Quantitative assessment of the dynamics of carbon and water use efficiency on the Loess Plateau in the context of complex climate change and its driving mechanisms is important for the improvement of the regional ecological environment and the enhancement of ecological service functions. In order to assess the impact of climate change and human activities on the carbon and water use efficiency of the Loess Plateau, this study investigates the spatial and temporal rates of change in CUE, WUE, and meteorological factors at the image metric scale using one-dimensional linear fit regression, investigates the spatial correlation between CUE and meteorological factors using partial correlation analysis, and quantifies the relative contributions of human activities to CUE and WUE using residual analysis. The following are the study’s conclusions: (1) The CUE and WUE of the Loess Plateau decreased geographically from 2000 to 2020, and both the CUE and WUE of the Loess Plateau exhibited a non-significant declining trend (p > 0.05), with the CUE falling at a rate of 0.001/10a (a: year) and the WUE decreasing at a rate of 0.047/10a (a: year). (2) From 2000 to 2020, the mean values of the CUE and WUE of the Loess Plateau were 0.60 and 1.75, respectively, with a clear spatial difference. (3) CUE was favorably linked with precipitation in 56.51% of the Loess Plateau, dispersed throughout the south-central portion of the Loess Plateau and Inner Mongolia, whereas the biased association with temperature was not statistically significant and often negative. (4) An examination of residuals revealed that human activities affected the trend of CUE and WUE to some degree. Only the WUE residuals of evergreen broadleaf forests exhibited a strong upward trend that was considerably influenced by people. In conclusion, this study used remote sensing image data and meteorological data to systematically analyze the spatial and temporal dynamic patterns of carbon use efficiency and water use efficiency on the Loess Plateau over the past 21 years, as well as the characteristics of their responses to climate change and human activities, thereby providing theoretical guidance for the study of carbon and water cycles in terrestrial ecosystems on the Loess Plateau.

Soil water infiltration is a key mechanism for meeting plant water demand and groundwater recharge cycles; however, unreasonable land use practices cause reduced infiltration capacity and greater soil erosion. To date, differences in the properties of aeolian sandy soil and Pisha sandstone soil under different utilization methods as well as in soil properties, aggregates, and infiltration among kind of soil types, remain poorly understood. In this work, 54 soil samples of cropland and grassland were selected to identify the unique characteristics of soil infiltration processes under transition from cropland to grassland and contributions of soil properties to soil infiltrability in the Loess Plateau of China. The results showed that converting cropland to grassland could enhance the stable infiltration capacity of shallow soils of aeolian sandy soil and loess soil by 43.6% and 35.7%, respectively. Compared with cropland, the root properties and soil aggregate formation of the three soil types increased during grassland use, with the largest increase in soil organic matter content (32.14%) and total porosities (6.4%). As determined by the ring knife method, the saturated infiltration capacity of Pisha sandstone soil was significantly lower than in aeolian sandy soil and loess soil (p < 0.5). Moreover, its saturated infiltration capacity of cropland was better than grassland. Spearman’s correlation analysis and structural equation modeling (SEM) revealed that soil infiltration capacity appeared to be the most influenced by soil organic matter, and aggregate structure. These results highlight that fifteen years of returning cropland to grassland is not enough to affect the infiltration ability of deep soil (≥20 cm), and this improvement requires longer term maintenance.