Hydrological and pedological effects of combining Italian alder and blackberries in an agroforestry windbreak system in South Africa

The Western Cape in South Africa is a waterscarce region which will likely receive less rainfall and higher air temperatures under projected climate change scenarios. The integration of trees within agricultural systems provides an effective measure for improving water retention on agricultural land. Studying an established and irrigated agroforestry system (AFS) combining alder (Alnus
cordata (Loisel.) Duby) as a linear windbreak with a blackberry (Rubus fructicosus L.) crop, we explore the water use dynamics of the intercrop as influenced by the windbreak element by combining methods from hydrology, soil science and forestry disciplines. Our objective is to explore whether
the AFS positively impacts the water balance by combining measurement campaigns to characterise the spatial variability of various key system properties with continuous monitoring. The campaigns encompassed extensive soil sampling to determine soil characteristics (nutrient concentrations, hy-
draulic conductivity, texture, water retention) in the laboratory as well as terrestrial laser scans of the field site, especially of the windbreaks. The continuous measurements covered meteorological, soil water content and soil water potential observations over a 6-month period (in summer). ... mehrThese
were applied to understand soil water dynamics during rain storms and dry spells, including root water uptake as well as soil water storage. We recorded a total of 13 rainfall events delivering 2.5–117.6 mm of rainfall with maximum intensities of 4.1 to 82.6 mm h$^{−1}$. Further analyses showed that infiltration is likely dominated by preferential flow, with rootwater uptake potentially occurring in two depth zones corresponding to different plant communities. While soil water content varied by depth and was influenced by physical and environmental factors, it was generally higher in the inter-
crop zone than within the windbreak-influenced zone. During dry spells, soil water content did not drop below the water content of the permanent wilting point (< −1500 kPa). Values corresponding to soil water tensions above 1000 kPa were recorded on several occasions; these were mitigated
by irrigation and, thus, did not result in water stress. Nutrient distribution and soil physical properties differed near the windbreak in comparison to the blackberry crop, and the carbon sequestration potential is great in comparison to monoculture farming.