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1.
This research aims to improve erosion control practice in the Loess Plateau, by studying the surface erosion processes, including splash, sheet/interrill and rill erosion in four contrasting soils under high rainfall intensity (120 mm h−1) with three-scale indoor artificial experiments. Four contrasting soils as sandy loam, sandy clay loam, clay loam and loamy clay were collected from different parts of the Loess Plateau. The results showed that sediment load was significantly impacted by soil properties in all three sub-processes. Splash rate (4.0–21.6 g m−2∙min−1) was highest in sandy loam from the north part of the Loess Plateau and showed a negative power relation with the mean weight diameter of aggregates after 20 min of rainfall duration. The average sediment load by sheet/interrill erosion (6.94–42.86 g m−2∙min−1) was highest in clay loam from middle part of the Loess Plateau, and the stable sediment load after 20 min showed a positive power relation with the silt content in soil. The average sediment load increased dramatically by rill and interrill erosion (21.03–432.16 g m−2∙min−1), which was highest in loamy clay from south part of the Loess Plateau. The average sediment load after the occurrence of rill showed a positive power relation with clay content and a negative power relation with soil organic matter content. The impacts of slope gradient on the runoff rate and sediment load also changed with soil properties. The critical factors varied for different processes, which were the aggregate size for splash erosion, the content of silt particles and slope gradient for sheet/interrill erosion, and the content of clay particles, soil organic matter and slope gradient for rill erosion. Based on the results of the experiments, specific erosion control practices were proposed by targeting certain erosion processes in areas with different soil texture and different distribution of slope gradient. The findings from this study should support the improvement of erosion prediction and cropland management in different regions of the Loess Plateau.  相似文献   

2.
《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   

3.
Soils play a key role in the global carbon cycle, and can be a source or a sink of atmospheric carbon (C). Thus, the effect of land use and management on soil C dynamics needs to be quantified. This study was conducted to assess: (1) the role of aggregation in enhancing soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations for different mulch rates, (2) the association of SOC and TSN with different particle size fractions, and (3) the temporal changes in the SOC concentration within aggregate and particle size fractions with duration of mulching. Two experiments were initiated, one each in 1989 and 1996, on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) in central Ohio. Mulch treatments were 0, 8, and 16 Mg ha−1 yr−1 without crop cultivation. Soil samples from 0–5 cm and 5–10 cm depths were obtained in November 2000; 4 and 11 years after initiating the experiments. Mulch rate significantly increased SOC and TSN concentrations in the 0–5 cm soil layer only. The variation in the SOC concentration attributed to the mulch rate was 41 per cent after 4 years of mulching and 52 per cent after 11 years of mulching. There were also differences in SOC and TSN concentrations among large aggregate size fractions, up to 2 mm size after 4 years and up to 0ċ5 mm after 11 years of mulching. There were also differences in SOC and TSN concentrations among particle size fractions. Variation in the SOC concentration in relation to particle size was attributed to clay by 45–51 per cent, silt by 34–36 per cent, and to sand fraction by 15–19 per cent. Bulk of the TSN (62–67 per cent) was associated with clay fraction and the rest was equally distributed between silt and sand fractions. The enrichment of SOC and TSN concentrations in the clay fraction increased with depth. The C:N ratio was not affected by the mulch rate, but differed significantly among particle size fractions; being in the order of sand >silt >clay. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

4.
《Geoderma》1986,37(1):29-43
The effect of antecedent moisture on rainfall erosion was evaluated in a series of field experiments by applying artificial rainfall at 50 mm h−1 (0.189 J m−2 s−1), to two Gray-Brown Luvisols on plots of 7.8 m2. The measured soil loss is significantly related to antecedent moisture. Extrapolations from the data indicate that soil loss may differ by as much as 800 times if the full range of antecedent soil moisture is considered. For the Guelph silt loam, the maximum soil moisture effect was observed at 20 min after the beginning of simulated rainfall.Torsional shear strength of remoulded samples at field bulk density was determined by using a mechanized torvane. Field shear strength was then estimated on the basis of the shear strength-soil moisture relationship established in the laboratory. Because sharp changes in both soil shear strength and soil loss were observed around the ‘vane shear’ liquid limit, we suggest that the influence of soil moisture is at least in part expressed via soil strength.  相似文献   

