Management strategies for reducing soil degradation through modeling in a GIS environment in northern Ethiopia catchment

Soil degradation by erosion is the most serious threat to food security in Ethiopia. Thus, effective management strategies (scenarios) that reduce soil degradation are crucial. However, the application of models such as Soil and Water Assessment Tool (SWAT) that simulate the impact of different scenarios on soil degradation by erosion in Ethiopia condition is limited. This study is aimed to evaluate the effectiveness of different scenarios in reducing runoff, sediment and soil nutrients losses using the SWAT model for the Mai-Negus catchment, northern Ethiopia. The highest erosion in terms of runoff, sediment yield, total nitrogen (TN) and phosphorus (TP) losses was simulated by the baseline scenario at the catchment outlet as 168 mm, 42,000 t year⁻¹, 22,400 and 1,360 kg year⁻¹, respectively. In contrast, the lowest runoff, sediment yield, TN and TP losses were simulated by the scenario that integrated land-use redesign and conservation measures (scenario 6c) at catchmen level as 50 mm, 9,215 t year⁻¹, 6,284 and 341 kg year⁻¹, respectively. These indicate that reduction of sediment, TP, TN and runoff losses by 78, 75, 72 and 70%, respectively, can be achieved by scenario 6c compared to the baseline scenario. Thus, scenario 6c appears relatively more effective as potential management strategy in reducing soil degradation than the other scenarios. This study demonstrates that SWAT model is powerful to select the most technically effective management strategies in reducing soil degradation in a catchment. However, further research is required related to the cost-benefits of such management strategies.     

Identifying critical sources of phosphorus export from agricultural watersheds

Surface runoff accounts for much of the phosphorus (P) input to and accelerated eutrophication of the fresh waters. Several states have tried to establish general threshold soil P levels above which the enrichment of surface runoff P becomes unacceptable. However, little information is available on the relationship between soil and surface runoff P, particularly for the northeastern United States. Further, threshold soil P criteria will be of limited value unless they are integrated with site potential for runoff and erosion. In response, the Natural Resource Conservation Service (NRCS) developed a P Index (PI), which ranks the vulnerability of fields as sources of P loss in runoff, based on soil P, hydrology, and land use. This study evaluated the relationship between soil and surface runoff P in a study watershed in central Pennsylvania. The relationship was then incorporated into the (PI), and its impact on the identification of critical source areas within the watershed was examined. Using simulated rainfall (6.5 cm h^–1 for 30 min), the concentration of dissolved P in surface runoff (0.2–2.1 mg l^–1) from soils was related (r ²=0.67) to Mehlich-3 extractable soil P (30–750 mg kg^–1). Using an environmentally based soil P threshold level of 450 mg kg^–1 determined from the soil-runoff P relationship, the PI identified and ranked areas of the watershed vulnerable to P loss. The vulnerable areas were located along the stream channel, where areas of runoff generation and areas of high soil P coincide, and where careful management of P fertilizers and manure should be targeted.     

Smallholders’ Soil Fertility Management in the Central Highlands of Ethiopia: Implications for Nutrient Stocks, Balances and Sustainability of Agroecosystems

Low agricultural productivity caused by soil degradation is a serious problem in the Ethiopian Highlands. Here, we report how differences in soil fertility management between farming systems, based either on enset (Ensete ventricosum) or on teff (Eragrostis tef) as the major crops, affect the extent of nutrient stocks, balances and ecosystem sustainability. We collected information on farmers’ resources and nutrient management practices from stratified randomly selected households in two watersheds in the Central Highlands of Ethiopia. In addition, we collected soil samples from each land use and calculated nutrient stocks, partial and full nutrient balances (N, P and K) for one cropping season. Our results show that farmers in the two farming systems manage their soils differently and that nutrient inputs were positively related to farmers’ wealth status. The watershed with the enset-based system had higher soil N and K stocks than the watershed with the teff-based system, while P stocks were not different. Management related N?and K fluxes were more negative in the teff-based system (?28 kg N ha^?1 yr^?1 and ?34 kg K ha^?1 yr^?1) than in the enset-based system (?6 kg N ha^?1 yr^?1 and ?14 kg K ha^?1 yr^?1) while P fluxes were almost neutral or slightly positive. Within the enset-based system, a strong redistribution of N, P and K took place from the meadows and cereals (negative balance) to enset (positive balances). Although in the teff-based system, N, P and K were redistributed from meadows, small cereals and pulses to maize, the latter still showed a negative nutrient balance. In contrast to nutrient balances at land use level, nutrient balances at the watershed scale masked contrasting areas within the system where nutrient oversupply and deficiencies occurred.     

