Effects of Light Environment and Fertility On Water Use of Two Zoysiagrass Genotypes Differing in Leaf Angle Orientation.

Erect leaves improve radiation penetration and distribution in plant canopies, which generally results in greater canopy photosynthesis and plant growth per unit land area. However, consequences of canopy structure for water relations are not as well known. Therefore, a field experiment was conducted at the University of Florida quantifying the effects of light environment and nitrogen fertility on evapotranspiration (ET) of erect (mean leaf inclination angle of fully expanded leaves was about 37°) and prostrate (mean leaf inclination angle of 17°) zoysiagrass genotypes. Grasses were fully established in 15.2 cm diameter by 50 cm depth pvc pots on a sand root-zone mix. Half the plants were established under white shade cloth (diffuse light) and half under natural sunlight. Nitrogen application rates for each variety were 0 and 5 g N m^-2 several days before data collection. Daily ET was measured gravimetrically over a 6-day data collection period. Across all treatments ET averaged about 5.5 mm d^-1. High N significantly (P<0.001) increased water use under all conditions. The erect genotype had significantly greater (P=0.002) ET per pot, especially at low N compared to the more prostrate genotype under natural light conditions. This effect was largely obviated (P=0.16) under growth in diffuse light conditions. Greater water use by the erect genotype was coupled with greater photosynthesis and shoot production. These findings indicate that zoysiagrass varieties that possess a prostrate growth habit may contribute to an overall reduction in actual turf water consumption.