Influence of Irrigation Frequency and Foliar Sprays of Potassium Sulfate and Proline on Maize Performance in Silty Loam Soil

This experiment was conducted in Kirkuk Governorate in a silty loam soil with the aim of studying the effect of irrigation interval, foliar application of potassium sulfate and proline, and the interaction between these factors on the growth and development of maize plants (Zea mays L.). The experiment included four irrigation intervals (4, 8, 12, and 16 days), and three concentrations of both potassium sulfate (K⁺ 41.5%) and proline: (0, 2500, and 5000 mg·L⁻¹) and (0, 100, and 200 mg·L⁻¹), respectively. These treatments were applied as foliar sprays in three replications for each treatment using a randomized complete block design (R.C.B.D). The potassium sulfate and proline sprays were applied 30 days after seed germination, with a second spray 30 days after the first. The results showed that increasing the irrigation interval significantly reduced leaf area, chlorophyll content index, grain potassium content, grain protein content, and grain yield compared to the control treatment (4-day interval). Foliar spraying with potassium sulfate at a concentration of 5000 mg·L⁻¹ significantly improved all growth and yield parameters. Spraying with proline at 200 mg·L⁻¹ significantly increased leaf area, grain potassium content, and grain protein content. The interaction between the 4-day irrigation interval and potassium sulfate at 5000 mg·L⁻¹ led to a significant increase in all studied traits. The combination of 5000 mg·L⁻¹ potassium sulfate and 200 mg·L⁻¹ proline resulted in significant increases in chlorophyll content index, grain potassium, and protein content. The treatment with a 4-day irrigation interval and 200 mg·L⁻¹ proline also significantly increased leaf area, grain potassium, and protein content. Additionally, the interaction between a 4-day irrigation interval and foliar application of 5000 mg·L⁻¹ potassium sulfate and 100 mg·L⁻¹ proline resulted in a significant increase in leaf area and chlorophyll content index. The combination of a 4-day irrigation interval and foliar application of 5000 mg·L⁻¹ potassium sulfate and 200 mg·L⁻¹ proline produced the highest values for grain potassium and protein content.