Soil Structural Stability and Water Retention Characteristics Under Different Land uses of Degraded Lower Himalayas of North‐West India

The lower Himalayan regions of north‐west India experienced a severe land‐use change in the recent past. A study was thus conducted to assess the effect of grassland, forest, agricultural and eroded land uses on soil aggregation, bulk density, pore size distribution and water retention and transmission characteristics. The soil samples were analysed for aggregate stability by shaking under water and water drop stability by using single simulated raindrop technique. The water‐stable aggregates (WSA) >2 mm were highest (17·3 per cent) in the surface layers of grassland, whereas the micro‐aggregates (WSA < 0·25 mm) were highest in eroded soils. The water drop stability followed the similar trend. It decreased with the increase in aggregate size. Being lowest in eroded soils, the soil organic carbon also showed an adverse effect of past land‐use change. The bulk density was highest in eroded lands, being significantly higher for the individual aggregates than that of the bulk soils. The macroporosity (>150 µm) of eroded soils was significantly (p < 0·05) lower than that of grassland and forest soils. The grassland soils retained the highest amount of water. Significant (p < 0·05) effects of land use, soil depth and their interaction were observed in water retention at different soil water suctions. Eroded soils had significantly (p < 0·05) lower water retention than grassland and forest soils. The saturated hydraulic conductivity and maximum water‐holding capacity of eroded soils were sufficiently lower than those of forest and grassland soils. These indicated a degradation of soil physical attributes due to the conversion of natural ecosystems to farming system and increased erosion hazards in the lower Himalayan region of north‐west India. Copyright © 2013 John Wiley & Sons, Ltd.     

Soil Moisture Variations with Land Use along the Precipitation Gradient in the North–South Transect of the Loess Plateau

Knowledge of soil moisture spatial variation with land use along the precipitation gradient is necessary to improve land management and guide restoration practice in the water‐limited Chinese Loess Plateau. This study selected 45 sampling points at 11 sites across the north–south transect of the Loess Plateau based on the precipitation gradient and land use. Results showed that the vertical profiles of soil moisture revealed large variations with the precipitation gradient changing, especially in the surface layer (0–100 cm). Significant linear correlation existed between the average soil moisture of the profile and the mean annual precipitation (MAP) for each land use type (p < 0·05). Hereinto, the soil moisture under the grassland was affected more greatly by precipitation. The soil moisture under each land use commonly revealed the trend as farmland > grassland > shrubland > woodland, while it might be higher under the woodland than the shrubland in the surface layer in regions with MAP <500 mm. The soil moisture of woodland or shrubland at the selected points was below or approximate to the permanent wilting point in regions with MAP <520 mm. Covariance analysis confirmed the effects of land use and MAP on the soil moisture in depth of 100–300 cm, and it showed land use did not pose significant effects in the surface layer. In addition, our study indicated that it is necessary to reconsider and re‐evaluate the current vegetation restoration strategy in the perspective of vegetation sustainability and soil water availability, in which woodland and shrubland were selected on a large scale in the arid and semi‐arid regions. Copyright © 2016 John Wiley & Sons, Ltd.     

Variations of Soil Organic Carbon Following Land Use Change on Deep‐Loess Hillsopes in China

Land use change is a key factor driving changes in soil organic carbon (SOC) around the world. However, the changes in SOC following land use changes have not been fully elucidated, especially for deep soils (>100 cm). Thus, we investigated the variations of SOC under different land uses (cropland, jujube orchard, 7‐year‐old grassland and 30‐year‐old grassland) on hillslopes in the Yuanzegou watershed of the Loess Plateau in China based on soil datasets related to soils within the 0–100 cm. Furthermore, we quantified the contribution of deep‐layer SOC (200–1,800 cm) to that of whole soil profiles based on soil datasets within the 0–1,800 cm. The results showed that in shallow profiles (0–100 cm), land uses significantly (p  < 0·05) influenced the distribution of SOC contents and stocks in surface layer (0–20 cm) but not subsurface layers (20–100 cm). Pearson correlation analysis indicated that soil texture fractions and total N were significantly (p  < 0·05 or 0·01) correlated with SOC content, which may have masked effects of land use change on SOC. In deep profiles (0–1,800 cm), SOC stock generally decreased with soil depth. But deep soils showed high SOC sequestration capacity. The SOC accumulated in the 100–1,800 m equalled 90·6%, 91·6%, 87·5% and 88·6% of amounts in the top 100 cm under cropland, 7‐year‐old grassland, 30‐year‐old grassland and jujube orchard, respectively. The results provide insights into SOC dynamics following land use changes and stressed the importance of deep‐layer SOC in estimating SOC inventory in deep loess soils. Copyright © 2017 John Wiley & Sons, Ltd.     

