Impact of Carbon Management and Irrigation Method on Metal Cycling within Semi-Arid Agricultural Soils.

To combat drought and dwindling water resources in California, many farmers have adopted efficient water-saving technologies. In Riverside, a semi-arid metropolitan of southern California, many in the historical citrus industry of the Arlington Heights greenbelt still use furrow irrigation as the primary irrigation method. As more farmers are encouraged to switch to other irrigation methods, altered irrigation patterns could lead to shifts in biogeochemical cycles that have not been fully characterized. In addition, increased soil carbon input in farms that retain ground cover or implement other means of carbon additions could also alter metal mobility. To differentiate the impact of irrigation method and carbon management practice on metal transport, we examined two orchards with similar land use, history, tree crop, and soil properties that differed in irrigation method and carbon input. One orchard utilizes furrow irrigation with relatively intense ground cover removal while the other uses micro-sprinkler irrigation and does not remove leaf litter or ground cover. Soil moisture and temperature sensors, vacuum lysimeters, and redox probes were installed at depths up to 1.5 meters between rows of both groves to monitor seasonal geochemical changes. Soil pore water was captured after irrigation events and analyzed for total metal (including Fe, Mn, As, Cr, Pb, Cd, and Cu) and aqueous Fe(II) concentrations. Soil cores were sampled along the profile and analyzed for total organic and inorganic carbon, total nitrogen, bulk and trace metal concentrations, particle size distribution, permanganate oxidizable carbon, and were subject to sequential and Fe-oxide extractions. To capture differences in soil respiration at these sites, CO₂ flux was monitored in situ using a Li-COR gas analyzer before and after irrigation. The results from this two-farm study will provide greater insight into the interactions between biogeochemical carbon and metal cycling that result due to adoption of specific agricultural management practices.