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1.

Purpose

The impact of agriculture on water resources has long been a problem associated with the formation of runoff, the siltation of lakes and reservoirs, and overall depletion of water quality. In Brazil, these problems are mainly related to soil degradation by water erosion. However, studies of catchment-scale erosion are still rare particularly in grain-producing regions which have adopted conservative tillage systems for soil protection. In order to contribute to a better understanding of the impact of conservation agriculture on water resources, this study determined the runoff coefficient and sediment yield for two agricultural catchments.

Materials and methods

Hydrological and sedimentological monitoring was conducted in two catchments: the Conceicao catchment is characterized by grain production in weathered soils and a gently sloping landscape, while the Guapore catchment is characterized by heterogeneous soils and topography. Both catchments have problems associated with water erosion.

Results and discussion

The magnitudes of annual runoff coefficients and sediment yield were high, even if compared to similar agricultural regions, including a catchment with widespread adoption of no-tillage. The sediment yield was 140 t km?2 year?1, and the runoff coefficient was 14 % for the Conceicao catchment, while the sediment yield was 270 t km?2 year?1, and the runoff coefficient was 31 % for the Guapore catchment. The results indicate that problems such as gullies, soil compaction, runoff, floods, siltation, and water quality depletion associated with the misuse of agricultural areas in terms of soil conservation and water use are still evident and important even in regions with widespread adoption of no-tillage systems.

Conclusions

The magnitudes of both runoff and sediment yield clearly indicate the need to adopt complementary practices of soil conservation measures, such as mechanical runoff control.  相似文献   

2.

Purpose

Hydrosedimentological studies conducted in the semiarid Upper Jaguaribe Basin, Brazil, enabled the identification of the key processes controlling sediment connectivity at different spatial scales (100–104 km2).

Materials and methods

Water and sediment fluxes were assessed from discharge, sediment concentrations and reservoir siltation measurements. Additionally, mathematical modelling (WASA-SED model) was used to quantify water and sediment transfer within the watershed.

Results and discussion

Rainfall erosivity in the study area was moderate (4600 MJ mm ha?1 h?1 year?1), whereas runoff depths (16–60 mm year?1), and therefore the sediment transport capacity, were low. Consequently, ～60 % of the eroded sediment was deposited along the landscape, regardless of the spatial scale. The existing high-density reservoir network (contributing area of 6 km2 per reservoir) also limits sediment propagation, retaining up to 47 % of the sediment at the large basin scale. The sediment delivery ratio (SDR) decreased with the spatial scale; on average, 41 % of the eroded sediment was yielded from the hillslopes, while for the whole 24,600-km2 basin, the SDR was reduced to 1 % downstream of a large reservoir (1940-hm3 capacity).

Conclusions

Hydrological behaviour in the Upper Jaguaribe Basin represents a constraint on sediment propagation; low runoff depth is the main feature breaking sediment connectivity, which limits sediment transference from the hillslopes to the drainage system. Surface reservoirs are also important barriers, but their relative importance to sediment retention increases with scale, since larger contributing areas are more suitable for the construction of dams due to higher hydrological potential.  相似文献   

3.
Cadmium (Cd), a naturally occurring element, is a potentially biotoxic metal in terrestrial and aquatic ecosystems. Whether it is biotoxic or not will depend upon the concentration in the soil, its bioavailability and its potential transfer through the ecosystem. However, little data are available for losses to waterways, especially via surface runoff. A study was conducted on two long-term trials under pasture to determine how the concentration of Cd in the soil was affected by different irrigation and fertiliser regimes and in turn how this affected the potential for transfer in surface runoff and outwash of flood irrigation. Concentrations of total Cd in the soil varied from 0.06 to 0.58 mg kg?1 and reflected different rates of P fertiliser applied (from 0 to 376 kg superphosphate ha?1?year?1), but was also less (20–25% compared to dryland) in treatments receiving more frequent irrigation when the same rate of P was applied. This indicated that there was potential for transfer. An experiment using simulated rainfall to generate surface runoff indicated that the major form of Cd lost was dissolved (on average 65% <0.45 μm) and could be predicted by water extraction of the soil. Loads of Cd in outwash were significant (0.17 to 0.92 g ha?1?year?1) and at least as great as the measured leaching losses in other studies. Loads confirmed the loss of Cd from each trial was largely dissolved, and related to soil water-extractable Cd and the frequency of irrigation. While Cd concentrations in sediment from ditches receiving outwash were enriched, indicating potential transfer to waterways, the effect will likely be small due to dilution and sorption by sediment and thereby localised to areas closer to the farm. However, to minimise any potential impact, management should be directed to minimising the occurrence of outwash (e.g. by better irrigation timing) or Cd transfer by using less Cd-rich P fertiliser or minimising P fertiliser use in areas susceptible to surface runoff.  相似文献   

