Development of a new thermal time model for describing tuber sprouting of Purple nutsedge (Cyperus rotundus L.)

Abstract

Tubers are the main means of propagation in purple nutsedge (Cyperus rotundus L.), one of the most troublesome weeds competing in crop and pasture systems throughout the world. Tuber sprouting is highly linked to temperature, the main environmental factor limiting the growth of purple nutsedge. In the present study, a new thermal time model was developed for describing the temperature-dependent tuber sprouting of purple nutsedge. This model was validated based on results from a laboratory tuber sprouting experiment performed under different temperature regimes. The proposed model is an integration of three equations comprising those of Gompertz, Dent like, and Segmented (GDS) functions, developed for describing cumulative sprouting, final sprouting and sprouting rate of purple nutsedge tubers respectively. The Gompertz-based model fitted the data well (R2 = 0.94, RMSE %< 10). This model was also able to predict lag time (time up to start of sprouting), final sprouting and sprouting rate. A Weibull-based model was only able to estimate temperature thresholds based on the final sprouting. Whereas, the GDS model predicted related temperature thresholds according to both final sprouting (optimal in the range of 20.31–29.72°C) and the absolute sprouting rate (optimum at 29.96°C). In conclusion, the proposed model is simple and includes parameters of a biological significance, simultaneously generating estimates of useful temperature thresholds and fitting cumulative tuber sprouting of purple nutsedge. Our study has also proved the superiority of the absolute sprouting rate index when calculating the temperature thresholds.