C and N Pools in a Brazilian Oxisol According to Tillage Systems and N Sources.

We assessed the effects of tillage and sources of N on soil C and N pools in an Oxisol from Southern Brazil. The experiment was established in 2012 using split-plots with maize (Zea mays L.) and black oat (Avena strigosa (Scherb) L.) double cropping system with four replications. The main plots (25x10m) had two soil tillage systems: conventional tillage (CT) and no-tillage (NT). The sub-plots (5x10m) had 140 kg total-N ha^-1 applied for maize either as urea (UR), pig slurry (PS), anaerobically digested pig slurry (ADS) and composted pig slurry (CS), besides a control without fertilization (CTR). Soil samples were collected in the 0-5, 5-10, 10-20, 20-30, 30-40 and 40-60 cm soil layers in 2017. C and N pools were isolated (Cambardella and Elliott, 1992) and stocks were compared in equivalent soil masses (ESM) (Wendt and Hauser, 2013). POC and PN pools were higher at the 0-5 cm soil layer of NT-CS (10.6 and 0.76 Mg ha^-1) in relation to other NT (7.0 and 0.51 Mg ha^-1) and CT treatments (3.9 and 0.25 Mg ha^-1). The tested N fertilization treatments had no effect on TOC and TN stocks regardless of tillage system and sampling layer. TOC stocks were higher under NT (18.6 and 13.8 Mg C ha^-1) than CT (12.4 and 12.4 Mg C ha^-1) at the both 0-5 and 5-15 cm soil layers, respectively. The same soil layers also had higher TN stocks under NT (1.53 and 1.19 Mg N ha^-1) than CT (1.04 and 1.04 Mg N ha^-1). Differences observed at the soil surface were sustained throughout the whole profile (0-60 cm), where TOC and TN stocks were 8.2 and 0.82 Mg ha^-1 higher in NT in comparison with CT.