Photosynthesis and Growth of Bermudagrass Swards. II. Growth Patterns as Estimated by Harvest and Gas Exchange Techniques1

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Abstract
Yield of ‘Coastal’ bermudagrass [(Cynodon dactylon (L) Pers.)] is reduced by frequent mowing. A field experiment was conducted to examine the influence of mowing frequency on dry matter yields and compare growth patterns estimated by harvest and CO2 exchange techniques. Plots were mowed either monthly (6 weeks in one cycle) or weekly from 20 June to 1 October. Dry matter yields, leaf area index, and CO2 exchange rates of the canopy (CER) were measured each week and dry matter accumulation was compared to estimates made from CER integrated over 24‐hour periods and summed over sampling intervals. Yields of total phytomass during the experimental period were 2,115 and 770 g m‐2 for plants cut monthly and weekly, respectively. Corresponding estimates from CER were 1,612 and 698 g m‐2. Lower leaf area indices and photosynthetic photon flux density (PPFD) interception in weekly‐ than in monthly‐cut plots largely accounted for the lower yields and CER. However, plants cut weekly also exhibited lower CER than plants cut monthly at equivalent PPFD interception values. The lower CER (per unit of intercepted PPFD) for plants cut weekly was attributed to accumulation of older leaves below the mowing height, whereas nearly all leaves were removed by monthly mowing. The methods used for measuring CER and predictions of growth from such measurements may be useful in studying carbon balance in grazed pastures.