Soil organic carbon storage in southern Illinois woodland and cropland

Many factors including land use, management history, soil type, climate, and soil landscape processes affect the dynamics of soil organic C (SOC). The primary objective of this research was to compare the storage of SOC on sloping woodland and cropland landscapes of southern Illinois. The cropland area was previously cultivated between the 1880s and the 1930s, used for crop production with forages in crop rotation between the 1930s and the 1960s, and remained in hayland from the 1960s to 1989. Since 1989, row crops were grown on a yearly rotation system using conservation tillage practices. The woodland area was never cleared and farmed but part of the landscape was subjected to periodic grazing before the 1960s. The SOC concentration of various soil layers, to a depth of 1 m, was measured and expressed on both a gravimetric and volumetric basis. The woodland landscape had significantly higher SOC in the surface layer (0-0.05 m) on all 6 landscape segments; however, the 0.05- to 0.15-m layer in the cropland landscape contained significantly more SOC. The subsurface rooting zone SOC values varied by landscape segment for both land uses. Results suggested that the cropland landscape retained 95% of the total SOC on a volumetric basis during the last 130 years of agricultural use. The years with forages may have increased the SOC of the cropland site and help offset losses due to soil erosion and aeration as a result of tillage. The woodland and agricultural landscapes appear to have similar amounts of SOC when the crop rotations included forages, cover crops, conservation tillage, and contour farming. Results suggest that southern Illinois soils can be used for cropland with conservation practices and forages while still maintaining the SOC levels of woodland.