Multi-parameter fingerprinting of sediment deposition in a small gullied catchment in SE Australia

The determination of relative contributions of potential sediment sources is an important step in the development of management strategies to combat soil erosion. In a 1.2 km² gullied catchment in southeastern New South Wales, multi-parameter fingerprinting of sediment deposited in successive downstream pools has identified gully walls as the dominant sediment source when the grazed pasture surface was the only other potential source. The median fractional contributions remained relatively steady in the successive downstream pools, with the gully walls responsible for between 90% and 98% of the pool sediment. This result was achieved despite the ratio of the source areas varying considerably between successive nested subareas. Reliability bounds on the predictions, accounting for limited sampling of sources, were well constrained and varied between 5.4% and 13.8%. Downstream of an unsealed road crossing, sediment from the road source dominated the pool sediments such that contributions from the pasture surface and gully sources could not be determined.     

Fingerprinting sediment sources in a typical karst catchment of southwest China

Due to the complex hydrogeological conditions in karst regions, it is difficult to measure sediment source contributions at a catchment scale directly. The objective of this study was to quantify the relative contributions of sediment sources and their temporal variability in a karst catchment in southwest China. Karst depressions can trap eroded sediment similar to a dam or reservoir and, thus, are representative and typical test beds for identifying sediment sources in karst regions. Three sediment cores were taken from a karst depression, 58 soil samples from three potential sediment sources were collected, and 18 soil properties were analyzed. The relative contributions of cropland, forestland, and fissure or crack soils were calculated using a multivariate mixing model. The fingerprinting results demonstrated that the cropland was the main sediment source in karst catchment. Specifically, according to the mean sediment contributions of the three deposited sediment cores, the sediment contribution from cropland topsoil was 69.3%, varying from 46.9% to 92.3%, and forestland soil and crack soil accounted for 8.6% and 22.1% of the sediment yield, and varying from 2.8% to 16.5% and 4.8%–36.6%, respectively. This result indicated that great attention should be paid when using only a single core to quantify sediment provenance. Due to the deposited sediment was generally disturbed as cropland in the karst depression, the area that has not been disturbed in recent decades in depression was more appropriate to trace sediment sources in karst catchment. To the best of our knowledge, this study was the first to quantify the contributions of sediment sources in the karst catchment of southwest China. This study provides valuable information and a preliminary reference for applying a composite fingerprinting technique to quantify sediment sources in karst catchments.     

Source areas of phosphorus transfer in an agricultural catchment,south-eastern Norway

Abstract

The strategy to mitigate phosphorus (P) losses in areas of arable cropping in Norway has focused on measures to reduce erosion. Risk assessment of erosion has formed the basis for implementation of the measures. The soil P content has increased during recent decades, motivating an evaluation of its effect on P transfer in the landscape. The present study describes the spatial variability of runoff P concentrations from an agricultural dominated catchment (4.5 km²), representative for agriculture in south-eastern Norway. The concentrations of suspended sediments (SS), total P (TP) and dissolved reactive P (DRP) in runoff from 22 subcatchments (0.3–263 ha) during one year (monthly and during runoff-events) were evaluated. Contributions from point sources were 38 kg TP yr^?1 compared to a total P loss of 685 kg yr^?1 from the whole catchment. During low flow, mean diffuse TP concentration in runoff from subcatchments varied from 28 to 382 µg l^?1. The mean low flow TP concentration was 39 µg l^?1 from the housing area (only diffuse runoff) and 33 µg l^?1 from the forested area. During high flow the highest diffuse TP concentration was measured in an area with high erosion risk and high soil P status. At the subcatchment level the transfer of SS varied from 25 to 175% of the whole catchment SS transfer. Correspondingly for TP, the transfer varied from 50 to 260% of the whole catchment TP transfer. For each of five agricultural subcatchments the slope of the relationship between TP and SS concentrations reflected the mean soil P status of the subcatchment. Erosion risk estimates were closely related to the SS concentration (R²=0.83). The study illustrates that soil P status in addition to soil erosion is an important factor for P transfer.     

元氏石榴品质与岩土地球化学特征关系研究

从农业地质研究的角度出发,探讨了成土母岩、土壤地球化学元素对元氏县石榴品质的影响.调查研究发现,在元氏县山区,品质好、产量高的石榴主要分布在黑云斜长片麻岩区,其主要原因是黑云斜长片麻岩风化层厚,裂隙发育,P、Sr、Mn、Zn含量高,Cr、Ni含量低,K含量虽低但主要以易被植物吸收的缓效态存在于黑云母中.土壤地球化学背景分析表明,优质石榴分布区与P、Sr、Mn、Zn的富集区吻合性最好,这也验证了元氏石榴优质产区分布和成土母岩黑云斜长片麻岩分布的一致性.     

