Long Term Influence of Fertility and Rotation on Soil Nitrification Potential and Nitrifier Communities

Abstract

The agricultural imprints on soil microbial processes manifest at various timescales, leaving many temporal patterns to present slowly. Unfortunately, the lack of long-term continuous agricultural field sites in North America has left gaps in our understanding of agricultural management on biogeochemical processes and their controlling microbiota. Nitrification, ammonium oxidation by bacteria and archaea, is a critical control point in terrestrial nitrogen fluxes by oxidizing cationic ammonium to anionic nitrate, promoting nitrate leaching. Moreover, nitrous oxide is produced during nitrification, contributing to massive nitrous oxide emissions from fertilized agroecosystems. Nitrification is sensitive to many macro and micro-ecological filters, as nitrifiers are obligate aerobes and are sensitive to numerous non-growth substrates and metal ions. This study sought to understand the long-term implications of various rotation and fertilizer regimes on nitrification potential and nitrifying bacterial communities in the Morrow Plots (Urbana, IL). The Morrow Plots was established in 1876 and are the longest continuous field experiments in North America, making it the only site in America capable of assessing the impact of over 140 years of agricultural management on nitrification. The Morrow Plots contrasts fertilizer (manure, inorganic, unfertilized) and rotation (continuous corn, corn-soy, corn-oat alfalfa), allowing us to explore how conventional vs. regenerative agriculture practices impact nitrifier communities. The results of this study suggest that fertilizer and rotation interact to promote distinct bacterial nitrifier communities. Nitrification potential is highest in manure corn-oat-alfalfa plots, suggesting ammonium availability is not solely responsible for active nitrifier communities. Various soil chemical variables, like CEC, Mg, and Ca, significantly influenced nitrifier community beta-diversity, using 16S rRNA amplicon sequencing, suggesting long-term accumulation of specific cations diverge microbial community assembly. While this study only uses nitrification potential enzyme activity instead of isotope analyses, it sheds light on the importance of various physiochemical drivers on nitrification potential and communities. The results support the need for a more precise exploration of the mechanisms controlling field-scale nitrification rates over large temporal scales. Put together, this study supports the importance of long-term field sites for understanding agricultural manipulations of microbial biogeochemical cycling and sheds light on the micronutrients influencing nitrifier communities and potential activity.

Nitrogen-Enriched Organic fertilizer (NEO) elevates nitrification rates shortly after application but has no lasting effect on nitrification in agricultural soils

“…The difference to agitated soil slurries was that NEO S and ammonium chloride had almost identical nitri cation rates. This con rms the hypothesis that ammonium accessibility is not solely responsible for active nitri er communities (Raglin et al, 2022).…”

Nitrogen Enriched Organic fertilizer (NEO) elevates nitrification rates shortly after application but has no lasting effect on nitrification in agricultural soils

“…However, our initial expectation of observing distinct potential nitri cation rates between fertilized and unfertilized soil, as indicated by similar studies (Mohanty et al, 2022;Raglin et al, 2022;Wang et al, 2018), was not observed in our experiments. This discrepancy could be attributed to the relatively short two-year treatment period or the possibility that nitri cation potentials are sustained through nitrogen mining from the relatively high soil organic matter (SOM) content in the non-fertilized treatment.…”

“…In addition to xed ammonium, clay minerals can sorb complex N-containing compounds, which can subsequently be mineralized to NH 4 + upon release (Nieder et al, 2011). While we did not speci cally study the taxonomic composition of the underlying nitri er communities, other studies have reported on functional redundancy among different taxonomic groups of nitri ers as a potential reason for the lack of a fertilizer-speci c response in eld soils (Gu et al, 2017;Raglin et al, 2022;Wu et al, 2011).…”

Responses of Soil Microbial Communities in Soybean–Maize Rotation to Different Fertilization Treatments

“…These data indicate that rotation reduced soil denitrification, as well as NO and N 2 O emissions, thereby reducing the loss of nitrogen from the soil. Moreover, rotation enhanced soil ammonification, nitrification, and nitrogen fixation, in addition to increasing soil NO 3 − -N and NH 4 + -N content [30][31][32].…”