Impacts of soil management on root characteristics of switchgrass

One approach to reducing the concentration of atmospheric carbon dioxide, w hich is a dominant greenhouse gas, is to develop renewable energy sources f rom biofuel crops. Switchgrass, (Panicum virgatum L.) as an energy crop, ca n partly mitigate potential global warming by supplementing fossil fuels an d sequestering carbon (C). Although switchgrass grown for energy may impact C sequestration via the input of root biomass, information on the impact o f soil management on switchgrass root growth is extremely limited. We deter mined the influence of row spacing, nitrogen (N) rate, switchgrass cultivar , and soil type on switchgrass root characteristics. Roots were mainly dist ributed in the surface soil (0-15 cm), and were 90.4 and 68.2% of the total in the intrarow and interrow profile, respectively. Nitrogen application a ltered root N but not C concentration, implying that any increase in C sequ estration by switchgrass roots will be due to increased root biomass rather than increased C concentration. Root weight density generally decreased in the interrow with wider row width, and N application generally did not aff ect root weight density. Root weight density in the Pacolet soil was higher than in the other four soils, and root density was 4.1 times higher in the Pacolet soil than in the Norfolk soil. Root mass in the Pacolet soil (36,3 27 kg ha(-1)) was 2.7 times greater than that found in the Norfolk soil (13 ,204 bg ha(-1)) within 150 cm of the soil surface. Differences in root char acteristics were found among cultivars: root weight density with 'Cave-in-R ock' switchgrass was 29.4 and 47.6% higher than 'Alamo' and 'Kanlow', respe ctively. Variations in switchgrass root biomass production owing to soil ty pe and cultivar suggest that site and cultivar selection will be important determinants of C sequestration by switchgrass roots. A potential benefit o f switchgrass is the reduced loss of nutrients associated with non-point po llution, owing to its deep root system that may extend 330 cm below the soi l surface. (C) 2000 Elsevier Science Ltd. All rights reserved.