Efficient Irrigation for Recreational Turf In the Cool-Humid Northeast: ET and Crop Coefficients.

Scheduling irrigation according to actual turfgrass evapotranspiration rates (ET_a) reduces waste and increases irrigation efficiency. Crop coefficients (K_c values) are used in association with weather station reference ET (ET₀) to predict ET_a. Experimentally-derived K_c 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 ET_a and K_c 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 2010 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^-1 yr^-1, 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 31.25 and 62.5 mm while golf main plots were mowed at 3.125 and 9.375 mm. Twenty-three daily ET_a (using weighing lysimeters), ET₀ and K_c values (calculated as ET_a/ET₀) were made during the summer months beginning in late June and ending late August in 2010 and 2011. Reference ET₀ values were effective in predicting daily ETa accounting for 60% of the total variation. FAO 56 over estimated ETa in 2010 (Kc=0.95) and under estimated ETa in 2011 (Kc=1.15). Within the same species, HOC had no significant effect on ETa and Kcs. Daily ETa and Kcs increased with leaf area (leaf growth rate and HOC). In 2010 and 2011, summer Kcs were significantly lower with golf turf than sports grass averaging 0.90 and 1.10, respectively. Fertilizing in summer with 49 kg N ha-1 (42% as SRN) caused significantly higher ETa and Kcs on only 3 dates in 2010 and 2011. Two more years of field testing are planned.