Shirin quantified the physiological mechanisms which underpin water stress responses for perennial ryegrass (Lolium perenne), tall fescue (Schedonorus phoenix), phalaris (Phalaris aquatica) and cocksfoot (Dactylis glomerata) monocultures at two sites, which differed in soil water holding capacity. From Year 2 pastures were allocated nil (-N) or non-limiting nitrogen (+N) fertiliser. In Year 2, mean annual DM production was 19.8 t/ha for +N and 9.20 t/ha for −N treatments grown on a soil with high plant available water at Ladbrooks. There were no yield differences among the species. However, on the shallow soil with low plant available water at Ashley Dene, the +N cocksfoot treatment produced 6.0 t DM/ha, which was more than the average of 3.2 t DM/ha for the other ±N species. The treatment effect at the Ashley Dene site was explained by the interaction between species and N fertility after 85 mm of rainfall in mid-January of 2016, when only the cocksfoot responded to the applied N. Yield differences in response to the different soil moisture and N conditions were quantified by calculation of growth rates in relation to thermal time, soil water extraction patterns, estimation of light interception and radiation use efficiency. A separate experiment quantified hydrothermal time for seedling establishment. The project was supervised by Prof. Derrick Moot, Dr Mark Bloomburg, Dr Alistair Black and Assoc. Prof. Rainer Hofmann.