Impact of a vegetative barrier on soil moisture and sediment deposition in a Semi-arid olive crop

A hedgerow is a linear strip of woody vegetation that, when strategically positioned, can act as a vegetative barrier. It reduces surface runoff velocity and promotes sediment deposition. Hedgerows and vegetative barriers are also landscape elements that provide several ecosystems services, like biodiversity enhancement. However, in semiarid regions, limited water availability might reduce their positive effects to an extend that still not fully understood.

We hypothesize that vegetative barriers also influence soil moisture profiles and sedimentation dynamics along their width. To test this hypothesis, we monitored soil moisture and sediment deposition over two years in a 30 m length, with a width ranging from 4 to 7 m, vegetative barrier downslope of an olive orchard in southern Spain. The basin of the hedgerow’s stretch is 0.13 ha with an average slope of 17.1%. Soil moisture was recorded using 16 continuous sensors and point measurements with a neutron probe (12 accesses to the neutron probe) for calibration. Soil moisture was measured at three zones along the hedgerow (upper, intermediate, and lower) and at four soil depths (0-15, 15-30, 30-60, and 60-90 cm), with the moisture sensor reading in the intermediate depth of each depth range. Sediment deposition was assessed using 26 erosion pins in the intermediate (12) and lower (12) sections. Rainfall data was registered using an autonomous rain gauge with a 10-minute resolution inside the experimental area. Erosion in the upslope area in the olive orchard was calculated using RUSLE. These data allowed comparison between erosion pin measurements inside the vegetative barrier and erosion estimates in the vegetative barrier catchment.

Our results revealed significant statistical differences in soil moisture and sediment dynamics. Soil moisture was higher in the intermediate and lower sections. Also, evolution of soil moisture in the top (0-15 cm) layer presented the highest temporal variability, while the other layers had a lower temporal variability. soil profiles showed distinct patterns across depths. In the intermediate and lower zone, the other layers had an average higher moisture during the years, which did not differ significantly among themselves. On the other hand, in the upper zone, the 15-30 cm layer had the highest average soil moisture content. Sediment deposition was greater in the intermediate zone, with a net accumulation in an erosion pin of 2.38 cm compared to 0.25 cm in the lower section. This resulted in a sediment trapping efficiency estimation in the vegetative barrier of 4%, lower than reported in previous studies. These findings suggest that hedgerows, far from competing with crops, can serve as valuable allies in soil conservation and water management- when they are properly located and managed.

Aknowledgment: Work was funded by Spanish Ministry of Science and Innovation (PID2019-105793RB-I00), project SCALE and TUdi  (EUHorizon2020 GA 862695 and 101000224), and a predoctoral fellowship (PRE2020-093846). It also received funds by project RELAND (PID2023-146177OB-C21 and PID2023-146177OB-C22) by MICIU/AEI/10.13039/501100011033 and by FEDER, UE.