Evaluation of Forage Sorghum Yield Quality and Quantity at Different Levels of Salinity and Irrigation Water under Subsurface Drip Irrigation System

Water stress and salinity are among the problems of agricultural production in many parts of the world. In this study, the effect of salinity (2, 5 and 8 dS/m), different irrigation levels (120%, 100%, 75%, and 50% of water requirement) and three harvesting times (cuttings) were investigated on some qualitative and quantitative parameters of sorghum silage in the Sistan region. The study was carried out using a factorial split plot design with 12 treatments and 3 replications. The results showed that increasing salinity and irrigation water depth decreased fresh and dry matter yield. However, no significant difference was observed between 100% and 75% crop water requirement treatments. Also, treatments with 2 and 5 dS/m salinity were not significantly different in feed production. Furthermore, the fresh and dry forage yields were higher in the second cutting than in the first and third harvesting. Decrease in irrigation water and increase in salinity decreased protein but increased carbohydrate and proline. The highest amount of protein (16.79 percent) was obtained in the second harvesting and at the salinity of 2 dS/m, while the highest amount of carbohydrates (10.79 mg/gFW) and proline (0.42 mg/gFW) belonged to the third harvesting with salinity of 8 dS/m. By increasing salinity in irrigation water and with the passage of time during the growing season, soil salinity increased and distribution of salinity in the soil profile was more uniform in the treatments that had no water stress. Thus, according to the results, 25% of the plant water consumption can be saved and irrigation with 75% of water requirement and salinity of 5 dS/m would have no significant effect on the amount of forage produced. The best forage quality for livestock consumption was obtained in the second harvesting. However, this experiment was done in one growing season and in the long time reduction in the amount of water and the use of salt water can cause soil salinization and accumulation of salts in the soil. Therefore, it is recommended that the experiment be repeated in the future, before making a final decision about reducing irrigation water.