Summary And Implications For Research Needs

Empirical evidence from the central US, Germany and the UK indicates that ET from M. x giganteus is greater than from typical annual crops and thus has the potential to reduce surface water flows and groundwater recharge where it replaces these annual crops on a large scale. A simulation study of the southern UK suggests that large-scale plantings of M. x giganteus may result in a reduction of ET (and thus more groundwater recharge and surface flows) if it were to replace C3 grasses and annual crops. More work needs to be done to quantify water use of M. x giganteus under a wide variety of conditions in order to establish relationships that will be useful for modelling the impacts in areas where production appears most economically feasible. It would also be useful to monitor the hydrology of small watersheds with substantial M. x giganteus plantings, to verify the scaling up of models based on plot and field observations.

Where M. x giganteus can be grown with little or no N fertilizer, nitrate leaching losses will likely be low compared to crops such as maize that have a high N requirement. However, because M. x giganteus is slow to establish, large losses of nitrate to leaching are possible during the establishment year, although the quantity will likely depend on weather and prior land use. More research is needed to quantify the N leaching and N2O emissions for a variety of N fertilizer rates and timings in settings where M. x giganteus responds to N fertilizer application. Additionally, the possibility of using cover crops in the establishment year to minimize N losses without inhibiting M. x giganteus establishment deserves investigation (Fig. 9).

Miscanthus x giganteus is also likely to sequester carbon, alter wildlife habitats and have other environmental consequences. Although M. x giganteus provides an economic advantage by producing high biomass per unit area and per unit of water transpired, the environmental costs and

Fig. 9. Annual leaching fluxes of nitrate and ammonium in ion exchange resin lysimeters at 50 cm depth under corn-soybean, switchgrass, and Miscanthus grown on central Illinois, USA Mollisols. Adapted from McIsaac et al. (in press).

benefits of large-scale plantings will depend on local conditions and the fraction of the landscape planted to M. x giganteus. The relative costs and benefits of reduced surface water flows or nitrate leaching, or other effects will vary in different contexts. Landowners, policy makers and citizens need reliable and locally relevant information about these impacts in order to make informed decisions about land management and policy alternatives. Since these consequences may occur over decades, mechanistic models based on empirical research are needed to provide reasonable projections of the impacts in a wide range of settings.

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