Impacts of Arid Land Agriculture and Flood Irrigation on Soil Quality, Water Dynamics, and Gas Transport

In this study, we apply the holistic approach of Critical Zone science to understand the impacts of flood irrigation on soil quality, water dynamics, and gas transport under climate variability in agricultural systems in arid areas, specifically investigating a pecan orchard in the Rio Grande valley in West Texas. Previous work at this site has demonstrated a significant amount (~10 wt %) of pedogenic carbonate has formed in the soils through the last century because of the irrigation practices, impacting water delivery to the root zone and clogging effective porosity. The heterogeneous nature of the soil parent material leads to different hydrologic and geochemical conditions in the subsurface and thus different pedogenic carbonate accumulation rates and salt buildup rates. For example, fingering of fine-grained clayey sediments has impacted the growth of some pecan trees in the orchard, resulting in smaller trees in these areas due to salt buildup, limited root growth and periodic reducing conditions. Extensive characterization of the orchard using the CZ approach has provided soil, gas, and water chemistry data; these data are used to inform numerical simulations of this system. Here, we use reactive transport models to predict the rate of formation of carbonate minerals and soil quality changes as the irrigation source changes from the Rio Grande water to the brackish groundwater available to the farmer. We also investigate the impact of subsurface heterogeneity in soil texture on secondary calcite formation rates and quantities in current conditions and with time in response to climate change, and clogged pores. Investigating these dynamics provides critical information for arid land carbon cycles, greenhouse gas dynamics, and regional agricultural sustainability.