Effect of partial replacement of potassium sources combined with cobalt on wheat (Triticum aestivum L.) growth and yield parameters.

This study evaluated the interactive effects of potassium (K) fertilizer sources and cobalt (Co) supplementation on the growth, yield, and grain quality of wheat (Triticum aestivum cv. Giza-95) under arid soil conditions in El-Nubaryia, Egypt. A split-split-plot field experiment was conducted over two consecutive seasons (2021/22 and 2022/23), testing five K-fertilization regimes (100% K2SO4, 75% K2SO4 + 25% KCl, 50% K2SO4 + 50% KCl, 25% K2SO4 + 75% KCl, and 100% KCl) with or without 10 mg L-1 cobalt. Results showed that both K source and Co significantly affected plant growth, yield traits, nutrient uptake, and biochemical constituents of wheat grains. Cobalt consistently increased plant height, tillering, spike number, spike length, and dry matter accumulation, while also enhancing grain filling, straw yield, and grain yield (up to 9.35 t ha-1 with 100% K2SO4 + Co). Grain nutritional quality improved markedly, with cobalt raising protein (by 3.5%), carbohydrates, starch, and soluble sugars (by up to 18.3%), while also increasing Zn, Mn, Cu, and Co concentrations in grains. All mixing ratios of potassium sulfate and potassium chloride produced better results than potassium chloride alone. Conversely, increasing KCl proportion reduced vegetative growth, yield, and nutrient enrichment, though cobalt partially alleviated these negative effects. Notably, cobalt enhanced Zn and Co uptake but slightly reduced Fe content. The findings indicate that partial substitution of K2SO4 with KCl can maintain satisfactory wheat productivity and grain quality, particularly when combined with cobalt application, whereas complete replacement with KCl is not recommended. Therefore, integrating cobalt supplementation with partial K2SO4 replacement represents a cost-effective and sustainable fertilization strategy for improving wheat production under arid and marginal soil conditions.