Greenhouse Gas Emissions from Salt-Affected Soils: Mechanistic Understanding of Interplay Factors and Reclamation Approaches

Abstract

Salt-affected soils contain high levels of soluble salts (saline soil) and exchangeable sodium (alkali soil). Globally, about 932 million ha (Mha), including 831 Mha of agricultural land, is salt-affected. Salinity and sodicity adversely affect soil microbial diversity and enzymatic activities, and thereby carbon and nitrogen dynamics and greenhouse gas (GHG) emissions from soils. In this review article, we synthesize published information to understand the impact of salinity and sodicity on GHG production and emissions from salt-affected soils, and how various reclamation amendments (gypsum, phosphogypsum, organic manure, biochar, etc.) affect GHG emissions from reclaimed soils. Nitrous oxide (N2O) and methane (CH4) emissions are of greater concern due to their 298 and 28 times higher global warming potential, respectively, compared to carbon dioxide (CO2), on a 100-year time scale. Therefore, CO2 emissions are given negligible/smaller significance compared to the other two. Generally, nitrous oxide (N2O) emissions are higher at lower salinity and reduced at higher salinity mainly due to: (a) higher ammonification and lower nitrification resulting in a reduced substrate for denitrification; (b) reduced diversity of denitrifying bacteria lowered down microbial-mediated denitrification process; and (c) dissimilatory nitrate reduction to ammonium (DNRA), and denitrification processes compete with each other for common substrate/nitrate. Overall, methane (CH4) emissions from normal soils are higher than those of salt-affected soils. High salinity suppresses the activity of both methanogens (CH4 production) and methanotrophs (CH4 consumption). However, it imposes more inhibitory effects on methanogens than methanotrophs, resulting in lower CH4 production and subsequent emissions from these soils. Therefore, reclamation of these soils may enhance N2O and CH4 emissions. However, gypsum is the best reclamation agent, which significantly mitigates CH4 emissions from paddy cultivation in both sodic and non-sodic soils, and mitigation is higher at the higher rate of its application. Gypsum amendment increases sulfate ion concentrations and reduces CH4 emissions mainly due to the inhibition of the methanogenesis by the sulfate reductase bacteria and the enhancement of soil redox potential. Biochar is also good among the organic amendments mitigating both CH4 and N2O emission from salt-affected soils. The application of fresh organic matter and FYM enhance GHG emissions for these soils. This review suggests the need for systematic investigations for studying the impacts of various amendments and reclamation technologies on GHG emissions in order to develop low carbon emission technologies for salt-affected soil reclamation that can enhance the carbon sequestration potential of these soils.

Changes in Enzyme Activities in Salt-Affected Soils during Incubation Study of Diverse Particle Sizes of Rice Straw

“…FDA is subject to hydrolysis by various enzymes, including proteases, lipases, and esterases, resulting in the production of fluorescein, which exhibits correlations with parameters of microbial biomass such as the ATP content and oxygen consumption and can provide a measurement of the comprehensive soil microbial activity [47]. In the present study, a trend similar to that of DHA was observed for FDA (Figure 2) due to the fact that salinity alters the osmotic and matric potential of the soil solution, thereby making it difficult for microbes to obtain water and nutrients [48]. Considering all three soils and enzymes, the peak was consistent up to 28 DAI, which was similar to the findings reported by Perucci [49], who observed that soil enzyme activities were significantly higher within 30 days of the addition of municipal compost residues.…”

Reduction of Greenhouse Gas Emissions by Replacing Fertilizers with Digestate

“…In Poland, these emissions have increased by nearly 10%, and by 2030 their decrease is estimated at 5% compared to the level in 2020 (European Council 2020). In the EU, 80% of GHG emissions in agriculture are the CH 4 emissions from enteric fermentation and the N 2 O emissions from soils, while around 10% is responsible for manure management and related CH 4 emissions (EEA 2022, Fagodiya et al 2022). Ruminants are animals whose digestive tracts produce large amounts of methane .…”

Different Cropping Patterns to Restore Saline-Alkali Soils in Northeast China Affect the Abundance of Functional Genes in the Soil Nitrogen Cycle

“…Saline-alkali soils contain high levels of soluble salts. Globally, about 932 million hectares (M ha), including 831 million hectares of agricultural land, are affected by salt damage [1]. Saline-alkaline soils have little productivity [2].…”