Assessment of Deep Water-Saving Practice Effects on Crop Coefficients and Water Consumption Processes in Cultivated Land–Wasteland–Lake Systems of the Hetao Irrigation District

Water scarcity, soil salinization, and desertification threaten sustainable agricultural ecosystems of Hetao irrigation district, Yellow River Basin (YRB). Precise quantification of soil water dynamics and plant water consumption processes is essential for the agricultural sustainability of the irrigation district. Therefore, this study mainly focused on the crop coefficients and water consumption processes of three representative plant types in the Hetao irrigation district, each corresponding to a specific land system: <i>Helianthus annuus</i> (cultivated land), <i>Tamarix chinensis</i> (wasteland), and <i>Phragmites australis</i> (lake). The SIMDualKc model was calibrated and validated based on situ observation data (soil water content and yield) during 2018 (conventional conditions), 2023 and 2024 (deep water-saving conditions). Results show strong agreement between simulated and observed soil moisture and crop yields. The results indicate that the process curves of <i>K_cb</i> (basal crop coefficient) and <i>K_cb</i>_adj (adjusted crop coefficient) nearly overlapped for the three plant types in 2018 and 2023. However, under the deep water-saving project implemented in 2024, the <i>K_cb</i>_adj process curves for all three plant types exhibited a significant reduction (approximately 15%). Soil evaporation fractions (<i>E</i>/<i>ET_c</i>_adj) were stable at 19-30% during the 2018, 2023, and 2024. The contribution of capillary rise to <i>ET</i> reached 38.61-43.18% in cultivated land (<i>Helianthus annuus</i>), 41.52-48.93% in wasteland (<i>Tamarix chinensis</i>), and 38.08-46.57% in lake boundary areas (<i>Phragmites australis</i>), which underscores the significant role of groundwater recharge in sustaining plant water consumption. Actual-to-potential transpiration ratios (<i>T_a</i>/<i>T_p</i>) during 2023-2024 decreased by 3-11% for <i>Helianthus annuus</i>, 5-12% for <i>Tamarix chinensis</i>, and 23% for <i>Phragmites australis</i> compared to <i>T_a</i>/<i>T_p</i> values in 2018. Capillary rise decreased approximately 10% during the whole system. Deep water-saving practices increased the groundwater depth and restricted groundwater recharge to plants via capillary rise, thereby impairing plant transpiration and growth. These findings provide scientific support for sustainable agriculture and ecological security in the Yellow River Basin.