A Combined Field, Experimental and Modeling Approach to Understand the Impacts of Flood‑Irrigation on Pedogenic CaCO3 and CO2 Dynamics in Arid-Lands
The University of Texas at El Paso
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 CO2 flux from agricultural CaCO3 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.