4.

Purpose

The Isábena catchment (445 km2), Spain, features highly diverse spatial heterogeneity in land use, lithology and rainfall. Consequently, the relative contribution in terms of water and sediment yield varies immensely between its subcatchments, and also temporally. This study presents the synthesis of ~2.5 years of monitoring rainfall, discharge and suspended sediment concentration (SSC) in the five main subcatchments of the Isábena and its outlet.

Materials and methods

Continuous discharge at the subcatchment outlets, nine tipping bucket rainfall and automatic SSC samplers (complemented by manual samples), were collected from June 2011 until November 2013. The water stage records were converted to discharge using a rating curve derived with Bayesian regression. For reconstructing sediment yields, the data from the intermittent SSC sampling needed to be interpolated. We employed non-parametric multivariate regression (Quantile Regression Forests, QRF) using the discharge and rainfall data plus different aggregation levels of these as ancillary predictors. The subsequent Monte Carlo simulations allowed the determination of monthly sediment yields and their uncertainty.

Results and discussion

The stage–discharge rating curves showed wide credibility intervals for the higher stages, with great uncertainties associated with the discharge rates, especially during floods. The water yield of the subcatchments differed considerably. The entire catchment’s output was dominated by the northernmost subcatchment (~360 mm year?1). The smaller, southern subcatchments featured much higher variability and lower runoff rates (55–250 mm year?1). The SSCs exhibited a wide range and can exceed 100 g l?1 for the central subcatchments, where most of the badlands are located. For the reconstruction of the sedigraphs, the QRF method proved suitable with Nash–Sutcliffe indices of 0.50 to 0.84. The specific sediment yield ranges from relatively low (32 t km?2 year?1) in the highly vegetated north to high values (3,651 t km?2 year?1) in areas with many badland formations.

Conclusions

The Isábena catchment shows high erosion dynamics with great variability in space and time, with stark contrasts even between adjacent subcatchments. The natural conditions make water and sediment monitoring and instrumentation very challenging; the measurement of discharge is particularly prone to considerable uncertainties. The QRF method employed for reconstructing sedigraphs and monthly yields proved well suited for the task.  相似文献   

5.
Development of improved soil erosion and sediment yield prediction technology is required to provide catchment stakeholders with the tools they need to evaluate the impact of various management strategies on soil loss and sediment yield in order to plan for the optimal use of the land. In this paper, a newly developed approach is presented to predict the sources of sediment reaching the stream network within Masinga, a large‐scale rural catchment in Kenya. The study applies the revised universal soil loss equation (RUSLE) and a developed hillslope sediment delivery distributed (HSDD) model embedded in a geographical information system (GIS). The HSDD model estimates the sediment delivery ratio (SDR) on a cell‐by‐cell basis using the concept of runoff travel time as a function of catchment characteristics. The model performance was verified by comparing predicted and measured plot runoff and sediment yield. The results show a fairly good relationship between predicted and measured sediment yield (R2=0·82). The predicted results show that the developed modelling approach can be used as a major tool to estimate spatial soil erosion and sediment yield at a catchment scale. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

6.