Effects of soil and crop management practices on yields,income and nutrients losses from upland farming systems in the Middle Mountains region of Nepal

On-farm runoff plots were established during 2004 and monitored for 4 years in the Pokhare Khola watershed (Nepal) in a completely randomized design with four replications of each three treatments: traditional Farmer Practice (FP) (Zea mays–Eleusine coracana), Reduced Tillage (RT; Z. mays–Vigna ungeuculata), and Commercial Vegetable with double dose of farm yard manure (CV; Z. mays–Capsicum species) to evaluate treatment effects on soil nutrient losses, nutrient balances and crop income on Bari land (rainfed terraces). Nutrient removal due to crop harvest was found to be significantly higher than nutrient loss through soil erosion, and CV treatment exhibited a significantly higher N uptake (123 kg ha⁻¹ year⁻¹) through crop harvest than other treatments. Moreover, the CV treatment produced significantly higher income per unit area of Bari land than the other treatments. Soil organic carbon and major nutrients losses (NPK) through soil erosion were minimal [25.5 kg ha⁻¹ year⁻¹ soil organic carbon (SOC) and 5.6:0.02:0.12 kg ha⁻¹ year⁻¹ nitrogen (N), phosphorus (P), potassium (K), respectively]. Result showed that no nutrients were lost through leaching. Nutrient losses due to soil erosion and runoff were lower than previously reported in the Middle Mountain region, indicating a need to re-evaluate the soil erosion and nutrient loss problems in this region. Interventions such as reduced tillage and double dose of FYM with vegetable production were found to be effective in maintaining soil fertility and increasing farm income compared to the traditional maize-millet production system. The nutrient balance calculations suggest that integrated nutrient management techniques such as residue incorporation and application of FYM with a minimum application of chemical fertilizer are potentially sustainable production approaches for the Mid-hills of Nepal.     

Seasonal runoff estimation of N and P in a paddy field of central Korea

The present study was carried out during a period of one year (from May 1, 1997 to April 30, 1998) to quantify seasonal runoff of N and P in a rice field with an area of 5,000 m². The total amount of runoff water was 1,043 mm during the cropping season and 281 mm during the non-cropping season. Nutrient concentrations in runoff water increased significantly during the period of fertilizer application and then decreased. During the non-irrigation period after harvest, however, the concentrations of tota -N were 3 to 4 mg l^–1. The annual runoff loading of total-N and total-P was 157.9 and 4.5 kg ha yr^–1. The runoff loading was 109.9 kg ha^–1 for total-N and 3.5 kg ha^–1 for total-P during the fertilizer application period (from May 13 to August 3, 1997). During the rainy season (from June 20 to July 20, 1997), the runoff loading was 66.1 kg ha^–1 for total-N and 1.9 kg ha^–1 for total-P. The runoff loading was 5.6 kg ha^–1 for total-N and 0.2 kg ha^–1 for total-P during the fallow stage (from October 1, 1997 to March 20, 1998) while it was 6.7 kg ha^–1and 0.4 kg ha^–1 for each nutrient during the plowing stage (March 20 to May 10, 1998). The loss of total-N and total-P was 68.2% and 63.9% of annual runoff loading during the fertilizer application stage, respectively. During the non-cropping season after harvest, however, the loss was 30.4% of total-N and 22.3% of total P. In summary, intensive long-term studies on various sites of nutrient management planning during the fertilizer application and rainy seasons are needed.     

