Simulation analysis of lucerne–wheat crop rotation on the Loess Plateau of Northern China

Abstract

The Agricultural Production System Simulator (APSIM) was parameterised and tested against datasets from two field experiments being conducted on Heilu soil at the Qingyang Research Station, Gansu, China as to investigate long-term lucerne productivity and management options of reducing impact of lucerne on winter wheat yield in a lucerne–wheat rotation system. With minimal parameterisation and configuration of the APSIM-Lucerne module, APSIM was able to simulate phenological development and seasonal growth of winter-dormant lucerne cultivar, Longdong compared with the observed data. Flowering date was accurately simulated using the established relationship between accumulated thermal time and mean photoperiod. After the APSIM-Lucerne module was configured for the seasonal variation in RUE (radiation use efficiency), the model simulated lucerne seasonal biomass production over three growing seasons in the continuous lucerne treatment with a root mean squared deviation (RMSD) of 1132 kg/ha (30% of the mean observed biomass). In the treatment where lucerne was removed in August 2001 and two winter wheat crops were sown and harvested in 2001/2002 and 2002/2003 growing seasons, APSIM simulated winter wheat crop biomass in both growing seasons with a RMSD of 1420 kg/ha (20% of the mean observed crop biomass). Wheat grain yield was simulated with a RMSD of 918 kg/ha (27% of the mean observed grain yield). Using measurements of drained upper limit (DUL) and lower limit (LL), and standard soil evaporation and runoff parameters, the model was able to simulate soil water dynamics and water use by lucerne in the lucerne-fallow, continuous lucerne and lucerne–wheat treatments. The long-term simulation suggested that under local climatic conditions, lucerne could produce 11,000 kg/ha biomass annually. The simulation also indicated that integrating lucerne with annual cropping could potentially reduce runoff and early removal improved soil water storage prior to sowing winter wheat and optimise wheat yield following lucerne in a lucerne–wheat rotation system. The findings from these long-term simulations suggest there is need to develop management strategies when lucerne is integrated with annual cropping system to improve soil water use and reduce runoff. There is also need to consider a balance between sustaining wheat yield and providing feed for livestock when developing management strategies for timing of lucerne removal and cropping option in lucerne-based rotation systems. The successful test of APSIM will give local researchers confidence to use the tool exploring cropping system issues in Northern China.