Land-Use Change Effects on Soil Organic Carbon and Total Soil Nitrogen in Temperate Grasslands.

There are several factors that influence the retention of soil organic carbon (SOC) and total soil nitrogen (TSN) including soil texture, climate, slope length and gradient, and current and past land-use. The purpose of this study was to compare the retention of SOC and TSN on sloping landscapes in prairies and croplands in western Iowa. The soils in the area were derived from loess over glacial till. A monument marker at the prairie site suggests the location has not been farmed since 1946 but may have previously been used for grazing. The cropland site utilized no-till management and a corn-soybean rotation. SOC concentrations of several layers and landscape positions were determined to a depth of 1 m at both sites. The prairie site had much higher SOC and TSN levels than the cropland at all landscape positions except for the depositional areas. In erosional landscape positions the SOC and TSN losses were not limited to surface layers and often occurred to the full 1 m sampling depth. Results suggest that the Iowa cropland retained about 49% of the SOC and 65% of the TSN that was present in the prairie. If climate change continues to push warmer temperatures north and forests and prairies are converted to cropland the results suggest that less SOC and TSN will be retained in the soil even with the use of no-till management.