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

Scheduling irrigation according to actual turfgrass evapotranspiration rates (ETa) reduces waste and increases irrigation efficiency. Crop coefficients (Kc values) are used in association with weather station reference ET (ET0) to predict ETa. 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 ETa 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 UN Food and Agricultural Organization report 56 (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, using four replicates arranged as a RCB design. 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 HOC while golf main plots were mowed at 3.125 and 9.375 mm HOC. Twenty-three daily ETa (using weighing lysimeters), ET0 (using FAO 56 equation) and Kc values (calculated as ETa/ET0) were made during the summer months beginning 21 June and ending 31 August, 2010. Reference ET values derived using the FAO 56 equation were effective in predicting daily ETa rates in the taller sports grass. Crop coefficients of “1.0” could theoretically be used in weather station software to compute an accurate estimate of actual ETa. However, a lower Kc value may be more appropriate for golf turf requiring a value approaching “0.80” (80% of reference ET). Two more years of field testing are planned.