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1.
Effects of earthworm casts on soil nutrient dynamics and their responses to changing moisture availability in subtropical ecosystems remain poorly understood. This study aimed to examine short-term carbon(C) and nitrogen(N) dynamics and their interactions with wetting-drying cycles in three different structural forms(i.e., granular, globular, and heap-like) of Amynthas earthworm casts. The rates of C and N mineralization in the earthworm casts were examined under two different wetting-drying cycles(i.e., 2-d and 4-d wetting intervals) using a rainfall simulation experiment. After three simulated rainfall events, subsamples of the earthworm casts were further incubated for 4 d for the determination of CO_2 and N_2O fluxes. The results of this study indicated that the impacts of wetting-drying cycles on the short-term C and N dynamics were highly variable among the three cast forms, but wetting-drying cycles significantly reduced the cumulative CO_2 and N_2O fluxes by 62%–83% and 57%–85%, respectively, when compared to the control without being subjected to any rainfall events. The C mineralization rates in different cast forms were affected by the amount of organic substrates and N content in casts, which were associated with the food preference and selection of earthworms. Meanwhile, the cumulative N_2O fluxes did not differ among the three cast forms. Repeated wetting and drying of casts not only enhanced aggregate stability by promoting bonds between the cast particles, but also inhibited microbial survival and growth during the prolonged drying period, which together hindered decomposition and denitrification. Our findings demonstrated that the interactions between the structural forms, aggregate dynamics, and C and N cycling in the earthworm casts were highly complex.  相似文献   

2.
To test the hypothesis that earthworm surface casts contribute to soil erosion and nutrient transfers in a temperate maize crop, two rainfall experiments were set up. One was focused on the erodibility of earthworm casts, the second examined in how casts affect water runoff and nutrient transfers. Casts produced from anecic and endogeic earthworm species were both analyzed. Visual observations in the field showed no cast transport but only cast disintegration and transfers of particles. Erodibility of newly deposited casts was high and differed significantly between age groups. Cast erosion was significantly positively related to initial mass when young but not when old. The paradox is that despite a high cast abundance (25% of the area) and obvious cast erosion, amounts of sediment and nutrient losses (C, N and P) in the runoff were at least twice as high without, than in the presence of, surface casts. Earthworm activities were shown to act as a physical brake for soil erosion by (i) creating a surface roughness with the deposition of surface casts and (ii) reducing water runoff by associated enhanced water percolation. Once the breaking-down point of the physical resistance of casts was reached, all surface casts were quickly disintegrated and finally completely washed away. The amount of particulate phosphorus recovered in water runoff was 34.7 mg P m− 2, while 128.5 mg P m− 2 was estimated to have been released from casts. The transfers were found to occur over a short-distance through successive deposition/suspension of soil particles in the water runoff.  相似文献   

