Cultivation Effects on the Amounts and Concentration of Carbon, Nitrogen, and Phosphorus in Grassland Soils1
- H. Tiessen,
- J. W. B. Stewart and
- J. R. Bettany2
Cultivation has substantially reduced the organic matter contents of many prairie soils. This study attempts to quantify the losses of C, N, and P from three prairie soils of different textures during cultivation. For this purpose cultivated and adjacent uncultivated soils (2 Cryoborolls and 1 Cryorthent) were sampled and their C, N, and P contents as well as their bulk densities and horizon depths were compared.
Reductions of about 35% in the C concentration were observed in clay and silt loam soils after 60 to 70 years of cultivation. At the same time reductions in N concentrations were greatly influenced by the presence or absence of legume [alfalfa, (Medicago sativa L.)] crops grown in the fields and losses varied between 18 and 34%. Phosphorus concentrations were reduced by 12% and all P losses were accounted for by the organic fraction. During a similar period of cultivation a lighter textured sandy loam had experienced greater reductions in C, N, and P concentrations of 46, 46, and 29%, respectively. In this soil P was lost from both the organic and inorganic fractions. Prolonged cultivation of 90 years did not result in a decrease in the rates of losses of C, N, and P on the silt loam soil.
Conversion of concentration data to area based total C, N, and P budgets resulted in a decrease in the differences seen between cultivated and uncultivated soils. This was caused by an increase of soil bulk densities under cultivation and by an increase in the standard deviations of the data due to variability of horizon depths in cultivated fields.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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