Induced soil degradation risks and plant responses by salinity and sodicity in intensive irrigated agro-ecosystems of seasonally-frozen arid regions

Abstract

Salinity and sodicity posing large risks to soil hydroecological functioning and agricultural production. However, a comprehensive investigating of the long-term salinity and sodicity dynamics and how these contribute to soil degradation risk and plant response in intensive irrigated agro-ecosystems is still scarce, especially in cold/arid agricultural regions. To quantify long-term soil degradation risk and plant response as driven by rainfall, irrigation and groundwater in seasonally-frozen arid regions, taking into account the influence of capillary flux from shallow brackish groundwater and annual soil freezing-thawing cycles and snowmelt infiltration to soil moisture (s), salinity (Cs) and sodicity (Ex), we coupled the Salt of the Earth (SOTE) model and the Wavelet Neural Network (WNN) model (i.e. SOTE-WNN model) as well as improved the Crop Response to the Soil Environment (ANSWER) model. The long-term dynamics of root zone s, Cs and Ex and therefore soil degradation risks and plant responses in irrigated agro-ecosystems in three different hydrological regions (i.e. ADFO: alluvial-diluvial-fan oasis; APOU: alluvial-plain oasis in the upper part; and APOL: alluvial-plain oasis in the lower part) in the Sangong River watershed (SRW) of northwestern China were investigated. The SOTE-WNN model was calibrated and validated using field comprehensive observations during April 2018–April 2021. The simulated results of root zone s, Cs and Ex resulted in a good agreement with the observed values in the SRW. Results showed that the s in the three hydrological regions has a similar periodic steady state with sawtooth pattern; the Cs is the largest in the APOL and corresponding the crop relative yield is the lowest; in the APOU the Ex is the largest and corresponding the soil degradation risk is the highest. Carried out sensitivity analysis revealed that the increase in rainfall and snowfall can clearly alleviate soil degradation by reducing soil alkalization in the root zone. The irrigation water quality is one of the primary controls on long-term dynamics of root zone s, Cs and Ex, and imposing adverse impact on soil hydraulic conductivity and agricultural crop productivity. The shallow groundwater table and quality have non-monotonic effects on the root zone s, Cs and Ex dynamics, the 2–3 m is the critical water table interval that limits soil salinization and alkalization hazards in the SRW. The results highlight that the trade-offs between irrigation water quality and water table need to be emphasized at appropriate spatial and temporal scales when promoting intensive irrigation practices in arid/cold climate regions.