Impact of Foliar Application of Iron and Zinc Sulfate on Forage Yield and Iron and Zinc Concentration in Corn Fodder (Zea mays L.)

This experiment was carried out in a field near the village of Takhshi Mahalle, located 5 km northwest of Gorgan city with geographical coordinates (54° 17´ 56 ʺ N) (52° 51´ 36 ʺ E) in 2022. The physical and chemical properties of the soil were measured at a depth of 0-30 cm in different parts of the farm and the final composite soil was analyzed in the laboratory. Water was measured using conventional methods of sampling and testing water and wastewater. The experiment was conducted as a randomized complete block design with 3 replications. The treatments included control (with distilled water), foliar spraying of iron sulfate micronutrient elements [FeSO4.7H2O (20%Fe)], zinc sulfate [ZnSO4.7H2O (22% Zn)], and iron sulfate + zinc sulfate at a concentration of 5 per thousand at the 4-leaf stage, the 8-leaf stage and both stages (4-leaf and 8-leaf). Foliar spraying was done in the early morning and drip irrigation was used. Plants were harvested 120 days after planting, washed with distilled water and dried with tissue paper. The samples were air-dried and then oven dried at 70˚C to a constant weight in a forced air-driven oven. Iron and zinc concentrations were determined by an atomic absorption device. In order to determine the protein percentage and yield in different treatments, total nitrogen was measured by the Kjeldahl method. The protein percentage and yield were calculated using the following formula:  
Statistical data were analysed using SAS software (9.4) and the mean values were compared using LSD tests (at 5% level).

The obtained results showed that all treatments effects were significant (P<0.01) (fresh forage P<0.05). Among all the treatments and measured traits, the control treatment showed the lowest value. The highest iron concentration with an average of 175.14 mg kg-1 was obtained using iron foliar spraying in both 8 and 4 leaf stages, which increased 22.73 and 34.39% in comparison with only using iron foliar application in 4 and 8 leaf stages, respectively. Zinc foliar spraying at both the 4 and 8 leaf stages resulted in the highest zinc concentration of 71.02 mg kg-1 in forage corn, increasing zinc concentration by 89.86% over the control. In both 4 and 8 leaf stages, an iron and zinc foliar application had the highest chlorophyll index with an average of 57.63. The highest nitrogen content, averaging 2.80%, was observed following foliar spraying of iron and zinc during both the 4 and 8 leaf stages. This represents an increase of 5% and 23.92% compared to iron and zinc foliar application treatments during the respective stages. Consequently, the highest yield and protein percentage were also attained, averaging 310.75 grams per square meter and 17.50%, respectively, with simultaneous foliar application of iron and zinc during both the 4 and 8 leaf stages. 

The optimal outcomes for measured traits were observed when iron and zinc were concurrently applied at both the 4 and 8 leaf stages. Therefore, it is advisable to administer iron and zinc simultaneously during these growth stages to ensure the attainment of forage with desirable quantitative and qualitative characteristics.