Nitrogen availability and pine seedling growth in organically- amended mine soils

Abstract

Adequate supply and availability of nitrogen (N) is a major factor hindering successful revegetation of reclaimed surface mines. Because topsoils are often unrecoverable, “topsoil substitutes”, made up of overburden materials devoid of N, are often used on reclaimed surfaces. Four replications of seven surface treatments were applied to 12 m² plots of 2:1 sandstone:siltstone material on a reclaimed coal surface mine in Wise Co., VA: 1) fertilizer (168 kg/ha N, 147 kg/ha P, and 139 kg/ha K), 2) limed (7.8 Mg/ha), fertilized topsoil (30 cm deep), 3) 112 Mg/ha sawdust + fertilizer + 336 kg/ha slow-release N, and 4-7) lime-treated municipal sewage sludge at rates of 22, 56, 112, and 224 Mg/ha. Nitrogen availability after 40 mo (as determined by aerobic and anaerobic incubations) in sawdust- and sludge-amended soils was two to 20 times higher than in fertilized and topsoil-amended soils. Moisture holding capacity was nearly twice as high in sawdust-amended soils as in all other treatments. Soil nitrate (NO₃⁻) levels (0-20 cm layer) in excess of 75 μg/g were detected in the 112 and 224 Mg/ha sludge plots 28 mo after application. Stem volumes of three-year-old pitch X loblolly pines (<i>Pinus rigida</i> X <i>taeda</i>) were four times larger in soils amended with sawdust + slow-release N and were twice as large in soils amended with 22 and 56 Mg/ha sludge compared to fertilized-only seedlings. Increased seedling mortality was observed in the 112 and 224 Mg/ha sludge treatments, possibly due to high soluble salt levels and/or manganese deficiencies. The availability of N from sawdust + slow-release N or sludge (≤ 56 Mg/ha) is better than that of inorganic fertilizer for sustained tree growth. These amendments are recommended for reclamation to the extent that they are economically available.