3.
Runoff sediment from disturbed soils in the Lake Tahoe Basin has resulted in light scattering, accumulation of nutrients, and subsequent loss in lake clarity. Little quantified information about erosion rates and runoff particle‐size distributions (PSDs) exists for determining stream and lake loading associated with land management. Building on previous studies using rainfall simulation (RS) techniques for quantifying infiltration, runoff, and erosion rates, we determine the dependence and significance of runoff sediment PSDs and sediment yield (SY, or erodibility) on slope and compare these relationships between erosion control treatments (e.g., mulch covers, compost, or woodchip incorporation, plantings) with bare and undisturbed, or ‘native’ forest soils. We used simulated rainfall rates of 60–100 mm h−1 applied over replicated 0·64 m2 plots. Measured parameters included time to runoff (s), infiltration and runoff rates (mm h−1), SY (g mm−1 runoff), and average sediment concentration (SC, g L−1) as well as PSDs in runoff samples. In terms of significant relationships, granitic soils had larger particle sizes than volcanic soils in bulk soil and runoff samples. Consequently, runoff rates, SCs, and SYs were greater from bare volcanic as compared to that from bare granitic soils at similar slopes. Generally, runoff rates increased with increasing slope on bare soils, while infiltration rates decreased. Similarly, SY increased with slope for both soil types, though SYs from volcanic soils are three to four times larger than that from granitic soils. As SY increased, smaller particle sizes are observed in runoff for all soil conditions and particle sizes decreased with increasing slope. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
The influence of drying and ageing on the stabilization of casts produced by the endoge′ic earthworm, Aporrectodea rosea, from a soil, which was hard-setting and low in organic matter, were investigated in the laboratory. Casts and uningested soil were aged-most for up to 32 days, dried for up to 21 days, or subjected to different wetting and drying cycles over 30 days. The dispersion index of aged-moist casts decreased from 0.40 to 0.25 over 32 days, while dispersion index of dried casts decreased from 0.40 to 0.01 over 21 days. The dispersion index of air-dried casts was not significantly increased by five cycles of wetting and drying. The dispersion index of dried casts was not significantly less than that of dried soil. In soils wetter than a matric potential of approximately –35kPa, stabilization of casts was probably due to a combination of cohesion of soil particles, age-hardening and growth of microorganisms. However, in soils drier than –35kPa, cementation was probably the major mechanism of stabilization. The addition of wheat straw to the soil prior to ingestion by earthworms increased dispersion from aged-moist casts, but did not influence dispersion from dried casts. The addition of wheat straw decreased the number of air-dried casts which slaked severely. The concentration of soluble carbohydrate decreased with dispersion index as casts and uningested soil were each dried. This suggested that soluble carbohydrate may have been denatured with or without being bonded to soil particles during drying. Received: 7 May 1996  相似文献   

5.
 The effects of a large species of anecic earthworm, Martiodrilus carimaguensis Jiménez and Moreno, on soil C and N dynamics were investigated in a native savanna and a man-made pasture of the eastern plains of Colombia. We compared, across time (11 months), the total C, total N, NH+ 4 and NO– 3 contents in the earthworm casts, the underlying soil and the adjacent soil. Additional sampling of root biomass and macrofauna was performed. In the two management systems, the total C and N contents were higher in casts (4.33–7.50%) than in the bulk soil (2.81–4.08%), showing that the earthworms selected food substrates with high organic contents. In general, C contents significantly increased during cast ageing (+100%), possibly because of CO2 fixation processes, dead root accumulation and/or macrofaunal activities in casts. In fresh casts, NH+ 4 levels were very high (294.20–233.98 μg g–1 dry cast) when compared to the soil (26.96–73.95 μg g–1 dry soil), due to the intense mineralisation processes that occurred during the transit of soil and organic matter through the earthworm gut. During the first week of cast ageing, NH+ 4 levels sharply decreased, while NH– 3 levels showed successive peaks in the casts, the underlying soil and the adjacent soil. These results suggested the rapid production of NO– 3 by nitrification processes in the fresh casts, followed by diffusion to the nearby soil, first vertically, then horizontally. After 2 weeks of cast ageing, NH+ 4 and NO– 3 levels only showed slight variations, likely because of organic matter protection in stable dry casts. The root biomass was higher (1.6–4.7 times) below the old earthworm casts. The ecological significance of these results is discussed. Received: 22 October 1998  相似文献   

6.
The susceptibility of some soils in the high rainfall zone of Nigeria to soil erosion must be measured regularly for better soil management. A number of techniques have been adopted for the determination of this soil loss parameter. The aim of this study is to determine the soil characteristics that relate significantly to erodibility. Soil samples collected from 0–20 cm depth from 10 different locations in the upper rainforest area were analysed for particle size distribution, water‐stable aggregates, exchangeable cations, organic carbon, soil dispersion and aggregating indices. The soils are mainly Acrisols, Nitosols, Gleysols and Ferralsol in the FAO classification while their textures are sands to sandy‐clay‐loam. They are very unstable in water as reflected in the higher values of WSA >0·50 mm and the mean‐weight diameter that ranged from 0·50 to 2·03 mm. The dispersion ratio for the soils are between 0·26 and 0·69 while clay dispersion ratio also ranged from 0·24 to 0·80. Revised universal soil loss equation (RUSLE) erodibility model values (K) were from 0·03 to 0·06 Mg h MJ−1 mm−1. These parameters can be effectively used in predicting soil erodibility, though their predictability varied in ranking of soil erodibility. In spite of this variability these indices can be used for potential erosion hazard determination by agricultural extension staff to avoid crop failures and other negative influence of soil erosion. The soil parameters are easy to determine and will be a valuable instrument when faster approaches to erosion control measures are required. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

