Allelopathic effects of water extract from three species of annual forage on seed germination and seedling growth

Weeds are one of the main limiting factors of forage production that seriously affect seedling emergence via the allelopathic effect in the planting stage of forage. In this study, two major weeds in farmland (Chenopodium glaucum and Leymus secalinus) with four set gradients (0.25, 0.50, 0.75, and 1.00 g·mL⁻¹) of water extract were used as test materials to evaluate the allelopathy effect on the germination of Sorghum sudanense, Setaria italica, and Echinochloa frumentacea seeds. The water extract of C. glaucum and L. secalinus showed different inhibitory effects on the germination and growth of three annual forages, and the effect increased with increasing concentrations of the extracts. During forage seed germination, the effects of water extracts of the two weeds on the seeds of the three forages were primarily reflected in the reduction of the germination rate and the delay in germination time. The predicted thresholds for the complete inhibition of S. italica by C. glaucum and L. secalinus were 0.3～0.6 g·mL⁻¹, whereas those of S. sudanense and E. frumentacea were 0.9～1.2 g·mL⁻¹. During forage seedling growth, the two weed water extracts influenced the aboveground and underground growth of the three forages. The low concentration of L. secalinus water extracts (less than 0.75 g·mL⁻¹) simultaneously affected the growth of E. frumentacea roots and seedlings, whereas the high concentration (1.00 g·mL⁻¹) showed inconsistent inhibitory effects on the growth of roots and seedlings. E. frumentacea exhibited higher allelopathic resistance to the two weed water extracts at concentrations below 0.50 and 0.25 g·mL⁻¹, whereas S. italica displayed weaker resistance primarily manifested in root length and seedling length inhibition. Although all three test forages were chemically inhibited by the two weed extracts, the seedling growth of each forage differed in their ability to tolerate their chemotaxis. The tolerance thresholds of S. sudanense and E. frumentacea to the two weed extracts were the same (0～0.75 g·mL⁻¹) and higher than those of S. italica (0～0.25 g·mL⁻¹). This study demonstrates that allelopathic effects can impede forage seedling establishment by influencing germination strategies, regulate aboveground and underground growth behavior, and inhibit their overall establishment. S. sudanense and E. frumentacea exhibit promising potential in combating C. glaucum and L. secalinus, respectively; planting these two more resistant forages could effectively mitigate weed impact, thereby providing a scientific foundation to establish and manage forage production.