Changing sediment yield as an indicator of improved soil management practices in southern Brazil

Catchment-level soil and water conservation programmes have been widely employed in Brazil. An important component of these programmes is the implementation of water and sediment monitoring projects to evaluate the impact of changes in soil management on water resources. In general, results from monitoring projects have been inconclusive, due to a series of difficulties associated with data collection and limited timeframes. This study presents results from a hydrosedimentological monitoring project undertaken in a small (1.19 km²) rural catchment in Southern Brazil before and after the introduction of conservation tillage practices implemented by the RS-RURAL — Program Against Rural Poverty. These practices, including use of winter cover crops and minimum tillage tobacco cultivation, were gradually adopted by local farmers. Data on precipitation, runoff volume, maximum flow and sediment yield were assembled for representative storm events occurring between May 2002 and March 2006, and analyzed to identify changes in the storm runoff and storm-period sediment response of the study catchment. The results provide evidence of statistically significant reductions in storm runoff, maximum flow rate and sediment yield after implementation of the conservation practices. Sediment sources were also investigated using the fingerprinting technique and this work demonstrated a statistically significant reduction over the study period in the proportion of the sediment contributed by fields (62% to 54%) and unmetalled roads (36% to 24%). This reduction was offset by an increased contribution of sediment from channel sources (2% to 22%). The increased proportion of sediment mobilized from the channel is in part a function of the reduced contribution from the two other sources, but it also reflects the reduction in sediment inputs to the channel from the fields and unmetalled roads, which results in an increase in the energy available for channel scour. Results emphasize the complexity of the relationship between sediment yield, the effects of climactic variability, and changes in land use and management.     

Use of Cs to estimate tillage- and water-induced soil redistribution rates on agricultural land under different use and management in central-south Chile

The purpose of this research was to evaluate the applicability of conventional ¹³⁷Cs sampling and a simplified approach, for estimating medium-term tillage- and water-induced soil erosion and sedimentation rates on agricultural land in Chile. For this purpose, four study sites under contrasting land use and management were selected in central-south Chile. First, a conventional ¹³⁷Cs approach, based on grid sampling was applied, adapting a mass balance conversion model incorporating soil movement by tillage to the site specific conditions of the study region. Secondly, using the same conversion model, the feasibility of estimating soil redistribution rates from measurements of ¹³⁷Cs inventories based on composite soil samples taken along contour lines was also tested at all four sites. The redistribution rates associated with tillage and water and the total rates estimated using both methods correlated strongly at all four sites. The conventional method provides more detailed information concerning the redistribution processes operating over the landscape. The simplified method is suitable for assessing soil loss and sediment accumulation in areas exhibiting simple topography and almost similar slopes along the contour lines. Under these conditions, this method permits faster estimation of soil redistribution rates, providing the possibility of estimating soil redistribution rates over larger areas in a shorter time. In order to optimise the costs and benefits of the methods, the sampling and inventory quantification strategy must be selected according to the resolution of the required information, and the scale and complexity of the landscape relief. Higher tillage- and water-induced erosion rates were observed in the annually ploughed cropland sites than in the semi-permanent grassland sites. Subsistence managed crop and grassland sites also show greater erosion effects than the commercially managed sites. The ¹³⁷Cs methods used permit discrimination between redistribution rates observed on agricultural land under different land use and management. The ¹³⁷Cs technique must be seen as an efficient method for estimating medium-term soil redistribution rates, and for planning soil conservation and sustainable agricultural production under the climatic conditions and the soil type of the region of Chile investigated.     

Modelling of soil nutrient budgets: an assessment of agricultural sustainability in Nepal

Abstract. Sustaining soil fertility under agricultural intensification and expansion onto marginal lands is a significant challenge in the Nepalese Middle Mountains. In a detailed watershed study it was shown that the overall soil fertility is poor, forest soils display the poorest conditions as a result of biomass removal, and sustaining agriculture is questionable due to the transformation from traditional to multiple cropping systems. Parent material is a significant factor influencing low phosphorus status while insufficient inputs create deficiencies in total carbon, nitrogen and bases. A nutrient budget model was developed to assess inputs, redistribution and losses relative to soil fertility. Yield, input and management data obtained from farm interviews, and soil analysis data were used in the calculation of nutrient budgets. Results from modelling indicate declining soil fertility under rainfed agriculture, forest and rangelands, and marginal conditions under irrigated agriculture subject to intensive cultivation. Nutrient deficits were relatively low for irrigated rice-wheat systems, which benefit from nutrient inputs via sediments and irrigation waters, but the introduction of triple cropping showed greater deficits. Nutrient balances were most critical under rainfed maize production where 94% of the farms were in deficit. Current shortages of organic matter make elimination of nutrient deficits problematic but improvement of composting, biological N-fixation and fertilizer efficiency and reducing erosion were found to be potential options.     