7.
《CATENA》2001,45(2):103-121
Equations used to calculate erodibility in the Water Erosion Prediction Project soil erosion model (WEPP) are based on erodibility studies in the USA and may not function well in another region. This study was conducted to: (i) analyze erodibility and infiltration characteristics of some predominant soils of southern Spain, and (ii) test equations used to calculate interrill erodibility in the WEPP model on these soils. The five soils chosen for this study in Andalusia, southwest Spain, were: two terrace soils (referred to as ‘Red and Yellow Alfisols’), an alluvial soil (‘Fluvent’), a shallow hillside soil (‘Inceptisol’), and a cracking clay soil (‘Vertisol’). A static, solenoid operated rainfall simulator was operated at an intensity of approximately 60 mm h−1 during a 60-min dry run followed by a 30-min wet run the next day on 0.75 m2 plots with 30% ridge slopes. Infiltration rates were high (always exceeding 50% except for the wet run of the Fluvent). The Fluvent had the lowest infiltration rate (0.00 mm min−1 at the end of the wet run) and highest soil loss (985 g m−2 h−1 in the dry run and 1557 g m−2 h−1 in the wet run). The Vertisol, Inceptisol and Red Alfisol had low soil loss (415, 605, and 527 g m−2 h−1 in the dry run and 824, 762 and 629 g m−2 h−1 in the wet run, respectively). Soil loss of the Vertisol doubled between dry and wet run and infiltration rate did not stabilize, suggesting that erodibility of Vertisols increases when they are wet. The Yellow Alfisol had lower final infiltration rate in the dry run (0.33 mm min−1) than in the wet run (0.58 mm min−1) and higher soil loss in dry run (1203 g m−2 h−1) than in wet run (961 g m−2 h−1), the reason still being unclear. Soil loss was significantly correlated to silt+very fine sand content (r=0.96), indicating that erodibility of these soils is determined by similar properties as soils in these soil orders in the USA. However, the equation for WEPP-interrill erodibility overestimated erodibility significantly (two to four times), indicating the need to develop new erodibility equations for the Mediterranean region. Infiltration rates were generally high and soil loss rates low compared to reports from the USA, suggesting that limited runoff generation is a primary reason for low erodibility of these soils.  相似文献   

8.
Water repellency is influenced by soil management and biological process. We carried out a 60‐day laboratory incubation experiment to evaluate the effects of straw amendment, together with the intensity and frequency of wetting and drying (W/D), on microbial processes and water repellency. One W/D cycle consisted of 1.5‐day wetting at −0.03 kPa from the soil core bottom and different drying lengths in a temperature‐controlled laboratory, resulting in different drying intensities. At a regular interval, soil respiration rate (SRR) on drying and wetting, soil microbial biomass C and N (SMB‐C and N), and soil water repellency (SWR) after the wetting were measured simultaneously. Rice straw amendment had a greater effect on SRR, but smaller influences on SMB and SMB‐C : N than W/D frequency and drying intensity. The first W/D caused the largest decrease in soil respiration and the soil respiration recovered partly in the subsequent W/D cycles. The increase in SMB and SMB‐C : N as well as metabolic quotient with W/D frequency and intensity suggested a shift of microbial community from bacterial dominance to fungal dominance. SWR was significantly related to SMB‐C (R2= 0.689, P < 0.001). However, this study was limited to these indirect measurements. Direct measurements of fungal biomass and microbial community are needed in the future. The results suggest that rice straw amendment in dry season may increase C sequestration due to reduced decomposition and stabilize soil structure due to the enhancement of microbial induced water repellency.  相似文献   

