Legacy Effect of Fertilization and Tillage Systems on Nitrogen Mineralization and Microbial Communities

Abstract

Core Ideas Soil C and N dynamics were still affected by past fertilization treatments (8 yr). Soil C and N dynamics were still affected by past tillage systems (3 yr). Ammonia‐oxidizing bacteria were affected by ammonium concentration and pH. Ammonia‐oxidizing bacteria and archaea were associated with N mineralization. Poultry litter (PL) is widely used as an alternative to inorganic fertilizers (IF) in conventional (CT) and no‐tillage systems (NT). The objective of this work was to evaluate the legacy effect of a 16‐yr factorial study that combined fertilization (PL or IF) and tillage (CT or NT) treatments on soil C and N pools and microbial communities. Soil samples were collected from the 0 to 5 and 5 to 20 cm depths after 8 and 3 yr of suspending fertilization and tillage, respectively. Samples were analyzed for total organic C (TOC), total organic N (TON), N mineralization rate (k0), and abundance of ammonia‐oxidizing bacteria (AOB) and archaea (AOA). The TOC and TON concentrations (range: 5.8–20.8 and 0.5–1.8 g kg−1, respectively) were affected by tillage system and fertilizer source. Legacies of fertilization and tillage affected k0 (range: 0.20–0.87 mg kg−1 d−1) which was correlated with TOC and TON (r2 ∼ 0.9). The abundance of AOA (5.3–7.6 log10 copies g−1) and AOB (7.1–8.9 copies log10 g−1) was greater in CT than NT in the 0 to 5 cm layer, whereas the opposite was observed in the 5 to 20 cm layer. Both AOA and AOB were associated with k0 (r2 = 0.5 and 0.8, respectively), suggesting the dependence of ammonia oxidizers on mineralization of the organic N pool. Our results indicate that 8 and 3 yr after fertilization and tillage treatments were suspended, soil C and N and microbial dynamics were still being influenced by previous management practices.