Evaluating Effects of Landscape Position and N Rates on Dissolved Organic Carbon (DOC) from Switchgrass (Panicum virgatum L.) Land in South Dakota.

This study was conducted for evaluating effects of three N fertilizer rates and landscape positions on dissolved organic carbon (DOC) leaching contents from a South Dakota landscape seeded to switchgrass. The DOC contents were measured from leachate samples from 36 suction lysimeters installed at 1.0 m depth and 36 positions at this study site, near Bristol, South Dakota, USA. The daily average DOC contents at backslope are significantly lower than that at shoulder and footslope. The shoulder’s DOC contents, however, are not significantly lower than that at footslope. The DOC contents at medium N rate are also significantly lower than that at low N rates but not significantly different at high N rate. The effects of positions and N rates on DOC contents were different in each of six years from 2009 to 2014. The results conclude that DOC contents from leachate in the switchgrass land were significantly influenced by landscape positions and N rates. There are positive relationships between DOC contents and precipitation or yields. Whereas there is no significant relationship between DOC contents and temperature or over time. These findings will assist in understanding mechanism of DOC contents changes with various parameters in the natural environment and crop managements, and evaluating carbon (C) budget in the switchgrass field. Future research would assess the long-term effects of above factors on DOC leaching contents and loss in switchgrass land.