Selection of crop cultivars suited to the location combined with astute management can reduce crop yield penalties in pasture cropping systems Dean T. Thomas A,D , Roger A. Lawes A , Katrien Descheemaeker B , and Andrew D. Moore A,C A CSIRO Sustainable Agriculture Flagship, Private Bag 5, Wembley, WA 6913, Australia. B Plant Production Systems, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands. C GPO Box 1600, Canberra, ACT 2601, Australia. D Corresponding author. Email: dean.thomas@csiro.au Abstract. Pasture cropping is an emerging farming-systems practice of southern Australia, in which winter grain crops are sown into an established stand of a winter-dormant, summer-growing perennial pasture. There is a pressing need to define times, locations and climates that are suitable for pasture cropping. To evaluate effects of management interventions, agro- environment, and possible interactions on crop and pasture productivity associated with pasture cropping, an AusFarm ® simulation model was built to describe a pasture-cropping system based on annual crop and subtropical grass. The model was parameterised using data from field research on pasture cropping with barley cv. Buloke and a C 4 subtropical grass, Gatton panic (Panicum maximum cv. Gatton), conducted at Moora, Western Australia. The simulation was run over 50 years using the historical climate data of five southern Australian locations (Cunderdin, Jerdacuttup, Mingenew, and Moora in Western Australia, and Karoonda in South Australia). Two wheat cultivars and one barley crop were considered for each location, to examine the impact of crop phenology on this farming system. Jerdacuttup and Moora favoured pasture cropping, with average barley-yield penalties of 10 and 12%. These locations were characterised by colder growing seasons, more plant-available water at anthesis, and more winter–spring rain. The cereal crops did not rely on stored soil moisture, growing instead on incident rain. The winter–spring growth of the Gatton panic pasture was highest at Mingenew. This generated a high yield penalty, 38% loss under pasture cropping, compared with the other locations. Changing the efficacy of a herbicide application to the pasture when the crop was sown had a strong effect on yield. Yield penalties at Moora and Mingenew reduced to 7 and 29%, respectively, when the proportion of live biomass killed by the herbicide was doubled. Utilisation of soil moisture by the Gatton panic pasture during summer and early autumn had little effect on subsequent grain yield, whereas reduced pasture growth during the winter–spring growing period had a substantial effect on crop yield. Pasture cropping can therefore succeed in agro-climatic regions where crops can be grown on incident rain and pasture growth is suppressed through low temperature or herbicide. Perennial pasture growth should be minimised during the crop growing period through the management of crop sowing date, nitrogen fertiliser application and C 4 grass suppression to minimise the effect on stored soil water at crop anthesis. Additional keywords: APSIM-GRAZPLAN model, panic grass, plant competition, simulation model, stubbles. Received 12 December 2013, accepted 25 March 2014, published online 7 October 2014 Introduction Pasture cropping is an emerging farming-system practice that has shown strong potential in parts of southern Australia, in which winter grain crops are sown into established stands of winter- dormant C 4 grasses (Millar and Badgery 2009; Dolling et al. 2010). This system capitalises on the divergent growth patterns of summer-active, perennial C 4 pastures and winter-active annual C 3 crops. By contrast, the predominantly annual farming systems of much of southern Australia have evolved to use Mediterranean- type winter–spring dominant rainfall patterns. In these systems, summer rain has been under-utilised historically, and the landscape remained in fallow outside the growing season. The C 4 grass-based pasture cropping systems are typically established on less fertile sandy soils, which have limited capacity to store soil moisture (Oliver and Robertson 2009), and rain over summer is either lost at the surface by evaporation or runoff, or it leaks into the ground-water (Hunt and Kirkegaard 2011; Ward 2006). The poor utilisation of water in annual plant-based systems during summer–autumn contributes to agricultural problems such as salinity, erosion, nutrient leaching, and acidity (Masters et al. 2006). Pasture cropping utilises growing-season rain for grain production and a combination of summer rain and unused soil Journal compilation Ó CSIRO 2014 www.publish.csiro.au/journals/cp CSIRO PUBLISHING Crop & Pasture Science, 2014, 65, 1022–1032 http://dx.doi.org/10.1071/CP13436