Change in soil organic carbon following the ‘Grain‐for‐Green’ programme in China

Agricultural soils are considered to have great potential for carbon sequestration through land‐use change. In this paper, we compiled data from the literatures and studied the change in soil organic carbon (SOC) following the ‘Grain‐for‐Green’ Programme (GGP, i.e., conversion from farmland to plantation, secondary forests and grasslands) in China. The results showed that SOC stocks accumulated at an average rate of 36·67 g m⁻² y⁻¹ in the top 20 cm with large variation. The current SOC storage could be estimated using the initial SOC stock and year since land use transformation (Adjusted R² = 0·805, p = 0·000). After land use change, SOC stocks decreased during the initial 4–5 years, followed by an increase after above ground vegetation restoration. Annual average precipitation and initial SOC stocks had a significant effect (p < 0·05) on the rate of change in SOC, while no significant effects were observed between plantation and natural regeneration (p > 0·05). The ongoing ‘Grain‐for‐Green’ project might make significant contribution to China's carbon sequestration. Copyright © 2009 John Wiley & Sons, Ltd.     

Management Effects on Soil Organic Carbon Stock in Mediterranean Open Rangelands—Treeless Grasslands

Soil organic carbon (SOC) is subject to relatively rapid changes. In grasslands soils, the management system influences these changes. Therefore, these soils play a crucial role in climate change mitigation. Current research has developed strategies and methodologies to help us understand their role as a carbon sink. In this study, the SOC and total nitrogen contents and stocks (SOC‐S) and their variation with depth were evaluated in annual crop rotations (cereal–fallow). Fifty soil profiles were sampled in the Los Pedroches Valley (southern Spain). This area consists of Mediterranean open rangelands—treeless grasslands with cereal–fallow rotation, under two management systems: long‐term (20 years) organic farming (OF) and conventional tillage (CT). The studied soils were Cambisols (CM), Leptosols (LP) and Luvisols (LV). The objective of this research was to determine any management system effects (OF vs CT) on SOC and total nitrogen contents and stocks and their variation with profile depth. It was observed that SOC concentration decreased with depth (Ah–Ap > Bw > C). The SOC concentration was higher in the top soil for all studied soils in OF compared with CT. The highest totals of SOC‐S were found in LV‐OF (66·01 Mg ha⁻¹) and the lowest in LP‐CT (21·33 Mg ha⁻¹). Significant differences (p < 0·05) between soils types and management practices were found in carbon stocks, increasing the SOC‐S in OF compared with that in CT in all studied soils; this increase was 75·25%, 85·73% and 234·88% for CM, LV and LP, respectively. The results indicated that management practices significantly influence SOC‐S in the Los Pedroches Valley and, consequently, OF in annual crop rotations (cereal–fallow) is an excellent alternative to CT that increases the SOC content in Mediterranean open rangelands—treeless grasslands environments. Copyright © 2013 John Wiley & Sons, Ltd.     

Soil Organic Carbon and Inorganic Carbon Accumulation Along a 30‐year Grassland Restoration Chronosequence in Semi‐arid Regions (China)

Carbon accumulation is an important research topic for grassland restoration. It is requisite to determine the dynamics of the soil carbon pools [soil organic carbon (SOC) and soil inorganic carbon (SIC)] for understanding regional carbon budgets. In this study, we chose a grassland restoration chronosequence (cropland, 0 years; grasslands restored for 5, 15 and 30 years, i.e. RG5, RG15 and RG30, respectively) to compare the SOC and SIC pools in different soil profiles. Our results showed that SOC stock in the 0‐ to 100‐cm soil layer showed an initial decrease in RG5 and then an increase to net C gains in RG15 and RG30. Because of a decrease in the SIC stock, the percentage of SOC stock in the total soil C pool increased across the chronosequence. The SIC stock decreased at a rate of 0·75 Mg hm⁻² y⁻¹. The change of SOC was higher in the surface (0–10 cm, 0·40 Mg hm⁻² y⁻¹) than in the deeper soil (10–100 cm, 0·33 Mg hm⁻² y⁻¹) in RG5. The accumulation of C commenced >5 years after cropland conversion. Although the SIC content decreased, the SIC stock still represented a larger percentage of the soil C pool. Moreover, the soil total carbon showed an increasing trend during grassland restoration. Our results indicated that the soil C sequestration featured an increase in SOC, offsetting the decrease in SIC at the depth of 0–100 cm in the restored grasslands. Therefore, we suggest that both SOC and SIC should be considered during grassland restoration in semi‐arid regions. Copyright © 2016 John Wiley & Sons, Ltd.     

