Improving Nutrient Uptake and Protein Yield of Rice through Integrated Nitrogen Management and Foliar Fe and Zn Application in Calcareous Soils

Rice (Oryza sativa L.)is one of the most important cereal crops worldwide, serving as the primary source of calories and nutrition for more than half of the global population. In Asia, where nearly 90% of rice is produced and consumed, it forms the dietary backbone for millions of smallholder farmers and consumers alike (Paramesha et al., 2025). However, sustaining high rice productivity while ensuring grain nutritional quality remains a major challenge undercurrent production systems. Intensive cultivation practices with high dependency on chemical fertilizers have resulted in soil nutrient depletion, reduced factor productivity, and deterioration of soil health (Walia et al., 2024). Among macronutrients, nitrogen (N) is the most yield-limiting element, but imbalanced application and low recovery efficiency often less than 40% lead to nutrient losses and environmental risks (Shrestha et al., 2020).

Integrated nutrient management (INM), which combines chemical fertilizers with organic sources such as farmyard manure (FYM), poultry manure, and vermicompost, has emerged as a sustainable approach for improving soil fertility, enhancing microbial activity, and increasing nutrient use efficiency (Paramesha et al., 2025). The addition of organic sources not only supplements plant nutrients but also improves soil physical properties and supports long-term productivity. Recent studies highlight that substitution of a portion of N fertilizers with organic manures can enhance nitrogen-use efficiency, reduce dependency on chemicals, and maintain yield stability in rice-based systems (Shrestha et al., 2020). Alongside macronutrient management, micronutrient deficiencies have gained increasing attention due to their dual role in crop productivity and human nutrition. Iron (Fe) and zinc (Zn) deficiencies are among the most widespread constraints in paddy soils, particularly under flooded anaerobic conditions that reduce micronutrient availability (Singh et al., 2018). These deficiencies not only lower rice yields but also contribute to “hidden hunger” inhuman populations dependent on rice as a staple food. Zinc is vital for enzyme activation, auxin metabolism, and grain filling, while iron plays a central role in chlorophyll synthesis, respiration, and electron transport. Global estimates suggest that more than two billion people suffer from Zn and Fe deficiencies and biofortification of rice grains with these nutrients is considered a promising solution to combat malnutrition (Ram et al., 2024; Liu et al., 2023).

Foliar application of micronutrients has been widely recommended as an efficient strategy to overcome soil-related limitations and improve nutrient uptake at critical growth stages. In rice, foliar sprays of FeSO₄ and ZnSO₄ during tillering and panicle initiation have been reported to improve nutrient accumulation, enhance photosynthetic efficiency, and increase grain micronutrient content (Ram et al., 2024). Moreover, the interaction between nitrogen management and micronutrient uptake is particularly important: higher nitrogen supply stimulates root activity and transporter expression, thereby enhancing Fe and Zn assimilation in rice plants (Singh et al., 2018). However, the combined impact of integrated N sources with foliar Fe and Zn application on rice yield and nutritional enrichment has not been adequately studied.

Given these gaps, the present study was undertaken to investigate the interactive effects of integrated nitrogen management and foliar application of Fe and Zn on rice. The aim was to assess how different combinations of organic and inorganic nitrogen sources, along with targeted foliar micronutrient supplementation, influence crop productivity, nutrient uptake, and grain nutritional quality under irrigated conditions.