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

Abstract

Cultivation of switchgrass ( Panicum virgatum L.) as an energy crop could lower atmospheric carbon dioxide (CO 2) 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 kg N ha −1 increased C storage in shoots by 207% and 27% when compared with annual applications of 0 and 112 kg N ha −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.