Department of Soil Science, Stellenbosch University, Stellenbosch, South Africa.
Sci Rep. 2023 Sep 13;13(1):15154. doi: 10.1038/s41598-023-41666-5.
Rooibos (Aspalathus linearis) is endemic to certain regions of the Western- and Northern Cape of South Africa, where it is also commercially grown. Being low-rainfall regions, information on the soil water balance of rooibos is essential, but such data is limited. Consequently, the effect of inorganic fertilisation and soil depth on soil water dynamics in a young rooibos plantation at Nardouwsberg, Western Cape were studied. Soil water content of plots planted to unfertilised and fertilised plants as well as that of bare soil were determined over the duration of the 2016/17 season. All treatments were replicated on shallow and deep soils sites and plant growth was determined at the end of the season. At the end of the study, the profile soil water content and evapotranspiration of the bare and planted plots were similar which prove that fallowing (water harvesting) is not an option in the sandy soils of this region. With the exception of the 20-30 cm root zone of the planted plots at the deep site, the water content decreased to levels below the permanent wilting point in the soil profile during summer. It was concluded that rooibos plants could survive through an adapted root system. A further survival method was proposed, involving moisture moved through evaporation from the deeper soil layers into the drying-front in the ~ 10-30 cm soil layer where a condensation-evaporation cycle enables rooibos to harvest small amounts of water. The highest shoot biomass with the longest taproot resulted from the unfertilised treatment on the deep soil thanks to higher soil water content, whereas the shoot and root biomass of the fertilised treatment at both sites were low due to high P soil concentration. This study revealed that unfertilised plants on deeper soils result in higher rooibos production under drought conditions.
路易波士茶（Aspalathus linearis）原产于南非西开普省和北开普省的某些地区，在这些地区也有商业种植。由于这些地区属于低降雨量地区，因此了解路易波士茶的土壤水分平衡情况非常重要，但相关数据却很有限。因此，本研究调查了西开普省纳德勒斯伯格的一个年轻路易波士茶园中，无机施肥和土壤深度对土壤水分动态的影响。在 2016/17 季节期间，测定了种植有未施肥和施肥植物以及裸地的样地土壤水分含量。所有处理均在浅层和深层土壤上进行了重复，并在季节结束时测定了植物生长情况。在研究结束时，裸地和种植地的土壤剖面水分含量和蒸散量相似，这证明在该地区的沙质土壤中休耕（集水）不是一个可行的选择。除了深层土壤种植样地的 20-30cm 根区外，在夏季土壤剖面的水分含量下降到低于永久萎蔫点的水平。研究结果表明，路易波士植物可以通过适应性根系存活下来。提出了一种进一步的生存方法，涉及通过从深层土壤蒸发到干燥前缘的水分转移，在 10-30cm 土壤层中发生凝结-蒸发循环，使路易波士能够收获少量水分。深层土壤上未施肥处理的最高地上生物量和最长主根，得益于较高的土壤水分含量，而两个样地的施肥处理的地上和地下生物量均较低，这是由于土壤中高浓度的磷所致。本研究表明，在干旱条件下，深层土壤上未施肥的植物会导致更高的路易波士产量。
