Introduction
Maize (Zea mays L.) is one of the most important crops globally, for human consumption and livestock feed as well as production of bioethanol. The intensive use of synthetic fertilizers for increasing the yields of this crop has raised serious concerns regarding soil degradation, environmental pollution, and sustainability of agricultural. To secure sufficient food for the growing global population sustainable agriculture practices are increasingly required. We investigate the application of smoke water, a cheap and ecofriendly plant growth promoter consisting of high amounts of plant growth-promoting compounds such as karrikinolides. This study investigates the impact of foliar-applied smoke water on the growth and agronomic performance of maize under field conditions.

Materials and Methods
Field experiments were conducted during growing season of 2021 at the Research Farm of Razi University, Kermanshah, Iran. Research Farm of Razi University is located in a Mediterranean semi-arid region with mean annual rainfall of 455 mm, mean annual temperature of 13.4°C and altitude of 1,320 m above sea level. This experiment was carried out as 3 × 3 + 1 (control) factorial arranged in a randomized complete block design (RCBD) with three replications. Three different concentrations of the smoke water (1:1000, 2:1000, and 3:1000 v/v) were applied to three different stages of growth of maize (six-leaf stage, BBCH code 16; tasseling stage, BBCH code 51; and silking stage (BBCH 61). Distilled water was applied to the control plots. Smoke water was prepared from equal proportions of wheat straw and alfalfa residues. Foliar applications were carried out during the early morning using a calibrated backpack sprayer. The maize hybrid ‘Simon’ was sown on June 10, 2021. Appropriate pollination management was implemented using maternal (PL62) and paternal (PL97) lines. Each experimental plot consisted of six rows, with 75 cm spacing between rows and 17–20 cm spacing between plants within rows. Irrigation was initially provided at weekly intervals during the early stages of crop development and was subsequently adjusted to every 10 days according to crop requirements. At physiological maturity, representative plant samples were collected to assess yield, yield components, grain quality, morphological characteristics, and germination-related traits. Measurements included biological yield, grain yield, yield components, crude protein content, harvest index, and selected morphological and seed germination characteristics.

Results and Discussion
Smoke-water application significantly influenced the majority of the measured traits compared with the control. The application of smoke water at a concentration of 2:1000 (v/v) at the tasseling stage (BBCH 51) resulted in the highest grain yield (7973.1 g m⁻²), representing a 73.6% increase over the control (4592.8 g m⁻²). This treatment also produced the highest values for several yield components, including the number of seeds per cob (335.9), cob weight (120.5 g), and biological yield (3482 g m⁻²), corresponding to increases of 81.2%, 68.4%, and 36.6%, respectively, compared with the control. Application of smoke water at 2:1000 during the six-leaf stage (BBCH 16) resulted in the highest cob core weight (26.14 g) and harvest index (26.08%). In contrast, the 3:1000 concentration applied at the same growth stage produced the highest crude protein content (11.08%) and plant height (166.6 cm). Regarding seed germination characteristics, application of 3:1000 smoke water at the silking stage (BBCH 61) resulted in the greatest germination rate, root length (6.65 mm), and seedling vigor index, with these parameters increasing by approximately 3% relative to the control. Notably, all smoke-water treatments increased the germination percentage to 100%, compared with 96.66% in the control; however, no significant differences were observed among smoke-water concentrations, suggesting a consistent stimulatory effect of smoke water on seed germination. The number of cobs per plant was not significantly affected by smoke-water application, indicating that this trait may be relatively stable and strongly influenced by genetic factors. Morphological characteristics were also affected by smoke-water concentration and application timing. The 3:1000 concentration applied at the six-leaf stage (BBCH 16) resulted in the greatest plant height and cob core diameter (27.13 mm). In contrast, cob length did not differ significantly among treatments, suggesting that this trait may be predominantly determined by genetic factors and is less responsive to foliar smoke-water application.

Conclusion
Results indicated that foliar application of smoke water can significantly enhance various agronomic traits as well as improve seed quality in maize. The highest values for grain and biological yields, number of seeds per cob and cob weight were obtained with the 2:1000 (v/v) concentration of smoke water, applied at the tasseling stage (BBCH 51). The treatment with a 3:1000 concentration of smoke water at silking improved several germination-related traits of maize, including root length and seedling vigor. Overall, smoke water shows potential as an inexpensive and eco-friendly biostimulant for improving maize productivity and seed quality under semi-arid conditions. Further studies are needed to optimize its concentration and application timing under different environmental conditions.