Germination and emergence of amaranth cultivars: water potential, temperature, seed size and sowing depth

Poor seedling emergence is a major limitation in establishing amaranth when there is insufficient moisture and high temperatures in the upper layer of the soil at sowing time. One method used to improve emergence and seedling vigor for deep sowing is the utilization of heavier or larger seeds because they have been found to increase percent emergence or germination. This study was conducted in order to identify (i) whether germination differences were detectable at different water potentials and temperatures, and (ii) whether emergence differences were detectable among different cultivars, seed size, and sowing depth. At all temperatures, with the exception of Don Manuel, seeds of all cultivars ceased to germinate when exposed to -0.8 MP a water potential. Optimum temperature was around 30"C in water stress. Don Juan was the most sensitive cultivar with a large reduction at 40°C, even in 0 MPa water conditions. Don Armando, Don Guiem and Don Manuel were practically temperature insensitive in water potentials from 0 to -0.4 MPa. Emergence percentage averaged across all cultivars and seed size significantly decreased as sowing depth increased from 53% at 2 cm to 29% at 4 cm and 12% at 6 cm. Medium and large size seeds had significantly more emergence percentage than small ones. Deep sowing significantly delayed emergence. These differences in average time to emergence (Ate) may be large enough to be of practical importance. In conclusion, data from this experiment show that even with favorable soil moisture, sowing amaranth deeper than 2 cm delayed and decreased emergence. The effect of high soil surface temperature on seedling emergence may not be a limiting factor under unlimited soil water conditions, but cultural practices that extend the period of high soil water potentials should be applied to improve the establishment of amaranth. Deeper sowing may be practical if seeding rates are adjusted to compensate for reduced percentage emergence associated with depth.

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