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Understanding the characteristics of the precipitation-use efficiency (PUE) of grassland ecosystems and its drivers is critical for predicting how ecosystem functions will respond to future climate change. In this study, we investigated several covarying biotic and abiotic factors (e.g., biomass, coverage, diversity, precipitation, temperature, and humid index (HI)) of 81 sites across a broad natural grassland gradient in the Loess Plateau of China to determine how PUE changes along a precipitation gradient and to assess the effects of biotic and abiotic factors on PUE. Our results showed that HI, below-ground biomass (BGB), vegetation coverage, and species diversity were the most important biotic factors in controlling PUE. HI had a higher positive indirect effect on PUE mainly through its influence on community characteristics. Our results suggest that precipitation and community characteristics are both important for the precipitation-use efficiency of natural grasslands across the arid and semiarid areas of the Loess Plateau. Additionally, improving the vegetation structure and increasing species diversity can help enhance the adaptability of grassland ecosystems to climate change. [ABSTRACT FROM AUTHOR]

There is debating over the question of whether the large-scale 'Grain for Green' program on the Loess Plateau of China threatens regional food security. Self-sufficiency index and cropland pressure index were used to assess food security on the Loess Plateau after the implementation of revegetation program. The results showed that the 'Grain for Green' program initially had a considerable impact on regional food security, where grain yield fell from 1999 to 2001, resulting in a lower grain self-sufficiency and increased farmland stress. Subsequently, grain yield in this region increased due to the elevated agricultural material input and increased construction of terraces and check dams. The grain self-sufficiency index would have increased to 96.55% if there were improvements to the agricultural conditions, such as fertilization and irrigation, which would have resulted in an increase in the crop yield per unit of 20%. However, the grain self-sufficiency increased to 105.25% via the construction of terraces and check dams. Thus, the government should further expand the 'Grain for Green' program in coordination with improvements to the agricultural production conditions and the construction of terraces and check dams on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Soil salinization is currently a constraint on agriculture development in irrigated areas throughout the world. This study was conducted to examine the temporal stability and periodicity of groundwater electrical conductivity (EC) in irrigation districts. To accomplish this, 51 observation wells were selected for analysis of groundwater EC. Relative difference analysis and the non-parametric Spearman rank correlation test were used to check EC temporal stability, while the Morlet wavelet analysis was applied to measure the periodic variation of groundwater EC and groundwater level of high and low salinity wells. The mean groundwater EC of the 51 wells did not show an increasing trend over the entire measurement period, but demonstrated a moderate spatial variability, with coefficient of variation values ranging from 61 to 72%. The groundwater EC exhibited a strong temporal stability with Spearman correlation coefficients ranging from 0.81 to 0.98. The mean EC representative location in the study area was well 2, showing a good relationship between groundwater EC and groundwater level. Changes in groundwater EC were mainly affected by lateral groundwater recharge sources in small time scales. However, the groundwater EC and groundwater level always showed an obviously inverse phase with a large time scale due to precipitation effects. In conclusion, the groundwater EC, lateral recharge sources, and irrigation time should be fully considered in irrigation to avoid soil salinization. [ABSTRACT FROM AUTHOR]

