Effects of Limited Irrigation on Forage Yield, Nutritive Value and Water Use Efficiency of Persian Clover (Trifolium Resupinatum) Compared to Berseem Clover (Trifolium Alexandrinum)

To evaluate the forage yield and quality of Berseem and Persian clover cultivars, a two-year experiment was conducted during two growing seasons (2017–2018 and 2018–2019). Irrigation was the main factor, including full irrigation (I₁₀₀), moderately limited (I₇₅), and severely limited irrigation (I₅₀). The sub-factor consisted of ten cultivars of clover, five of which were Persian clover (Pars, Aleshtar, Eghlid, Harat, and Zabol) and five cultivars of Berseem clover (Karaj, Elite, Ekinaton, Vienna, and Alex). The results showed that the highest dry matter (DM) and crude protein (CP) yield under all irrigation levels were obtained from the Berseem clover cultivars. Imposing limited irrigation reduced the DM yield, digestible dry matter (DDM) yield and content, CP yield, dry matter intake (DMI), and relative feed value (RFV) of forage, whereas the content of CP, water-soluble carbohydrates (WSC), neutral detergent fiber (NDF), and acid detergent fiber (ADF) increased. Irrigation water use efficiency (IWUE) for DM, DDM, and CP yield under limited irrigation were also increased. Comparison of two groups of Persian and Berseem clover cultivars also showed that with increasing drought stress intensity, in Berseem cultivars, DM yield, DDM yield and content, and RFV decrease was higher. Increasing IWUE under limited irrigation was higher in Persian cultivars for DM and DDM yield. Overall, Berseem clover had higher forage yield and water use efficiency in all irrigation regimes, and the forage quality of this species showed more sensitivity to drought. Abbreviations :I₁₀₀, I₇₅, and I₅₀, full, moderately limited, and severely limited irrigation (equivalent to 100, 75, and 50% weekly evaporation and crop water requirement, respectively); DM, dry matter; CP, crude protein; ADF, acid detergent fiber; NDF, neutral detergent fiber; DDM: digestible dry matter; WSC, water-soluble carbohydrates; DMI, dry matter intake; RFV, relative feed value; IWUE, irrigation water use efficiency.