5.
Knowledge of the generation of subsurface flow for hillslopes is important for controlling agricultural nonpoint nutrient losses. This study used a physically based hillslope hydrologic model HYDRUS‐2D to assess the sensitivity of simulated subsurface flow to the interactions between precipitation, soil texture and land use. Soil moisture data from 1 January 2013 to 23 August 2014 at two monitoring sites on a tea plantation hillslope were used to calibrate the van Genuchten–Mualem hydraulic parameters for this model. For six different textural classes (loamy sand, loam, silt, silt loam, clay loam and clay) and four land‐use types (tea garden, forest, grassland and bare soil), scenario‐based simulations were carried out for varied precipitation intensities (6.0, 15.0, 30.0, 45.0, 60.0 and 76.0 mm/day) and frequencies (time intervals of 1, 5, 10, 15, 20 and 25 days). Results indicated that the hillslope run‐off was dominated by subsurface flow, which was influenced by precipitation and antecedent moisture conditions. A threshold value of 0.18 m3/m3 of mean hillslope soil moisture was observed for the initiation of subsurface flow. High precipitation intensity (i.e. 75.0 mm/day) substantially increased subsurface flow for all soil textures. In addition, the sensitivity of the bare soil hillslope to rainfall patterns was more than two times higher than that of the vegetated (i.e. grassland, tea garden and forest) hillslope. These findings suggest that extreme precipitation events and land‐use change will increase the risks of subsurface flow on hillslopes. Therefore, optimal fertilizer application strategy and land‐use planning should be proposed for controlling the hillslope nonpoint nutrient losses.  相似文献   

6.
Degradation of soil physical quality, following deforestation and cultivation, is a major soil‐related constraint to an intensive use of soil for crop production in subhumid regions of subSaharan Africa. Use of crop residue mulch is an important strategy to minimize the risks of soil degradation. Therefore, a three‐year experiment was conducted to study the effects of five rates of mulch application (0, 2, 4, 6 and 8 Mg ha−1 season−1) on soil physical properties and growth and yield of maize (Zea mays). Mulch rate of rice straw significantly increased maize grain and stover yields during the first season, and the stover yield during the second season. In comparison with the control, the grain yield increased by 20 per cent at 2 Mg ha−1 of mulch rate and by 33 per cent at 8 Mg ha−1 of mulch rate. The rate of increase was 0·16 Mg ha−1 for grain yield and 0·38 Mg ha−1 for stover yield for every Mg of mulch applied. The increase in stover yield during the second season was 67 per cent for 8 Mg ha−1 mulch rate compared with the unmulched control. Effects of mulch rate on soil physical properties were confined mostly to the surface 0–5 cm depth. For this depth, mulching decreased bulk density from 1·17 Mg m−3 for control to 0·98 Mg m−3, and penetration resistance from 1·54 kg cm−2 to 1·07 kg cm−2 for 8 Mg ha−1 of mulch rate. Application of mulch up to 16 Mg ha−1 yr−1 for three consecutive years had no effect on soil physical properties below 5 cm depth. Experiments were probably not conducted for a long enough period. For mulch farming to be adopted by farmers of West Africa, it must be an integral part of the improved farming system. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

7.
Agricultural activities emit greenhouse gases (GHGs) and contribute to global warming. Intensive plough tillage (PT), use of agricultural chemicals and the burning of crop residues are major farm activities emitting GHGs. Intensive PT also degrades soil properties by reducing soil organic carbon (SOC) pool. In this scenario, adoption of no‐till (NT) systems offers a pragmatic option to improve soil properties and reduce GHG emission. We evaluated the impacts of tillage systems (NT and PT) and wheat residue mulch on soil properties and GHG emission. This experiment was started in 1989 on a Crosby silt loam soil at Waterman Farm, The Ohio State University, Columbus, Ohio, USA. Mulching reduced soil bulk density and improved total soil porosity. More total carbon (16.16 g kg−1), SOC (8.36 mg L−1) and soil microbial biomass carbon (152 µg g−1) were recorded in soil under NT than PT. Mulch application also decreased soil temperature (0–5 cm) and penetration resistance (0–60 cm). Adoption of long‐term NT reduced the GHG emission. Average fluxes of GHGs under NT were 1.84 g CO2‐C m−2 day−1 for carbon dioxide, 0.07 mg CH4‐C m−2 day−1 for methane and 0.73 mg N2O‐N m−2 day−1 for nitrous oxide compared with 2.05 g CO2‐C m−2 day−1, 0.74 mg CH4‐C m−2 day−1 and 1.41 mg N2O‐N m−2 day−1, respectively, for PT. Emission of nitrous oxide was substantially increased by mulch application. In conclusion, long‐term NT reduced the GHG emission by improving the soil properties. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

