Panicum virgatum

Cultivation Details

Panicum virgatum is a plant, originally of the temperate zone, that has spread into the subtropics and tropics. It grows best in areas where annual daytime temperatures are within the range 17 - 32°c, but can tolerate 6 - 36°c^[1]. It can be killed by temperatures of -10°c or lower, though new growth can be damaged at -1°c^[1]. It prefers a mean annual rainfall in the range 500 - 1,100mm, but tolerates 350 - 2,700mm^[1]. Grows in any moderately fertile, well-drained soil in a sunny position^[2]. A drought resistant plant, it is easily grown in average to wet soils and in full sun to part shade^[1]. Prefers a pH in the range 6 - 7, tolerating 4.9 - 8.2^[1]. Plants have particularly heavy growth in late spring and early summer^[3]. The plant has the potential to produce the biomass required for production of up to 380 litres of ethanol per metric ton. This gives it the potential to produce over 400 litres of ethanol per hectare, compared to 270 for sugarcane and 160 for corn. However, there is debate on the viability of switchgrass, and other bio-fuels, as an efficient energy source. University of California, Berkeley professor Tad Patzek argues that switchgrass has a negative ethanol fuel energy balance, requiring 45% more fossil energy than the fuel produced^[1]. The plant photosynthesize by a more efficient method than most plants. Called the 'C4 carbon-fixation pathway', this process is particularly efficient at high temperatures, in bright sunlight and under dry conditions^[1]. As an open pollinated species, switchgrass expresses tremendous genetic diversity, with wide variations in its basic chromosome number (2n = 18), typically ranging from tetraploid to octoploid. Morphologically switchgrass in its southern range can grow to more than 3 m in height, but what is most distinctive is the deep, vigorous root system, which may extend to depths of more than 3.5 m^[1].. It reproduces both by seeds and vegetatively and, with its perennial life form, a stand can last indefinitely once established. Standing biomass in root systems may exceed that found aboveground, giving perennial grasses such as switchgrass, an advantage in water and nutrient acquisition even under stressful growing conditions^[1].