Labile and stable nitrogen and carbon in mine soil reclaimed with manure-based amendments

Organic C and nutrients in manure can improve degraded mine soil quality if they are retained in the soil. Composting manure or mixing manure with a high C/N ratio material before application could facilitate this improvement. The effects of these manure stabilization techniques on N and C retention in mine soil were investigated in two incubation experiments with six treatments: unamended soil, lime and fertilizer (14.3 Mg ha ^-1), two rates of composted poultry layer manure (78 and 156 Mg ha ^-1), and layer manure mixed with paper-mill sludge (PMS) (50 Mg ha ^-1 manure, 102 and 183 Mg ha ^-1 PMS) to provide C/N ratios of 20 and 30. In one experiment, amendments were laboratory applied just before incubation; in the other, amendments were field applied 1 yr before incubation. Carbon dioxide evolution and labile N and C were measured during incubation and microbial biomass N was determined at the end of the incubations. In laboratory-amended soil, all treatments produced similar quantities of labile N while compost and manure + PMS treatments resulted in stable soil N pools that were 2.5 to 2.7 times larger than in the unamended soil. In field-amended soils, stable N pools were similarly increased by compost and manure + PMS treatments. Large CO ₂ production and microbial biomass N from manure + PMS treatments suggested that rapid microbial turnover of N was an important factor in stabilizing manure N. These results indicate that the combined manure + PMS amendment was as effective as composting in building stable N pools in mine soil.