Purpose

Closed erosion plots have been used extensively to investigate soil loss and its spatial variation within a watershed. However, erosion rates measured on closed plots at various locations within a watershed may not reflect the “real world” conditions due to plot boundary problems. The purpose of this study was to identify runoff and sediment sources in a semi-arid, complex terrain catchment by using the data collected from open plots, nested catchments, and tunnel systems.

Materials and methods

The study catchment, in the Loess Plateau of China, was partitioned into various-level geomorphic units. Runoff and sediment discharges were measured from 55 storm events between 1963 and 1968 on open plots and nested catchments. Storm flows were also monitored in 14 rainfall events from the tunnel systems between 1989 and 1990. This study combined the data collected from the two periods to investigate runoff and sediment sources from the different geomorphic units of the catchment.

Results and discussion

On the four open plots (S1, S2, S3, and S4) of the hill slope, total runoff depths of 128.5 mm (S1), 84.3 mm (S2), 101.92 mm (S3), and 141.73 mm (S4) were recorded from all the events over the first period, which correspondingly produced total sediment yields of 3.056 kg m?2 (S1), 9.058 kg m?2 (S1), 42.848 kg m?2 (S3), and 97.256 kg m?2 (S4). The number of runoff events also varied due to a non-uniformity in runoff generation among the different geomorphic units of the catchment. Tunnel flows generally had higher mean sediment concentrations than catchment outflows. Three nested catchments located from the headwaters (C1) to the mouth of the catchment (C3) generated total runoff depths of 120.02 mm (C1), 143.92 mm (C2), and 149.43 mm (C3), and correspondingly produced sediments yields of 62.01 kg m?2 (C1), 144.02 kg m?2 (C2), and 123.92 kg m?2 (C3) for the first period.

Conclusions

Significant variations in runoff and erosion existed within the catchment. The spatial variation of runoff generation on the hill slopes resulted from the variation of soil infiltration. Sediment produced from the lower hill slope zone was disproportionally higher than that from the upper hill slope zone. Nevertheless, a significant portion of the sediment eroded on the lower slope zone was caused by runoff generated from the upper slope zone. Tunnel erosion also played a significant role in sediment production.  相似文献   

7.

Purpose

Severe soil erosion is caused by wind and water acting separately or in combination or sequentially and is an important factor affecting dryland ecosystems, especially in the severely eroded “water–wind erosion crisscross region” on the Loess Plateau. Thus, the aim of the study was to determine the magnitudes of wind and water erosion under simulative conditions and explore the mechanisms of their interactions.

Materials and methods

We analyzed the interaction between these two types of erosion by exposing a sandy loessial soil with an artificial rill to simulated wind at four speeds (0, 1, 8, and 15 m s?1) and then to simulated rainfall, measuring runoff, sediment yield, and characterizing changes in rill morphology. This simulated the transition period between the dry (windy) and wet seasons.

Results and discussion

The time to runoff initiation depended on both wind speed and rainfall intensity, but rainfall had a larger impact on runoff. At the 15 m s?1 wind speed, the total runoff significantly (P?<?0.05) increased by 33.3 kg when the rainfall intensity was increased to 120 from 60 mm h?1. Under the 120 mm h?1 rainfall intensity, the total sediment yields increased significantly (P?<?0.05) with increasing wind speed. Erosion sediment yields increased by 9.7, 16.3, and 70.4 % with increasing wind speed under all three rainfall intensities when compared with a no wind case. Changes in rill morphology caused by wind erosion were a factor that affected the erosion processes of subsequent rainstorms.

