Effects of Foliar and Soil Application of Potassium (K) Nutrition on Soybean Mineral Uptake.

Potassium (K) is an essential nutrient for plant growth, development, yield, and quality. K regulates enzymatic processes in the plant, helps maintaining essential mineral uptake, and essential for pod and seed formation in soybean plants. The objective of the present study was to investigate the effective rate and mode of application of K which will positively modulate mineral uptake by soybean plants. Soybean cultivar (Pioneer 95Y70, maturity group 5.7) was grown in the greenhouse. Two repeated greenhouse experiments were conducted. The plants were arranged in a complete block design with four replicates. Plants were treated with K₂SO_4, which was applied in two modes (foliar and soil) of application and two rates. For the foliar application, the K rates were 1.75 and 2.5%; for soil application, the K rates were 190 mg/kg and 380 mg/kg. The applications were performed at V3 (vegetative stage) and repeated at R3 (beginning of pod setting/initiation) stage. A week after the second treatment, leaf samples were collected and analyzed for mineral composition. Results were analyzed using Proc GLM in SAS. The results showed that leaf K concentration was higher in foliar treatment compared to control. Nitrogen (N) had a small increase at 1.75% of foliar K and at 190 mg/kg soil application. Leaf sulfur (S) concentration was most favorable (higher) at both rates of foliar applications compared to the control. Boron (B) and Zinc (Zn) decreased in all treatments, whereas Fe concentrations was higher at low rate of foliar application compared to control. We concluded that foliar K application at both rates (1.17 and 2.5%) seem to be more effective than soil application for maintaining leaf K and S concentrations. The effects of K on micronutrient composition, especially, B, Zn, and Fe, and the mechanisms controlling these alterations are underway.