Effects of Drought Stress on Red Clover-Grass Mixed Stands Compared to Grass Monoculture Stands in Nitrogen-Deficient Systems

Drought stress is one of the major abiotic stress factors affecting forage production; thus, it is essential to obtain a better understanding of how forage responds to drought. The main objective of this study was to evaluate how legume-grass mixed forage stands respond to drought stress when compared to grass monoculture. A greenhouse pot experiment was conducted using a red clover (Trifolium pratense L.)—timothy grass (Phleum pratense L.) mixed stand and a timothy monoculture stand, where plants were subjected to severe drought (20% field capacity—FC), moderate drought (40% FC), and well-watered (80% FC) conditions for four weeks and subsequently allowed to recover for another four weeks by adjusting moisture back to 80% FC. Both moderate and severe droughts significantly reduced the shoot biomass of the mixed stand, while no difference was exhibited in the timothy monoculture. The shoot biomass and nitrogen fixation capacity of red clover were reduced under drought stress. However, red clover plants subjected to moderate drought were able to recover shoot growth and nitrogen fixation capacity during the recovery phase, allowing more biologically fixed nitrogen and shoot nitrogen production similar to the plants growing under well-watered conditions. Overall, the results demonstrate that the inclusion of legumes in forage mixtures enhances resilience to moderate drought stress.