Manure-Driven Reduction of Inorganic Fertilizer Improves Bulb Yield and Post-Harvest Storability of Shallot (Allium cepa var. ascalonicum) in the Wet Tropical Lowlands of Bengkulu, Indonesia

Abstract

Shallot production on the acid soils of the wet tropical lowlands relies on heavy inorganic fertilization, and harvested bulbs deteriorate quickly under humid storage. We tested whether composted cattle manure can replace part of the inorganic NPK requirement without reducing bulb yield, and whether the replacement improves storability. A randomized complete block design with six treatments and four replications was run on an Ultisol in Bengkulu, Indonesia. Treatments combined 10 t ha⁻¹ of manure with 100, 75, 50, 25, or 0% of the recommended NPK rate, and full-dose NPK without manure served as the reference. Manure with 75% NPK gave the highest fresh bulb yield (15.56 t ha⁻¹, 18.3% above the reference) and dry bulb yield (12.40 t ha⁻¹). Manure with 50% NPK matched the reference yield and raised the partial factor productivity of nitrogen from 88 to 192 kg kg⁻¹. After eight weeks of ambient storage, weight loss fell from 22.2% in the reference to 15.1% with manure and 50% NPK, and marketable bulbs rose from 63.9% to 82.2%. Adding manure to the full NPK dose raised dry bulb yield but did not improve storability. Soil organic carbon and pH were higher in all manure treatments. Under a fixed manure base, cutting inorganic fertilizer by 25 to 50% served yield and storability better than the full dose in this soil and season.