Kinetics of net nitrification associated with soil aggregates under conventional and no-tillage in a subtropical rice soil

Abstract

Tillage effects on soil nitrification kinetics at the aggregate scale were studied for a subtropical rice soil. Soil samples were separated into large aggregates (>2.0 mm), macro-aggregates (2.0-0.25 mm), micro-aggregates (0.25-0.053 mm) and silt + clay fractions (<0.053 mm) by wet-sieving. The net nitrification process was simulated by a zero-and first kinetics model. Conventional tillage (CT) increased the proportion of the silt + clay fraction by 60% and decreased large-aggregates by 35% compared to ridge with no-till (RNT). Regression analysis showed that the time-dependent kinetics of net nitrification were best fitted by a zero-order model for the large-aggregates and silt + clay fraction but a first-order kinetic model for macro-and microaggregates and whole soil, regardless of tillage regime. Both potential nitrification rates (V p ) and net nitrification rates (V a ) were higher for macroaggregates than microaggregates. The potential nitrification (N p ) for whole soil under RNT was 38.7% higher than CT. The V p and V a for whole soil was 88.5% and 64.7% higher under RNT than CT, respectively. Although nitrification was stimulated under RNT, the kinetics model of nitrification was not affected by tillage. This inferred that the interaction between substrates and enzymes involved in nitrification associated with aggregates was not altered by tillage. For this soil, nitrifying microorganisms were mainly associated with macro-and microaggregates rather than large-aggregates and silt + clay fractions.

Soil aggregate size influences the impact of inorganic nitrogen deposition on soil nitrification in an alpine meadow of the Qinghai–Tibet Plateau

“…Aggregate sizes had a significant effect on the nitrification rate (Jiang et al, 2011). In the present study, higher nitrification rates were found in 2-4 mm aggregates than in the other three aggregates under both N addition treatments.…”

“…Muruganandam, Israel & Robarge (2010) found that a higher nitrification rate associated with 0.5-1 mm aggregates than 2-4 and <0.25 mm aggregates. In addition, Jiang et al (2011) reported that nitrification rates were higher for the 2-0.25 mm fraction than the 0.25-0.053 mm fraction. We further separated the 0.25-2 mm aggregates into 0.25-1 and 1-2 mm aggregates and found higher nitrification rates in the 1-2 mm aggregates.…”

Soil aggregates as biogeochemical reactors and implications for soil–atmosphere exchange of greenhouse gases—A concept

“…This change could be attributed to inhibited methanotrophic activity induced by aggregate destruction under tillage, or alternatively, to a smaller quantity of anoxic microsites within the no-tillage macro-aggregates maintained by intra-aggregate pore architecture and connectivity (e.g., Brewer, Calderón, Vigil, & Fischer, 2018). In contrast, both Jiang, Shi, Liu, and Wright (2011) and Plaza-Bonilla et al (2014) reported that soil tillage did not affect aggregate N 2 O production. tionship (e.g., Ebrahimi & Or, 2018), many abiotic and biotic factors that could regulate aggregate reactivity have not been studied.…”

Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem

“…fungal hyphae and roots). The hierarchical order of aggregates might lead to the differences in the distribution and availability of soil organic matter (SOM) 22 26 . Previous studies have shown that land use can affect the C and N within aggregates, and the degree of its influence depends on soil texture and management measures 3 4 27 .…”