Converting perennial energy crops cup plant and field grass to arable cropping affects weed infestation, soil nitrogen mineralisation, and subsequent silage maize yield

erennial energy crop (PEC) fields need to be reintegrated into the farm's crop rotation when yield performance declines after years of use or when the farm operation requires it. In this study, 8-year-old stands of cup plant (Silphium perfoliatum L.) and lucerne grass followed by field grass were converted to arable cropping, while continuous silage maize (Zea mays L.) grown over the same period served as a control. The study aimed to assess changes in the weed flora, control of cup plant regrowth, pre-crop value of PECs for subsequently grown maize and N release through mineralization of crop litter and soil organic matter in the first year after converting the PECs. The previously practiced cropping systems resulted in widely divergent maize weed populations. About 90% of the cup plant volunteers were successfully eliminated by two treatments of herbicides containing clopyralid. Maize following cup plant exhibited a faster soil cover, earlier male and female flowering, taller plants and a 10.6% and 13.6% higher aboveground biomass yield than former field grass and maize respectively. The N release by mineralization of 222 and 238 kg N ha⁻¹ following cup plant and field grass conversion, respectively, clearly exceeded the 129 kg N ha⁻¹ observed in the maize control. The residual mineral nitrogen in the 90 cm soil profile after the maize harvest was also significantly higher in the former field grass and cup plant plots than in the maize control. The excess N in the first year after reverting to annual cropping runs the risk of N leaching. Given that N fertilization is substantially reduced after cup plant and field grass conversion, maize appears to be a well-suited follow-up crop due to its good suppression of cup plant volunteers and high N uptake capacity which helps minimize nutrient losses to the environment.