The significance of drilling date and crop cover with reference to soil erosion by water,with implications for mitigating erosion on agricultural land in South East England

Early drilling of autumn‐planted cereals is strongly advised in UK government publications targeted at farmers, in part as a measure to combat soil erosion by water. However, in years when rainfall is heavy in early autumn, this strategy is ineffective. Late drilling of autumn‐planted cereals also increases the risk of erosion, but for a different reason: crop cover develops more slowly in cooler weather, resulting in a longer exposure of nearly bare ground. The crucial factor affecting both strategies is the timing of autumn and early winter rainfall. We discuss a conceptual model based on the notion of a ‘window of opportunity’ for erosion, comprising the relationship between drilling date, date of attainment of a sufficiently protective crop cover and the timing of rainfall; variations are presented for different weather conditions and management choices. Of these three factors, only the date of drilling can be chosen by the farmer. The date of attaining a sufficiently protective crop cover can only be predicted approximately. The timing of rainfall cannot be predicted. Thus, erosion control advice to farmers, which is based on choice of date of drilling to minimize erosion during the ‘window of opportunity’, is both difficult to formulate and likely to be ineffective. Sites at risk of erosion need to have better thought‐out mitigation measures in place, rather than relying on a fortuitous temporal pattern of autumn and winter rainfall to minimize the risk of erosion.     

Using Cs measurements to validate the application of the AGNPS and ANSWERS erosion and sediment yield models in two small Devon catchments

Distributed erosion and sediment yield models are being increasingly used for predicting soil erosion and sediment yields in agricultural catchments. In most applications, validation of such models has commonly been restricted to comparison of the predicted and measured sediment output from a catchment, because spatially distributed information on rates and patterns of soil redistribution within the catchment has been lacking. However, such spatially distributed data are needed for rigorous model testing, in order to validate the internal functioning of a model and its applicability at different spatial scales. The study reported in this paper uses two approaches to test the performance of the agricultural non-point source pollution (AGNPS) and areal non-point source watershed environmental response simulation (ANSWERS) erosion and sediment yield models in two small catchments in Devon, UK. These involve, firstly, comparison of observed and predicted runoff and sediment output data for individual storm events monitored at the basin outlets and, secondly, information on the spatial pattern of soil redistribution within the catchments derived from ¹³⁷Cs measurements. The results obtained indicate that catchment outputs simulated by both models are reasonably consistent with the recorded values, although the AGNPS model appears to provide closer agreement between observed and predicted values. However, the spatial patterns of soil redistribution and the sediment delivery ratios predicted for the two catchments by the AGNPS and ANSWERS models differ significantly. Comparison of the catchment sediment delivery ratios and the pattern of soil redistribution in individual fields predicted by the models with equivalent information derived from ¹³⁷Cs measurements indicates that the AGNPS model provides more meaningful predictions of erosion and sediment yield under UK conditions than the ANSWERS model and emphasises the importance of using information on both catchment output and sediment redistribution within the catchment for model validation.     

Feasibility of using FGD gypsum to conserve water and reduce erosion from an agricultural soil in Georgia

Crop production in Georgia and the Southeastern U.S. can be limited by water. Highly-weathered, drought-prone soils are susceptible to runoff and erosion. Rainfall patterns generate runoff producing storms followed by extended periods of drought during the crop growing season. Thus, supplemental irrigation is often needed to sustain profitable crop production. Increased water retention and soil conservation would efficiently improve water use and reduce irrigation amounts/costs and sedimentation, and sustain productive farm land, thus improving producer's profit margin. Soil amendments, such as flue gas desulfurization (FGD) gypsum, have been shown to retain rainfall and/or irrigation water through increased infiltration while decreasing runoff (R) and sediment (E). Objectives were to quantify rainfall partitioning and sediment delivery improvements with surface applied FGD gypsum from an Ultisol managed to conventional till (CT) and to assess the feasibility of using FGD gypsum on agricultural land in southern Georgia. A field study (Faceville loamy sand, Typic Kandiudult) was established (2006, 2007) near Dawson, GA managed to CT, irrigated cotton (Gossypium hirsutum L.). FGD gypsum application rates evaluated were 0, 1.1, 2.2, 4.5, and 9 Mg ha^− 1. Gypsum treatments and simulated rainfall (50 mm h^− 1 for 1 h) were applied to 2-m wide × 3-m long field plots (n = 3). Runoff and E were measured from each 6-m² plot (slope = 1%). FGD gypsum plots averaged 26% more infiltration (INF), 40% less R, 58% less E, 27% lower maximum R rates (R_max), and 2 times lower maximum E rates (E_max) than control plots. Values of INF and water for crop use increased, and R, E, R_max, and E_max decreased as FGD gypsum application rate increased. Values of INF, R, E, R_max, and E_max for 9 Mg ha^− 1 plots were as much as 17% greater, 35% less, 1.9 times less, 35% less, and 1.9 times less than those from other FGD gypsum plots, respectively; and 40% greater, 40% less, 2.2 times less, 52% less, and 2.9 times less than those from control plots, respectively. Applying FGD gypsum to agricultural lands is a cost-effective management practice for producers in Georgia that beneficially impacts natural resource conservation, producer profit margins, and environmental quality. Agriculture in the Southeast provides a viable market for the electric power industry to convert disposal costs of FGD gypsum into a profitable commodity.     

