Long-term fertilization effects on 13C natural abundance, soil aggregation, and deep soil organic carbon sequestration in an Alfisol

Although the C-13 ((13)Carbon) natural abundance method is used to study soil C dynamics, scanty information is available on long-term fertilization effects on soil C sequestration rates along with delta C-13 in surface (0-30 cm) and deep (30-90 cm) soil layers and their relationships with crop productivities in subtropics. Hence, soil aggregation, delta C-13 in bulk soils and aggregates, C pools, and sequestration rates were studied in an Indian Alfisol under a 43-year old wheat (Triticum aestivum L.)-based cropping system. Treatments were as follows: no mineral fertilizer and no manure (unfertilized control), 100% recommended dose of nitrogen (N), 100% N and 100% recommended phosphorus (NP), 100% N, 100% P, and 100% recommended potassium (NPK), NPK + lime (NPKL), 150% recommended NPK (1.5NPK), and NPK + farmyard manure at 10 Mg ha(-1) (NPKF). Plots with NPKF contained 50% higher soil organic C than NPKL in surface soil (0-15-cm layer). In the 0-90-cm profile, soil organic C accumulation and sequestration rates in NPKF were similar to 0.15 and 0.11 Mg ha(-1) yr(-1) higher than NPKL plots, respectively. The NPKF plots had higher glomalin-related soil protein and greater recalcitrant C than NPKL, 1.5NPK, and NPK in surface soil. The NPKF plots had higher delta C-13 values within bulk soils and their aggregates than NPKL and NPK. There were significant correlations between deep soil C sequestration rates with mean crop productivities and delta C-13 with deep soil C sequestration rates. Overall, NPKF application had the largest surface and deep soil C sequestration with highest crop productivity and hence is recommended.