8.
In addition to nitrogen (N), phosphorus (P) and sulfur (S) elements are also essential to conversion of biomass carbon into soil humus. Therefore, soil analyses were done on two long‐term mulching experiments initiated in 1989 and 1996 on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) soil in central Ohio to assess P and S dynamics in soil for different rates of mulching. Mulch treatments were 0, 8 and 16 Mg ha−1 y−1 without any crop cultivation. Our objectives were to assess: (i) the effect of different mulch rates on P and S concentrations, and soil organic carbon sequestration; (ii) association of available and total P and S with different particle size fractions; and (iii) temporal changes in available and total P and total S concentrations within aggregate and particle size fractions with duration of mulching. Soil samples from 0 to 5 and 5 to 10 cm depths were obtained in November 2000. Mulch rate significantly increased Bray‐P in 0 to 5 and 5 to 10 cm depths but had no significant effect on total P after 4 years of mulching. Total P concentration in the 5 to 10 cm layer increased significantly with mulch application after 11 years, but the total S concentration was not affected. Total P in aggregates>2 mm size at 5 to 10 cm depth was significantly higher than whole soil after 11 years of mulching. More than 50 per cent of the total P was associated with clay fraction, and P concentration increased with duration of mulching. The enrichment factor for total P was in the order: clay>sand>silt. Total S concentration in aggregates increased with increase in aggregate size for both depths, and was in the order: clay>sand>silt. The clay fraction accounted for 48 per cent of total S after 4 years of mulching and 50 per cent after 11 years of mulching. The enrichment factor of S in clay and sand fractions increased with duration of mulching and with depth for clay, and decreased for sand. The C:P and C:S ratios decreased both with duration of mulching and particle size. Availability of P and S is essential for humification of carbon input in crop residue mulch. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

9.
Soil erosion and runoff were monitored from 1988 to 1990 on a Miamian soil (Typic Hapludalf) of 5-6 per cent slope using field runoff plots. Four treatments were studied: (i) disk-plough up and down the slope to 0.3 m depth (DP); (ii) disk-plough up and down the slope followed by a protective netting (PN); (iii) uncultivated fallow without any vegetation followed by surface soil removal (R); (iv) uncultivated fallow with natural vegetation followed by ploughing (F). Mean annual runoff losses were 6, 114 and 128 mm, or 4, 20 and 18 per cent of the rainfall, and mean annual soil losses were 1.2, 85.0 and 64.0 Mg ha−1 in 1988, 1989 and 1990, respectively. Mean runoff amounts were 26, 69, 116 and 118mm and mean annual soil losses were 0.4, 23.2, 58.6 and 118 Mg ha−1 for the F, PN, DP and R treatments, respectively. In comparison with DP, PN decreased annual runoff by 40.3 per cent and annual soil loss by 79.5 per cent. The high mean soil loss for the R treatment was due to erosion following soil removal. An additional 2920 Mg ha−1 of surface soil was removed from the R treatment in May 1990. The F treatment reduced runoff by 78, 77 and 62 per cent and reduced soil loss by 99.7, 99.4 and 98.4 per cent compared with the R, DP and PN treatments, respectively. Mean losses of K, Ca, Mg and P were 1.3, 4, 1 and 01 kg ha−1, respectively for F, 3, 16, 5 and 0.3kg ha−1, respectively, for PN, 5, 31, 1 and 0.6kg ha−1, respectively, for DP, and 3, 32, 12 and 0.4 kg ha−1, respectively, for R. Soil and nutrient losses for each treatment were in the order R > DP > PN > F. The soil organic carbon (SOC) content was significantly affected by soil erosion and management treatments, and ranged from 0.98 per cent for the R treatment to 2.3 per cent for the F treatment. Soil surface removal for the R treatment in 1990 reduced water-stable aggregates (WSA) by 9.0 per cent, SOC by 0.6 per cent, and clay content of the uppermost 0-50 mm depth by about 7.0 per cent. Mean total porosity (ft) ranged from 0.43 for the F to 0.52 for the DP treatment. Cumulative infiltration for 3h ranged from 13 cm for R to 34cm for PN, with corresponding infiltration rates of 4 cm h−1 and 13 cm h−1, respectively. Regardless of the treatment, there were also temporal changes in soil properties. In comparison with 1988, measurements made in 1990 showed a significant decrease in WSA of 21.3 per cent, an increase in clay content of 2.8 per cent, and a decrease in SOC of 0.39 per cent. Runoff and soil losses were significantly correlated with the mean weight diameter (MWD), SOC, bulk density (pb) and available water capacity (AWC). Plant height measured 8 weeks after planting (WAP) for the R treatment was reduced by 33.3 per cent, 33.0 per cent and 29.0 per cent compared withh DP, PN and F, respectively. Nitrogen uptake by maize plants (Zea mays L.) 10 WAP for the R treatment was lower by 15 per cent, 8 per cent, and 6 per cent compared with the DP, PN and F treatments, respectively, while P uptake was lower by 33 per cent, 32 per cent and 29 per cent, respectively, compared with the same treatments. Grain yield was 9.78 Mg ha−1 for PN, 9.76 Mg ha−1 for DP, 8.64 Mg ha−1 for F and 6.60 Mg ha−1 for R during the 1990 crop season. Grain yield was reduced by about 32.4 per cent in the R treatment compared with the PN treatment, representing a maize grain yield reduction of 158 kg ha−1 for each centimeter of soil lost.  相似文献   

