Adapting soils to salt: Effects of saline irrigation on soil C and N turnover

Salinization is an increasing threat to global food security. Sea-level rise and storm surges drive coastal salinization, while inland salinization is driven by intensive fertilization and low-quality irrigation. High salt levels cause osmotic stress, which impairs plant growth and microbial activity, ultimately degrading soil health and food production. Both the EU and UN recognize soil salinization as a major global challenge requiring urgent action. 

This study is part of the EJP SOIL project SoilSalAdapt, with Norwegian partners funded by the Research Council of Norway. The project explores adaptation strategies to soil salinization in a temperate climate. Experiments indicate that controlled saline irrigation can promote salt tolerance in soil microbes, suggesting that saline irrigation may serve as a proactive climate adaptation measure. This sub-study examines the legacy effect of previous salt exposure on soil biogeochemical turnover of carbon and nitrogen in response to a new shock salinization event.

Specifically, this study investigates 1) oxic microbial respiration and carbon use efficiency, 2) anoxic respiration and denitrification end-product stoichiometry, and 3) nitrification potential rates and the relative contributions of ammonia-oxidizing bacteria and archaea.

Denitrification completeness was strongly impacted by the salt treatment, particularly in the low-fertilization scenario, were salt seems to reduce nitrous oxide production per total denitrification. Nitrification rates responded differently to historical salinity in clay and sand soils, but the saline shock converged rates across soil types at a lower overall level.

At the EGU conference, I will present our findings and discuss how soil-based adaptation strategies can support resilient food production under ongoing and future climate pressures.