Conclusions

Our results provide a basis for hypothesizing trends of wind and water erosion, highlight the importance of wind and water erosion acting in conjunction in semi-arid ecosystems, and are conducive for developing a more integrated perspective of wind–water dynamics on the Loess Plateau.
  相似文献   

8.
Mercury (Hg) dynamics was evaluated in contaminated sediments and overlying waters from Tagus estuary, in two sites with different Hg anthropogenic sources: Cala Norte (CNOR) and Barreiro (BRR). Environmental factors affecting methylmercury (MMHg) production and Hg and MMHg fluxes across sediment/water interface were reported. [THg] and [MMHg] in solids (0.31–125 μg g?1 and 0.76–201 ng g?1, respectively) showed high variability with higher values in BRR. Porewater [MMHg] (0.1–63 ng L?1, 0.5–86% of THg) varied local and seasonally; higher contents were observed in the summer campaign, thus increasing sediment toxicity affecting the sediment/water Hg (and MMHg) fluxes. In CNOR and BRR sediments, Hg availability and organic carbon were the main factors controlling MMHg production. Noteworthy, an upward MMHg diffusive flux was observed in winter that was inverted in summer. Although MMHg production increases in warmer month, the MMHg concentrations in overlying water increase in a higher proportion compared to the levels in porewaters. This opposite trend could be explained by different extension of MMHg demethylation in the water column. The high concentrations of Hg and MMHg and their dynamics in sediments are of major concern since they can cause an exportation of Hg from the contaminated areas up to ca. 14,600 mg year?1 and an MMHg deposition of up to ca. 6000 mg year?1. The results suggest that sediments from contaminated areas of Tagus estuary should be considered as a primary source of Hg for the water column and a sink of MMHg to the sedimentary column.  相似文献   

9.
The impacts of soil erosion on soil structure, nutrient, and microflora have been extensively studied but little is known about the responses of autotrophic bacterial community and associated carbon (C)-fixing potential to soil erosion. In this study, three abandoned croplands (ES1, ES2, and ES3) and three check dams (DS1, DS2, and DS3) in the Qiaozi watershed of Chinese Loess Plateau were selected as eroding sites and depositional sites, respectively, to evaluate the impacts of soil erosion on autotrophic bacterial community and associated C-fixing potential. Lower abundance and diversity of autotrophic bacteria were observed in nutrient-poor depositional sites compared with nutrient-rich eroding sites. However, the relative abundances of obligate autotrophic bacteria, such as Thiobacillus and Synechococcus, were significantly enhanced in depositional sites. Deposition of nutrient-poor soil contributed to the growth of obligate autotrophic bacteria. The maximum microbial C-fixing rate was observed in DS1 site (5.568?±?1.503 Mg C km?2 year?1), followed by DS3 site (5.306?±?2.130 Mg C km?2 year?1), and the minimum was observed in ES2 site (0.839?±?0.558 Mg C km?2 year?1). Soil deposition significantly enhanced microbial C-fixing rate. Assuming a total erosion area of 1.09?×?107 km2, microbial C-fixing potential in eroded landscape can range from 0.01 to 0.06 Pg C year?1. But its effect on the C pool recovery of degraded soil is limited. Dissolved organic C (DOC) was the main explanatory factor for the variation in soil microbial C-fixing rate (72.0%, P?=?0.000).  相似文献   

10.
Abstract

Nitrous oxide (N2O) emissions were measured monthly over 1 year in three ecosystems on tropical peatland of Sarawak, Malaysia, using a closed-chamber technique. The three ecosystems investigated were mixed peat swamp forest, sago (Metroxylon sagu) and oil palm (Elaeis guineensis) plantations. The highest annual N2O emissions were observed in the sago ecosystem with a production rate of 3.3 kg N ha?1 year?1, followed by the oil palm ecosystem at 1.2 kg N ha?1 year?1 and the forest ecosystem at 0.7 kg N ha?1 year?1. The N2O emissions ranged from –3.4 to 19.7 µg N m?2 h?1 for the forest ecosystem, from 1.0 to 176.3 µg N m?2 h?1 for the sago ecosystem and from 0.9 to 58.4 µg N m?2 h?1 for the oil palm ecosystem. Multiple regression analysis showed that N2O production in each ecosystem was regulated by different variables. The key factors influencing N2O emissions in the forest ecosystem were the water table and the NH+ 4 concentration at 25–50 cm, soil temperature at 5 cm and nitrate concentration at 0–25 cm in the sago ecosystem, and water-filled pore space, soil temperature at 5 cm and NH+ 4 concentrations at 0–25 cm in the oil palm ecosystem. R2 values for the above regression equations were 0.57, 0.63 and 0.48 for forest, sago and oil palm, respectively. The results suggest that the conversion of tropical peat swamp forest to agricultural crops, which causes substantial changes to the environment and soil properties, will significantly affect the exchange of N2O between the tropical peatland and the atmosphere. Thus, the estimation of net N2O production from tropical peatland for the global N2O budget should take into consideration ecosystem type.  相似文献   

11.

