Research in Western Australia (WA) for the last few years reveals that in the warm and low rainfall environments of the northern agricultural region, wide rows (50 cm or more) can produce better lupin yields than narrow rows (25 cm or less) due to improved soil-crop water relations. However, in the broader sense the influence of wide row cropping on crop nutrition and nutrient management is still largely unknown in WA cropping systems. The simulation model, ROOTMAP can be used as a tool to understand the interactions between root systems and availability of soil water and nutrient in the rooting environment, and develop research hypotheses that can be tested under field conditions to develop better nutrient management practices for wide row cropping. ROOTMAP was parameterised for a deep yellow sandy soil from Moora, WA to simulate soil water dynamics and lupin root growth. Two contrasting seasons (wet vs. dry) in Moora were chosen when conducting the two simulation case studies. In the first case study, 8 simulated treatments were designed to evaluate lupin root growth in the rows and between the rows and P uptake when the row spacing and P fertilisation rate below seeds were altered in both dry and wet seasons. The second case study was designed to explore root growth response and P uptake, when P fertiliser was banded in the rows and at 8, 13, 18 and 23 cm away from the rows using a 50 cm row spacing. The simulations suggest that in wide row cropping, where lupin plants are planted closely in the seeding rows, having sufficient P supply in the rows is critical to reduce competition among roots for soil P, to improve penetration and proliferation of the roots into deep soil layers, and to encourage root growth and proliferation between the rows. However, in a wide row (= > 50 cm) cropping, banding all P in the rows sometimes could create P toxicity problem for lupins and may result in increased horizontal soil P stratification that could affect nutrient management for following crops (such as wheat) when using a narrow row spacing (< = 25 cm). Thus, to develop best P management in lupin-based rotation systems, there is a need to further explore different P placement strategies (such as banding some P in the rows and some away from the rows at seeding or deep banding > 10 cm).