The Effects of Long‐term Fertiliser Applications on Soil Organic Carbon and Hydraulic Properties of a Loess Soil in China

Based on a 28‐year in situ experiment, this paper investigated the impacts of organic and inorganic fertiliser applications on soil organic carbon (SOC) content and soil hydraulic properties of the silt loam (Eumorthic Anthrosols) soils derived from loess soil in the Guanzhong Plain of China. There were two crop (winter wheat and summer maize) rotations with conventional tillage. The treatments included control without fertiliser application, organic manure application (M), chemical fertiliser application (NP), and the application of organic manure with chemical fertiliser (MNP). The results showed that the 28‐year organic manure applications (M and MNP) significantly (p < 0·05) increased SOC content at surface layer (0–10 cm), but the effect of chemical fertilisers alone on SOC was not significant. Organic manure treatments (M and MNP) apparently improved soil hydraulic properties. Compared with control, field capacity and total porosity significantly (p < 0·05) increased while soil bulk density significantly (p < 0·05) decreased for organic manure applications. The M and MNP treatments increased soil water retentions by 3·2–10·8%, which was dependent of suction tensions. However, the NP treatment had no significantly impact on soil water retention compared with control. Neither organic nor inorganic fertiliser applications significantly changed saturated hydraulic conductivity. However, a clear difference was observed for unsaturated hydraulic conductivity between the M and the control at 0–5 cm. Overall, long‐term applications of organic manuring increased SOC content and amended soil hydraulic properties. However, the effects of chemical fertilisers on these soil properties were limited. Copyright © 2015 John Wiley & Sons, Ltd.     

Simulation Study of the Impact of Permanent Groundcover on Soil and Water Changes in Jujube Orchards on Sloping Ground

Land degradation is recognized as a major environmental problem in rainfed fruit orchards on the Chinese Loess Plateau. Six treatments were used to investigate surface runoff and soil moisture by means of simulated rainfall experiments: (i) a control (clean cultivation) (CC); (ii) strip cock's foot (Dactylis glomerata L.) cover (SCF); (iii) strip crown vetch (Coronilla varia L.) cover (SCV); (iv) strip bird's foot trefoil (Lotus corniculatus L.) cover (SBF); (v) strip white clover (Trifolium repens L.) cover (SWC); and (vi) complete white clover cover (WCC). The time to runoff was significantly longer under WCC than under other treatments (p < 0·05). The total runoff volume and sediment yield were significantly greater under CC than under the vegetation cover treatments (p < 0·05). The mean infiltration rate under WCC and CC was the largest and lowest and differed significantly from that under other treatments (p < 0·05). The change of soil water storage was the largest under WCC and the least under CC. The soil moisture was significantly greater under SCF than under other treatments (p < 0·05). Treatment SCF seemed to be the best groundcover for rainfed sloping jujube orchards on the Chinese Loess Plateau. Copyright © 2014 John Wiley & Sons, Ltd.     

