Comparative Effects of Organic and Inorganic Fertilizer Amendments on Growth and Yield of Spring Rice (Oryza sativa L.) in Eastern Terai, Nepal

Spring rice (Chaite Dhan) is an important complement to monsoon rice in Nepal, yet its productivity in the eastern Terai is constrained by suboptimal nutrient management and low adoption of locally available organic amendments. Although organic manures and oilseed cakes are widely promoted, comparative field evidence ranking the major locally accessible amendments against recommended inorganic fertilizer under uniform conditions remains scarce for this region, which limits evidence-based extension advice. This study therefore evaluated seven fertilizer treatments on the growth and yield of spring rice (cv. Hardinath-1) at Gadhi Rural Municipality-3, Sunsari, Nepal, under a randomized complete block design with three replications during the spring season of 2025. Treatments comprised recommended inorganic fertilizer (NPK 120:40:50 kg ha⁻¹), Farm Yard Manure, goat manure, poultry manure, vermicompost, and mustard seed cake (each at 6 t ha⁻¹), and an unfertilized control. Data were analyzed by analysis of variance with means separated by the least significant difference test at p ≤ 0.05. Mustard seed cake was the only treatment that significantly out-performed all others, recording the greatest plant height (110.53 cm), flag leaf area (54.14 cm²), filled grains panicle⁻¹ (115.93), grain yield (5.07 t ha⁻¹) and biological yield (10.94 t ha⁻¹), with the second-lowest grain sterility (28.75%). Inorganic NPK promoted favorable early vegetative growth but was progressively surpassed by mustard seed cake during the reproductive and yield-formation phases. Grain yields of the remaining treatments, including the unfertilized control, did not differ significantly from one another, indicating appreciable residual soil fertility at the site. These findings identify mustard seed cake at 6 t ha⁻¹ as a practical, locally available organic amendment that can raise spring rice yields in the eastern Terai and offer smallholders a sustainable alternative to imported inorganic fertilizer, pending confirmation in multi-season trials.