Biotic and abiotic stresses are among the most significant factors reducing productivity in arid and semi-arid regions, where water is the primary limiting factor for plant growth. Sorghum possesses several advantageous physiological characteristics—including drought and salinity tolerance, higher water-use efficiency compared to other forage crops, relatively high yield, desirable forage quality, and suitability for storage as both dry fodder and silage—which make it particularly valuable in these environments. Strategies to utilize saline water effectively include selecting salt-tolerant cultivars, applying saline water during growth stages of lower sensitivity, and blending saline and non-saline water to reduce overall salinity. Although sorghum exhibits relative tolerance to soil and irrigation-water salinity, leaf-area expansion, carbon assimilation, stem elongation, and dry-matter accumulation are significantly constrained under high salinity.
Materials and Methods
This experiment was conducted over two growing seasons (2019–2020 and 2020–2021) at the Zahak Agricultural Research Station (Sistan, Iran), using a split-plot arrangement in a randomized complete block design with three replications. Main-plot treatments were three irrigation-water salinity levels: non-saline (2–3 dS m-1, control), moderate (4–6 dS m-1), and severe (6–8 dS m-1). Sub-plot treatments comprised six promising forage sorghum genotypes (Pegah, Mansour, Speedfeed, KFS15, KFS16, and KFS17). Based on soil test recommendations, ammonium phosphate (250 kg ha-1) and urea (100 kg ha-1) were applied at planting; an additional 100 kg ha-1 urea was top-dressed when plants reached 35–40 cm in height. Sowing occurred on 15 March each year. Each sub-plot consisted of six 5-meter-long rows with 50 cm spacing between rows and 6 cm spacing between plants. At the panicle emergence stage, after removing the two border rows and 0.5 m from both ends of each plot, samples were harvested from an area of approximately 8 m². Recorded traits included days to flowering, plant height, tiller number, stem diameter, leaf number, leaf area, fresh and dry forage yields.
Results and Discussion
The combined analysis of variance revealed that plant height, stem diameter, tiller number, leaf number, leaf area, protein content, fresh forage yield, and dry forage yield were significantly affected (p ≤ 0.01) by salinity, genotype, and their interaction. Under non-saline conditions (2–3 dS m-1), ‘Mansour’ produced the highest fresh forage yield (146.94 t ha-1), leaf area (261 cm2), and protein content (15.03%). The Speedfeed cultivar under normal irrigation ranked second with a protein content of 14.75%, following Mansour. The lowest protein content was observed in lines KFS17 and KFS16, with means of 11.70% and 11.85%, respectively, under high-salinity irrigation. Protein content declined in all genotypes with increasing salinity; ‘Mansour’ exhibited the greatest reduction (23.7%). Under severe salinity (6–8 dS m-1), ‘Pegah’ maintained superior plant height, stem diameter, tiller and leaf numbers, and achieved higher fresh forage yield (72.01 t ha-1) and dry forage yield (21.30 t ha-1) yields than the other entries. Fresh forage yields decreased significantly across all genotypes as salinity rose (p ≤ 0.01); the lowest fresh yield (38.96 t ha-1) was recorded in KFS15 under severe salinity. The highest dry forage yields under non-saline irrigation were obtained by ‘Mansour’ (38.71 t ha-1) and KFS17 (38.40 t ha-1), whereas the lowest dry forage yield (22.33 t ha-1) occurred in KFS16 at 6–8 dS m-1.
Conclusion
The study demonstrated significant genotypic differences in forage sorghum’s response to irrigation-water salinity. While all measured traits declined as salinity increased, ‘Mansour’ excelled under non-saline conditions, and ‘Pegah’ showed superior tolerance under moderate to high salinity, maintaining higher biomass and protein levels. These results suggest that selecting genotypes based on their salinity-response profiles can optimize forage yield and quality in salt-affected environments. Given the escalating salinity of irrigation water in the Sistan region, the cultivation of ‘Pegah’ offers a practical and resilient strategy to sustain forage production and support local livestock systems. |