9.
The effect of different factors and preparation conditions of monofraction samples from the arable horizon of leached chernozem on soil erodibility and its relationship with soil tensile strength (STS) has been studied. The exposure of samples at 38°C reduces their erodibility by two orders of magnitude. The drying of samples, on the contrary, increases their erodibility. It has been shown that erodibility decreases during the experiment. It has been found that the inoculation of soil with yeast cultures (Naganishia albida, Lipomyces tetrasporus) reliably increases the STS value in 1.5–1.9 times. The sterile soil is eroded more intensively than the unsterile soil: at 4.9 and 0.3 g/(m2 s), respectively. The drying of soil followed by wetting to the initial water content (30%) has no significant effect on the STS value in almost all experimental treatments.  相似文献   

10.
Abstract

In the Rougiers de Camarès area (in the south of France), hillslopes are very susceptible to water erosion. This is the result of physical features (steep slopes, soft bedrocks, thin soils), climatic aggressiveness (frost, storms), as well as farming systems (intensive tillage, short crop cycles, land consolidation). The objective of this work was to study the relationships between soil erodibility, macroaggregate stability, and carbon content of surface samples (0–10 cm), in a Rougiers Entisol (Lithic Udorthent) under various management practices (flat or raised moldboard ploughing, superficial tillage, direct drilling, with inputs in the form of mineral fertilizers or sheep manure). The soil erodibility was assessed by field rainfall simulation (60 mm h‐1) on manually retilled bare dry soil; water‐stable macroaggregation (>0.2 mm) was assessed by wet‐sieving, after immersion in water. Runoff, turbidity and soil losses were linked to water‐stable macroaggregation and carbon content in the 0–10 cm layer. During the first 30 minutes of rainfall, runoff and soil losses were closely correlated with topsoil initial water‐stable macroaggregation, but not with topsoil carbon content (although there was a correlation between water‐stable macroaggregation and carbon content). At the end of the rain (runoff steady state), turbidity and soil losses were closely correlated with topsoil carbon content, and to a lesser extent, with water‐stable macroaggregation. Water‐stable macroaggregation (which prevents crusting) and carbon content (which has an effect upon liquidity limit, among others) were thus important determining factors of erodibility for the studied soil. The influence of management practices on soil erodibility was therefore dependent upon their effects on these factors.  相似文献   

11.
 We investigated whether, under a temperate climate and in a maize crop, earthworm casts could contribute to soil erosion and further favour the exportation of phosphorus by runoff waters. Recording of casts was made in compacted (wheel-tracks) and non-compacted inter-rows, for a 2-month period in spring. To assess the rainfall impact on cast evolution, half of the observation sites were protected against rain splash by a nylon mesh placed above the soil surface. The water runoff was collected and analysed for sediment contents and phosphorus concentration. The mean annual production of surface casts was calculated to be 34 kg (dry weight) year–1 kg–1 earthworm (fresh weight). Synchronization between cast erosion and rainfall events was shown under natural conditions (unprotected sites). The erosion rate was 4 times greater over rainy periods than dry ones, reaching 80% of cast numbers. It appeared that not the runoff effect but the splash effect, due to the kinetics of the drops, disrupted casts. Newly formed casts disappeared first, with the erosion rate decreasing twofold for casts more than 10 days old. Cast erosion and runoff, as well as worm casting activity, were greater under compacted sites than under non-compacted sites, indicating an influence of earthworms on soil erosion from compacted soils. The total phosphorus content was similar in casts and uningested soil (0.80 mg phosphorus g–1). Potential phosphorus losses from cast erosion was calculated to reach 25–49 mg phosphorus m–2 per rainfall event depending on soil compaction. The amounts of particulate phosphorus recovered in water runoff after each rainfall event varied from 1 mg to 11 mg phosphorus. These results are compared and discussed. Received: 20 October 1998  相似文献   

