黄土丘陵区枣农复合系统土壤水分利用与竞争

探明黄土丘陵区农林复合系统植物土壤水分利用策略对评价其配置合理性与可持续性具有重要意义。论文以黄土丘陵区枣农(枣树+农作物)复合系统为对象,测定不同生育期植物木质部水和土壤水氧稳定同位素比率(δ~(18)O),利用IsoSource模型分析了复合系统中枣树与间作农作物(黄花菜和饲料油菜)土壤水分利用策略,判断两种复合系统作物间是否发生水分竞争。结果表明:枣树各时期对表层(0~20 cm)土壤水利用较少,在旱季主要使用中层(20~60cm)和深层(60~200 cm)土壤水,雨季有显著降雨后主要利用中层土壤水。黄花菜、饲料油菜在旱季对低雨量有效降雨反应灵敏,但其仍主要利用中层土壤水,雨季显著降雨后两者对表层土壤水利用比例显著增加。总之枣树与黄花菜和饲料油菜土壤水分利用策略存在明显区别,但在较为干旱的5月和7月对中层和深层土壤水存在明显竞争。因此可在枣树株间修建深度为40 cm肥水坑,增加中层和深层土壤含水量,促进枣树根系向下生长,缓解水分竞争对枣树生长和产量造成的不利影响。

Soil Water Use and Competition in Jujube-crop Systems in Loess Hilly Region

Since the initiation of the “Grain for Green” project by the Chinese central government in 1999, jujube orchards have been increased rapidly in the hilly region of the Loess Plateau. However, most of these orchards were managed as clean cultivation, which resulted in serious water loss and soil erosion and therefore affected jujube yields and quality. Therefore, we introduced two local economic crops, feed Brassica napus and Hemerocallis fulva, to establish agroforestry to conserve soil and water and raise farmer's income. However, these introduced crops may compete for soil water with jujube trees, and serious water competition can affect the growth and yield of jujube. The primary objective of this study was to investigate water use strategy at different growth stages of plants by using stable oxygen isotope (¹⁸O) and Isosource model to evaluate their feasibility in the jujube-crop agroforestry systems. Three potential water sources were identified: shallow (0-20 cm), middle (20-60 cm) and deep soil water (below the 60 cm). The results showed that during the growth period of 2015, jujube trees primarily absorbed soil water in middle and deep layers and used only a small quantity of soil water at surface soil during the whole study period. More specifically, jujube trees mainly used soil water in the middle and deep soil layers in the dry season and in middle layer in the rainy season. The water use of the feed Brassica napus and Hemerocallis fulva were sensitive to small effective rainfall during the dry season. However, they still mainly used middle-layer soil water during the whole season. Nonetheless, the contribution of surface soil water to these two crops increased after apparent rainfall events in the rainy season. Generally, the three kinds of plants had different water using strategies, and there was certain degree of competition in the use of middle-layer soil water in May and July. The results can provide guidance for the jujube-crop agroforesty systems on the Loess Plateau from the point of soil water competition.