Purpose

The assessment of climate change impacts on the sediment cycle is currently a primary concern for environmental policy analysts in Mediterranean areas. Nevertheless, quantitative assessment of climate change impacts is still a complex task. The aim of this study was to implement a sediment model by taking advantage of sediment proxy information provided by reservoir bottom deposits and to use it for climate change assessment in a Mediterranean catchment.

Materials and methods

The sediment model was utilised in a catchment that drains into a large reservoir. The depositional history of the reservoir was reconstructed and used for sediment sub-model implementation. The model results were compared with gauged suspended sediment data in order to verify model robustness. Then, the model was coupled with future precipitation and temperature scenarios obtained from climate models. Climatological model outputs for two emission scenarios (A2 and B2) were simulated and the results compared with a reference scenario.

Results and discussion

Model results showed a general decrease in soil moisture and water discharge. Large floods, which are responsible for the majority of sediment mobilisation, also showed a general decrease. Sediment yield showed a clear reduction under the A2 scenario but increased under the B2 scenario. The computed specific sediment yield for the control period was 6.33 Mg ha?1 year?1, while for the A2 and B2 scenarios, it was 3.62 and 7.04 Mg ha?1 year?1, respectively. Furthermore, sediment transport showed an increase in its time compression, i.e. a stronger dependence of total sediment yield from the largest event contributions.

Conclusions

This study shows a methodology for implementing a distributed sediment model by exploiting reservoir sedimentation volumes. This methodology can be applied to a wide range of catchments, given the high availability of reservoir sedimentation data. Moreover, this study showed how such a model can be used in the framework of a climate change study, providing a measure of the impact of climate change on soil erosion and sediment yields.  相似文献   

12.
Runoff may cause losses of micronutrients from soils. This can result in environmental problems such as contaminant transfers to water or a decrease in soil fertility. Appropriate soil management may reduce these micronutrient losses. This study examined the effect of applying crop residues to the soil surface on iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) losses by runoff. Runoff and sediment yield were measured on 1-m2 plots using a rainfall simulator with constant 65 mm h?1 intensity. Eight successive rainfall applications were performed at 65 mm each. Corn (Zea mays L.) straw was applied to plots at rates ranging from 0 to 8 t ha?1. Both total and dissolved concentrations of the micronutrients studied were decreased by corn straw applications. After 520 mm cumulative rainfall, total soil losses ranged from 150 to 15354 kg ha?1 depending on the amount of corn straw applied. Total micronutrient concentrations in runoff were as follows: Fe from 14.98 to 611.12 mg L?1, Mn from 0.03 to 0.61 mg L?1, Cu from 0.10 to 1.43 mg L?1, and Zn from 0.21 to 5.45 mg L?1. The relative contribution of the dissolved fraction to the total micronutrient content loss was low, but varied depending on the nutrient, being less than 1 percent for Fe and Mn and almost 10 percent for Zn. Total and dissolved concentrations in runoff of the studied elements decreased exponentially as the rate of applied corn straw increased. In conclusion, the addition of corn straw to soil reduced micronutrient losses.  相似文献   