12.
Organic upland soils store large amounts of humified organic matter. The mechanisms controlling the leaching of this C pool are not completely understood. To examine the effects of temperature and microbial cycling on C leaching, we incubated five unvegetated soil cores from a Podzol O horizon (from NE Scotland), over a simulated natural temperature cycle for 1 year, whilst maintaining a constant soil moisture content. Soil cores were leached with artificial rain (177 mm each, monthly) and the leachates analysed for dissolved organic carbon (DOC) and their specific C‐normalized UV absorbance determined (SUVA, 285 nm). Monthly values of respiration of the incubated soils were determined as CO2 efflux. To examine the effects of vegetation C inputs and soil moisture, in addition to temperature, we sampled O horizon pore waters in situ and collected five additional field soil cores every month. The field cores were leached under controlled laboratory conditions. Hysteresis in the monthly amount of DOC leached from field cores resulted in greater DOC on the rising, than falling temperature phases. This hysteresis suggested that photosynthetic C stimulated greater DOC losses in early summer, whereas limitations in the availability of soil moisture in late summer suppressed microbial decomposition and DOC loss. Greater DOC concentrations of in‐situ pore waters than for any core leachates were attributed to the effects of soil drying and physico‐chemical processes in the field. Variation in the respiration rates for the incubated soils was related to temperature, and respiration provided a greater pathway of C loss (44 g C m−2 year−1) than DOC (7.2 g C m−2 year−1). Changes in SUVA over spring and summer observed in all experimental systems were related to the period of increased temperature. During this time, DOC became less aromatic, which suggests that lower molecular weight labile compounds were not completely mineralized. The ultimate DOC source appears to be the incomplete microbial decomposition of recalcitrant humified C. In warmer periods, any labile C that is not respired is leached, but in autumn either labile C production ceases, or it is sequestered in soil biomass.  相似文献   

13.
The wind erosion equation (WEQ) was used for several decades for predicting soil loss by wind erosion, but few systematic studies on the uncertainty of predicting wind erosion have been conducted. Several researchers found that WEQ is not accurately representing soil erosion and under‐represents soil erodibility that consequently results in WEQ underestimations. WEQ was modified under Canadian conditions for the National Agri‐Environmental Health Analysis and Reporting Program, referred as (WEQ‐NAHARP). The model, input, and parameter uncertainties that control model efficiency were used to analyze the local and universal uncertainties for WEQ‐NAHARP. One and ninety‐nine percentiles were used as lower and upper boundaries of uncertainty bound when using general likelihood uncertainty estimation for estimating the uncertainty of WEQ‐NAHARP's prediction. The soil erodibility (I ), climate factor (C ), and soil surface roughness factor (K ) were found as the three most sensitive factors in predicting wind erosion in WEQ‐NAHARP. The vegetation cover factor (V ) was discovered not sensitive to the prediction model as it is less than 1,000 kg ha−1 and became very sensitive as V ‐value is greater than 5,000 kg ha−1 . Field length along the prevailing wind erosion direction (L ) and V have lower local sensitivity indexes than the other three factors. WEQ‐NAHARP underestimated wind erosion rate of Pampas, Argentina, and overestimated at Washington State, USA. This probably reflected the nature of WEQ‐NAHARP's behavior, which had a great uncertainty of its prediction. The model appears to underestimate total annual soil loss for coarse soil and overestimate annual soil loss for finer soil. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

14.
The western interior portions of Puerto Rico offer optimal climatic conditions for coffee cultivation. However, land and water degradation result when abrupt topographic relief and high annual rainfall combine with forest conversion for coffee farming. Small‐scale rainfall simulation experiments were conducted to quantify runoff and erosion from four land surface types (i.e., mulched, weed‐covered, and bare soils under active cultivation, and unpaved roads) representative of coffee farms in Puerto Rico. Results show that mulch‐covered soils had runoff coefficients similar to those from undisturbed forested conditions (~4%), and that they eroded at rates about a quarter of those for bare cultivated soils. Weed‐covered soils had surprisingly high runoff coefficients (~70%), yet their erosion rates were only three‐fourths of those for bare soils. Annualized erosion rates from unpaved roads were 65 Mg ha−1 y−1, or ten times greater than bare soils and about a hundred times higher than weed‐ or mulch‐covered surfaces. Farm‐scale sediment production estimates amount to ~11 Mg ha−1 y−1, about two‐orders of magnitude higher than under forested conditions. At the farm‐scale, only 2 – 8% of the total sediment is potentially attributable to cultivated hillslopes. In contrast, unpaved roads may account for over 90% of the sediment budget, even though they comprise only 15% of the farm surface area. Therefore, while providing mulch or a vegetative cover to bare cultivated soils should be part of effective soil management, mitigating the effects of coffee cultivation on downstream water resources must focus on the unpaved road network as the primary sediment source. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

