Whole farm implications of lucerne transitions in temperate crop-livestock systems

Lucerne (Medicago sativa L.) is valued by producers with integrated crop-livestock systems. The multiple benefits of periods of lucerne leys to either livestock or to crop production have been widely reported; however, the importance of managing lucerne leys to whole farm profit and production has not and is best suited to a whole of system modelling study. This paper reports a simulation study aimed at better understanding the mixed farming systems that include short-term (3-year) phases of lucerne: specifically, the effects of terminating lucerne leys at different times prior to cropping. Simulations of mixed farming systems with the same soil type, crop rotation and proportional land use were conducted along a rainfall transect in a temperate environment in south-eastern Australia. Spring versus summer termination of the lucerne ley prior to cropping in autumn were compared. Although farming systems where lucerne was terminated in spring had higher crop production (mostly because of increased N at sowing) than those where lucerne was terminated in summer, the opposite was true for livestock production. Livestock production was higher in systems with summer termination mostly because of higher ewe condition scores at mating. When these sometimes positive and sometimes negative effects were evaluated at the whole of farm scale, in cases except the low rainfall site, allowing the lucerne ley to grow as late as possible prior to cropping was the most profitable management strategy in medium to high rainfall systems as it resulted in more lambs that were sold at heavier weights and the systems were more profitable, less costly, more efficient and less risky than those where leys were terminated in spring.