Extent and Duration of Gas-Phase Soil Oxygen Depletion in Response to Flood-Irrigations in Two Pecan Orchards

Abstract

Pecan orchards in the Mesilla Valley of New Mexico are routinely flooded as a means of irrigation. The effect of flooding on gas-phase soil oxygen concentration in mature orchard settings has received little scientific scrutiny. The object of the research was to determine the oxygen levels in the soil following flood irrigation for two orchards with loam and silty clay soil types, and to determine if oxygen levels affected photosynthesis and nut yield. Galvanic oxygen sensors housed in diffusion chambers were buried in the orchards at 4 depths within the top meter of soil providing hourly data for the 2004 growing season. In addition, carbon dioxide flux measurements were made above the canopy. Oxygen levels decreased after flood irrigation but the duration of depleted oxygen levels was most pronounced in the 25-cm depth and only occurred for 1 to 6 days depending on the soil type. The accumulative hours of oxygen levels below 13% and 10% were similar at the two sites for the 50-cm depth but were 50% higher at the silty clay soil site compared to the loam soil at the 25-cm depth. However, the data at the loam site indicated that the high frequency flood irrigation did not lower oxygen levels for sufficient time to cause a reduction in photosynthesis and yield. Photosynthesis data show that as long as oxygen levels are above 12% at the 50-cm depth and 7% to 10% in the top 25-cm depth, a mature pecan orchard can be flood irrigated and conversion to sprinkler or trickle irrigation is not needed to prevent reduction in yield due to oxygen stress.