Relationship Between Crop Coefficients and Plant Characteristics in the Cool-Humid New England Region.

Practices that promote low evapotranspiration rates (ET) help to conserve water. Scheduling irrigation according to actual turfgrass ET (ETT) increases irrigation efficiency. Crop coefficients (Kc values) are used in association with weather station reference ET (ET0) to predict ETT. The primary factor affecting ETT (and ET0) is evaporative demand. Experimentally-derived Kc values can be calculated as a simple ETT-to-ET0 ratio. Irrigation amounts increase with Kcs and Kcs increase with ETT. Higher canopy resistance (higher shoot density) and lower leaf area components (slower leaf growth rates and narrow leaf width) can decrease ETT and Kcs. Canopy resistance and leaf area play a secondary role to climatic factors in their effect on ETT. Unlike ET0, however, ETT can be altered by mowing height of cut (HOC), mowing frequency and nitrogen fertilization, which can alter canopy resistance and leaf area components. The objective of this study was to investigate canopy resistance and leaf area and their relationship with ETT and Kc values. Golf species (creeping bentgrass, CB; Agrostis stolonifera L. ‘Memorial’) maintained as green and fairway turf were compared with sports grass species (Kentucky bluegrass, KB; Poa pratensis L. ‘Touchdown’ and perennial ryegrass, PR; Lolium perenne L. ‘Exacta’). Reference ET0 values were computed using the FAO 56 equation and ETT was measured using weighing lysimeters. 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 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. Crop coefficients and ETT increased with greater leaf growth rates (r=0.66, n=48), lower shoot density (r=-0.67, n=48) and with greater leaf width (r=0.67, n=48). Compared to tall grass KB and PR, short grass CB exhibited 2 times slower leaf growth rate, 75% narrower leaf width, and 5 times greater shoot density. As such, tall grass KB and PR exhibited significantly lower canopy resistance and higher leaf area components than short grass CB. Compared to un-fertilized plots, fertilizing in summer with 49 kg N/ha (82% as SRN) increased leaf growth rates on PR by 27% and increased PR ETT and Kcs by 17%. Fertilizing with N had no effect on ETT, Kcs and leaf growth rates of CB. N fertilization had no effect on density and leaf width of any species. Higher HOC decreased density by 15% and increased ETT and Kcs by 10%. HOC had no effect on leaf growth rates.