Abstract:

The Northern China Agro-Pastoral Ecotone （NCAPE）， a critical zone for ecological security and agro-pastoral production， faces multiple pressures including water scarcity， food security challenges， and land degradation. This study investigates the profound impacts of land-use changes driven by center-pivot irrigation （CPI） systems on regional soil and water resources， focusing on the transition from natural grasslands （NG） to cultivated pastures in semi-arid sandy areas. Results include： （1） Groundwater depletion： large-scale CPI adoption significantly enhanced vegetation productivity （NDVI yearly growth rate： 0.011， P<0.05） but exacerbated groundwater over-extraction. Deep groundwater levels （>20 m depth） exhibited an annual net decline （ΔGD=0.67±0.05 m）， significantly greater than in shallow （≤10 m） and intermediate （10-20 m） aquifers （P<0.05）. （2） Enhanced land productivity： CPI systems intensified land resource utilization. Oat-irrigated plots showed significantly higher biomass carbon （206.2 g·m⁻²）， nitrogen （14.7 g·m⁻²）， and phosphorus （2 092.8 mg·m⁻²） densities compared to NG. Nitrogen density in the 1-m soil profile also increased markedly （P<0.05）. （3） Desertification risks： potentially desertified CPI plots （DL） had significantly lower soil organic carbon， total nitrogen content， and organic carbon density than NG （P<0.05）， even under fertilization. Future agricultural intensification must address dual constraints of water and sand dynamics through optimized crop structures and precision irrigation management. Building a modern agro-pastoral system aligned with regional water-sand equilibrium is essential to harmonize ecological security and food production in the NCAPE.

Key words: cultivated grassland, groundwater depth, irrigation, land use, semi-arid sandy land