10.
The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL−1 and was below the Japanese standard (10 BqˑL−1). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL−1) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL−1) and forest (0.7–5.2 BqˑL−1) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha−1 yr−1 following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr−1 for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha−1) contents.  相似文献   

11.
《Geoderma》2002,105(1-2):125-140
This paper presents a method that can be used to quantify and map soil losses at field scale produced by extreme rainfall events. The amounts of sediment produced by overland flow and concentrated overland flow (inter-rill, rill and gully erosion) at the agricultural plot scale are evaluated from elevation differences computed from very high resolution digital elevation models (DEMs), from before and just after an extreme rainfall event. Geographical Information Systems (GIS) techniques are used to analyse the multi-temporal spatial data. The research case study presented makes reference to a mechanised vineyard plot located in the Alt Penedès–Anoia region (Catalonia, Spain). The rainfall event, which occurred in June 2000, registered 215 mm, 205 mm of which fell in 2 h 15 min. The average intensity of the downpour was 91.8 mm h−1, with a maximum intensity in 30-min periods of up to 170 mm h−1. The erosivity index R reached a value of 11,756 MJ ha−2 mm h−1, 10 times greater than the annual value for this area. The volume of soil detached by the rainfall, as measured by the proposed method, was 828±19 m3. About 57% of those materials were deposited in other parts within the same plot. The balance was negative, with a total 352±36 m3 of soil loss from the plot, which represented a rate of 207±21 Mg ha−1. The paper analyses the characteristics of the rainfall event in relation to historical data and discusses the proposed method for soil erosion mapping at plot scales in relation to other measurement methods.  相似文献   

12.
Computer simulation was used for predictive analysis of the effects of weather and soil type on crop yield in the U.S.crop insurance program.The Environmental Policy Integrated Climate (EPIC) model was modified to include hail weather events,which completed the modifications necessary to simulate the four most frequent causes of crop yield loss (hail,excessive wet,excessive cold,and excessive dry) associated with soil type in Kansas,USA.At the region level,per hectare yields were simulated for corn,wheat,soybean,and sorghum.We concluded that it was possible to predict crop yields through computer simulation with greater than 93% accuracy.The hail damage model test indicated EPIC could predict hail-soil-induced yield losses reasonably well (R2 > 0.6).The investigation of soil type influence on dryland sorghum and wheat production indicated that Wymore silty clay loam soil and Kenoma silt loam produced the highest sorghum yields statistically;Kuma silt loam,Roxbury silt loam,Crete silty clay loam,and Woodson silt soils produced the second highest sorghum yields statistically;and Richfiled silt loam,Wells loam,and Canadian sandy loam produced the lowest sorghum yields.By contrast,wheat production showed less sensitivity to soil type variation.The less sensitive response of wheat yields to the soil type could be largely due to the unconsidered small-scale variability of soil features.  相似文献   

13.
In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl2 and Ca(NO3)2 of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg2+ and Ca2+ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.  相似文献   

