The effect of the combination of nitrogen fertilizer and seaweed extract on the content of macro- and micro-nutrients in Hashemi rice variety

To increase rice yield, excessive nitrogen is often applied, which may reduce grain quality. This study evaluated the effect of nitrogen fertilizer and seaweed extract on the macro- and micronutrient content in the grain and straw of Hashemi rice during the 2021 and 2022 growing seasons in northern Iran. A split-plot design with three replications was used, with nitrogen fertilizer at five levels (0%, 25%, 50%, 75%, and 100% of the plant’s requirement) as the main plot, and foliar application of seaweed extract at four concentrations (0, 0.5, 1, and 1.5 L ha⁻¹) as the sub-plot. Nitrogen and seaweed significantly affected all measured traits, though their interaction was only significant for nitrogen and potassium in grain, and potassium, zinc, manganese, and iron in straw. The 75% nitrogen level produced the highest SPAD value (35), paddy yield (4014 kg ha⁻¹), and biological yield (7690.8 kg ha⁻¹). However, 25% and 50% nitrogen led to the highest nitrogen use efficiency. Foliar application of 1 L ha⁻¹ seaweed extract resulted in the highest values for most traits, with no significant difference compared to the 1.5 L ha⁻¹ level. The positive response of rice to both readily and less-available mineral uptake highlights the potential of seaweed-based biofertilizers to enhance rice nutrition and yield