Many Australian cotton growers sow rotation crops after irrigated cotton assuming that they will improve soil quality, reduce pest and disease incidence, and maintain profitability of cotton. Commonly used rotation crops include wheat, faba bean and field pea (Cooper, 1999). Research suggests, however, that in cracking clay soils, wheat may be a better rotation crop than legumes such as field pea and faba bean due to several factors; viz. wheat results in better soil structure, is more tolerant of moderate salinity and high sodicity, facilitates recycling of Ieached N and is not an alternative host for black root rot of cotton (Hulugalle et al. 1999, 2001, 2002). Consequently sowing wheat after cotton results in greater long-term profitability than sowing legumes (Hulugalle et al. 1999, 2001, 2002). With respect to soil N, short-term studies suggest that legumes sown after cotton can greatly increase root zone soil N (Rochester et al, 1998). Over a long-term, however, differences in soil N between legumes and wheat are less dramatic due to recycling of leached N by the latter (Hulugalle et al, 1999, 2001).