Short-range variation in a Wisconsin soilscape (USA)

Resumo

Here we report on the variation of a soilscape in south central Wisconsin, USA. The variation in soil properties and soil features results in four soil order (Entisols, Inceptisols, Alfisols and Mollisols). Observations were made along a 200 m transect in a field that was cultivated since 1870. Slopes ranged from 7.5% on the back slope to 0% in the lower part. The soilscape had a total relief difference of 7.0 m. The soils were studied by 41 soil pits (60 cm), 6 soil pits (125 cm), 15 soil augers (100 cm), and ground-penetrating radar imagery. The summit and shoulder consist of coarse glacial outwash (loamy sands) over limestone whereas the lower part is lacustrine sediments over coarse outwash (loams, silty loams). The A-horizon thickness ranged from 14 to 52 cm with thick A horizons at the toeslope that also had the lowest soil pH. The soil organic carbon (SOC) contents of the A horizons ranged from 11.6 to 46.9 g C kg^–1, and the higher contents are in the lower part of the soilscape. SOC stocks (0–20 cm depth) ranged from 50 to 70 Mg C ha^–1 on the summit and backslope, but were 80 to 95 Mg C ha^–1 in the flat part of the soilscape. The lowest soybean yields (1.6 Mg ha^–1) were found at the summit and the highest yield (6.3 Mg ha^–1) at the lower end of the backslope. Soybean yields were correlated to the thickness of the A horizon, and every 10 cm increase in A horizon thickness yielded an extra 0.6 Mg soybeans ha^–1. Analysis of spherical magnetic particles was used to estimate soil erosion rates that were highest on the backslope (16.2 Mg ha^–1 yr^–1) and rates of soil deposition in the lowest part of the soilscape was 18.8 Mg ha^P1 yr^–1. It seems that there is no net soil and SOC loss within this soilscape. All in all, we found 4 soil taxonomic orders within 200 m. The variation in this soilscape was substantial and probably enhanced by 140 years of cultivation.