Effect of soil pH and texture on the ratio of denitrification end products

Abstract

Nitrous oxide (N₂O) is a potent greenhouse gas that contributes to stratospheric ozone depletion and global climate change. Denitrification has two potential end products, N₂O and dinitrogen (N₂), and the ratio of these end-products is controlled by various factors. Soil pH and texture are two factors that have potential biological, chemical, and physical effects on denitrification. This study aims to quantify the influence of soil pH on the ratio of denitrification end-products in Oklahoma soils with different soil textures. Four field soils encompassing three distinct soil textures were incubated in the laboratory under natural pH, more acidic pH (amended with sulfuric acid H₂SO₄), and more basic pH (amended with potassium hydroxide KOH), with an overall, tested pH ranging from 2 to 10. Denitrification end-products were measured in the laboratory using the acetylene inhibition technique and further estimated using a process-based biogeochemical soil model. Both the laboratory and model results showed that soil pH and texture influenced the ratio of the denitrification end-products, here referred to as the N₂O ratio. Generally, as soil pH increased the N₂O ratio decreased, although both lab and model results indicated that this relationship was not strictly linear. Soil texture has an indirect effect on the N₂O ratio, where the results showed the same type of soil has a different N₂O ratio. The clay percentage of the soil has a linear positive correlation with the N₂O ratio based on this study’s findings. In conclusion, soil pH is a controlling factor in the ratio of denitrification end-products and warrants further research to sufficiently quantify this nonlinear relationship, particularly when considering its effects in different soil textures