Strategies for Reducing Supplemental Irrigation of Cool-Season Lawns through Species Selection, Mowing Practices, and Irrigation Scheduling

2019-05-14T19:38:22Z (GMT) by Jada S Powlen
Water resources for outdoor areas, such as lawns and landscapes, continues to become limited in many urban areas, especially in times of acute drought stress. Lawn species selection and cultural practices, such as mowing height, can strongly influence overall seasonal water needs. While previous research has reported various lawn species water use rates and differences in the ability of some cultivars to maintain green coverage during acute drought stress, little is known regarding the irrigation requirements of cool-season lawn species when using a deficit irrigation strategy based on a green coverage target threshold (e.g. 60-80% green) approach. Two greenhouse studies were conducted to screen various candidate species and seed mixtures in a sandy media. The highest water use and worst appearance/green coverage was associated with an inexpensive commercial lawn mixture; and the lowest water use and best appearance was generally associated with improved Kentucky bluegrass (Poa pratensis L.: KBG) cultivars. Field studies were conducted to quantify the irrigation requirements of drought susceptible (DS) and improved, drought tolerant (DT) KBG and tall fescue [Schedonorus arundinaceus (Schreb.): TF] cultivars, blends and mixtures at two mowing heights (5.1 or 8.9 cm). Results from a 74-day field study using a deficit irrigation replacement approach with a 70% green coverage threshold (GCT70) irrigation trigger, demonstrated water savings of approximately 73 to 78% when using a DT TF (60.3 mm) as compared to 100% evapotranspiration (ET­o) replacement (223.4 mm) and a conventional lawn irrigation approach (268.5 mm), respectively. The time to reach the GCT70 generally ranked: TF=TF:KBG mixture>KBG and ranged from 18.0 days for DS ‘Right’ KBG and 52.5 days for DT ‘RainDance’ TF. Among TF and KBG cultivars using the GCT­70 irrigation approach, DT TF required 35 to 68% less supplemental irrigation compared to DT and DS KBG cultivars (92.1 vs. 187.3 mm), respectively. Within KBG cultivars, the DT ‘Desert Moon’ required one-half the irrigation of DS Right (92.1 vs. 187.3 mm), while there were no differences among TF cultivars for irrigation needs. Mowing height did not affect KBG irrigation needs, but TF at 5.1 cm showed increased visual quality and green coverage, and significantly reduced irrigation requirements. Field research also compared species mixtures and blends using DS and DT KBG and TF to determine the amount of a DT species/cultivar that would enhance drought performance with ratios ranging from 25-100% DT as well as 90:10 TF:KBG mixtures. The quantity of a DT KBG in a blend, and DT TF in a TF:KBG mixture reduced irrigation needs, whereas the drought rating of the KBG cultivar in a TF:KBG mixture had no significant effect. In summary, these studies continue to demonstrate that significant supplemental lawn irrigation savings can be achieved by the selection of superior DT species and cultivars combined with a deficit irrigation replacement approach compared to other cool-season species and conventional irrigation practices.