Impact of 47 Years of No Tillage and Stubble Retention on Soil Aggregation and Carbon Distribution in a Vertisol

Aggregation often provides physical protection and stabilisation of soil organic carbon (C). No tillage (NT) coupled with stubble retention (SR) and nitrogen (N) fertiliser application (90 N, 90 kg N ha⁻¹ application) can help improve soil aggregation. However, information is lacking on the effect of long‐term NT, SR and N fertiliser (NT, SR + N) application on soil aggregation and C distribution in different aggregates in vertisols. We analysed the soil samples collected from 0‐ to 30‐cm depth from a long‐term (47 years) experiment for soil aggregation and aggregate‐associated C and N. This long‐term field experiment originally consisted of 12 treatments, having plot size of 61·9 × 6·4 m, and these plots were arranged in a randomised block design with four replications, covering an area of 1·9 ha. Soil organic C concentrations as well as stocks were significantly higher under the treatment of NT, SR + N only in 0–10 cm compared with other treatments such as conventional tillage, stubble burning + 0 N (no N application) and conventional tillage, SR + 0 N. Mineral‐associated organic C (MOC) of <0·053 mm was 5–12 times higher (r  = 0·68, p  < 0·05, n  = 32) compared with particulate organic C (POC) (>0·053 mm) in the 0‐ to 30‐cm layer. We found that NT, SR + N treatment had a positive impact on soil aggregation, as measured by the mean weight diameter (MWD) through wet sieving procedure, but only in the top 0‐ to 10‐cm depth. MWD had significant positive correlation with water stable aggregates (r  = 0·67, p  < 0·05). Unlike MWD, water stable aggregates were not affected by tillage and stubble management. Large macroaggregates (>2 mm) had significantly higher organic C and N concentrations than small macroaggregates (0·25–2 mm) or microaggregates (0·053–0·25 mm). We also found that N application had a significant effect on MWD and soil organic C in vertisols. It is evident that better soil aggregation was recorded under NTSR90N could have a positive influence on soil C sequestration. Our results further highlight the importance of soil aggregation and aggregate‐associated C in relation to C sequestration. Copyright © 2016 John Wiley & Sons, Ltd.     

Management of Grazing Intensity in the Semi‐Arid Rangelands of Southern Australia: Effects on Soil and Biodiversity

Overgrazing contributes to rangeland degradation altering plant community composition, erosion and biodiversity. Little unanimity in the literature exists on the effects of livestock grazing on soil carbon and biodiversity, in part, due to uncontrolled grazing pressure from native and feral animals. Paired paddock contrasts at three, long‐term (>8 years) study locations in the southern Australian rangelands were used to examine the effects of managing grazing intensity through the use of exclusion fencing and rotational grazing on soil organic carbon (SOC), soil nitrogen (TN), ground cover and biodiversity (flora and invertebrates). Grazing management had no effect on SOC or TN on grey soils (Vertisols), but for red soils (Lixisols), significantly higher levels of SOC were found for both the 0 to 5 and 5 to 10‐cm soil depths (0·3% and 0·27% respectively) and associated with increased TN. We found strong and consistent relationships among SOC and higher perennial (p < 0·001), higher litter (p < 0·05) cover and close proximity to trees (p < 0·05). Managing grazing intensity resulted in significantly higher perennial ground cover (p < 0·001) on Vertisols (8·9 to 11%) and Lixisols (12·5 to 15%) and higher plant diversity (both native and exotic) but negatively impacted invertebrate diversity, indicating trade‐offs between production and resources. We provide evidence that the effects of grazing management on SOC are mediated by ground cover and increased organic matter supply and/or reduced soil carbon redistribution (erosion), which indicates that the management of grazing intensity may provide a tool to avoid soil carbon loss in rangelands. Copyright © 2016 John Wiley & Sons, Ltd.     

东祁连山不同退化草地植物群落特征与土壤养分特性

为探究东祁连山不同退化草地植物群落特征、土壤养分特性及其相关性,以轻度退化草地、中度退化草地和重度退化草地为研究对象,采用野外调查、室内测定和数据统计分析相结合的方法,分析了不同退化草地植被特征、土壤养分特性及其之间的相关性。结果表明:(1)从轻度退化草地-重度退化草地,植物群落特征(地上生物量、高度、密度、频度和总盖度)整体呈现降低趋势,且差异显著(P<0.05),中度退化草地Margalef指数、Shannon指数和Evenness指数最高,Dominance指数最低;(2)研究区植物共有19科38属41种,生态适应性较强的植物主要集中在豆科、禾本科、菊科和蔷薇科,不同退化草地植被型分别为矮生嵩草(K.humilis)+赖草(Leymus secalinus)、矮生嵩草+高山唐松草(Thalictrum alpinum)、矮生嵩草+赖草,其中矮生嵩草是各退化草地的优势种,不同退化草地的功能群以杂类草占优势,其次是禾草类,毒草类所占的比例最少;(3)随草地退化程度加重,土壤速效氮、有效磷、有机碳和含水量呈降低的趋势,而pH整体呈现升高的趋势;(4)不同退化草地土壤因子对植被生长贡献率最高分别为速效氮、有效磷和含水量。综上,随着草地退化程度加重,植物群落结构向单一趋势过渡,土壤养分含量减少,且土壤因子对植物贡献率也相应发生变化。     

