Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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黄土高原北部生长季土壤氮素矿化对植被和地形的响应
No full text氮素矿化是陆地生态系统氮循环的重要过程, 对氮素有效性有着重要影响。本文在黄土高原北部六道 沟小流域选取退耕年限相近的油松和柠条坡地, 用原位培养法测定生长季节(4—10 月)不同坡位冠层下和冠层 外 0~10 cm 和 10~20 cm 土层土壤氮素矿化速率, 以确定该区氮素矿化的季节动态特征和主要影响因素。结果 表明, 研究区生长季土壤矿质氮以铵态氮为主, 其含量在 0~10 cm 和 10~20 cm 土层分别占矿质氮总量的 61% 和 70%, 并随生长季的推移而升高。油松林上坡位和中坡位土壤铵态氮显著高于下坡位土壤, 柠条林不同坡位 铵态氮差异不显著。土壤硝态氮和矿质氮不受坡位的影响, 但与林型和采样位置有关, 冠层下硝态氮在油松林 与冠层外相近, 在柠条林则高于冠层外。生长季土壤氮素矿化在 0~10 cm 土层由硝化作用引起, 在 10~20 cm 土层则由硝化和铵化作用共同引起。铵化速率在生长季初期较高, 中期较低, 并受坡位、林型和采样位置的影 响。土壤硝化和矿化速率在油松林不受采样位置影响, 但是在柠条林则以冠层下较高。硝化和矿化速率在冠 层下以下坡位土壤最高, 在冠层外则以下坡位土壤最低。柠条林促进了冠层下土壤氮素的硝化和矿化过程, 有 利于矿质氮的积累; 油松林对矿质氮和氮素矿化的影响不受采样位置影响。</p
Plant Water Use Strategy in Response to Spatial and Temporal Variation in Precipitation Patterns in China: A Stable Isotope Analysis
No full textSpatial and temporal variation in precipitation patterns can directly alter the survival and growth of plants, yet in China there is no comprehensive and systematic strategy for plant use based on the effects of precipitation patterns. Here, we examined information from 93 published papers (368 plant species) on plant xylem water stable isotopes (delta D and delta O-18) in China. The results showed that: (1) The slope of the local meteoric water line (LMWL) gradually increased from inland areas to the coast, as a result of continental and seasonal effects. The correlation between delta(D) and delta O-18 in plant stem water is also well fitted and the correlation coefficients range from 0.78 to 0.89. With respect to the soil water line, the delta O-18 values in relation to depth (0-100 cm) varied over time; (2) Plants' main water sources are largely affected by precipitation patterns. In general, plants prioritize the use of stable and continuous water sources, while they have a more variable water uptake strategy under drought conditions; (3) There are no spatial and temporal variations in the contribution of the main water source (p > 0.05) because plants maintain growth by shifting their use of water sources when resources are unreliable
Understanding land use and cover change impacts on run-off and sediment load at flood events on the Loess Plateau, China
No full textThe Loess Plateau has been experiencing large-scale land use and cover changes (LUCCs) over the past 50 years. It is well known about the significant decreasing trend of annual streamflow and sediment load in the catchments in this area. However, how surface run-off and sediment load behaved in response to LUCC at flood events remained a research question. We investigated 371 flood events from 1963 to 2011 in a typical medium-sized catchment within the Plateau in order to understand how LUCC affected the surface run-off generation and sediment load and their behaviours based on the analysis of return periods. The results showed that the mean annual surface run-off and sediment load from flood events accounted for 49.6% and 91.8% of their mean annual totals. The reduction of surface run-off and associated sediment yield in floods explained about 85.0% and 89.2% of declines in the total annual streamflow and sediment load, respectively. The occurrences of flood events and peak sediment concentrations greater than 500 kg/m(3) showed a significantly downward trend, yet the counterclockwise loop events still dominated the flood event processes in the catchment. The results suggest that LUCC over the past 50 years resulted in significant changes in the water balance components and associated soil erosion and sediment transportation in the catchment. This was achieved mainly by reducing surface run-off and sediment yield during floods with return period of less than 5 years. Runoff-sediment load behaviour during the extreme events with greater than 10-year return periods has not changed. Outcomes from this study are useful in understanding the eco-hydrological processes and assisting the sustainable catchment management and land use planning on the Loess Plateau, and the methodologies are general and applicable to similar areas worldwide
Effects of nitrogen addition on soil oxidisable organic carbon fractions in the rhizospheric and bulk soils of Chinese pines in north-western China (vol 56, pg 192, 2018)
No full textFeldspathic sandstone addition and its impact on hydraulic properties of sandy soil
