Italian ryegrass desiccation periods on corn performance: is growth inhibition due to the release of plant allelochemicals or nitrogen immobilization?

Abstract There are contradictions among researchers and farmers about the best time between Italian ryegrass desiccation and corn sowing. Therefore, this study aimed to evaluate: the effects of different desiccation periods of annual Italian ryegrass (Lolium multiflorum Lam.) and nitrogen fertilization management on corn development; and to determine whether growth inhibition is due to the release of plant allelochemicals or nitrogen immobilization. The results indicated that the presence of ryegrass straw caused a corn yield reduction of approximately 2,128 kg ha-1. Corn seed germination speed and germinability were not significantly different for the aqueous ryegrass extracts collected 15 and 30 days after desiccation, regardless of their concentration. Corn seedling coleoptile length, when subjected to increasing concentrations of ryegrass extract, was reduced by approximately 230 and 320% reduction in comparison with the control. Epicatechin and caffeic acid were identified in ryegrass root and shoot extracts, these substances are known to have an allelopathic effect. Our results showed that Italian ryegrass desiccation periods of less than 30 days before corn sowing had affected the germination and emergence of corn, due to nitrogen immobilization and allelopathic influences of caffeic acid and epicatechin, released as residues decomposed. These resulted in corn plants with a shorter stature at the beginning of their development and decreased grain yield. From this, it can be concluded that nitrogen management on the day of sowing and desiccation 30 days before corn planting can prevent the negative effects of Italian ryegrass on corn development and yield.