13.
Considerable attention has been paid recently to the influence of surface rock fragments on hydrological and erosional processes, although much of this research has been done on disturbed soils under laboratory conditions. I have studied the effects of rock fragments on soil infiltration, runoff and erosion under field conditions using simulated rainfall on bare areas of natural soils within typical Mediterranean scrubland characterized by patchily distributed vegetation. Sample areas were chosen where rock fragments cover more than half the surface within unvegetated patches. Twenty experiments were carried out by applying rain at an intensity of 55 mm h?1 for 60 minutes. This approach shows that rock fragments (i) retard ponding and surface runoff, and (ii) give greater steady‐state infiltration rates and smaller interrill runoff discharges, sediment concentrations and interrill erosion rates. A second set of six experiments was carried out by applying rainfall at an intensity of 55 mm h?1 for two runs of 60 minutes. The second run was initiated 10 minutes after the first. During this interval, surface rock fragments were removed in order to measure their effects on infiltration, interrill runoff and erosion rates. In this way, I showed that water and soil losses are reduced by the rock fragments. After the removal of rock fragments the steady‐state infiltration rate diminished from 44.5 to 27.5 mm h?1 and the runoff coefficient, sediment concentration and erosion rates were, respectively, 3, 33 and 39 times greater than they were before the rock fragments were removed.  相似文献   

14.
黄土丘陵沟壑区不同空间尺度流域泥沙输移比研究   总被引：1，自引：1，他引：0  
泥沙输移比是定量表征流域内侵蚀产沙-河道输沙特征的重要指标。探讨了不同尺度流域泥沙输移比计算的可能性与方法,以黄土丘陵沟壑区的径流小区、小流域、水文站实测资料为基础,利用径流小区观测资料和单元小流域侵蚀模数2种方法,对4种空间尺度流域的泥沙输移比进行了估算。结果表明:(1)对于面积在10~100km2的小流域,利用2种方法计算的泥沙输移比结果非常接近,说明在没有小区观测资料时,用单元小流域计算流域泥沙输移比是可行的。(2)对于土壤侵蚀类型单一的水文站控制流域,在没有面积>1km2单元小流域资料的情况下,可以用面积1~10km2小流域或面积10~100km2小流域作为单元小流域来计算泥沙输移比而对于侵蚀类型不同的支流其误差范围有些偏大。(3)流域治理措施的实施对于泥沙输移比的减少具有明显的效果,但治理措施减沙效应的发挥具有一定的滞后性。  相似文献   

15.
Abstract: Soil quality indicators and nematode abundance were characterized in a loessial soil under long‐term conservation tillage to evaluate the effects of no‐till, double‐disk, chisel, and moldboard plow treatments. Indicators included soil electrical conductivity (EC), soil texture, soil organic matter (SOM), and total particulate organic matter (tPOM). Nematode abundance was positively correlated with EC, silt content, and total POM and negatively correlated with clay content. Clay content was the main source of variation among soil quality indicators and was negatively correlated with nematode abundance and most indicators. The gain in SOM in the no‐till system amounted to 10887 kg over the 24 years or 454 kg ha?1 year?1, about half of this difference (45%) resulting from soil erosion in plowed soils. The balance of gain in SOM with no till (249 kg ha?1 year?1) was due to SOM sequestration with no till. No‐till management reduced soil erosion, increased SOM, and enhanced soil physical characteristics.  相似文献   

