Lablab was grown in two field experiments at Narrabri, NSW. The aim was to determine the effect of irrigation and N fertiliser on dry matter production and N fixation by lablab in order to assess its potential as a green manure crop for use within a cotton farming system. The experiments found that dry matter production, water-use efficiency (WUE) of dry matter production and the amount of N fixed by lablab was increased by more frequent irrigation. Optimal WUE of dry matter production was found to be 55 kg ha WUE of N fixation was not affected by irrigation frequency and was 0.62 kg ha mm. Lablab N fixation was reduced from a maximum of 189 to 95 kg N ha by increasing rates of N fertiliser from O to 240 kg N ha' . The WUE of lablab compares favourably with other crops. With full irrigation lablab has the potential to produce up to 16000 kg dry matter ha' and fix up to 189 kg N ha.