Annual Burning Enhances Biomass Production and Nutrient Cycling in Degraded Imperata Grasslands

The invasive species Imperata cylindrica is a dominant grass covering a large part of degraded lands of India. Imperata is managed through traditional annual burning, a practice that is prevalent throughout tropical grasslands. A field experiment was conducted to quantify the effects of burning on aboveground and belowground biomass production and soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Ave P), potassium (K⁺), calcium (Ca⁺), and magnesium (Mg⁺) concentrations in 0‐ to 15‐cm soil depth under Imperata grassland. The burnt site had 44% and 14% higher aboveground and belowground biomass over the un‐burnt control plots after 300 days of the fire event. The concentrations of SOC, TN, and Ave P increased soon after the fire but decreased regressively with time after the fire in both micro and macro soil aggregate size fractions. In contrast, concentrations of K⁺, Ca⁺, and Mg⁺ increased up to 30 days after the fire in both soil aggregate fractions. Burning did not significantly alter the stoichiometric ratios (C : N, C : P, and N : P) in macro aggregates. However, burning significantly reduced the C : N, C : P, and N : P ratios in micro aggregates during the first 0–30 days. Fire increased nutrient stocks (kg ha⁻¹) by 20–35% in the burnt site in comparison to an un‐burnt control site. It is concluded that the conventional practice of annual burning increases soil nutrients in surface soils and supports higher biomass production in Imperata‐covered degraded lands. Copyright © 2017 John Wiley & Sons, Ltd.     

Soil Quality Indicators in Relation to Land Use and Topography in a Small Catchment on the Loess Plateau of China

Better understanding of how the loess soils respond to topography and land use under catchment‐scale vegetation restoration is needed to enable science‐based land management interventions for the policy‐driven “Grain‐for‐Green” eco‐restoration program in the Loess Plateau of China. The objective of this study was to characterize the relationships of four selected soil quality indicators to land use under vegetation restoration and topography for a small catchment (0·58 km²) in the Loess Plateau. The major land uses established in the catchment are cropland, fallow (i.e., natural revegetation), grassland, and jujube orchard. The four soil quality indicators were soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), and mean root zone soil water content during the wet season (MRZSWwet). SOC, STN, and MRZSWwet were significantly different (p < 0·05) for different land uses. Grassland showed the highest values for these three properties, whereas cropland had relatively low values for SOC and STN. Land use had no effect on STP, although the lowest value was observed in grassland. Spatial analysis showed that various relations between soil quality indicators and topography (slope and elevation) were observed. These relations were generally weak for most of them, and they varied with land uses. Further analyses indicated that land uses, slope, and elevation had significant effects on the relations between different soil quality indicators. The results here should provide useful information for the further development of “Grain‐for‐Green” program. Copyright © 2012 John Wiley & Sons, Ltd.     

CHANGES IN SOIL ORGANIC CARBON UNDER EUCALYPTUS PLANTATIONS IN BRAZIL: A COMPARATIVE ANALYSIS

Proper assessment of environmental quality or degradation requires knowledge of how terrestrial C pools respond to land use change. Forest plantations offer a considerable potential to sequester C in aboveground biomass. However, their impact on initial levels of soil organic carbon (SOC) varies from strong losses to gains, possibly affecting C balances in afforestation or reforestation initiatives. We compiled paired‐plot studies on how SOC stocks under native vegetation change after planting fast‐growth Eucalyptus species in Brazil, where these plantations are becoming increasingly important. SOC changes for the 0–20 and 0–40 cm depths varied between −25 and 42 Mg ha⁻¹, following a normal distribution centered near zero. After replacing native vegetation by Eucalyptus plantations, mean SOC changes were −1·5 and 0·3 Mg ha⁻¹ for the 0–20 and 0–40 cm depths, respectively. These are very low figures in comparison to C stocks usually sequestered in aboveground biomass and were statistically nonsignificant as demonstrated by a t‐test at p < 0·05. Similar low, nonsignificant SOC changes were estimated after data were stratified into first or second rotation cycles, soil texture and biome (savanna, rainforest or grassland). Although strong SOC losses or gains effectively occurred in some cases, their underpinning causes could not be generally identified in the present work and must be ascribed in a case basis, considering the full set of environmental and management conditions. We conclude that Eucalyptus spp. plantations in average have no net effect on SOC stocks in Brazil. Copyright © 2012 John Wiley & Sons, Ltd.     

