The Effect of Irrigation Water Quality, Oil Residue Pollution Levels, and the Interaction between them on the Growth, Yield, and Quality of Sunflower (Helianthus annuus L.) Crop

Abstract

A greenhouse field trial was conducted in the Al-Hussayniya district of Karbala Governorate, Iraq, during 2025 to investigate the effects of irrigation water quality and oil residue contamination on sunflower (Helianthus annuus L.) cv. Kuban. The experiment evaluated three irrigation-water sources (freshwater, well water and wastewater), four oil residue contamination levels (0, 25, 50 and 75 g kg⁻¹ soil) and their interactions. A two-factor experiment was arranged in a randomised complete block design with three replicates. Freshwater irrigation generally improved the measured growth, yield and seed-quality traits compared with well water and wastewater. Across the irrigation-water treatments, freshwater recorded the highest mean plant height (146.0 cm), chlorophyll content (47.7 SPAD), 300-grain weight (24.83 g), grain yield (162.32 g plant⁻¹) and seed oil concentration (37.91%). The maximum protein concentration (20.86%) was recorded under freshwater irrigation without oil contamination, while wastewater irrigation produced the lowest values for most traits. Increasing oil residue contamination reduced the measured growth and yield traits. Plant height decreased from 155.1 to 109.1 cm, chlorophyll content from 49.4 to 38.7 SPAD, 300-grain weight from 25.39 to 21.25 g and grain yield from 164.65 to 117.66 g plant⁻¹ as contamination increased from 0 to 75 g kg⁻¹ soil. The interaction analysis indicated that the best overall plant response occurred under freshwater irrigation without oil contamination, whereas the weakest response was observed under wastewater irrigation at the highest contamination level (75 g kg⁻¹ soil). These findings indicate that irrigation water quality strongly influenced sunflower performance under oil-contaminated soil conditions and that poor-quality water intensified the adverse effects of oil residue contamination.