Soil Acidity from Long-term Use of Nitrogen Fertilizer and Its Relationship to Recovery of the Nitrogen
- Von D. Jolley and
- W. H. Pierre
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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