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Soil organic carbon is very important to increase crop yield. Understanding the composition changes and migration characteristics of SOC under different irrigation conditions in arid oasis areas is of great significance for the sustainable development of agro-ecosystem and the estimation of carbon balance of farmland ecosystem in arid areas. In this paper, classical statistics and geostatistics were used to study the leaching characteristics and migration laws of soil organic carbon under different irrigation conditions in Minqin Oasis, and the leaching amount and loss process and mechanism of SOC under different irrigation conditions were quantified. The research results showed that: (1) Irrigation increased the average 0–100 cm SOC content. After irrigation, SOC content decreased first and then increased with the increase in soil depth, with the maximum value of 8.56 g/kg and the minimum value of 1.82 g/kg. Compared with that before irrigation, SOC content in 0–30 cm surface layer was in leaching state, SOC content in 30–70 cm surface layer was accumulated, and SOC content in 70–100 cm surface layer had no obvious change. (2) Water was an important factor affecting soil carbon. The greater the irrigation amount, the higher the carbon leaching rate and the greater the migration amount. The SOC content in 0–30 cm soil layer was most significantly affected by irrigation, and the migration amount of SOC gradually decreased with the increase in soil depth. The maximum leaching rate of SOC was 36.8%, the minimum leaching rate was 13.5%, and its average leaching rate was 23.4%. (3) Due to the influence of soil infiltration rate under water, SOC content in different irrigation periods showed that the greatest SOC occurred in the 0–70 cm layer, and SOC content in soil was basically the same as that in non-irrigated areas on the fifth day after irrigation. (4) Precipitation, plastic film mulching, soil physical and chemical properties and other environmental factors were important factors affecting the migration and change in SOC content. [ABSTRACT FROM AUTHOR]

Accurately quantifying the evaporation loss of surface water is essential for regional water resources management, especially in arid and semi‐arid areas where water resources are already scarce. The long‐term monitoring of stable isotopes (δ18O and δ2H) in water can provide a sensitive indicator of water loss by evaporation. In this study, we obtained surface water samples of Shiyang River Basin from April to October between 2017 and 2019. The spatial and temporal characteristics of stable isotopes in surface water show the trend of enrichment in summer, depletion in spring, enrichment in deserts and depletion in mountains. The Local Evaporation Line (LEL) obtained by the regression of δ2H and δ18O in surface water has been defined by the lines: δ2H = 7.61δ18O + 14.58 for mountainous area, δ2H = 4.19δ18O − 17.85 for oasis area, δ2H = 4.08δ18O − 18.92 for desert area. The slope of LEL shows a gradual decrease from mountain to desert, indicating that the evaporation of surface water is gradually increasing. The evaporation loss of stable isotopes in surface water is 24.82% for mountainous area, 32.19% for oasis area, and 70.98% for desert area, respectively. Temperature and air humidity are the main meteorological factors affecting the evaporation loss, and the construction of reservoirs and farmland irrigation are the main man‐made factors affecting the evaporation loss. [ABSTRACT FROM AUTHOR]

Along with the growth of the population and economic and social development, water consumption in the upper-middle reaches of inland rivers is increasing, which has resulted in long-term cutout in the lower reaches of the river, shrinkage and drying up of the wetlands around the terminal lakes, and has caused a series of ecological problems at the same time. In order to protect the fragile ecological environment, comprehensive harnessing projects have been carried out in many inland river basins in China, in which adopting ecological water conveyance to rehabilitate degraded terminal lakes and wetlands is an important means. From June 2014 to October 2017, the water in the upper-middle reaches of the Shiyang River Basin and the lake water of the terminal lake after ecological water conveyance was sampled. The effects of ecological water conveyance on the characteristics of surface water and groundwater were analyzed using, for example, the Piper triangle diagram, Gibbs boomerang envelope model, and mixing diagram. After ecological water conveyance, the ion concentration of water in Qingtu Lake was higher overall, and ion concentration of water in the unstable catchment was higher than that of the stable catchment. The time variation was characterized as high in the summer half year and low in the winter half year. The water of Qingtu Lake is of high and large salinity, and its hydrochemical type is Na–SO4 (Cl), which is obviously different from the water in the middle-upper reaches of the Shiyang River Basin. The effects of silicate weathering and evaporation crystallization are the main factors leading to the high ion concentration in the water of Qingtu Lake. Ecological water conveyance and the strong evaporation of arid areas have intensified the salinization of water and soils in Qingtu Lake. Meanwhile, implementing the ecological water conveyance policy in the terminal lake has also led to shortage of water resources for agricultural irrigation in the middle reaches of the Shiyang River Basin. The serial negative ecological effects of the ecological water conveyance should be emphasized. [ABSTRACT FROM AUTHOR]

• The mulching film is conducive to field drainage after excessive water input. • The mulching film reduces loss of soil water and improves water use efficiency. • The irrigation amount is assessed based on whether it is covered by plastic film. In arid areas, where water resources are extremely scarce, the consumption of agricultural water resources is generally higher than 80% of the total water resources. Reasonable irrigation practices and effective water conservation methods are critical to the efficient utilization of water resources. In order to analyze the rationality of existing irrigation mode and evaluate the effect of plastic mulch on irrigation water migration, this research monitored the hydrogen and oxygen stable isotopic composition of soil water in Minqin oasis farmland located in the arid area of Northwest China. We used the soil water balance equation and the Craig-Gordon model to quantify the infiltration and evaporation of soil water. The result shows: (1) After irrigations in the corn growing season, the average irrigation water of 29.9 ± 4.2% (29.0 ± 6.7 mm), 29.6 ± 2.9% (28.4 ± 2.7 mm) and 30.3 ± 4.3% (29.0 ± 3.5 mm) penetrated into the soil layer of 0–10 cm, 10–50 cm, and 50–100 cm respectively. The field drainage under plastic film mulching was higher than that of no film mulching. (2) Plastic film mulching is the main reason for the difference in SWlc-excess of the surface layer. The evaporative loss of 0–5 cm soil water in non-mulched soil was generally higher than that of plastic-mulched soil. During the whole corn growing season, plastic film mulching effectively reduces evaporation losses of surface soil water and improves water use efficiency. The results of the reserch are very useful for understanding the hydrological process of agricultural lands in arid oases, improving agricultural irrigation water utilization rates, and optimizing water conservation models. [ABSTRACT FROM AUTHOR]