No full textFeldspathic sandstone could be used as an effective conditioner to improve the physical quality of sandy soil, and increase the crop yield there. To determine the effects of feldspathic sandstone content on soil hydraulic properties in a sandy soil, the present study added 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% (no sandy soil) of feldspathic sandstone to sandy soil. Changes in hydraulic parameters were investigated and the results showed addition of feldspathic sandstone increased saturated water content by 37%-61% and field capacity by 29%-44%, and decreased saturated hydraulic conductivity from 10.19 to 0.58 cm h(-1) of the sandy soil. Further data analysis demonstrated that with increasing content of feldspathic sandstone, the parameter n of soil water retention curve in Van Genuchten model dropped from 1.807 to 1.333. The same decreasing trend is detected in parameter a of infiltration rate (3.841-0.703) in Kostiakov formula (i = at(-b)) and parameter a(1) of wetting front (6.901-1.174) in the empirical equation (X = a(1)t(b1)). In terms of hydraulic parameters, 40% feldspathic sandstone and 60% sandy soil, optimally matching indices of loess soil, were the best mixing ratio for sandy land restoration
Impact of Land Use Change on Hydrologic Processes in a Large Plain Irrigation District
No full textLand use is the main factor that influences catchment hydrologic processes, and a better understanding of its effect is important for future land use planning and water resource management. By applying the Soil and Water Assessment Tool (SWAT), we assessed the effects of land use changes on major hydrologic processes (evapotranspiration (ET), discharge, river) on a large plain irrigation district, the Hetao Irrigation District (HID), China. The results indicated that SWAT was a useful tool for simulating the effects of land use changes on regional hydrologic processes. Human activities were the main factors that directly influenced land use in the HID. Land use changes had important impacts on the hydrologic processes of the HID. During 1995-2010, the land use changed greatly in the HID, leading to the changes in ET and discharge. The peak value of ET coincided with the exuberant crop growth period in the maximized sown crop area. In 1995s, wheat maximized the sown area and ET peaked in June; when sunflower and corn maximized the sown area in 2010s, ET peaked in July and August. The increased ET reduced discharge in the same period in the HID. Land use change affected the period and quantity of water diversion in the irrigation district. The quantity of water diverted in 1995 was greater than that in 2010, indicating that land use change significantly impacted the water quantity of the river, which was the water source of the irrigation district. This study will be a reference for future land use planning and water resource management in the irrigation district
Soil internal forces initiate aggregate breakdown and splash erosion
No full textSoil erosion is a severe ecological and environmental problem and the main cause of land degradation in many places worldwide. Soil aggregate breakdown is the first key step of splash erosion and is strongly influenced by soil internal forces, including electrostatic, hydration, and van der Waals forces. However, little is known about the influence of soil internal forces on splash erosion. In this study, we demonstrated that both splash erosion rate (SER) and soil aggregate breaking strength (ABS) were significantly affected by soil internal forces. SER and ABS increased first (from 1 to 10(-2) mol L-1) then became stable (from 10(-2) to 10(-4) mol L-1) with decreasing electrolyte concentration in bulk solution. The electrolyte concentration of 10(-2) Mol L-1 in bulk solution was the critical point for both soils in splash erosion and soil aggregate stability. The experimental results can be well interpreted by the theoretical analysis of soil internal forces. The surface potential and electric field around soil particles increased with decreasing electrolyte concentration, thereby increasing the electrostatic repulsive force among soil particles. This phenomenon led to soil aggregate breakdown and release of fine soil particles. Soil splash erosion rate and aggregate stability showed a linear relationship (R-2 = 0.83). Our results suggest that soil internal forces induce soil aggregate breakdown and then release of fine soil particles when the soil was wetted, supplying the original material for splash erosion. Furthermore, the raindrop impact force is the driving mechanism causing soil particle movement. In summary, splash erosion could be due to the coupling effects of soil internal forces and the raindrop impact force. Our study provides a possible internal controlling method for reducing splash erosion by adjusting soil internal forces between soil particles
Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau, China
