Abstract
Abstract. An accurate assessment of soil water balance components (SWBCs) is necessary for improving irrigation strategies in any water-limited environment. However, quantitative information on SWBCs is usually challenging to obtain, because none of the components (i.e., irrigation, drainage, and evapotranspiration) can be easily measured under actual conditions. Soil moisture is a variable that integrates the water balance components of land surface hydrology, and the evolution of soil moisture is assumed to contain the memory of antecedent hydrologic fluxes, and can thus be used to determine SWBCs from a hydrologic balance. A database of soil moisture measurements from six experimental plots with different treatments in the middle Heihe River basin of China was used to test the potential of a such a database for estimating SWBCs. We first compared the hydrophysical properties of the soils in these plots, such as vertical saturated hydraulic conductivity (Ks) and soil water retention features, for supporting SWBC estimations. We then determined evapotranspiration and other SWBCs using a method that combined the soil water balance method and the inverse Richards equation (a model of unsaturated soil water flow based on the Richards equation). To test the accuracy of our estimation, we used both indirect methods (such as power consumption of the pumping irrigation well and published SWBCs values at nearby sites) and the water balance equation technique to verify the estimated SWBCs values, all of which showed good reliability with respect to our estimation method. Finally, the uncertainties of the proposed methods were analyzed to evaluate the systematic error of the SWBC estimation and any restrictions regarding its application. The results showed significant variances among the film-mulched plots in both the cumulative irrigation volumes (652.1–867.3 mm) and deep drainages (170.7–364.7 mm). Moreover, the un-mulched plot had remarkably higher values in both cumulative irrigation volumes (1186.5 mm) and deep drainages (651.8 mm) compared with the mulched plots. Obvious correlation existed between the volume of irrigation and that of drained water. However, the ET demands for all of the plots behaved pretty much the same, with the cumulative ET values ranging between 489.1 and 561.9 mm for the different treatments in 2016, suggesting that the superfluous irrigation amounts had limited influence on the accumulated ET throughout the growing season due to the poor water-holding capacity of the sandy soil. This work confirmed that relatively reasonable estimations of the SWBCs in coarse-textured sandy soils can be derived by using soil moisture measurements; the proposed methods provided a reliable solution over the entire growing season and showed a great potential for identifying appropriate irrigation amounts and frequencies, and thus a move toward sustainable water resources management, even under traditional surface irrigation conditions.
Highlights
Arid inland river basins in northwestern China are unique ecosystems consisting of ice and snow, frozen soil, alpine vegetation, oases, deserts, and riparian forest landscapes, in a delicate eco-hydrological balance (Liu et al, 2015)
We investigated the difference caused by the location of the time domain reflectometry (TDR) by comparing the soil water dynamics of an un-mulched flat plot (NT1, which was independent of the TDR location) and filmmulched ridge plots (NT2–NT6, which were affected by the TDR location) after irrigation, and found that the underestimation caused by the location of the TDR was mainly significant in the top 30 cm of the soil layer
A database of soil moisture measurements taken in 2016 from six experimental fields in the middle Heihe River basin of China was used to test the potential of a soilmoisture time series for estimating the soil water balance components (SWBCs)
Summary
Arid inland river basins in northwestern China are unique ecosystems consisting of ice and snow, frozen soil, alpine vegetation, oases, deserts, and riparian forest landscapes, in a delicate eco-hydrological balance (Liu et al, 2015). Among these inland basins, the Heihe River basin (HRB) is one of the largest (Chen et al, 2007). Nitrate contamination in groundwater, saving water, and increasing water and nitrogen use efficiency, are turning out to be important steps toward sustainable agriculture in this region (Hu et al, 2008; Yu et al, 2019) – steps that are being implemented by developing effective irrigation schedules (Su et al, 2014)
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