Turfgrass Evapotranspiration. 11. Responses to Deficit Irrigation1

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Abstract
In the arid west, deficit irrigation has contributed significantly to efficient utilization of water resources. In order to understand possible benefits of deficit irrigation in turfgrass management, yield must be defined in terms of gain from water expended. Turfgrass quality influences the aesthetic appeal and physical comfort of urban environments. The effect of deficit irrigation on turfgrass quality was studied using small lysimeters where root systems were confined and evapotranspiration (ET) was limited to the amount of irrigation. In most cases there was a sharp change in slope of the quality vs. ET relationship for turfgrass. Kentucky bluegrass (Poa pratensis L. var. 'Merion') decreased about 10% in quality with an irrigation schedule providing up to a 279% ET deficit. Larger deficits resulted in greater relative decreases in quality. When ET was maintained at greater than 30% deficits, the quality rating of Kentucky bluegrass was lower if mowed at 2 cm than when mowed at 5 cm. When N fertility was low, maximum ET and maximum quality were decreased, but the response of quality to irrigation deficits greater than 27% was similar. The response of tall fescue (Festuca arundinaceaSchreb. var. 'Rebel') to deficit irrigation was similar to that of Kentucky bluegrass. Buffalograss [Buchloe dutyloides(Nutt.) Engem.], however, responded with notable differences. Decreasing ET also had an effect on microclimate. Turfgrass canopy temperature increased 1.7°C for each 10% decrease in irrigation up to 70% decrease suggesting that, during summer months, if irrigation is limited, the effect on urban climate may become a concern.