Toposequence-driven variability on soil properties redistribution at irrigated semi-arid landscape, Northeastern Algeria

Agriculture in semi-arid Mediterranean regions contributes significantly to local food production and rural livelihood.  Nevertheless, it depends strongly on irrigation to sustain crop production and soil fertility. With the terrain complexity present, irrigation can lead to downward and lateral transfer of soil particles and nutrients, thus intensifying and accelerating the complex interplay between leaching and erosion, which in turn, reduce soil productivity and create spatial fertility imbalances. This study addresses the lack of knowledge about these processes to support better soil management in  Bir Bouhouch irrigated perimeter with complex terrain characteristics in northeastern Algeria , which represents a strategic agricultural area mainly producing cereals .The area has been used for intensive agriculture since the expansion of irrigation schemes in recent decades .In This study  the vertical and catenary variability of physicochemical characteristics of soils were examined. Four soil profiles along a toposequence from the summit (P1), to the toeslope (P4) were described and soils samples were collected in different depth to physicochemical characterization (texture, pH and electrical conductivity in water (EC), active lime, organic matter (OM), total nitrogen and extractable phosphorus. All profiles showed alkaline pH (8.10–8.60) with low EC (0.23–0.58 dS/m) that increased progressively from the summit to the teslope as well as with depth. Surface horizons (0- 60 cm) at downslope profiles showed finer textures with transition from silty clay to loamy clay and higher OM contents (up to 17.2 g/kg) compared with the summit (9.00 g/kg), indicating possible downslope colluvial accumulation. Active lime increased but followed a bi-profile sequence along surface (from 55 to 145 g/kg for P1-P2 and from 35 to 105 g/kg for P3-P4) and with depth reflecting a possible carbonate leaching and re-precipitation under alkaline conditions, locally forming caliche horizons. Extractable P concentrations ranged from 0.05 to 0.07 mg/kg and were enriched at lower slope positions at surface horizons. Besides total N (0.8–1.5 g/kg) showed limited vertical and lateral variation. These patterns demonstrate that soil variability along the transect can be mainly controlled by the topography-driven redistribution and carbonate dynamics enhanced by irrigation.

This work was funded by national funds through FCT – Fundação para a Ciência e a Tecnologia, I.P., under the projects UIDB/04129/2020 and UID/04129/2025 (LEAF) and LA/P/0092/2020 (TERRA).