14.
《CATENA》2004,55(1):79-90
Vineyards are one of the lands that incur the highest soil losses in Mediterranean environments. Most of the studies that report about this problem only focus on soil losses and few investigations have addressed the nutrient losses associated with erosion processes during the storms. The present research evaluates the loss of nitrogen, phosphorus and potassium in vineyard soils located in a Mediterranean area (NE Spain), after an extreme rainfall event recorded on 10 June 2000. The total rainfall of this event was 215 mm, 205 mm of which fell in 2 h 15 min. The maximum intensity in 30-min periods reached 170 mm h−1. This rainfall produced a large amount of sediments both inside and outside the plots, with the consequent soil mobilisation and loss of nutrients. The estimate of soil loss was based on the subtraction of two very accurate digital elevation models (DEMs) of different dates in GIS, and measures of the nutrient content of sediment collected in the plot. Soil loss in the study plot reached 207 mg ha−1. Most sediment was produced by concentrated surface runoff. Nutrient losses amounted as 108.5 kg ha−1 of N, 108.6 kg ha−1 of P and 35.6 kg ha−1 of K. The proposed method allowed mapping the sediment contribution and deposition areas and the distribution of the nutrient load and losses within the plot.  相似文献   

15.
This research aimed to determine the optimum nitrogen fertilization rate on three soils for producing biomass sweet sorghum (Sorghum bicolor cultivar M81E) and corn (Zea mays cultivar P33N58) grain yield and to compare their responses. The research was conducted in Missouri in rotations with soybean, cotton, and corn. Seven rates of nitrogen (N) were applied. Sweet sorghum dry biomass varied between 11 and 27.5 Mg ha?1) depending on year, soil type, and N rate. Nitrogen fertilization on the silt and sandy loam soils had no effect (P > 0.05) on sweet sorghum yield grown after cotton and soybean. However, yield increased in the clay soil. Corn grain yielded from 1.3 to 12.9 Mg ha?1, and 179 to 224 kg N ha?1 was required for maximum yield. Increasing biomass yield required N application on clay but not on silt loam and sandy loam in rotations with soybean or cotton.  相似文献   

16.
Abstract. Usual residue-management options are to remove the residue, use it as mulch with or without undercutting or to incorporate it into the soil. While the role of surface mulch in evaporation has been widely studied, the information on the effect on evaporation of mulch with undercutting or residue incorporated into soil, particularly in relation to soil type and evaporativity (Eo) is lacking. We studied the effect of wheat straw used in various ways on the course of evaporation loss from soil columns with three soils at Ludhiana, India and one soil at Bushland, Texas, USA, under two Eo's Energy-limited evaporation rates under mulch (Eom) followed the soil-specific relation Eom/Eo= a e(bRes+cEo), where Res is residue rate t/ha and a, b and c are constants; Eo, is expressed in mm/d. In an effort to model the total evaporation (CE) during the energy-limited stage ‘U’ was obtained from appropriate CE versus time curves and (CE-U) was regressed over (t - ti)0.5 to obtain the slope ‘α’ (Ritchie 1972) for the soil-limited evaporation stage. The observed ‘U’ was independent of mulch rate and Eo but was strongly affected by soil type, Values of ‘α’ decreased with increase in mulch rate and decrease in Eo and coarseness of soil. The otherwise short lived benefit of evaporation reduction with mulch per se, which peaked after a few days was maintained when residue was mixed with soil at the stage when evaporation reduction reached a maximum; this benefit continued for several weeks. Cumulative evaporation values computed from ‘U’ and ‘α’ agreed closely with the observed values under straw mulch for loamy sand and clay loam soils and for ‘undercut’ and ‘residue mixed’ treatments on all soils regardless of Eo, and for all situations under small Eo. However, for sandy loam and silt loam soils under Eo of 10 mm/d, the modified square root of the time function of Jalota et al. (1988) gave a better fit.  相似文献   

17.
Applying constant precipitation intensity, which does not occur in natural events, is one of the main limitations concerning rainfall simulators in soil erosion studies. The present work evaluated the InfiAsper rainfall simulator operating with a new control panel to program rainfalls with different precipitation intensities (PI). Infiltration rates and soil and water losses were evaluated in a Distrophic Acrisol (clay loam texture) with simulated rainfalls of 30 mm and duration of 40 min, considering advanced (AD), intermediate (IN), delayed (DE), and inverted intermediate (II) patterns, all with PI peaks of 110 mm h?1, and a constant (CT) pattern. The experimental design was in randomized blocks with five treatments (rainfall patterns) and experimental units measuring 2.5 × 2.5 m. The simulator worked satisfactorily, applying the rainfall according to the preconfigured programs. The simulated rainfall with the CT and II patterns did not promote runoff nor soil loss. Infiltration and runoff rates varied according to the applied rainfall pattern, reaching 97.8 and 27.3 mm h?1 (AD), 82.1 and 39.5 mm h?1 (IN), and 76.2 and 49.7 mm h?1 (DE), respectively. Soil loss and surface runoff totaled each 4.77 g m?2 and 3.9 mm (AD), 6.70 g m?2 and 6.8 mm (IN), and 6.03 g m?2 and 7.0 mm (DE). The InfiAsper simulator modified enables varying precipitation intensity besides obtaining satisfactory results in the field and information consistent with the expected characteristics of natural rainfall patterns. In the intermediate and delayed rainfall patterns, soil and water losses are higher than in the advanced.  相似文献   

