The persistence of color response after fertilizer treatments is a key indicator of turfgrass performance. Tropical carpetgrass (Axonopus compressus (Swartz) Beauv.) is widely used throughout subtropical area, was selected as the subject of this study. Five nitrogen (N) treatments applied monthlyat the application rate of both 7.5 and 15.0 g N/m2 as ammonium nitrate (AN), 2.5 and 7.5 g N/m2 as a 14-6.2-11.6 (NPK) slow release fertilizer (SRF), and 7.5 g N/m2 as AN+2.5 g N/m2 as SRF. The trial was performed twice in the greenhouse over 9 week period in two growing seasons. Leaf chlorophyll content, N content, leaf area, plant biomass, and the growth characteristics were measured. Results indicated that the first leaf, third leaf, and third/first leaf ratios of chlorophyll meter readings (CMR) increased with N treatments to the control. Linear regressions indicated that dry weight-based (Ndw) or leaf area-based N (Na) concentrations were highly correlated with CMR during both growing seasons. However, CMR correlated better with Ndw better than with Na. According to the regressions of leaf N and total dry weight, the critical range of N could be 2.6 to 3.1%. If based on the regressions of leaf N and CMR 3/1, the range of N could be 2.7 to 3.0%. Both ranges are very close. Therefore, CMR3/1 could be a criterion to measuring the N status in tropical carpet grass. This investigation showed that CMR offer an alternative to tissue testing for N status and can be used to identify fertilizer N recommendations.
Key words: Carpetgrass, chlorophyll meter readings, N content, dry weight, leaf area.
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