Management of soil pH promotes nitrous oxide reduction and thus mitigates soil emissions of this greenhouse gas

Abstract

While concerns about human-induced effects on the Earth's climate have mainly concentrated on carbon dioxide (CO₂) and methane (CH₄), reducing anthropogenic nitrous oxide (N₂O) flux, mainly of agricultural origin, also represents an opportunity for substantial mitigation. To develop a solution that induces neither the transfer of nitrogen pollution nor decreases agricultural production, we specifically investigated the last step of the denitrification pathway, the N₂O reduction path, in soils. We first observed that this path is mainly driven by soil pH and is progressively inhibited when pH is lower than 6.8. During field experiments, we observed that liming acidic soils to neutrality made N₂O reduction more efficient and decreased soil N₂O emissions. As we estimated acidic fertilized soils to represent 37% [27-50%] of French soils, we calculated that liming could potentially decrease France's total N₂O emissions by 15.7% [8.3-21.2%]. Nevertheless, due to the different possible other impacts of liming, we currently recommend that the deployment of this solution to mitigate N₂O emission should be based on local studies that take into account agronomic, environmental and economic aspects.

Figure 1

The capacity of soils to reduce N₂O, expressed as the r_max indicator and shown on the RMQS grid.

Figure 2

The experimental points of r_max against soil pH and the function relating r_max and soil pH obtained by the GBM.

Figure 3

In situ N₂O emissions measured (mean and standard deviations obtained from the 9 replicates per treatment) in E1 (upper panel) and E2 (lower panel). *Indicates significant (p < 0.05) differences for results obtained on limed plots and control ones. In E1, liming events were of 1 t CaO applied in September 2013 and 2014. Nitrogen fertiliser was spread on 14/05/2014 (60 kg of N ha⁻¹) and on 09/03/2015 (70 kg of N ha⁻¹), on 30/03/2015 (50 kg of N ha⁻¹), and on ¹0/05/2015 (60 kg of N ha⁻¹). In E2, liming event was of 1.5 t CaO in September 2013 and organic matter was applied at the same date. Mineral fertilisers were spread on 2/05/2014 (50 Kg N ha⁻¹) and on 9/05/2014 (50 Kg N ha⁻¹). The “pig manure” plots did not receive the second input.

Figure 4

Changes in the indicators (pH, r_max and index) of the capacity of soil to reduce N₂O during E1 (left) and E2 (right). Error bars represent standard deviations (n = 3).

Figure 5

Map of soil N₂O reduction phenotypes in France obtained from the RMQS database.