## 7 Potential Research Directions and Thoughts  
Most studies focus on predicting soil salinity at shallow depths (0 to 60 cm) [35; 150; 151]. However, field observations indicate that the salinity layer is primarily concentrated in deeper soil layers (1 to 2 m). Controlling salinity at these depths is crucial for efficient water utilization. Due to its location in deeper soil layers, long-term and multidimensional observational data are necessary to accurately assess salt concentration at this profile depth. Therefore, insights gathered from long-term observations using remotely sensed data may be essential for understanding the salinity of deeper soils. As air and soil temperatures rise, the melting of snow in spring (between March and April) replenishes soil moisture in agricultural fields. The process of freezing leads to the upward redistribution and enrichment of soil water and salts. Deep soil salts migrate upward, which is the primary cause of the rapid accumulation of surface soil salts during spring. Long-term observations reveal similarities in the distribution patterns of soil salinity between the winter-spring and summer seasons [39; 152]. This phenomenon is attributed to microtopography and groundwater level [79]. The increase in spring salinity may indicate potential latent soil salinity or salinization during the growing season. Surface spectral information gathered from multi-temporal remote sensing images during this period can synthesize hydrological and hydraulic characteristics, such as soil texture, salt content, groundwater-surface water interactions, and soil hydraulic properties. Irrigation volume is a critical indicator for managing soil salt inputs to the tillage layer during the crop-growing season [153]. Numerous on-farm observations have demonstrated a strong correlation between evapotranspiration and irrigation volume. For instance, 70-74% of water is lost through evapotranspiration throughout the growing season for winter wheat, while the percentage for corn is 72.90%. By calculating the amount of evapotranspiration, the irrigation water requirement can be indirectly estimated [154]. Results from dry matter accumulation tests indicated that crop water consumption and biomass decreased as soil salinity increased [155]. Evaptotranspiration (ET) can be estimated from remotely sensed data; for example, the SEBAL algorithm can be applied on the GEEplatform using JavaScript(v14) and Python APIs (v3.9). GEE provides access to the complete Landsat dataset and hourly ERA5 terrestrial data. Subsequently, ET datasets were calculated for various regions across the globe using geeSEBAL (v0.1) [156]. As the reclamation history extends, the soil salt aggregation layer gradually descends. The prolongation of this history facilitates the drainage of salts and alkalis. Previous studies indicate that soil salinity is highest after 10 years of continuous cropping, but it reaches its lowest point after 15 years of continuous cropping [157]. Over time, the soil is likely to develop sulfate-type salinity with increasing years of continuous cropping. Similar findings have been reported in the Manas Oasis [158] and the Yellow River Delta [159]. Data on tillage years can be extracted from Landsat series imagery. Over the past 40 years, extensive areas of desert, grassland, and shrubland have been converted into agricultural land. However, the type of vegetation that was initially present on this land was closely linked to soil hydrology and physical properties. While these areas have now been transformed into farmland, the physical properties of the soils have not changed nearly as significantly as the land use or crop types. The initial characteristics associated with historical land use records may provide valuable background information [160]. When the salt content in the soil exceeds the tolerance level of crops, aboveground plant biomass and yield are suppressed to varying degrees.