Assessing the yield of spring and autumn-sown sugar beet in Mashhad and Neyshabor, Khorasan using a simulation model

Sugar beet (Beta Vulgaris L.) is the major crop in Khorasan province which is mainly grown in spring. However, autumn sowing has a lot of advantages including lower crop water requirement and higher water use efficiency. Accordingly, this research was performed to compare the yield of storage organ in spring and autumn-sown sugar beet and determine the most appropriate sowing date of autumn-sown sugar beet in two locations of Mashhad and Neyshabor in Khorasan province. The SUCROS crop simulation model was employed to simulate growth and development of spring and autumn-sown sugar beet in two locations (Mashhad and Neyshabor) in Khorasan province under potential conditions. The model was evaluated using two independent experiments. The first experiment was a field one based on a randomized complete block design with four replications. The experimental factors included three cultivars (Fiama, Magnolia and Nagano) and four levels of nitrogen application (0, 80, 160, 250 kg N ha−1). In the second experiment, four levels of irrigation regimes along with four levels of nitrogen application (control, 90, 180 and 170 kg N ha−1) were investigated. The evaluated model was used to perform simulation experiments. The simulation experiments consisted of a factorial combination of six sowing dates including two spring dates (March 6 and May 6) and four autumn dates (October 2, October 17, November 1 and November 16) in two locations of Mashhad and Neyshabor. The results showed that maximum fresh and dry yield of storage organ were observed on October 2 (104191 and 26047.6 kg ha-1, respectively). The results of group comparisons of fresh and dry yield also indicated the superiority of autumn sowing dates compared with spring sowing dates. In additions, the autumn sowing dates had better performance than spring sowing dates in terms of maximum leaf area index and gross assimilation rate at both locations. Water use efficiency was also higher in autumn sowing compared to the spring sowing (2.57 and 1.67 kg dry weight of storage organ per m3). Overall, autumn sowing sugar beet in Khorasan province benefits from more rainfalls, higher water use efficiency, lower evapotranspiration and water requirements over season compared with spring sowing. In addition, autumn sowing sugar beet could use precipitations during autumn and winter which consequently result in more production with less water. The optimum sowing dates among four autumn sowing dates were October 2 and 17 at both locations.