18.
Subsistence farmers in Africa depend largely on the soil organic matter to sustain crop productivity. Long-term changes in soil organic carbon and nitrogen were measured after woodland clearance for smallholder subsistence farming or for commercial farming. The contents of organic carbon and nitrogen in soil under reference woodlands were largest (53.3 t C ha−1, 4.88 t N ha−1) in a red clay soil (∼ 50% clay + silt), followed by a granitic sand (∼ 12% clay + silt; 22.8 t C ha−1, 1.47 t N ha−1) and least (19.5 t C ha−1, 0.88 t N ha−1) in a Kalahari sand (∼ 5% clay + silt). Organic carbon declined rapidly under cultivation to attain new equilibria within 10 years on all smallholdings. Greatest losses occurred in soils that initially contained most carbon and nitrogen in the order: red clay (22.4 t C ha−1 and 1.0 t N ha−1) > granitic sand (13.2 t C ha−1 and 0.8 t N ha−1) > Kalahari sand (10.6 t C ha−1 and 0.5 t N ha−1). On the clay soil, commercial farming with intensive use of mineral fertilizers and incorporation of maize stover led to more gradual decline: at equilibrium, contents of carbon and nitrogen were 15 t C ha−1 and 1.7 t N ha−1 greater than on smallholdings with similar soil and climate. In the Kalahari sand the δ13C of organic C remained constant after woodland clearance, and maize contributed less than 10% of the total C even after 55 years. The δ13C signature increased slightly with increasing duration of cultivation by smallholders in the granitic sands and red clay soil where maize contributed 29% and 35% of the C at equilibrium. Under more productive commercial farming, the carbon derived from maize accounted for 50% of the total after 10 years of cultivation and 67% at equilibrium. The persistence of woodland carbon in the sandy soil is attributed to chemical stabilization resulting from large concentrations of lignin and polyphenols in the tree litter, or as charcoal.  相似文献   

19.
Water-repellent(WR) soil greatly influences infiltration behavior. This research determined the impacts of WR levels of silt loam soil layer during infiltration. Three column scenarios were utilized, including homogeneous wettable silt loam or sand, silt loam over sand(silt loam/sand), and sand over silt loam(sand/silt loam). A 5-cm thick silt loam soil layer was placed either at the soil surface or 5 cm below the soil surface. The silt loam soil used had been treated to produce different WR levels, wettable, slightly WR, strongly WR, and severely WR. As the WR level increased from wettable to severely WR, the cumulative infiltration decreased. Traditional wetting front-related equations did not adequately describe the infiltration rate and time relationships for layered WR soils. The Kostiakov equation provided a good fit for the first infiltration stage. Average infiltration rates for wettable, slightly WR, strongly WR, and severely WR during the 2 nd infiltration stage were 0.126, 0.021, 0.002, and 0.001 mm min~(-1) for the silt loam/sand scenario,respectively, and 0.112, 0.003, 0.002, and 0.000 5 mm min~(-1) for the sand/silt loam scenario, respectively. Pseudo-saturation phenomena occurred when visually examining the wetting fronts and from the apparent changes in water content(?θ_(AP)) at the slightly WR,strongly WR, and severely WR levels for the silt loam/sand scenario. Much larger ?θAPvalues indicated the possible existence of finger flow. Delayed water penetration into the surface soil for the strongly WR level in the silt loam/sand scenario suggested negative water heads with infiltration times longer than 10 min. The silt loam/sand soil layers produced sharp transition zones of water content. The WR level of the silt loam soil layer had greater effects on infiltration than the layer position in the column.  相似文献   

20.
Soil cover and rainfall intensity (RI) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity (RI) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h− 1) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h− 1 of rain, while under RI of 65 mm h− 1, the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ERSOC) in the sediment. The amount of runoff sediment rather than the ERSOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ERSOC were high and positively correlated with the ER values of particles smaller than 20 µm (p < 0.01). Although the sediment contained substantially more fine fractions (fine silt and clay, < 20 µm), the original soil and runoff sediment were still of the same texture class, i.e. silt clay loam.  相似文献   

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