Carbon, nitrogen and natural abundance of 13C and 15N in biogenic and physicogenic aggregates in a soil with 10 years of pig manure application

Abstract Successive applications of pig manure to the soil can increase carbon and nitrogen content in soil aggregates, with emphasis on those from biogenic origin. The objective of this work was to evaluate how the application of different types and amounts of pig manure for a long time (2002–2012) in the soil influences the formation of aggregates. Thus, we separated and quantified soil aggregates according to their formation (i.e., biogenc and physicogenic), and evaluated the total organic carbon (TOC), total nitrogen (TN) and the natural abundance of 13 C and 15 N in biogenic and physicogenic aggregates in an area with 10 years of pig slurry (PS) and deep litter (DL) applications, using no-till system (NTS) in a crop succession with black oats and maize. Soil samples from the 0–5 and 5–10 cm layers were collected in treatments without application of manure (control), with application of PS and DL at rates equivalent to single (90 kg ha −1 ) (PS90 and DL90) and double (180 kg ha −1 ) (PS180 and DL180) the N recommendation for maize. Aggregates were classified in biogenic and physicogenic, and TOC, TN, 13 C and 15 N were evaluated. We found higher proportions of biogenic aggregates in treatments with PS and DL, as compared to the control treatment. Formation of physicogenic aggregates predominated in the control, for both depths. The highest values of TOC and TN and lowest of 13 C were found in the DL90 and DL180 treatments. Biogenic aggregates had higher TOC and TN content in comparison to physicogenic agregates. In the surface layer, 15 N values were higher in treatments with manure, as compared to the control, and in the 5–10 cm layer, DL90 and DL180 had the highest values, as compared to PS90, PS180 and control. The physicogenic aggregates had higher 15 N values than the biogenic ones, in the 5–10 cm layer. After 10 years of pig manure additions, the formation pathway of biogenic aggregates predominates compared to that of physicogenic aggregates. Application of PS90 and PS180 did not change soil TOC, TN, and 13 C inconparison to the control treatment, while application of DL90 and DL180 increased those parameters. Use of PS and DL increased 15 N values in the soil surface layer in both biogenic and physicogenic aggregates, as compared to the control. Furtermore, there was no change in 13 C between types of aggregates for all treatments evaluated. Application of PS and DL increases the TOC and TN in biogenic aggregates, as compared to physicogenc aggregates, with consequent reduction in 15 N values for biogenic aggregates in comparison to physicogenic aggregates.