profile decreased rapidly with strong fluctuation. Soil desiccation rates in Luochuan, Baishui, Yan􀆳an and Jingning were 59.6, 56.9, 63.9 and 64.9 mm per year, respectively, but they kept at a relatively low level and fluctuated with annual and seasonal rainfall changes at the later stage. The soil moisture in profiles varied sharply, the humidity declining annually. Dry soil layers occurred in the 13th, 11th, 7th and 6th year in Luochuan, Baishui, Yan􀆳an and Jingning respectively, and the thickness of desiccated soil layer increased annually. In the 20-year-old orchards of the four sites, dry soil layers all have already exceeded 11 m in thick, and the soil moistures in 3-15 m layers remain steady after that. There were significant differences in water productivities and soil desiccation effects among the apple orchards at the four sites, and the soil water could be sustainably used by the apple orchards at the four sites for about 20-25 years.