Conversion of ammonium to nitrate and abundance of ammonium-oxidizing-microorganism in Tropical soils with nitrification inhibitor

Gabriel Barth,Heitor Cantarella,Rafael Otto,Risely Ferraz Almeida,Godofredo Cesar Vitti,Elke Jurandy Bran Nogueira Cardoso

doi:10.1590/1678-992x-2018-0370

Abstract

The use of nitrification inhibitors (NIs; dicyandiamide - DCD) is an alternative to reduce oxidation of ammonium (NH4 +-N) to nitrate (NO3 – -N) in the soil, reducing NO3 – -N losses from fertilization practices. Based on the hypothesis that DCD reduces conversion of NH4 +-N to NO3 – -N in tropical soils and inhibits ammonia oxidizing microorganisms (AOM) abundance, soils from the Piracicaba region, Sao Paulo, with different textures (sand, loam and clay) were incubated with ammonium sulphate (AS) and DCD. Contents of NH4 +-N, NO3 – -N, soil pH, and AOM abundance were quantified periodically. Ammonium sulphate increased AOM abundance in all soils, but AS+DCD presented AOM abundances similar to the control. During 90 days of incubation, the effectiveness of DCD in reducing NO3 – -N production was 1.8, 86.4, and 145.6 mg kg–1, while the effectiveness of DCD in reducing AOM abundance was 1.2, 3.0 and 2.3 × 10–3 g soil–1 for sandy, loamy, and clayey soils, respectively. DCD effectiveness was greater in loamy and clayey soils due to the naturally low nitrification in sandy soils. Application of AS treated with DCD showed potential not only to reduce NO3 – -N production in loamy and clayey soils, but also to decrease the soil nitrification rate. Overall, DCD was effective in reducing AOM abundance and conversion of NH4 +-N to NO3 – -N in loamy and clay soils evaluated here. The increase in clay content directly influences DCD effectiveness in reducing conversion of NH4 +-N to NO3 – -N.

Highlights

Nitrogen (N) is a plant nutrient that plays a key role in sustainability and agricultural production (Yan et al, 2014)
Opposite to the NH4+-N content, which reduced over the incubation period in the loamy and clayey soils, the content of NO3–-N increased over the incubation period in both soils, represented by a negative correlation of -0.94 and -0.82 (p < 0.05) between NH4+-N and NO3–-N, respectively
The results reported here support the hypothesis that DCD inhibits ammonia oxidizing microorganisms (AOM) abundance in tropical soils, similar to previous evidence obtained under temperate conditions

Summary

Introduction

Nitrogen (N) is a plant nutrient that plays a key role in sustainability and agricultural production (Yan et al, 2014). N losses from fertilization practices have become an issue due to increased leaching of nitrate (NO3–-N), emission of nitrous oxide (N2O) and release of (H+) proton, contributing to global warming, biodiversity loss, soil acidification and water eutrophication (Chen et al, 2015). The use of nitrification inhibitors (NIs) is an alternative to reduce oxidation of NH4+-N to NO3–-N in the soil. Dicyandiamide (DCD, C2H4N4) is a NI that limits or reduces NO3–-N formation from NH4+-N or ammonium-producing fertilizers (Rodgers, 1986). Previous studies indicate that DCD regulates soil N transformations and increases plant productivity (Yang et al, 2016). The soil texture effect on DCD effectiveness is poorly understood, especially under tropical soil conditions, which present a peculiarity to the predominance of low activity clay and low soil organic matter (SOM)

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Discussion

Conclusion