<![CDATA[Fertilizer practice in highland vegetable farming is generally set by habit rather than marginal calculation, while its economic evaluation rarely moves beyond average income comparison. This study analyses the cost and income structure of cauliflower farming across levels of chemical fertilizer substitution, identifies treatments on the economic efficiency frontier through dominance analysis and marginal rate of return, measures the eco-efficiency of each treatment, and tests whether economic and ecological efficiency constitute a trade-off or a co-benefit. A quantitative descriptive method was applied to on-farm experimental data on cauliflower cv. Spring 70 in Siponjot Village, highland North Sumatra, during the 2025 growing season, comparing full chemical fertilization following farmer practice with 25 and 50 percent dose reductions substituted by cattle manure and the biofertilizer Fertomax or Bioneensis, plus a completely randomised design experiment with four replications. Data were analysed using partial budgeting, dominance analysis, marginal rate of return, partial factor productivity of nutrient, the eco-efficiency ratio, analysis of variance, and the least significant difference test. Reducing the chemical fertilizer dose raised production by 17.6 to 30.1 percent relative to the control, with treatment K50+PF1 recording the lowest fertilization cost of IDR 7,341,270 and IDR 5,515,873 per hectare and the highest revenue cost ratio, 6.18. Conventional farmer practice was economically dominated in both series because cheaper yet more profitable alternatives existed. The marginal rate of return towards K75+PF1 reached only 35.4 percent under Fertomax but 132.9 percent under Bioneensis, indicating that the optimum dose depends on the type and price of the biofertilizer used. Partial factor productivity of nutrient rose by 111.7 and 114.5 percent while the eco-efficiency ratio more than doubled, and analysis of variance confirmed highly significant differences with an F value of 42.68. No trade-off was found between economic and ecological efficiency, but rather a consistent co-benefit pattern.]]>
