SOIL NITROGEN RELATIONSHIPS IN SPOIL MATERIAL GENERATED BY THE SURFACE MINING OF LIGNITE COAL

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Abstract
Three acid, surface-mined soils and an adjacent undisturbed soil were evaluated for nitrification potentials and nonexchangeable NH4+-N retention to better understand N mechanisms and improve the reclamation efficiency of these soils. The mined soils nitrified a maximum of only 7% of an added 100 ppm NH4+-N, although the undisturbed soil nitrified 93% of the applied N. Total N digestion showed one mined soil to have a nonexchangeable NH4+-N retention capacity of 6.2 meq/100g. Organically retained NH4+-N accounted for 73% of the total retention. Another procedure utilizing differences in exchangeable NH4+-N between moist and dried samples as estimates of nonexchangeable NH4+-N retention, showed retentive capacities of the mined soils ranging from 4.1 to 7.8 meq NH4+-N/100g. Lignite exhibited a retentive capacity of 46.0 meq NH4+-N/100g. Nonexchangeable retention was significantly correlated with the residual lignite content of the soil. Low nitrification potentials and large nonexchangeable NH4+-N retention capacities suggested that applied NH4+-N fertilizers might be inefficient in the mined soils.

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