Root-Zone Salinity in Irrigated Arid Farmland: Revealing Driving Mechanisms of Dynamic Changes in China’s Manas River Basin over 20 Years
The risk of soil salinization is prevalent in arid and semi-arid regions, posing a critical challenge to sustainable agriculture. This study addresses the need for accurate assessment of regional root-zone soil salt content (<i>SSC</i>) and understanding of underlying driving mechanisms,...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-11-01
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| Series: | Remote Sensing |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2072-4292/16/22/4294 |
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| Summary: | The risk of soil salinization is prevalent in arid and semi-arid regions, posing a critical challenge to sustainable agriculture. This study addresses the need for accurate assessment of regional root-zone soil salt content (<i>SSC</i>) and understanding of underlying driving mechanisms, which are essential for developing effective salinization mitigation and water management strategies. A remote sensing inversion technique, initially proposed to estimate root-zone <i>SSC</i> in cotton fields, was adapted and validated more widely to non-cotton farmlands. Validation results (with a coefficient of determination <i>R</i><sup>2</sup> > 0.53) were obtained using data from a three-year (2020–2022) regional survey conducted in the arid Manas River Basin (MRB), Xinjiang, China. Based on this adapted technique, we analyzed the spatiotemporal distributions of root-zone <i>SSC</i> across all farmlands in MRB from 2001 to 2022. Findings showed that root-zone <i>SSC</i> decreased significantly from 5.47 to 3.77 g kg<sup>−1</sup> over the past 20 years but experienced a slight increase of 0.15 g kg<sup>−</sup><sup>1</sup> in recent five years (2017–2022), attributed to cultivated area expansion and reduced irrigation quotas due to local water shortages. The driving mechanisms behind root-zone <i>SSC</i> distributions were analyzed using an approach combined with two machine learning algorithms, eXtreme Gradient Boosting (XGBoost) and SHapley Additive exPlanation (SHAP), to identify influential factors and quantify their impacts. The approach demonstrated high predictive accuracy (<i>R</i><sup>2</sup> = 0.96 ± 0.01, root mean squared error <i>RMSE</i> = 0.19 ± 0.03 g kg<sup>−</sup><sup>1</sup>, maximum absolute error <i>MAE</i> = 0.14 ± 0.02 g kg<sup>−</sup><sup>1</sup>) in evaluating <i>SSC</i> drivers. Factors such as initial <i>SSC</i>, crop type distribution, duration of film mulched drip irrigation implementation, normalized difference vegetation index (NDVI), irrigation amount, and actual evapotranspiration (<i>ET<sub>a</sub></i>), with mean (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mfenced close="|" open="|"><mrow><mrow><mi>SHAP</mi><mo> </mo><mi>value</mi></mrow></mrow></mfenced></mrow></semantics></math></inline-formula>) ≥ 0.02 g kg<sup>−1</sup>, were found to be more closely correlated with root-zone <i>SSC</i> variations than other factors. Decreased irrigation amount appeared as the primary driver for recent increased root-zone <i>SSC</i>, especially in the mid- and down-stream sections of MRB. Recommendations for secondary soil salinization risk reduction include regulation of the planting structure (crop choice and extent of planting area) and maintenance of a sufficient irrigation amount. |
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| ISSN: | 2072-4292 |