Soil-water-use Characteristics of Precision-irrigated Buffalograss and Kentucky Bluegrass

As landscape water conservation becomes more important in the American West, pubic interest in using low water-use turfgrasses is increasing. Little is known about soil water extraction characteristics that contribute to low water use. We investigated how buffalograss (Buchloë dactyloides (Nutt.) Engelm) and Kentucky bluegrass (Poa pratensis L.), considered to be low and high water-use species, respectively, extract soil water in terms of rooting depth and use of available water. Leaf canopy temperature, air temperature, and vapor pressure deficit (VPD) were measured, and a relationship developed between leaf canopy temperature minus air temperature (TL-TA) and VPD for each species under well-watered conditions. This regression was significant within each species but not different between the two species. During soil drying, changes in soil water content were tracked to incipient water stress where TL-TA increased above the well-watered TL-TA:VPD relationship. Within seven days of soil drying, Kentucky bluegrass reached incipient water stress when nearly 50% of the total water was depleted in its 0.6-m-deep root zone. Buffalograss, however, reached incipient water stress after 22 days of soil drying, when it had depleted nearly 60% of soil water to a 0.9-m depth. Ninety-four percent of the Kentucky bluegrass root system was in the top 0.3 m of the soil compared to 62% for buffalograss. These results present rooting depth and water extraction patterns of these species that can be used to determine more precise irrigation scheduling in the West