The effects of irrigation and cultivation on the quality of desert soil in central Iran

Cultivation of irrigated desert soils in Central Iran is one way of utilizing under‐exploited land to produce more food. This study explores the value of soil quality indicators as measures when converting desert to croplands. Soil samples from unfarmed desert, wheat and alfalfa sites in the Abarkooh Plain (Central Iran) were taken from 0–10, 10–20 and 20–30 cm depths. Soil quality indicators including organic carbon, total nitrogen, carbohydrate, particulate organic carbon (POC) in aggregate fractions, and aggregate water‐stability were determined. The desert soils contained organic carbon of 0·26–0·56 g kg⁻¹, total nitrogen of 0·05–0·08 g kg⁻¹ and carbohydrate of 0·03–0·11 g kg⁻¹ at 0–30 cm depth. Across this depth, the contents of organic carbon, total nitrogen and carbohydrate in wheat were about 3–7, 2–3 and 6–26‐times higher than those of desert soils, respectively. These values for alfalfa were 5–12, 3–4 and 7–35 times, respectively. The POC (near zero in desert soils) and generally other soil quality indicators showed greater improvement in alfalfa than in wheat fields. The results indicated a significant decrease in proportion of the fraction <0·05 mm in cultivated soils, whereas the proportion of the large aggregate size classes (2–4 and 1–2 mm) was increased by irrigation and cultivation. A significant improvement in aggregate water‐stability was observed in cultivated soils. At all depths, a large portion of the total soil organic carbon was stored in the fractions <0·05 mm for desert and macroaggregates (0·25–2 mm) for cultivated soils. Copyright © 2010 John Wiley & Sons, Ltd.     

退化演替对高山草地植被和土壤理化特性影响

[目的]分析3种不同草地退化阶段(轻度退化,中度退化和重度退化)草地植被和土壤理化特性的变化规律,为类似区域退化草地植被恢复提供有效途径。[方法]野外植被调查、土壤取样和室内分析。[结果]草地退化不同阶段草地植物群落组成和物种多样性均有差异,退化对草地土壤理化特性有明显影响。重度退化草地土壤容重显著高于轻度退化草地(p0.05)。轻度和中度退化样地0—10cm土壤空隙度显著高于重度退化草地。重度退化草地的土壤有机质、全碳、全钾、全磷和有效钾均明显小于轻度退化草地(p0.05),但土壤pH值和有效氮含量没有显著变化。[结论]高山草地退化演替对该区土壤物理特性具有显著影响。     

Experimental Warming Aggravates Degradation‐Induced Topsoil Drought in Alpine Meadows of the Qinghai–Tibetan Plateau

Climatic warming is presumed to cause topsoil drought by increasing evapotranspiration and water infiltration, and by progressively inducing land degradation in alpine meadows of the Qinghai–Tibetan Plateau. However, how soil moisture and temperature patterns of degraded alpine meadows respond to climate warming remains unclear. A 6‐year continuous warming experiment was carried out in both degraded and undegraded alpine meadows in the source region of the Yangtze River. The goal was to identify the effects of climatic warming and land degradation on soil moisture (θ ), soil surface temperature (T _sfc ), and soil temperature (T _s ). In the present study, land degradation significantly reduced θ by 4·5–6·1% at a depth of 0–100 cm (p  < 0·001) and increased the annual mean T _sfc by 0·8 °C. Warming with an infrared heater (radiation output of 150 W m⁻²) significantly increased the annual mean T _sfc by 2·5 °C (p  < 0·001) and significantly increased θ by 4·7% at a depth of 40–60 cm. Experimental warming in degraded land reversed the positive effects of the infrared heater and caused the yearly average θ to decrease significantly by 3·7–8·1% at a depth of 0–100 cm. Our research reveals that land degradation caused a significant water deficit near the soil surface. Experimental warming aggravated topsoil drought caused by land degradation, intensified the magnitude of degradation, and caused a positive feedback in the degraded alpine meadow ecosystem. Therefore, an immediate need exists to restore degraded alpine meadow grasslands in the Qinghai–Tibetan Plateau in anticipation of a warmer future. Copyright © 2017 John Wiley & Sons, Ltd.     