16.
Abstract

To assess their impacts on net global warming, total greenhouse gas emissions (mainly CO2, N2O and CH4) from agricultural production in arable land cropping systems in the Tokachi region of Hokkaido, Japan, were estimated using life cycle inventory (LCI) analysis. The LCI data included CO2 emissions from on-farm and off-farm fossil fuel consumption, soil CO2 emissions induced by the decomposition of soil organic matter, direct and indirect N2O emissions from arable lands and CH4 uptake by soils, which were then aggregated in CO2-equivalents. Under plow-based conventional tillage (CT) cropping systems for winter wheat, sugar beet, adzuki bean, potato and cabbage, on-farm CO2 emissions from fuel-consuming operations such as tractor-based field operations, truck transportation and mechanical grain drying ranged from 0.424 Mg CO2 ha?1 year?1 for adzuki bean to 0.826 Mg CO2 ha?1 year?1 for winter wheat. Off-farm CO2 emissions resulting from the use of agricultural materials such as chemical fertilizers, biocides (pesticides and herbicides) and agricultural machines were estimated by input–output tables to range from 0.800 Mg CO2 ha?1 year?1 for winter wheat to 1.724 Mg CO2 ha?1 year?1 for sugar beet. Direct N2O emissions previously measured in an Andosol field of this region showed a positive correlation with N fertilizer application rates. These emissions, expressed in CO2-equivalents, ranged from 0.041 Mg CO2 ha?1 year?1 for potato to 0.382 Mg CO2 ha?1 year?1 for cabbage. Indirect N2O emissions resulting from N leaching and surface runoff were estimated to range from 0.069 Mg CO2 ha?1 year?1 for adzuki bean to 0.381 Mg CO2 ha?1 year?1 for cabbage. The rates of CH4 removal from the atmosphere by soil uptake were equivalent to only 0.020–0.042 Mg CO2 ha?1 year?1. From the difference in the total soil C pools (0–20 cm depth) between 1981 and 2001, annual CO2 emissions from the CT and reduced tillage (RT) soils were estimated to be 4.91 and 3.81 Mg CO2 ha?1 year?1, respectively. In total, CO2-equivalent greenhouse gas emissions under CT cropping systems in the Tokachi region of Hokkaido amounted to 6.97, 7.62, 6.44, 6.64 and 7.49 Mg CO2 ha?1 year?1 for winter wheat, sugar beet, adzuki bean, potato and cabbage production, respectively. Overall, soil-derived CO2 emissions accounted for a large proportion (64–76%) of the total greenhouse gas emissions. This illustrates that soil management practices that enhance C sequestration in soil may be an effective means to mitigate large greenhouse gas emissions from arable land cropping systems such as those in the Tokachi region of northern Japan. Under RT cropping systems, plowing after harvesting was omitted, and total greenhouse gas emissions from winter wheat, sugar beet and adzuki bean could be reduced by 18%, 4% and 18%, respectively, mainly as a result of a lower soil organic matter decomposition rate in the RT soil and a saving on the fuels used for plowing.  相似文献   

17.
The aim of this study was to evaluate the effect of biochar and organic soil amendments on soil physicochemical and microbial load, carbon sequestration potential, nutrient uptake and yield of groundnut in acidic red soil under rainfed condition. Biochar was prepared from red gram, cotton, maize stalk and mesquite wood using pilot scale slow pyrolysis biochar unit. The above sources of biochar at the rate of 2.5 and 5 t ha?1 and enriched farmyard manure 0.75 t ha?1, composted coir pith 10 t ha?1 and arbuscular mycorrhizae 100 kg ha?1 were applied as basal with required nitrogen, phosphorous and potassium fertilizer. Biochar amendment at the rate of 5 t ha?1 reduced the bulk density from 1.41 to 1.36 g cm?3 and increased the soil moisture 2.5%. With respect to soil chemical changes, it raised soil pH from 5.7 to 6.3; increased the cation exchange capacity 1.4 cmol+ kg?1 and enhanced the carbon buildup 4.4 t ha?1. The significant differences in bacteria, fungi and actinomycetes population were observed between biochar and control. The nitrogen, phosphorous and potassium were better utilized under biochar and composted coir pith, which was 21, 5 and 20 kg ha?1 higher than control. The experimental results suggested that application of biochar to acidic red soil favoured good soil physical, chemical and biological environment, and these positive changes influenced growth and yield attributes and enhanced pod yield 29% over control.  相似文献   

18.
Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N2O, and N2 emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO 3 ? -rich (340 mg N?kg?1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C2H2, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g?C kg?1 (equivalent to 2.5 t?C ha?1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N2 production (398–524 μg N?kg?1) was significantly higher than N2O (84.6–190 μg N?kg?1) and NO (196–224 μg N?kg?1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N?kg?1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO 3 ? in vegetable soil but enhanced N2O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N2O production reached 13,645–45,224 μg N?kg?1 from soil and could be ranked as RG?>?CMV?>?WS?>?CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils.  相似文献   