15.
Permissible erosion rate also known as soil loss tolerance (‘T’ value) is defined as maximum erosion that can take place on a given soil without degrading its long‐term productivity. In India, default ‘T’ value of 11·2 Mg ha−1 y−1 is used for devising land restoration strategies for different types of soils. However, ability of soil to resist degradation varies with soil type, depth and physico‐chemical characteristics. Therefore, the present investigation was undertaken to determine ‘T’ value of different landforms of Delhi State by taking into account the soil saturated hydraulic conductivity (SHC), bulk density (BD), organic carbon, erodibility and soil pH. Soil state was defined by a quantitative model and scaling functions were used to convert soil parameters to a 0–1 scale. The normalised values were multiplied by appropriate weighting factors based on relative importance and sensitivity analysis of each indicator. Categorical rankings of I, II or III were assigned to soil groups based on overall aggregate score. ‘T’ value of different landforms of Delhi State was computed using the guideline of USDA‐Natural Resource Conservation Services. Majority of landforms of Delhi had ‘T’ value of 12·5 Mg ha−1 y−1, except for the soils of hill terrain, dissected hill, pediment and piedmont plain, where ‘T’ value ranged from 5 to 10 Mg ha−1 y−1. These ‘T’ values could be used for conservation planning and will help the planners in devising suitable land restoration strategies. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

16.
Earthworms are recognized to increase soil porosity, reorganize soil structure, and stimulate soil microflora and nutrient mineralization. The properties of earthworm casts should depend both on earthworm species or ecological group and on soil properties. Interactions between earthworm species and soil types have been suggested, but only poorly demonstrated. In order to better understand those interactions, two hypotheses led our study: (1) Soil type has a greater influence on cast properties than earthworm; (2) Earthworms from different species influence cast properties differently; (3) The intensity and direction of the impact of each earthworm species on cast properties vary with soil properties. Fifteen physical and chemical variables (N–NH4+, N–NO3−, total organic C and N, C/N ratio, CaCO3, pH, P, K+, Mg2+, Mn2+, Na+, CEC, moisture, wettability) were measured in casts of three earthworm species (Lumbricus terrestris, Allolobophora chlorotica and Aporrectodea rosea) produced in three temperate soils. Univariate and multivariate analyses showed that earthworm species and soil types significantly impacted cast properties. pH, Nt, K and Mg contents were interactively altered by both factors. Multivariate analysis showed that a difference of soil type had a major impact on casts properties (62%) compared to the impact of a difference of earthworm species (10%). Cast properties were most impacted by L. terrestris, then by A. chlorotica and last by A. rosea. The response ratio (ratio of the properties of the casts to the properties of the bulk soil) was used to quantify the effect of earthworm species compared to the control soil. It showed a higher response of variables in casts in nutrient-rich soils, especially in casts of L. terrestris. The interactions between earthworm species and soil types on cast properties were discussed with regards to earthworm ecology, properties of the soil, and earthworm modifications of cast microflora.  相似文献   

17.
《CATENA》2001,44(2):111-132
The weathering of a Late Miocene gypsum-calcareous mudstone outcropping in large badland areas of SE Spain, under a semi-arid Mediterranean climate, was studied by means of two experimental approaches. Field and laboratory experiments were carried out to reproduce, though in accelerated form, some of the weathering conditions of the consolidated mudstone. In the laboratory, three sequences of 5, 10 and 20 wetting–drying cycles were produced on undisturbed blocks of fresh mudstone samples. At the end of the three sequences, samples were analysed for their micromorphology, elemental and soluble salt chemistry, and total mineralogy. Unweathered dry samples, as blanks, and permanently wet samples were also analysed. In the field, two small plots of freshly exposed mudstone were monitored over 3 years for their response to natural weathering in terms of morphological changes and sediment output. The porosity was increased by a few wetting–drying cycles, as assessed by significant increases in water absorption capacity of the mudstone. A combination of three factors is responsible for mudstone weathering: repeated cycles of wetting–drying, the presence of geologically-induced cracks and fissures, and dissolution–crystallisation of relatively soluble minerals, gypsum being the most abundant within this category. A few wetting–drying cycles were sufficient to reveal ion migration (specially Na+, Ca++, Mg++, SO4−, HCO− and Cl−) within the mudstone, explaining mineral dissolution. In the field, surface weathering rates from 0.7 to 8 mm year−1 were measured. Weathering rates were found to be proportional to the number of rainfall events during the sampling periods, confirming what was found in laboratory conditions, namely, that the number of wetting–drying cycles has the greatest influence on weathering. These weathering rates might be considered as the probable range of incision rates under present semi-arid conditions.  相似文献   

