Efficient liquid slurry land application requires knowledge of nutrient content, proper application rate and crop needs. An improved understanding of the cycling of biogas slurry N is a prerequisite for making better use of this N source. The efficiency of nitrogen (N) derived from biogas slurry must be determined to optimize use of N and reduce impact on the environment. Keeping in view, a pot experiment was initiated to estimate crop N uptake from biogas slurry and chemical fertilizer that applied to Komatsuna (Brassica campestris L.) using 15N isotope dilution method. In this experiment 180 kg N ha-1 of 1.0 atom % 15N excess ammonium chloride was used. Nitrogen derived from biogas slurry (Ndfs) and recovered-N (N rfs) in Komatsuna was measured to know the effects of applied slurry on the performance of the crop and nutrient dynamics in a Brown Lowland Soil, Fluvisols west Japan. It was found out that 15N uptake was slightly higher in chemical fertilizer compared to slurry application. In addition, N uptake derived from chemical fertilizer (Ndfc) was better than that taken from soil (Ndfs). Fertilizer use efficiency (FUE- 15N) was lower in slurry treatment (47.2%) than chemical fertilizer (65.9%). The relative efficiency (slurry use efficiency/chemical use efficiency *100) was varied in Komatsuna roots and leaves. © 2006 Asian Network for Scientific Information.