Irrigation Water Quality Effects on Soil Carbon Fractionation and Organic Carbon Dissolution and Leaching in a Semiarid Calcareous Soil

Irrigation water quality and soil organic matter content influence crop yields and soil properties such as salinity and soil particle aggregation. We used laboratory column and batch studies and soil carbon fractionation to study potential organic carbon (OC) losses from a Typic Torrifluvent with 0.79% total OC and 4.7% inorganic carbon ([IC] as carbonates). About 4% of the total OC fraction was determined to be water-soluble OC (SOC). Under saturated flow, a significant amount of SOC (20%-35%) was lost from this soil (Pima clay loam) with just two pore volumes of irrigation water. Sodium- and sulfate-rich waters and rainwater were up to twice as effective at releasing SOC as waters dominated by calcium and chloride ions. Not all OC losses can be attributed to well-known soil particle dispersive effects of sodium and rainwater. Soluble OC losses were also highly correlated to the progressive dissolution of the soil IC fraction. Water quality has a measurable impact on OC and IC losses from CC-poor carbonate-rich soils. Changes in irrigation water quality may increase OC leaching from the plow layer and favor increased denitrification and potentially carbon sequestration in and below the root zone of irrigated semiarid soils.