Romaine lettuce (Lactuca sativa var. longifolia Lam) is a leafy vegetable that is commercially produced worldwide. Nitrogen (N) is one of the most important elements among plant nutrients. Its effects are related to the growth and yield of the crops; however, excessive synthetic fertilizer application can have adverse environmental effects and additional economic costs. Organic fertilizers like manure and compost release nutrients slowly for plant growth and enhance soil fertility. The aim of this study was to evaluate the combined rates of mineral nitrogen and vermicompost application on growth and yield of romaine lettuce (Lactuca sativa var. longifolia Lam.). The experiment was conducted at the crop station of the Royal University of Agriculture, Phnom Penh, Cambodia. The experiment consisted of five treatments with three replications, and treatments were: (i) 100% N fertilizer + 0% vermicompost (control), (ii) N fertilizer 75% + Vermicompost 25%, (iii) 50% N fertilizer + 50% vermicompost, (iv) 25% N fertilizer + 75% Vermicompost, and (v) 0% N fertilizer + 100% Vermicompost. Plants samples were taken from five random plants and analysed for plant height (cm), leaf number (No.), leaf area (cm 2 ), weight per plant (g), estimated non- marketable yield (t/ha), estimated marketable yield (t/ha) and estimated total yield (t/ha). Soil samples were collected at 0-20 cm depths and analysed for soil pH, SOM (%), total nitrogen (%), soil hardness (kg/cm2), situResp@ (Abs) and POXC (mg kg -1 ). In general, the combined treatment of 50% of N fertilizer and 50% of vermicompost showed the best performance on growth and yield of romaine lettuce; including high leaf area, fresh weight per plant, estimated marketable yield and estimated total yield. Furthermore, POXC was also the highest among treatments. In conclusion, the combination of the organic and inorganic fertilizers (N50% + V50%) showed the best results when compared with full application of N fertilizer. 

Keywords: growth, lettuce, mineral fertilizer, vermicompost, yield.