Using spectral reflectance to document water stress in bermudagrass grown on water repellent sandy soils

To conserve natural water resources, athletic fields may be mandated to follow phase water restrictions. In order to optimize irrigation reduction, early plant responses to water stress need to be identified to avoid loss in turfgrass performance and the requirement of additional irrigation to overcome water stress. Current irrigation scheduling based on using potential evapotranspiration (ET) and water stress indices are not suitable for all growing conditions, especially in the water repellent sand soils of South Florida. This experiment was conducted to use spectral reflectance as a means to document normal and progressive water stress in 'Tifgreen' bermudagrass (Cynodon dactvIon (L.) Pers. X Cynodon transvattlensis Burn Davy) grown on a native water repellent sand soil. Three consecutive trials were conducted, in which bermuclagrass was subjected to either no irrigation until severe visual wilt (non-irrigated) or irrigated daily (irrigated) over a dry down period. Visual assessment of turf quality and localized dry spot occurrence verified that bermudagrass receiving daily irrigation was not water-limited and bermudarass receivin-no irrigation was experiencing sensor was used to monitor changes in plant architecture as a means to determine early water stress. Monitoring near-IR/red ratios determined mid-day depression when water demand is at the highest as well as overnight rehydration in both bermudagrasses. At the end of the dry down period, pooled trial morning near-IR/red ratios-afternoon near-IR/red ratios from non-irrigated bermudagrass was significantly greater than irrigated bermudagrass (P = 0.0035), documenting severe water Stress from the non-irrigated bermudagrass. Spectral reflectance allows real-time, site-specific bermudagrass water stress evaluation before it is visually identifiable. Using spectral reflectance as an early warning detection tool can be used for better irriuation decisions including pre-emptive irriuation to avoid water stress, compared to models based on predetermined ET and water stress indices. Copyright (c) 2007 John Wiley & Sons, Ltd.