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This article in SSSAJ

  1. Vol. 41 No. 2, p. 368-373
    Received: July 14, 1976
    Accepted: Oct 7, 1976

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Soil Acidity from Long-term Use of Nitrogen Fertilizer and Its Relationship to Recovery of the Nitrogen1

  1. Von D. Jolley and
  2. W. H. Pierre2



Two N-rate experiments in which corn (Zea mays L.) had been grown continuously for 15 and 17 years were used: (i) to study quantitatively the amounts of acidity that had been developed at different levels of N fertilization and (ii) to determine to what extent the acidity produced can be explained and predicted from the amounts of N recovered in the crops and in the soil as NO3-N and organic N. The measured acidity was compared with the acidity calculated from N recovery, and both were expressed as percentages of the theoretical (potential) acidity developed from nitrification.

No significant increases in acidity were found in either soil below a depth of 30 cm. With amounts of applied N that produced near-maximum yields, soil nitrate accumulation was small, and the measured acidity (CaCO3 requirement) was < 30% of the theoretical or potential. When excessive amounts of N were applied, however, relatively large amounts of NO3-N were found in the profile, and nearly 50% of the theoretical acidity was developed. The calculated CaCO3 requirements from N recovery at near-maximum yields tended to be smaller than that measured in the soil. This difference in the Galva soil profile was accounted for in part by a decrease in acidity between 30 and 45 cm, probably caused by nitrate absorption and by denitrification in these layers. With excessive N applications, the CaCO3 requirements calculated from N recovery were in very close agreement to that measured, averaging 48% and 47% of the theoretical, respectively.

Because the acidity calculated from N recovery essentially accounted for the acidity actually found and because the corresponding N recovery was only 68% (Table 6), the 32% of the N unaccounted for evidently was lost without an equivalent amount of base. Thus, the deficit in the acidity found provides corroborative evidence to the N-recovery data that a substantial amount of the N applied in fertilizer was lost from the soils without an equivalent amount of base. Under the conditions of these experiments, this loss probably was through denitrification.

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