Crop Coefficients for Recreational Turf in the Cool-Humid New England Region.

Crop Coefficients for Recreational Turf in the Cool-Humid New England Region Scheduling irrigation according to actual turfgrass evapotranspiration rates (ETT) reduces waste and increases irrigation efficiency. Crop coefficients (Kc values) are used in association with weather station reference ET (ET0) to predict ETT. Experimentally-derived Kc values need to be developed at the local level to ensure optimum turf function and effective irrigation efficiency. The objective of this study was to measure ETT and Kc values comparing golf species (creeping bentgrass, Agrostis stolonifera L. ‘Memorial’) maintained as green and fairway turf with sports grass species (Kentucky bluegrass, Poa pratensis L. ‘Touchdown’ and perennial ryegrass, Lolium perenne L. ‘Exacta’). Reference ET0 values were computed using the FAO 56 equation. Studies were initiated in 2011 at the Joseph Troll Turf Research Center, South Deerfield, MA. Species main plots were arranged as a complete factorial with two nitrogen (N) levels, 98 and 196 kg N/ha/yr, with four replicates arranged as a RCB. All species by N main plots were split according to two heights of cut (HOC) with sports grass maintained at 3.125 and 6.25 cm while golf main plots were mowed at 0.3125 and 0.9375 cm. Twenty-three, 30, and 26 daily ETT (using weighing lysimeters), ET0 and Kc values (calculated as ETT/ET0 ratio and using regression slope estimates) were made during the summer months beginning in late June and ending late August in 2011, 2012, and 2013, respectively. FAO 56 ET0 values were effective in predicting daily ETT accounting for 61, 84, and 68% of the total variation in 2011, 2012, and 2013, respectively. Crop coefficients derived using regression slope and the simple ratio methods were in agreement. FAO 56 ET0 over estimated ETT of short grass golf turf (3-yr Kc=0.96, ETT=4.11 mm/d) and under estimated ETT of tall grass (3-yr Kc=1.20, ETT=5.08 mm/d). Higher HOC significantly increased ETT and Kcs by 10%. Fertilizing in summer with 49 kg N/ha (82% as SRN) increased ETT and Kcs on PR by as much as 15% compared to unfertilized plots. FAO 56 derived Kcs based on 3-yr averages ranged from 0.92 to 1.00 for short grass canopies and for tall grass canopies ranged from 1.15 to 1.27.