| Scope and method of study. (I) The relationships among NDVI, nitrogen (N) fertilization and irrigation were examined and the individual contributions of N and irrigation on NDVI were measured. Two common bermudagrass (Cynodon dactylon [L.] Pers.) cultivars ‘Yukon’ and ‘Riviera’, were managed under three irrigation and six nitrogen treatments during the growing seasons in 2003 and 2004. Tissue moisture, tissue nitrogen, NDVI, green NDVI (GNDVI), and chlorophyll concentration response to N fertilization and irrigation were measured. (II) The Airfield sand system and a modified USGA system were examined for soil factors that affect turf growth potential. ‘Tifsport’ bermudagrass (Cynodon dactylon L. × C. transvaalensis Burtt-Davy) was established on both systems and managed similar to an athletic field. Canopy temperature, soil temperature, soil volumetric water content, soil gravimetric water content, and root density at the 0.0–7.6, 7.6–15.2, and 0.0–15.2 cm sand layers were evaluated monthly from May to October in 2003 and 2004. Turf visual quality was evaluated during 2004.;Findings and conclusion. (I) Both NDVI and GNDVI were good indices of turf quality. The average NDVI of 0.82 and 0.85 were determined to the minimum acceptable and target turf quality indices on bermudagrass. The results from path analysis suggested that NDVI was mainly influenced by tissue moisture and chlorophyll concentration. Tissue N had a small direct influence on NDVI, and a much larger indirect influence through tissue moisture and chlorophyll. (II) This study found that the two systems did not differ in soil temperature, canopy temperature, soil gravimetric water content, and root mass at 7.6–15.2 cm and 0.0–15.2 cm sand layers. The Airfield sand system had higher volumetric water content at a depth of 12 cm and less root density in 0.0–7.6 cm layer than the modified USGA sand system, but these differences did not affect the turf quality. Root density seasonal change suggested that bermudagrass root growth declined when the soil temperature excess of 21°C. Both of the systems had significantly higher water content and higher root density at low elevations compared with high elevations. |