Use of agricultural by-products to study the pH effects in an acid tea garden soil

The amelioration of an acid Alfisol from a tea garden was studied by incorporating various plant materials: canola straw, wheat straw, rice straw, corn straw, soybean straw, peanut straw, faba bean straw, Chinese milk vetch shoot and pea straw prior to incubation for a maximum of 65 days. Soil pH increased after incubation with all the incorporated materials with the legumes causing the largest increases. The final soil pH was correlated with ash alkalinity ( r ² = 0.73), base cations ( r ² = 0.74) and N content ( r ² = 0.93) of the applied materials. It was assumed that the incubation released the base cations in plant materials as they decomposed which ultimately increased the base cation saturation of the soil. Similarly, soil exchangeable Al was also decreased with the incorporation of the legume plant materials and corn straw and rice straw. Our investigation demonstrated that legumes are the preferred choice for controlling the soil acidity and also for reducing the toxicity of Al in acid soils.     

Use of a regression method to partition sources of ecosystem respiration in an alpine meadow

The partitioning of ecosystem respiration (ER) into plant respiration (PR), aboveground-part respiration (AGR), root respiration (RR), and microbial respiration (MR) components is crucial for understanding the responses of carbon cycling in terrestrial ecosystems to climate change. Here, we present the ER-PB/AGB regression method, which is a modification of the SR-BGB method (PB, plant biomass; AGB, aboveground biomass; SR, soil respiration; BGB, belowground biomass) and is based on the assumption of a linear relationship between biomass and respiration rate for the partitioning of ER into PR, AGR, RR, and MR. Diurnal measurements of CO₂ flux and biomass analysis were conducted in three Kobresia (Kobresia pygmaea, Kobresia humilis, and Kobresia tibetica) meadows on the Qinghai-Tibetan Plateau. We found significant linear relationships between ER and PB/AGB in the three meadows. However, the relationships between measured SR and BGB were either not significant or lower than those between ER and PB/AGB. The relative contributions of respiration components (AGR, RR, MR) to ER decreased consistently in the order AGR > MR > RR in the three Kobresia meadows. The contributions of RR and MR to SR calculated by the proposed ER-PB/AGB method differed widely among the three meadows and were consistently higher (RR) and lower (MR) than those by the SR-BGB method in all three meadows. Compared with the SR-BGB technique, our ER-PB/AGB regression method proved capable of determining more accurately the temporal changes in a larger number of respiration components.     

Soil carbon sequestration and crop yield in response to application of chemical fertilizer combined with cattle manure to an artificially eroded Phaeozem

Organic manure application is a feasible approach to alleviate the deterioration of soil erosion on soil organic carbon (SOC). However, to what extent manure application can restore carbon contents in SOC fractions in the eroded Phaeozems remains unknown. A 5-year field experiment was conducted in an artificially eroded Phaeozem with up to 30 cm of topsoil being removed. Chemical fertiliser, or chemical fertiliser plus cattle manure was applied. The contents of SOC were 23.6, 21.6 and 15.1 g C kg^?1 soil for non-soil removal control, 10 and 30 cm of topsoil removal, respectively. Compared with the chemical fertiliser-only treatment, the chemical fertiliser plus manure application markedly increased SOC contents by 30–45% and C sequestration rates by 7.1–9.0-fold, especially in the fraction of 53–250 μm particulate organic carbon. However, with manure applied, SOC content in the fraction of mineral associated organic carbon in the 30 cm topsoil-removed soil was 2.9 g kg^?1, 14.7% less than control (3.4 g kg^?1). The combination of chemical fertliser and manure application effectively restored SOC in the eroded Phaeozems mainly through increasing the size of 53–250 μm particulate organic C fraction, but did not improve the SOC stability in severely eroded Phaeozems.