Effect of maternal nitrogen and drought stress on seed dormancy and germinability of Amaranthus retroflexus

Amaranthus retroflexus L. is an importunate annual weed in many cropping systems of different countries. The main aim of this study was to investigate the effects of maternal nitrogen and drought stress on the seed dormancy and germinability of A. retroflexus. Field experiment was carried out in a factorial based on randomized complete block design, with four potential levels of soil water (-2, -6, -8 and -10 bar) and three levels of nitrogen (0, 100 and 200 kg/ha). The germination characteristics of the seeds were measured at three different times (1 month, 6 months and 1 year after harvesting). Results showed that drought stress had positive effects on breaking of A. retroflexus seed dormancy until 6 months after seed harvesting. Seeds that were developed under severe water stress exhibited the highest germination percentage and germination rate. The results obtained from this study revealed that application of 100 kg/ha nitrogen during seed development increases germinability of A. retroflexus, whereas application of 200 kg/ha nitrogen induced seed dormancy. Furthermore, 100 kg/ha nitrogen application in the field along with 200 ppm gibberellic-acid treatment during seed after-ripening showed the highest germination percentage and germination rate for seeds after 6 months harvesting. Results also indicated that after-ripening significantly increased seed germination and germination rate of A. retroflexus. These findings indicate that long-term management of the soil seed bank in this species requires more stringent control due to the changes in germination timing, as detected in this study.