Many perennial grasses have been indicated as having superior attributes as energy plants such as having high biomass yield and a wide variety of ecological functions. Since the mid-1980s there has been increasing interest in the use of perennial grasses as energy plants in US and Europe as the biomass materials of perennial grasses can be readily converted to energy through combustion, gasification and liquefaction. In US, the Herbaceous Energy Crops Research Program (HECP), was established in 1984 with funding from the US Department of Energy (DOE). HECP has evaluated 35 potential herbaceous crops of which 18 were perennial grasses, and has indicated that switchgrass (Panicum virgatum), a native perennial grass, has the greatest potential as an energy plant. In 1991, the DOE′s Bioenergy Feedstock Development Program (BFDP), which evolved from the HECP, decided to focus research on a "model" crop system and to concentrate research resources on switchgrass, in order to rapidly achieve its maximal output as a biomass crop. In Europe, about 20 perennial grasses have been tested and four perennial rhizomatous grasses (PRG), namely miscanthus (Miscanthus spp.), reed canary grass (Phalaris arundinacea), giant reed (Arundo donax) and switchgrass were chosen for further exploration.
There are many ecological benefits could be achieved from the production and use of perennial energy grasses. The substitution of fossil fuels or of raw materials based on fossil fuels by biomass of perennial grasses is an important contribution to reduce CO2 emissions. Also, unlike annual crops, the need for soil tillage in growing perennial grasses is limited to the year in which the plants are established. The ecological advantages of the long periods without tilling may include reduced risk of soil erosion and a likely increase in soil carbon content. Furthermore, due to the recycling of nutrients by their rhizome systems, perennial grasses have a low demand for nutrient inputs. Since they have fewer natural pests than most crops, they may also be produced with little or no pesticide use. Some of the perennial grasses have also been indicated to have tolerance to heavy metals and can therefore be used for the recovery of heavy metal-polluted soils. Studies also show that an increase in abundance and activities of different animal species, especially birds, mammals and insects, occur in stands of perennial grasses due to relatively long period of free of soil disturbance, late harvest of the grasses in winter to early spring and the insecticide-free systems. These indicate that growing perennial grasses can provide ecological services in agricultural production systems, and can also function as elements in landscape management and as habitat for different animal species.
The aim of this review is to summarize previous studies on selecting perennial grasses for bioenergy production in US and Europe, and to give an overview of the characteristics of the four most investigated perennial rhizomatous grasses as energy plant. A new approach of exploiting non-food crops on the non-agricultural lands in China is proposed. It is very important and urgent to develop bioenergy production in China, and it is expected that perennial grasses will be set for a comeback through a number of different energy conversion pathways in the future.