Response of Different Population Densities of Fine Rice to Variable Organic and Inorganic Fertilizer Regimes under Agro-Climatic Conditions of Southern Khyber Pakhtunkhwa of Pakistan

Fine rice production in semi-arid regions such as Dera Ismail Khan is limited by suboptimal plant density and nutrient management. To address these constraints, a field experiment was conducted at the Agricultural Research Institute, Dera Ismail Khan during 2023 using a randomized complete block design with split-plot arrangements and three replications. Plant population densities (20 × 20 cm, 25 × 25 cm, and 30 × 30 cm) were assigned to main plots, while organic and inorganic fertilizer regimes were tested in sub-plots, including sole NPK, NPK with Zn, press mud, ash, Organic-77, and their combinations. Significant variations were observed across population densities, fertilizer regimes, and their interactions. The narrowest spacing (20 × 20 cm) combined with integrated nutrient management (NPK 120:60:60 kg ha⁻¹ + Zn 12 kg ha⁻¹ + press mud 10 t ha⁻¹ + ash 10 t ha⁻¹ + Organic-77 25 kg ha⁻¹) produced the highest paddy yield (8.30 t ha⁻¹) and net return (Rs. 407,700 ha⁻¹). This treatment also enhanced crop growth rate, net assimilation rate, and leaf area index, while reducing spikelet sterility. Wider spacing (30 × 30 cm) improved panicle length and kernel weight per panicle but resulted in lower overall yield performance. The study concludes that maintaining 20 × 20 cm spacing along with integrated organic and inorganic fertilizer management substantially improves growth, productivity, and profitability of fine rice under semi-arid conditions of Southern Khyber Pakhtunkhwa. These findings provide practical recommendations for farmers to achieve sustainable rice production and higher economic returns in resource-constrained environments.