Effect of soil moisture on overwintering of alkali bulrush (Bolboschoenus maritimus) rhizome and prediction of cardinal temperatures required for tubers sprouting

Bulrush is one the most important weed of paddy rice. Pot and lab experiments were carried out in order to study some of its ecophysiological characteristics. In the first study, the effects of soil moisture (6, 12, 24, 34 percent based on soil dry weight, and permanent flood as control) on overwintering of bulrush tubers and its growth in following year was determined. In the second experiment, the cardinal temperatures required for tubers germination was investigated. The results showed that survival and overwintering of bulrush tubers in 6, 12 and 24 percent moisture was 10, 30 and 82 percent respectively, and fell sharply in higher humidity. In addition, the number and fresh weight of tubers and also length and fresh weight of bulrush rhizomes in 6% moisture was 100, 58, 70 and 92 percent lower compared to field capacity treatment (24 percent moisture level). The maximum germination occurred at 25 to 30 degrees Celsius and the minimum germination at 40°C and the highest germination rate in 30°C. By considering the low survival rate and a considerable reduction in vegetative organs of bulrush in low soil moisture, drainage and tillage of paddy fields after the rice harvesting is a means of reducing overwintering populations and management of this weed. Minimum temperature required for germination of bulrush, compared with rice growing base temperature (12°C), and the growth of bulrush before transplanting rice, indicates well adoptability of bulrush to paddy rice ecosystems and the need to provide appropriate integrated solution for its management.