基于van Genuchten模型的渭北苹果园土壤水分能量特征分析

针对渭北地区干旱缺水,果树生长发育受限的客观实际,开展了苹果树生育期0～150 cm土壤水吸力动态变化规律研究。依据渭北果园土壤剖面构型,将离心机法与水汽平衡法相结合,按照发生学土层,逐层测定了供试土壤水分特征曲线,并用van Genuchten模型拟合。基于该模型,将在幼龄果园、老龄果园以及农田定期逐层监测的土壤水分含量转化为土壤水吸力,以农田为对照,评价植果条件下土壤水分的胁迫状况。结果表明,van Genuchten模型能很好地拟合渭北果园耕层、农田耕层、黑垆土层及黄土母质层的水分特征曲线,拟合精度均达0.96以上。渭北地区农田受干旱胁迫较严重,3月中旬－7月初,0～100 cm土层均处于水吸力高于3.98的重度胁迫状态;受植被冠层覆盖及果树生育期的影响,干旱对果树的胁迫程度较农田小,对老龄果园胁迫程度比对幼龄果园的大,幼龄果园在3月中旬－5月初、5月底－7月初仅0～20 cm土层为高水吸力区,直至6月中旬－7月中旬高水吸力区才延伸到40～70 cm土层;老龄果园在3月中旬－4月底的0～40 cm土层、5月底－7月中旬的30～100 cm土层和7月中旬－8月底的0～20 cm土层为高水吸力区。可得出,渭北不同园龄苹果园在不同生育期的不同深度土层会间歇性地出现高水吸力的土壤水分胁迫区,但相对于农田而言,果园受到的干旱胁迫相对较轻,渭北地区植果有助于缓解干旱胁迫。

Analysis on soil moisture energy feature of apple orchards in Weibei area based on van Genuchten model

Abstract: In arid and semi-arid regions, the emergence of dry soil layer can limit apple tree''s growth, development and yield. This study investigated the spatio-temporal variability of soil water suction in apple orchards in Weibei area, northwest China. As the growth of fruit tree was restricted by drought and water deficit in Weibei area, water suction dynamics in 0-150 cm soil profile during apple tree growth stage was investigated in the present study. We chose both young (<10 years) and old (>20 years) orchards, as well as cropland (control), which located in the same site conditions. Stratified sampling was performed at different growth stages of apple trees from March to September, and the moisture in 0-150 cm soil profile was measured using the oven-drying method. According to the soil profile constitutions in Weibei orchard, the centrifuge method and vapor balance method was integrated to measure soil water characteristic curves of tested soil based on the soil genetic layer. The van Genuchten model was used to fit the water characteristic curves. Soil moisture in young orchards, old orchards and farmlands was converted to soil water suction based on the van Genuchten model. The drought stress of planting fruit was evaluated with the farmland as control. The results showed that the van Genuchten model could well fit soil moisture characteristic curves in orchard topsoil, farmland arable layer, black loessial soil and loess subsoil in Weibei, and the fitting accuracy reached 0.96. Orchard soil moisture gradually decreased from mid-March to early July (loss phase), followed by an increase till the end of September (recovery phase). Farmland was greatly impacted by drought stress in Weibei area, and the 0-100 cm soil layer was with water suction higher than 3.98 (heavy water stress) from mid-March to early July. Affected by vegetation canopy cover and fruit growth period, the impacts of drought on orchard were smaller than that on farmland, while the impacts on old orchard were greater than that on young orchard. The high water suction for young orchards occurred at 0-20 cm soil layer from mid-March to early May and from late May to early July, and extended to 40-70 cm soil layer from mid-June to mid-July. The high water suction for old orchards occurred at 0-40 cm soil layer from mid-March to the end of April, at 30-100 cm soil layer from the end of May to mid-July and at 0-20 cm soil layer from mid-July to the end of August. In conclusion, high water suction can appear intermittently in different growth stages and different soil depths for apple orchards with different ages. The influences of drought stress on orchards are smaller than that on farmland and during the recovery phase, "seasonal interior water stress" can be restored in apple orchards, and thus, planting fruit is helpful to alleviate drought stress in Weibei area.