Competition of Palmer Amaranth and Corn Under Different Irrigation Regimes

Water stress and weed competition emerge as pivotal stressors during the development of corn. This two-year study evaluated the effect of Amaranthus palmeri (AMAPA) on corn at varying densities (1, 2, and 4 plants per m−1) under two different irrigation (full and deficit) regimes. Water use efficiency and leaf water potential values were evaluated to determine the effects of different irrigation water amounts and AMAPA densities on corn water consumption. AMAPA height and fresh weight were also measured along with corn growth parameters. The results indicated that corn height, first ear height and number of rows in corn ear decreased by 14.5%, 22.1% and 9.47% on average with the effect of deficit irrigation compared to full irrigation. Under the pressure of four AMAPA plants, ear diameter, ear length, number of grains in a row of ears, ear weight and grain yield decreased by 10.7%, 22.4%, 26.3%, 43.0% and 43.1% on average compared to monoculture corn. Deficit irrigation increased water use efficiency values, while AMAPA density decreased these values. While this study demonstrated that a reduction in irrigation and an increase in AMAPA density exerted adverse effects on the growth parameters of corn, it was also observed that under deficit irrigation conditions, AMAPA did not demonstrate superiority over corn, which possesses a high degree of competitive power in comparison to other C3 summer crops.