Soil aggregate stability as affected by fertilization type under semiarid no-tillage conditions

Agricultural management practices play an important role in soil organic carbon (SOC) protection within soil aggregates. However, there is a lack of information on the effects of N fertilization on C protection within aggregates under no-tillage (NT) systems. The effects of organic fertilization (with pig [Sus scrofa] slurry and poultry manure) and mineral N fertilization on soil aggregation and physical C protection dynamics under NT soils were investigated. Two experiments were established in a semiarid area of northeastern Spain. In the organic fertilization experiment, treatment with pig slurry at two N rates (100 and 200 kg N ha−1), poultry manure (100 kg N ha−1), and a control (0 kg N ha−1) treatment were compared. In the mineral fertilization experiment, increasing rates of N fertilizer (0, 40, 80, 120, and 160 kg N ha−1) were compared. Water-stable macroaggregates (>0.250 mm) and their C concentration, the distribution of dry-sieved aggregates, total SOC and microbial biomass carbon (MBC) were quantified in the soil surface in two cropping seasons. Organic fertilizers slightly increased the proportion of water-stable macroaggregates but caused no differences in MBC, SOC, or water-stable macroaggregate C concentration. In the mineral N fertilization experiment, similar water-stable macroaggregate, water-stable macroaggregate C and SOC concentrations were observed among N fertilizer doses. Overall differences in water-stable macroaggregates between sampling dates were greater than differences between fertilization treatments. Our study demonstrates that, in the short-term, the use of organic or mineral N fertilizers hardly improves the stability of the macroaggregates and their C protective capacity when NT is performed. This finding could be related to the limitations imposed by water in the Mediterranean areas and the buffering effect of long-term NT adoption on soil aggregate stability and C protection