Effects of mowing height of cut and nitrogen on FAO-56 PM crop coefficients for recreational turf in the cool-humid region

Irrigating recreational turf requires ET (evapo-transpiration) replacement for water conservation and to sustain optimal leaf growth and turf function under traffic stress. Lysimeter measured actual ET (ET_a) can be estimated using a reference crop ET (ET_o) from meteorological data adjusted using a crop coefficient (K_c, ET_a/ET_o) to correct for cultural affects on ET_a. Previous studies have not fully investigated the effects of turf culture on K_c. The objective of this research was to develop reliable K_c when ET_o is computed using the FAO-56 Penman-Monteith equation, with K_c adjusted according to the effects on ET_a of two mowing heights of cut (HOC), two N rates, and three species. Creeping bentgrass (CB) as golf turf and Kentucky bluegrass (KB) and perennial ryegrass (PR) as sports-lawn turf were planted in South Deerfield, MA. Species and two N rates (98 and 196 kg N ha^–1 yr^–1) were arranged as main plots (3.12 by 1.56 m). Main plots were split according to HOC, with KB and PR mowed at 3.125 and 6.25 cm and CB mowed at 0.3125 and 0.9375 cm. Crop coefficients were calculated as ET_a:ET_o ratio and using linear regression (slope) estimates during July and August from 2011 to 2013. Results were similar between the two K_c methods. Adjustments to K_c values are necessary to account for variations in leaf growth rates (r = 0.66, n = 48, P £ 0.001) caused principally by HOC, with N having some influence on PR. Golf HOC (CB) ranged from 0.90 to 1.00 in K_c while sports-lawn turf HOC (KB and PR) ranged from 1.15 to 1.25.