Characteristics of deep soil desiccation of apple orchards in different weather and landform zones of Loess Plateau in China

In order to assess the deep soil desiccation and its regional distributing characteristics in apple production areas of the loess plateau, the research was carried out via widely observations of soil moisture in 0－1 500 cm soil layers of apple orchards in different weather and landform zones on the Loess Plateau. The soil water amount, soil moisture distribution in deep soil profile and soil desiccation of 32 apple orchards in semi-humid loess terrace-land zone (Ⅰ), semi-humid and prone drought loess highland zone (Ⅱ), and semi-humid prone drought and semi-arid loess hilly zone (Ⅲ) were analyzed and compared, and soil desiccation characteristics of apple orchards were assessed quantitatively. The results showed that, 1) Average soil moisture in 0-1 500 cm soil layers of apple orchards in zoneⅠ,Ⅱ and Ⅲ was 17.53%, 13.44% and 10.29%, respectively, average available soil water storage was 1 273.70, 973.98 and 864.05 mm, respectively, average soil water overuse was 199.93, 465.10 and 362.70 mm, , respectively, and average soil desiccation rate was 8.47, 26.29 and 23.44 mm/a in three zones, accordingly. Soil moistures and desiccated soil layer distributions in apple orchards were affected by weather, landform, irrigation, apple tree age and planting density; 2) Soil moisture of apple orchards with supplementary or regular irrigation was significantly higher than that of dryland orchards in the same zone at whole observed depth of soil layers, and no soil desiccation or limited soil desiccation occurred, while relatively deep desiccated soil layers existed in dryland orchards; 3) SDI (soil desiccation index) of apple orchards with supplementary or regular irrigation in ZoneⅠ, Ⅱand Ⅲ was -8%, -11% and -34%, respectively, while SDI of dryland apple orchards was 32%, 50% and 46%, with desiccated soil layer thickness of 790, 1297 and over 910cm in three zones correspondingly. The results can provide a scientific basis and basic data for deep soil water sustainable utilization of apple orchards and sustainable development of apple production bases on the Loess Plateau