Impact of row spacing, nitrogen rate, and time on carbon partitioning of switchgrass

Cultivation of switchgrass (Panicum virgatum L.) as an energy crop could lower atmospheric carbon dioxide (CO2) levels by replacing fossil fuel and sequestering carbon (C). Information on the details of C partitioning within the switchgrass–soil system is important in order to quantify how much C is sequestered in switchgrass shoots, roots, and soil. No studies of C partitioning in a switchgrass–soil system under field conditions have been conducted. This study was aimed at determining the impact of agricultural management practices, such as row spacing and nitrogen (N) application rate, on C partitioning within the switchgrass–soil system; changes in C partitioning with time after switchgrass establishment were also considered. The results indicate that C storage in switchgrass shoots was higher with wide than narrow rows, and increased with N application rates. These responses were due to higher yields with wide than narrow rows and higher yields as N application rate increased. Carbon storage in shoots was 14.4% higher with 80-cm than 20-cm row spacing. Annual application of 224 kgNha−1 increased C storage in shoots by 207% and 27% when compared with annual applications of 0 and 112 kgNha−1, respectively. Carbon storage increased by 62% over time from 1995 to 1996 in newly established switchgrass on sandy loam soil in the coastal plain of Alabama. Rate of C increase in roots (72%) was higher than in shoots (49%) between 1995 and 1996. Carbon storage was in order of soil C > root C > shoot C in both 1995 and 1996. The root/shoot ratio of C storage was 2.2. It appears that C partitioning to roots plays an important role in C sequestration by switchgrass.