18.
Unpaved roads play an important role in soil loss in small watersheds. In order to assess the impact of these unpaved roads in the Loess Plateau of China, runoff and sediment yields from road‐related sources must be quantified. Field rainfall simulation experiments were conducted under three slope gradients and five rainfall intensities on unpaved loess roads in a small watershed. Results showed that the runoff generation was very fast in loess road surface (time to runoff < 1 min) and produced a high runoff coefficient (mean value > 0·8). Soil loss rates were decreased as surface loose materials were washed away during a rainstorm. Rainfall intensity, initial soil moisture, and slope gradient are key factors to model surface runoff and sediment yield. Soil loss on loess road surface could be estimated by a linear function of stream power (R2 = 0·907). Four commonly interrill erosion models were evaluated and compared, and the interrill erodibility adopted in the Water Erosion Prediction Project model was determined as 1·34 × 106 (kg s m−4). A new equation taking into account different parameters like rainfall intensity, surface flow discharge, and slope gradient was established. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

19.
In the European Union, the maintenance of soil quality is a key point in agricultural policy. The effect of additions of dairy cattle (Bos taurus) manure (DCM) during a period of 11 years were evaluated in a soil under irrigated maize (Zea mays L.) monoculture. DCM was applied at sowing, at wet‐weight rates of 30 or 60 Mg ha−1yr−1 (30DCM or 60DCM). These were compared with a mineral‐N treatment (300 kg N ha−1, MNF), applied at six to eight emerged leaves and with a control (no N, no manure). Treatments were distributed in a randomized block design. Factors analysed were stability against wetting stress disaggregation, porosity, soil organic carbon (SOC) fractions and earthworm abundance, studied eight months after the last manure application. The application rate of 30DCM increased aggregate stability and the light SOC fraction, but not the pore volume, nor the earthworm abundance, compared with MNF. The DCM rates did not result in unbalanced agronomic advantages versus MNF, as high yields (12–16 Mg ha−1 yr−1) were obtained. In Mediterranean environments, the use of DCM should be encouraged mainly because of its contribution to the light SOC fraction which protects dry macro‐aggregates from implosion (slaking) during the wetting process. Thus, in intensive agricultural systems, it protects soil from physical degradation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

20.
Soil erosion has serious off-site impacts caused by increased mobilization of sediment and delivery to water bodies causing siltation and pollution. To evaluate factors influencing soil erodibility at a proposed dam site, 21 soil samples collected were characterized. The soils were analyzed for soil organic carbon (SOC), exchangeable bases, exchangeable acidity, pH, electrical conductivities, mean weight diameter and soil particles’ size distribution. Cation exchange capacity, exchangeable sodium percentage, sodium adsorption ratio, dispersion ratio (DR), clay flocculation index (CFI), clay dispersion ratio (CDR) and Ca:Mg ratio were then calculated. Soil erodibility (K-factor) estimates were determined using SOC content and surface soil properties. Soil loss rates by splashing were determined under rainfall simulations at 360?mmh?1 rainfall intensity. Soil loss was correlated to the measured chemical and physical soil properties. There were variations in soil form properties and erodibility indices showing influence on soil loss. The average soil erodibility and SOC values were 0.0734?t?MJ?1?mm?1 and 0.81%, respectively. SOC decreased with depth and soil loss increased with a decrease in SOC content. SOC significantly influenced soil loss, CDR, CFI and DR (P??1. Addition of organic matter stabilize the soils against erosion.  相似文献   

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