放牧对希拉穆仁草原土壤入渗过程影响的定量评估

为定量评估放牧对草原土壤入渗的影响,了解和防治放牧造成的水土流失,科学评估草原水文调节功能,采用双环入渗法研究了放牧对典型草原土壤入渗性能的影响,并收集影响土壤入渗的环境特征变量.结果表明:(1)土壤入渗能力均受到放牧活动的干扰,随着放牧强度的增加,土壤初渗速率、稳渗速率减小,达到稳渗时的历时缩短,而轻度放牧对土壤入渗...     

SOIL ORGANIC CARBON STOCK AND FRACTIONS IN RELATION TO LAND USE AND SOIL DEPTH IN THE DEGRADED SHIWALIKS HILLS OF LOWER HIMALAYAS

The proportional differences in soil organic carbon (SOC) and its fractions under different land uses are of significance for understanding the process of aggregation and soil carbon sequestration mechanisms. A study was conducted in a mixed vegetation cover watershed with forest, grass, cultivated and eroded lands in the degraded Shiwaliks of the lower Himalayas to assess land‐use effects on profile SOC distribution and storage and to quantify the SOC fractions in water‐stable aggregates (WSA) and bulk soils. The soil samples were collected from eroded, cultivated, forest and grassland soils for the analysis of SOC fractions and aggregate stability. The SOC in eroded surface soils was lower than in less disturbed grassland, cultivated and forest soils. The surface and subsurface soils of grassland and forest lands differentially contributed to the total profile carbon stock. The SOC stock in the 1.05‐m soil profile was highest (83.5 Mg ha⁻¹) under forest and lowest (55.6 Mg ha⁻¹) in eroded lands. The SOC stock in the surface (0–15 cm) soil constituted 6.95, 27.6, 27 and 42.4 per cent of the total stock in the 1.05‐m profile of eroded, cultivated, forest and grassland soils, respectively. The forest soils were found to sequester 22.4 Mg ha⁻¹ more SOC than the cultivated soils as measured in the 1.05‐m soil profiles. The differences in aggregate SOC content among the land uses were more conspicuous in bigger water‐stable macro‐aggregates (WSA > 2 mm) than in water‐stable micro‐aggregates (WSA < 0.25 mm). The SOC in micro‐aggregates (WSA < 0.25 mm) was found to be less vulnerable to changes in land use. The hot water soluble and labile carbon fractions were higher in the bulk soils of grasslands than in the individual aggregates, whereas particulate organic carbon was higher in the aggregates than in bulk soils. Copyright © 2012 John Wiley & Sons, Ltd.     

黄土高原4种植被类型对土壤物理特征及渗透性的影响

以黄土高原丘陵沟壑区李家堡乡的荒草地、文冠果林地、沙棘林地和柠条灌丛为研究对象,采用野外采样与室内分析相结合的方法,研究了4种植被类型土壤的物理特征及其渗透特征。结果表明:随土层深度的增加,土壤容重大体呈增加趋势,而土壤各孔隙度和通气度呈下降趋势。4种植被类型中荒草地的土壤容重最大,孔隙度及通气度最小,而柠条灌丛的土壤容重最小,孔隙度及通气度最大。土壤水分物理特征值为柠条灌丛最大,文冠果林和沙棘林次之,荒草地最小;柠条灌丛0—40cm土层土壤最大持水量、毛管持水量、最小持水量、最大蓄水量、排水能力比荒草地分别高出了23.00%,22.51%,15.02%,12.76%,61.28%,且方差分析表明差异显著。4种植被类型的土壤水分入渗过程符合对数曲线,各土层土壤的渗透性系数R~2为0.937 9~0.986 9,且F检验均达到极显著水平(P0.001)。与荒草地相比,柠条灌丛的入渗速率和水源涵养功能显著高于荒草地,能更好地改变土壤物理特征,应该增加柠条灌丛林的营造。