Quantification of the Water Absorption Pattern of Purple Nutsedge (Cyperus rotundus) Tubers and Evaluation of Their Sprouting Behavior in Different Storage Conditions

Tubers are considered as the most important vegetative organs in reproduction of purple nutsedge, as one of the most troublesome weeds worldwide. Therefore, it is great of importance to investigate the properties of the tuber response to the surrounding environment such as absorption and loss of water. Water uptake is the first step in the sprouting process, though the pattern of water uptake by purple nutsedge tubers has not been documented. Loss of water in tubers is one of the potent factors in reducing their ability to sprouting. Three separate experiments were carried out to investigate the absorption and loss of water content of purple nutsedge tubers.

In the first experiment, the tubers were placed in a water bath at temperatures of 10, 20, 30, and 40 ° C. Then, the weight of the tubers was measured at different times (24 till 3600 minutes). The water uptake percentage of tubers at different temperatures was studied by fitting the Peleg model. In the second experiment, the initiation day of sprouting was investigated at constant temperatures of 10, 20, 30, and 40 ° C. In the third experiment, water loss and sprouting percentage of tubers were evaluated in two conditions refrigerator (4° C) and room (22 to 25 ° C).

The results showed that the initial water content of tubers was 42% and absorbed 10% extra water after being immersed in water. The water uptake behavior was based on the Peleg model at two stages: (1) rapid uptake (less than 420 minutes (7 hours), and (2) a low uptake with a gentle slope afterward. In the Peleg model, the parameters K1 (minutes *.%weight -1) and K2 (%-1) are water absorption rate and water absorption capacity, respectively. The K1 parameter was negatively against temperature. The highest and lowest values were 49.56 and 28.55 at 10 and 40 ° C, respectively. On the other hand, the trend of the K2 was constant (0.1) at 10-30 °C but was 0.08 at 40 °C. The two-parameter Hyperbola model was superior to the Peleg and predicts the highest water absorption and time to 50 percent water absorption parameters. The results showed that sprouting of purple nutsedge tubers at 10, 20, 30, and 40 °C occurred after 14.44, 6.57, 3.24, and 3.12 days, respectively. Keeping the tubers in the room (22-25 °C) and refrigerator (4 °C), sprouting stopped after 3 and 9 months, respectively. The time required for 50% reduction of sprouting in the room and refrigerator was estimated to be 1.3 months (39 days) and 5.12 months (154 days), respectively. The time required for 50% loss weight of tubers in the room and refrigerator was 1.981 months (59 days) and about 6 months (180 days), respectively. Overall, weight loss (water loss) up 11.85%, resulted in 50% reduction in tuber sprouting.

Maximum water uptake in tubers occurred in less than 420 minutes (seven hours) at all temperatures. Slow sprouting in tubers at low temperatures is not associated with an obstacle in water absorption. Tubers lost half of their sprouting ability by losing water about 12%. On the other hand, the results show that the tubers at cool temperatures (4 °C) lose their water and sprouting capacity less than the ambient temperature (22 to 25 °C).