19.
Tropical deforestation and land use change is often perceived as the major cause of soil loss by water erosion and of sediment load in rivers that has a negative impact on the functioning of hydropower storage reservoirs. The Sumberjaya area in Sumatra, Indonesia is representative for conflicts and evictions arising from this perception. The purpose of this study as part of a Negotiation Support System approach was to assess sediment yield both at plot and catchment scale and to relate it to a variety of possible clarifying factors i.e. land use, geology, soil and topography. Sediment yield at catchment scale per unit area, was found to be 3–10 times higher than soil loss measured in erosion plots. A stepwise regression showed that the dominant factors explaining sediment yield differences at catchment scale in this volcanic landscape were a particular lithology (Old Andesites) and slope angle followed by the silt fraction of the top soil. In lithologically sensitive areas soil loss at the plot scale under monoculture coffee gardens decreases over time from on average 7–11 Mg ha? 1 yr? 1 to 4–6 Mg ha? 1 yr? 1, mainly because of the development of surface litter layers as filters and top soil compaction in the areas without litter, but remains higher than under shade coffee systems or forest. The runoff coefficient under monoculture coffee remains on average significantly higher (10–15%) than under forest (4%) or under shade coffee systems (4–7%). In lithologically stable areas soil loss remained below 1.8 Mg ha? 1 yr? 1 and the runoff coefficient below 2.5% under all land use types, even bare soil plots or monoculture coffee gardens. Less than 20% of the catchment area produces almost 60% of the sediment yield. The reduction of negative off-site effects on e.g. the life time of a storage reservoir would benefit greatly from an improved assessment of the lithologies in volcanic landscapes and the consideration of potential sediment source and sink areas. In lithologically sensitive areas, a shift from sun to shade coffee systems may result in reducing surface runoff and soil loss, although water erosion at the plot scale is not the main contributor to sediment yield at the catchment scale. The quantification of land use effects on dominant erosive processes such as river bank and river bed erosion, landslides and the concentrated flow erosion on footpaths and roads can contribute to more targeted efforts and relevant incentives to reduce (or live with) sediment load of the rivers.  相似文献   

20.
Phosphorus (P) release from bottom sediments can be a significant source to the overlying water column, potentially maintaining and enhancing algal growth and eutrophic conditions in lakes and reservoirs. Thus, the objectives of this study were to: (1) measure P flux under aerobic and anaerobic conditions from intact sediment cores collected at Beaver Reservoir, northwest Arkansas, (2) evaluate the spatial variability in measured sediment P flux under aerobic and anaerobic conditions along the reservoir, and (3) compare external and internal P loads to Beaver Reservoir. Six intact sediment cores were collected at three sites representing the lacustrine, transitional, and riverine zones during June 2003, September 2003 and February 2004 and incubated for 21 days in the dark at ～22°C. Three cores from each site were incubated under aerobic conditions and anaerobic conditions. Water samples were collected from the overlying water column in each core daily for the first five days and every other day thereafter and analyzed for soluble reactive phosphorus (SRP). Water removed from the core was replaced with filtered lake water, maintaining a constant overlying water volume of 1 l. Sediment P flux under anaerobic conditions (<0.01–1.77 mg m?2 day?1) was generally greater than that measured under aerobic conditions (<0.01–0.89 mg m?2 day?1). Some spatial variability existed in sediment P flux where P flux was generally greatest at the sites in the riverine and transitional zones. Maximum sediment P flux was observed under anaerobic conditions in cores collected from the transitional zone during September 2003. Average sediment P flux under aerobic conditions (0.09 mg m?2 day?1) and anaerobic conditions (0.31 mg m?2 day?1) was greater than the external P flux (0.05 mg m?2 day?1) estimated from the Beaver Reservoir tributaries. Results showed that the annual internal P load (7 Mg year?1) from bottom sediments in Beaver Reservoir was less than 10% of the annual external P load (～81 Mg P year?1). The internal P load was significant, but it would not currently be cost effective to manage this P source given the large surface area of Beaver Reservoir.  相似文献   

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