Abstract: Soil salinization is a global problem affecting 10% of agricultural soils, particularly in arid lands. This study investigated calcite (CaCO₃) loading by flood-irrigation in the arid southwest of the United States and its effect on C-cycling. To evaluate the impact of flood-irrigation on CaCO₃ buildup, a natural soil and two flood-irrigated agricultural soils were studied in El Paso, TX.

Impacts of agriculture were constrained with ⁸⁷Sr/⁸⁶Sr and ¹³C of environmental samples and determined flood-irrigation as the major source of Ca²⁺ and C in pedogenic carbonates. We calculate that 29% of soil calcite is naturally formed and measured a mixing of atmospheric, organic and calcite-sourced CO₂. Field and flow-through column experiments revealed that soil moisture in conjunction with atmospheric pressure-pumping control calcite kinetics and CO₂ efflux and also identified pore-fluid EC as a proxy for calcite-sourced CO₂ efflux events.

This work found a previously unmeasured CO₂3 precipitation, driven by irrigation. These results provide a new conceptual model that can be applied regionally of the driving mechanisms of salinization and C-cycling in arid-land agriculture.