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TURFGRASS SCIENCE

Double Exponential Model Describes Decay of Hybrid Bermudagrass Thatch

Division of Professional and Technical Studies, Edison College, 8099 College Pkwy. S.W., P.O. Box 60210, Building C-101, Fort Myers, FL 33906-6210

^* Corresponding author (lberndt{at}edison.edu).

Empirical modeling helps understand decay processes. The objective of this research was to find a suitable model, and then use it to describe decay of thatch from hybrid bermudagrass [Cynodon dactylon (L.) Pers. x Cynodon transvaalensis Burtt-Davy]. The carbon dioxide–carbon released from ‘Tifdwarf’ and ‘Tifeagle’, each 24 h over 20 d, was plotted as percent C remaining vs. time. Four empirical models were fit to these data to determine which one best minimized residual sum of squares. The model best meeting this condition was the four-parameter double exponential model. Of the models tested, it was the only one to pass all tests for normally distributed population, constant variance, and independence of residuals. Fitting this model to percent C remaining data identified two C pools for each cultivar, a fast pool and a slow pool, with differing sizes and rate constants. Fast-pool turnover times were similar. Slow-pool turnover times differed, with Tifdwarf decaying faster than Tifeagle, which may have been a function of Tifeagle having a higher stolon mass with more lignin and a wider C:N. When data were corrected for microbial growth efficiency, slow-pool turnover times decreased. This implied cultural practices that increase microbial growth efficiency may help convert slow pool into biomass, reduce slow-pool turnover times, and ultimately enhance the decay of thatch.

Abbreviations: CO₂–C, carbon dioxide–carbon • FP, fast pool • MGE, microbial growth efficiency • MPN, most probable number • OC, organic carbon • PM, potentially mineralizable • PRESS, predicted residual error sum of squares • SP, slow pool • TD, ‘Tifdwarf’ • TE, ‘Tifeagle’ • TT, turnover time