Abstract
The distribution of organic and inorganic N forms in virgin soil profiles and their cultivated, fertilized analogues is compared. Eight agriculturally important soil series, representative of different U.S. cropping areas, are included. In six of eight cases, total N and organic C contents were lower in the cultivated soils. Comparing all soils on an average basis, total N and organic C losses for the cultivated surface horizons were 33 and 42 percent, respectively. Corresponding losses for the profiles were 13 and 17 percent. The chemical pattern of organic N forms in the virgin soil profiles tended to be preserved upon either a gain or loss of original N. Although nitrate levels were generally higher in the cultivated profiles, in most cases the potential to convert soil organic N forms to mineral N was considerably higher in the virgin profiles. Nonexchangeable ammonium levels as measured by HF extraction averaged 145 ppm N in the cultivated profiles, representing a 16 ppm increase. There was no evidence for inability of the regular Kjeldahl procedure to recover all the nitrogen in either the virgin soil profiles or their cultivated analogues. In general, findings observed on a profile basis were similar to those observed on a surface soil basis, but the magnitude of the differences tended to be less on a profile basis. The distribution of organic and inorganic N forms in virgin soil profiles and their cultivated, fertilized analogues is compared. Eight agriculturally important soil series, representative of different U.S. cropping areas, are included. In six of eight cases, total N and organic C contents were lower in the cultivated soils. Comparing all soils on an average basis, total N and organic C losses for the cultivated surface horizons were 33 and 42 percent, respectively. Corresponding losses for the profiles were 13 and 17 percent. The chemical pattern of organic N forms in the virgin soil profiles tended to be preserved upon either a gain or loss of original N. Although nitrate levels were generally higher in the cultivated profiles, in most cases the potential to convert soil organic N forms to mineral N was considerably higher in the virgin profiles. Nonexchangeable ammonium levels as measured by HF extraction averaged 145 ppm N in the cultivated profiles, representing a 16 ppm increase. There was no evidence for inability of the regular Kjeldahl procedure to recover all the nitrogen in either the virgin soil profiles or their cultivated analogues. In general, findings observed on a profile basis were similar to those observed on a surface soil basis, but the magnitude of the differences tended to be less on a profile basis. © Williams & Wilkins 1975. All Rights Reserved.