Temporal stability analysis evaluates soil water sustainability of different cropping systems in a dryland agricultural ecosystem

The Loess Plateau is a typical dryland agricultural region where water shortages are the primary limiting factor for crop production. Deep soil moisture plays a crucial role in the regulation of seasonal water shortages, however, the distribution of soil water and its temporal variation in the deep soil profile (i.e., below 2.0 m) are usually unknown in a dryland agricultural field. A field study of three cropping systems (i.e., WWC, continuous winter wheat; SMC, continuous spring-maize; and WMR, a rotation of winter wheat and spring maize) and three tillage practices (i.e., NT, no tillage; ST, subsoiling tillage; and CT, conventional tillage) was carried out in a semi-arid region, and the crop yield, vertical distribution patterns and temporal variability of the soil moisture in a 5.0 m soil profile were studied to evaluate the effect of the various management strategies on the soil water sustainability. The results indicated that the WMR and SMC systems combined with ST practice obtained higher crop yield and water use efficiency, compared to the WWC system. And the time-averaged soil moisture for the three cropping systems differed significantly (P < 0.05). The WWC system can utilize soil water below 2.0 m and caused greater soil water depletion in the 0–5.0 m soil layer. However, no significant differences in the soil water content were found among the different tillage practices. The top soil layer showed a higher index of temporal stability (ITS) value for all cropping systems, but the ITS increased with soil depth in the deep soil profile (below 3.0 m) with the WWC system. Ultimately, the most time-stable depth (MTSD) for estimating the mean soil moisture of the profile was determined to be the 2.0–3.0 soil layer for all three systems based on the ITS values, but the mechanism by which the MTSD was formed differed for the various cropping systems. The soil moisture at the MTSD under WMR and SMC had high temporal stability, and contributed to better soil water sustainability in a dryland agricultural field. These findings may provide helpful base references for evaluating the effect of different management strategies on the soil water and the temporal stability parameters of soil moisture, as well as their impact on the sustainability of the deep soil moisture in a dryland agricultural field.