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

Abstract

Perennial 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.

The perennial biogas crops cup plant (Silphium perfoliatum L.) and field grass pose better autumn and overwintering habitats for arthropods than silage maize (Zea mays L.)

“…The present study is based on a field experiment that was established at the JKI Institute for Crop and Soil Science in Braunschweig (52,296 °N: 10,438 °E) in the spring of 2012 (Schittenhelm et al, 2021). The site is elevated 76 m above sea level with a mean long‐term (1962–2006) annual air temperature and precipitation of 9.1°C and 616 mm, respectively.…”

“…The novel PEC cup plant ( Silphium perfoliatum L.) is another promising candidate for diversifying bioenergy cropping and is gaining increasing attention as an alternative to silage maize. The area cultivated with cup plants in Germany has steadily increased from about 400 ha in 2015 to around 6000 ha in 2020 (Schittenhelm et al, 2021). This development was supported by (i) the significant reduction of costs for establishing cup plant stands through sowing instead of planting (Frölich et al, 2016), (ii) gradually capping of maize inputs to biogas plants to a maximum mass‐based share of 44% from 2021 onwards (EEG, 2017) and (iii) the introduction of cup plant as a new type of ecological focus area under the EU Greening Programme (European Commission, 2018).…”

Nitrogen acquisition and retention pathways in sustainable perennial bioenergy grass cropping systems

“…As N fertilizer does not always increase biomass production, the intricacies of N acquisition pathways in perennial grasses should be addressed. N budget assessments for Miscanthus proposed N sources of unknown origin (Davis et al., 2010; Dohleman et al., 2012), and implicated N fixation and N mineralization as potential N acquisition pathways (Davis et al., 2010; Eckert et al., 2001; Keymer & Kent, 2014; Schittenhelm et al., 2021; Wewalwela et al., 2020).…”

“…However, it is important to note that high mineralization rate leads to the active mining of SOM reserves, posing a sustainability issue for long‐term cultivation. Intriguingly, however, research also suggests that perennial tall grasses can delay N depletion in soil by counterbalancing the enhanced mineralization rates through increased SOM stocks (Fu et al., 2022; Schittenhelm et al., 2021), which can be further facilitated by biological N fixation.…”