• Sand cover delayed the runoff initiation times; increased soil loss significantly. • Sand cover changed runoff from infiltration- excess to saturation- excess. • Sand mulch on the slope accelerated rill formation and development. Soil erosion was severe in the wind-water erosion crisscross region of the northern Loess Plateau of China, where aeolian sand cover may enhance water erosion. In order to evaluate the effects of sand cover on runoff, soil loss and rill information, a series of rainfall simulation experiments was conducted in two contrasting treatments. One is a bare loess soil slope serving as a control, and another is a sand-covered loess slope (namely sand cover treatment). Nine simulated rains, 60 min each, were applied to each treatment in duplicates. The results showed that the runoff generation mechanism changed from infiltration-excess runoff in the control to subsurface saturation-excess runoff in the sand cover treatment. The runoff initiation was delayed about three folds in the sand cover treatment as compared to the control. Total runoff volumes and total soil loss in the sand cover treatment in each event were 1.1–1.2 times and 1.9–9.3 times those in the control treatment. A paired t -test showed that the runoff rates were greater in sand cover than in control in all events except for the last run at P < 0.05. The soil loss rates were greater in sand cover than in control for all events except the first rain at P < 0.05. Measured total rill length, width, and degree of rill dissection in the sand cover treatment were much greater than those in the control. The rill erosion of sand cover slope was dominated by the shallow and wider rills, while loess slope was dominated by the narrow and deeper rills. The results clearly indicated that a sand layer overlying a less pervious loess soil facilitated return flow and thus accelerated rill formation and development. This finding is in line with the common understanding that return flow in layered soil can promote rill formation and cause severe rill erosion, which is also important to understand the effect of wind-blown sand cover on water erosion in the wind-water erosion crisscross region. [ABSTRACT FROM AUTHOR]

Revegetation and check dam construction are two widely applied soil erosion control measures on the Loess Plateau of China. They play important roles in sediment yield reduction. However, it remains unclear how these large-scale land-use changes and in-channel structures affect water yield and sediment load on the watershed scale. A combination of field work and modeling exercises were used to quantitatively assess the effects of land-use changes and check dam construction on hydrological processes in the Wuding River watershed. The study area suffered important land-use changes with increases in forestland and grassland, coupled with decreases in cropland, from 1980 to 2010. A large number of check dams were constructed from 1970 to 1980. Runoff and sediment yield in the watershed showed significant decreasing trends, with change points occurring in the early 1970s. Human activity contributed to 75% and 89% of runoff and sediment changes, respectively. The simulations showed that in a scenario without check dams, runoff and sediment increased by 12% and 11.7%, respectively. Vegetation recovery reduced runoff and sediment yield. 'Grain for Green' resulted in decreasing runoff and sediment levels, and reforestation had more hydrological regulatory effects compared with scenarios involving the conversion of cropland to grassland. Moreover, the combination of revegetation and check dam construction had a greater impact on water yield and sediment transportation. Check dams provide short-term flood control and sediment reductions, whereas land-use changes are long-term sustained soil 24 erosion control measures. It may be more efficient to combine check dam construction with revegetation strategies. [ABSTRACT FROM AUTHOR]

Soil respiration is a large carbon flux from terrestrial ecosystems to the atmosphere, and small variations in soil respiration can prominently influence the global carbon (C) cycle. The vegetation changes could directly affect soil respiration. The large-scale "Grain for Green" project carried out on the Loess Plateau, China has importantly affected the contribution of soil respiration to atmospheric carbon dioxide (CO 2 ). Therefore, it is important to study the effects of vegetation restoration on soil respiration. We selected four land-use types: crop, forest, shrub, and grassland in the Zhifanggou watershed to analyze variation in soil respiration during dry and rainy seasons. Furthermore, the source of CO 2 emissions from soil respiration was identified using isotopes. The results showed that soil respiration in the rainy season was significantly higher than that in the dry season (P < .05). Soil respiration in the dry season was as follows: shrubland (1.04 μmol m -2  s -1 ) > cropland (0.72 μmol m -2  s -1 ) > forestland (0.44 μmol m -2  s -1 ) > grassland (0.33 μmol m -2  s -1 ). However, grass and forestland had significantly higher soil respiration than shrub and cropland in the rainy season (P < .05). Roots were the main source of soil respiration in cropland, which contributed >70% of CO 2 emissions. Following revegetation, litter contributed more to soil respiration than roots or soil microorganisms at >68% of soil respiration. Our results provide a theoretical basis for assessing C balance in terrestrial ecosystems., (Copyright © 2019 Elsevier B.V. All rights reserved.)