Benefits from Intercropped Forage Sorghum–Red Clover Under Drought Stress Conditions

To investigate the sorghum–clover intercropping systems under different levels of drought stress, an experiment was conducted as split plots based on a randomized complete block design with three replications in a semi-arid region of Iran during the 2016 and 2017 cropping seasons. Drought stress at three levels (supply 100, 75, and 50% of soil moisture deficit: I₁₀₀, I₇₅, I₅₀, respectively) as the main factor and cropping system at eight levels (including three replacement intercropping, three additive intercropping, and sole cropping of sorghum and red clover) as sub-factor were evaluated. The results showed that the highest dry matter and crude protein yields (26.53 and 2.54 Mg ha⁻¹, respectively) were recorded in the intercropping system of 100% sorghum +100% clover (S₁₀₀C₁₀₀) under the I₁₀₀ irrigation regime. Increasing the proportion of clover in intercropping systems increased the crude protein content, dry matter digestibility, dry matter intake, net energy for lactation, and relative feed value (RFV), whereas increasing the proportion of sorghum in intercropping systems improved the forage yield. As the intensity of drought stress increased, the RFV increased in all cropping systems except the clover monoculture and intercropping system of 25% sorghum +75% clover (S₂₅C₇₅). The highest land equivalent ratio (LER) under I₁₀₀, I₇₅, and I₅₀ irrigation regimes (1.82, 1.73, and 1.71, respectively) were calculated in the S₁₀₀C₁₀₀ intercropping system. Overall, the S₁₀₀C₁₀₀ intercropping system under the I₇₅ irrigation regime is recommended for semi-arid regions due to saving water while producing desired forage yield and quality.