Experiments to establish the response of cotton plant to soil water stress under different soil types, climatic conditions and fruiting loads have shown that (i) the response of cotton to water stress is different on different soils (eg heavy clay vs. sandy-loam) (ii) these differences can be accounted for when soil moisture content is normalised for water holding capacity, expressed as the fraction of transpirable soil water (FTSW) (iii) that climate, especially evaporative demand, can cause plant stress even when the crop has adequate soil moisture and (iv) there is no difference in soil water extraction and therefore root development by crops with different levels of fruit retention.Field experiments were run over three cotton seasons at three sites with widely different soil types around Narrabri NSW. The response of the cotton plant to moisture stress, imposed by skipping irrigations around flowering, was measured as leaf water potential using a pressure chamber. Cotton plants were found to behave in the same way to moisture stress on all soil types when the soil water holding capacity of the soil was taken in to account and expressed as a percentage or fraction of transpirable soil water (FTSW). Over the three seasons prevailing climatic conditions have a large effect on the ability of the plant to cope with a given level of soil moisture deficit. Even under low levels of soil moisture deficit, on high evaporative demand days plants often experienced stress which had an impact on yield. There are some climatic conditions under which the cotton plant is unable to take up enough moisture even from a soil profile with readily available water that the plant will become stressed no matter if more water is applied. Identifying these conditions and their management implications are the subject of ongoing research.The results of this research will provide a basis for refined irrigation management through understanding the effect of climate and soil type to reduce water stress and providing decision points for future management. This information will also be included in decision support systems through inclusion in future versions of HydroLOGIC.A separate experiment conducted over two seasons also in Narrabri showed no difference in soil moisture extraction and therefore extent of root development between crops that have high and low levels of fruit retention before cutout. High retention crops (such as BG II®) should be irrigated in a similar manner to lower retention cotton. The high level of early reproductive development does not appear to affect the below ground vegetative development of the crop. A preliminary experiment was also conducted to investigate partial rootzone drying in cotton. This showed no benefit from partial rootzone drying in terms of cotton plant stomatal control, biomass production or yield.This project has significantly improved our understanding of basic responses of cotton to soil moisture stress and how this is influenced by climate and soil type. This knowledge is vital in developing improved irrigation strategies for cotton and achieving maximum yield from applied water.