Long-term cultivation impacts on selected soil properties in the northern Great Plains

Long-term cultivation impacts soil properties. During the early 1920s a study comparing non-cultivated and cultivated soils was done in eastern SD (Beadle, McCook, Minnehaha, and Union Counties), USA. The objectives of the current study were to: (1) determine the long-term (>80 years) impact of cultivation on selected soil properties; and (2) establish baseline soil data that can be used for future comparisons. Sample sites were located in well-drained summit and upper backslope positions. These topographic positions are strongly influenced by erosion processes from tillage, wind, and water. Previous studies at other locations in the region suggest that one might expect a loss of 10-20 cm of soil in >80 years of cultivation at these topographic positions. In the early 1920s the soils were tested for carbon (C) (total, organic, inorganic), total nitrogen (N), total sulfur (S), total calcium (Ca), total phosphorus (P), total potassium (K), and total magnesium (Mg). The 1920s study sites were resampled at 0-15, 15-50, and 50-100 cm depths and analyzed for C (total, organic, inorganic), N (total, nitrate-N), extractable P, extractable K, delta N (15N/14N or δ15N) for total N, delta C (13C/12C or δ13C) for total C, and pH. Long-term cultivation (>80 years) in the northern Great Plains of the United States has caused many significant reductions in surface soil (0-15 cm) extractable P, extractable K, surface pH, total C, organic C, total N, and δ15N for total N. In addition, the organic C to total N ratio for the 15-50 cm depth of cultivated soils was significantly lower when compared to non-cultivated soils. Cultivation caused significant increases in nitrate-N, delta C, inorganic C, and in the total C to total N and inorganic C to total N ratios (15-100 cm depths). Soil properties varied significantly with increasing soil depth. Soil pH, δ13C for total C, inorganic C, total C to total N ratio, and inorganic C to total N ratio increased significantly as soil depth increased. Nitrate-N, extractable P, extractable K, δ15N for total N, organic C, and total N decreased significantly as soil depth increased. Soil carbon changes at the sample sites are a combined result of differences in the reference surface elevation, carbon mineralization, and redistribution of carbon due to erosion. Changes in soil nutrient levels reflect crop removal, leaching, erosion, and pedogenic processes.