Modeling the Sprouting of Cyperus Rotundus L. Tubers in Response to Soil Temperatures under Soil Solarization

Abstract

Experiments were conducted to characterize and predict the sprouting of tubers of purple nutsedge (Cyperus rotundus L.) in response to temperature. Tubers were collected from the University of Hawaii Waimanalo Experiment Station and allowed to sprout in 9 cm petri dishes on 2 layers of moistened filter paper in incubators. In experiments to determine methodology it was demonstrated that tubers often initiate growth, but shoots do not continue to elongate. Tubers were therefore counted as sprouted when at least one shoot exceeded 1.0 cm in length. Daily counting of sprouted tubers depressed final cumulative sprouting by 1 to 15 percentage points. Tubers from water-stressed plants sprouted faster and had higher final sprouting than tubers from well-watered plants. Experiments using constant and diurnally alternating temperatures showed that sprouting rate and final cumulative sprouting are increased by temperature alternation. To develop a sprouting model, tubers were exposed to all combinations of constant and alternating temperatures from 20 to 45 C in 5 degree increments. Cumulative sprouting of the tubers over time at each temperature regime was characterized by fitting the Richards function. Response surface regression was used to predict the four parameters of the Richards function for tuber sprouting at any temperature regime. A model was developed utilizing the predicted Richards parameters to predict cumulative tuber sprouting in response to daily minimum and maximum soil temperature. The model satisfactorily predicted daily and final cumulative tuber sprouting in the field from observed daily minimum and maximum soil temperatures. Predicted final cumulative sprouting for the bare soil treatment was within 8 percent of observed sprouting, and for the solarized treatment within 4 percent. This study demonstrated the ability of soil solarization to increase final cumulative tuber sprouting and to concentrate tuber sprouting in time. Soil solarization has potential as part of an integrated control program for purple nutsedge in combination with a systemic herbicide such as glyphosate.