Crop Yield Response to Partial Root Drying Compared with Regulated Deficit Irrigation

Abstract

In the face of dwindling water resources, methods that reduce the volume of water applied in irrigation are desirable. These methods include partial root drying and regulated deficit irrigation. The study was conducted in the west of Iran, on the Karafs Plain in the Hamedan Province, in order to investigate the crop yield response to partial root drying compared with regulated deficit irrigation in a semiarid region with limited water resources. The plant studied in this experiment was sugar beet. The experiments were carried out over two consecutive seasons in 2013 and 2014, respectively, using split plots in randomized blocks with three replications. The main blocks included: full irrigation (FI), three levels of partial root drying: 85 (PRD85), 75 (PRD75), 65% (PRD65), and regulated deficit irrigation at three levels: 85 (RDI85), 75 (RDI75), and 65% of the crop water requirement (RDI65). The sub-blocks encompassed two levels of 100 (f100) and 75% (f75) of N-fertilizer requirements. Sugar beet of the Canaria variety was utilized in the study. The effect of the irrigation treatments was significant on all quantitative and qualitative characteristics of the sugar beet. By increasing the amount of irrigation water, root (R) and white sugar yields (WSY) increased, and sugar content decreased. The highest root and white sugar yields obtained were through FI treatment with a mean root and white sugar yields of 54,235 and 7,803 kg ha−1, respectively; however, its difference with PRD85 treatment yield was non-significant (with a mean root and white sugar yields of 51,113 and 7,644 kg ha−1, respectively). The highest water productivity of root (WP (R)) and white sugar yield (WP (WSY)) obtained were through PRD85 treatment with a mean WP (R) and WP (WSY) of 5.57 and 0.83 kg m−3, respectively. Also, results of this study showed that the root yield, white sugar yield, WP (R), and WP (WSY) in all PRD treatments when compared to RDI treatments were higher at similar irrigation levels. The WP (R) of PRD65 treatment increased 13.4% as compared to the RDI65 treatment. WP (WSY) of PRD85, PRD75, and PRD65 treatments increased 7.8%, 11.3%, and 17.2% as compared to RDI85, RDI75, and RDI65 treatments, respectively. Also, PRD irrigation treatments held less impurities of α-amino-N, K and Na than the RDI treatments. Therefore, the PRD irrigation compared with RDI irrigation causes reduction in dry stress to the root and reduces the absorption of impurities. The effect of fertilizer treatments on sugar content, white sugar content, and all of the quantitative attributes of sugar beet were significant. With the increase in the application of N-fertilizer, root and white sugar yields increased, and sugar content decreased. Therefore, under such experimental conditions, applying the PRD85 treatment is recommended to prevent yield loss while saving 15% of irrigation water. What’s more, the study showed that among the various fertilizer treatments applied in the study, f100 treatment showed the best results.