The experimental work was finished in 2011. A turfgrass irrigation handbook in Norwegian was published in November 2013 and the English version is ready for publication in February 2014. The reason why the project is not finished as of 1 January 2014 and the grant from STERF is withheld is a delay in the scientific publications from the project. We expect to rectify this by June 2014. The major findings in the project are:
• Turfgrass crop coefficient (Kc) and thus actual evapotranspiration (ET) rate were always about two-fold higher on the first day after replenishing the soil water content to field capacity (FC) than on subsequent days. Avoiding irrigation to FC is therefore a key factor to save water.
• There were only minor differences in Kc among the cool-season turfgrass used on golf courses in Scandinavia.
– Among grasses used for greens, red fescues and colonial bentgrass transpired 50- 60% more water than velvet bentgrass on the first day after replenishment to FC. On the first day, creeping bentgrass also had higher ET than velvet bentgrass (+40%), although not as high as the fescues or colonial bentgrass. On the second and following days after replenishment to FC, differences in ET rate were not significant. For these days, the average Kc on greens was 0.83. – Among grasses used on fairways, perennial ryegrass and slender and strong creeping red fescue had higher Kc (2.9-3.3) than chewings fescue (2.2) on the first day after irrigation to FC. Kentucky bluegrass was intermediate, with a Kc of 2.5. With a mean value of 0.90, differences between grasses were not significant on the second and following days after irrigation to FC.
• Deficit irrigation to 70% of FC six times per week on greens (average water use per irrigation: 2.4 mm) or two times per week on fairways (6 mm) resulted in consistently better turf quality, fewer dry spots and a reduction in total water use of about 30% compared with deep and infrequent irrigation to FC once per week.
• Use of soil surfactant improved turf quality, but the need for surfactants was less with frequent deficit irrigation than with infrequent irrigation to FC.
• The distribution uniformity (DU) of the irrigation system was determined on selected greens on three golf courses participating in the project. Low DU and a risk of surface runoff mean that it may be difficult to implement daily deficit irrigation without watering by hand.