No full textKnowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0-400 cm soil layer based on a long-term (2004-2016) experimental data in the northern Loess Plateau region, China. Soil bulk density (BD), saturated soil hydraulic conductivity (Ks), field capacity (FC) and soil organic carbon (SOC) in 2016, as well as the volumetric soil moisture content during 2004-2016, were measured in four vegetation types, i.e., shrubland (korshinsk peashrub), artificial grassland (alfalfa), fallow land and cropland (millet or potato). Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0-40 cm soil layer, and fallow land significantly increased FC and SOC in the 0-10 cm soil layer. Soil water storage (SWS) significantly declined in shrubland and grassland in the 40-400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland (alfalfa) and shrubland (peashrub) improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region
Effects of water stress on water use efficiency of irrigated and rainfed wheat in the Loess Plateau, China
No full textThe Loess Plateau, the largest arid and semi-arid zone in China, has been confronted with more severe water resource pressure and a growing demand for food production under global changes. For developing sustainable agriculture in this region, it is critical to learn spatiotemporal variations in water use efficiency (WUE) of main crops (e.g. winter wheat in this region) under various water management practices. In this study, we classified irrigated and rainfed wheat areas based on MODIS data, and calculated the winter wheat yield by using an improved light use efficiency model. The actual evapotranspiration (ETa) of winter wheat and the evapotranspiration drought index (EDI) were also investigated. Then we mainly examined the synergistic relationship between crop yield, ETa, and WUE, and analyzed the variations in WUE of irrigated and rainfed wheat under water stress during the 2010-2011 growing season. The results suggested that winter wheat in the Loess Plateau was primarily dominated by fainted wheat. The average yield of irrigated wheat was 3928.4 kg/ha, 22.2% more than that of rainfed wheat. High spatial heterogeneities of harvest index (HI) and maximum light use efficiency (epsilon(max )) were found in the Loess Plateau. The ETa of irrigated wheat was 102% more than that of rainfed wheat. The ratio of irrigated and rainfed wheat under no water stress was 31.55% and 17.16%, respectively. With increasing water stress, the WUE of rainfed wheat decreased more quickly than that of irrigated wheat. The WUE variations in winter wheat under water stress depended strongly on the synergistic effects of two WUE components (crop yield and ETa) and their response to environmental conditions as well as water management practices (irrigated or rainfed). Our findings enhance our current understanding of the variations in WUE as affected by water stress under various water use conditions in arid and semi-arid areas. (C) 2018 Elsevier B.V. All rights reserved
Soil moisture dynamics and dominant controls at different spatial scales over semiarid and semi-humid areas
No full textSoil moisture dynamics plays an active role in ecological and hydrological processes, and it depends on a large number of environmental factors, such as topographic attributes, soil properties, land use types, and precipitation. However, studies must still clarify the relative significance of these environmental factors at different soil depths and at different spatial scales. This study aimed: (1) to characterize temporal and spatial variations in soil moisture content (SMC) at four soil layers (0-40, 40-100, 100-200, and 200-500 cm) and three spatial scales (plot, hillslope, and region); and (2) to determine their dominant controls in diverse soil layers at different spatial scales over semiarid and semi-humid areas of the Loess Plateau, China. Given the high co-dependence of environmental factors, partial least squares regression (PLSR) was used to detect relative significance among 15 selected environmental factors that affect SMC. Temporal variation in SMC decreased with increasing soil depth, and vertical changes in the 0-500 cm soil profile were divided into a fast-changing layer (0-40 cm), an active layer (40-100 cm), a sub-active layer (100-200 cm), and a relatively stable layer (200-500 cm). PLSR models simulated SMC accurately in diverse soil layers at different scales; almost all values for variation in response (R-2) and goodness of prediction (Q(2)) were > 0.5 and > 0.0975, respectively. Upper and lower layer SMCs were the two most important factors that influenced diverse soil layers at three scales, and these SMC variables exhibited the highest importance in projection (VIP) values. The 7-day antecedent precipitation and 7-day antecedent potential evapotranspiration contributed significantly to SMC only at the 0-40 cm soil layer. VIP of soil properties, especially sand and silt content, which influenced SMC strongly, increased significantly after increasing the measured scale. Mean annual precipitation and potential evapotranspiration also influenced SMC at the regional scale significantly. Overall, this study indicated that dominant controls of SMC varied among three spatial scales on the Loess Plateau, and VIP was a function of spatial scale and soil depth