|BACKGROUND: Green manure and graminaceousmanure crops have several benefits, such as improving soil physical and chemical propertiesand utilizing excessive greenhouse nutrients that they have a potential to be a water pollutant source. METHODS AND RESULTS: The objective of this study was to investigate nitrogen (N) supplying capabilities of green manure and graminaceous manure cropsfor lettuce (Lactuca sativa L) and Chinese cabbage (Brassica campestris L) grown under greenhouse conditions. For this two leguminous manures (Crotalaria juncea (Cr.) and Sesbaniaexaltata (Se.) and two graminaceous manures (Sorghum bicolor; Haussolgo (Ha) and Sudangrass (Sg) in the greenhouse were grown, cut, and incorporated into the greenhouse soil before planting. Chemical nitrogen (N) fertilizer rate was estimated based on N recommendation for lettuce and Chinese cabbage. 100% of the N recommended rates (1N) were 70 kg N ha-1 for lettuce and 60 kg N ha-1 for Chinese cabbage and 50% of the N recommendation rates (0.5N) were 35 kg N ha-1 for lettuce and 30 kg N ha-1 for Chinese cabbage. Nitrogen treatments were control (0N), Cr., Se., Cr + 0.5 N, Se + 0.5 N, Ha + 0.5 N, Sg+0.5 N, and N recommendation rate (1N). Incorporated N from green manure and graminaceous manure crops were 130, 116, 93, and 87 kg N ha-1 for Cr., Se, Ha, and Sg, respectively, Lettuce and Chinese cabbage were grown after incorporated green manure crops into the greenhouse soil. There was no significant difference in lettuce and Chinese cabbage yieldsunder N treatments except control (0 kg/ha).Nitrogen use efficiency (NUE) was from 44% to 73% and the highest NUE was under Se. treatment. Although yields were not statistically different under N treatments except control, actual yield increase ranged from 170 to 1,100 kg/ha for lettuce and ranged from 2,770 to 5,210 kg/ha for Chinese cabbage compared to yield under N recommendation rate. Estimated economic benefit from this would be higher approximately between W2, 770,000 and W5, 210,000/ha under N treatments except control than the N recommendation rate. CONCLUSION: These results suggest that incorporating green manure crops, such as Cr. and SeSe, into soil or adding 0.5 N after incorporation of them can be beneficial in many ways in that it increases economic return because of yield increase, reduces the use of chemical N, and decreasesthe negative environmental impact on water quality because excessive N in the greenhouse soil can be used by green manure crops during the fallow.