Nitrogen export by runoff from agricultural plots in two basins in China

Runoff and sediment yields from agricultural fields are major sources of nitrogen (N) entering lakes in China. Export of sediment and N can be impacted by soil and cropping management practices, but there is relatively little information on N leaving agricultural fields in lake basins in China. Sediment and surface runoff N from a series of field plots in two experimental lake basins were evaluated in situ under simulated rainfall conditions. Objectives of the study were to evaluate the effects of crop cover, slope, and fertilizer application on N in surface runoff and eroded soils. Sediment yields varied from 4.3 to 299.0 g m^-2, depending on management practice. Mean dissolved nitrogen (DN) and total nitrogen (TN) concentrations are 1.35 and 5.4 mg L^-1, respectively, in Lake Taihu basin, while mean DN and TN concentrations are 2.66 and 4.3 mg L^-1, respectively, in Lake Baiyangdian basin. For all experimental plots in two basins, weighted average concentrations of N for total-N, dissolved N and sediment N are 1.0-5.0 mg L^-1, much higher than 0.2 mg L^-1, indicating a problem in lake eutrophication due to high N concentration from agricultural surface runoff. The estimated mean annual export of total N was 6.0 and 14.7 kg ha^-1 yr^-1 for Baiyangdian and Taihu lake basins, respectively. The study showed that significantly more N (approximately ranging from 10 to 90 of total N) exported was associated with sediment, constituting a long-term source of potentially bioavailable N in lakes.     

Optimal integration of nuclear energy and water management into the oil sands operations

An energy optimization model is presented that includes nuclear energy and water management into the oil sands industry. The proposed model determines the most suitable configuration of energy commodities and oil producers for a given oil production scenario at minimum cost while meeting environmental constraints. The proposed model was validated using data reported in the literature for the future oil sands operations in 2030. Likewise, the proposed integrated energy optimization model was used to determine the 2030 oil sands operations using recent information reported in the literature. The results show that the energy model is a practical tool that can be used to evaluate future oil production scenarios, identify the key parameters that affect the oil sands operations, and can also be used for planning and scheduling of the energy and oil producers for this industry. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

Model based scenario studies to optimize the regional nitrogen balance and reduce leaching of nitrate and sulfate of an agriculturally used water catchment

Oxidation of pyrite by nitrate (autotrophic denitrification) was identified as the main cause for sulfate increase in drinking water wells in an agriculturally used watershed, located in the north of Lower Saxony (Germany). Nitrate, which inducts this microbial catalyzed process, is drained into ground water predominantly from agricultural fertilization. The increase of sulfate in the ground water can only be stopped by reducing nitrate leaching into the ground water. To analyze the negative influence of agricultural fertilization on the quality of ground water different fertilization strategies were deducted for an investigated area of 890 ha. Calculated on the basis of nutrient balance of soil surface, the current average nitrogen balance in the investigated area amounts to 91 kg N ha^-1 a⁻¹. Farm-gate balance of nutrients is a strong indicator for assessing potential nutrient losses caused by leaching. This indicator shows comparable accuracy to the calculated nutrient balance of soil surface which demands, however, much more data input for calculations. Nitrate concentrations in seepage water in 2 m depth layer of the soil from agricultural fields were simulated with the model HERMES for the whole investigated area (agricultural land + forest). The nitrate concentration in seepage water was calculated for the whole area on the basis of farm-gate nutrient balance as an annual average, which amounts to 14.0 mg NO₃–N l⁻¹ (62 mg NO₃ l⁻¹). In order to keep the nitrate concentration of the ground water below the threshold value for drinking water (EU-water directive: 11.3 mg NO₃–N l⁻¹ (50 mg NO₃ l⁻¹) and to limit pyrite oxidation, different scenarios with simulation studies to optimize fertilization measures were developed. Only those scenarios which assured reduction of an average nitrate concentration in the drainage water below 11.3 mg NO₃–N l⁻¹ (50 mg NO₃ l⁻¹) without profit cuts for the farms were analyzed.

水环境评价模型综述

水环境评价模型是用数学的手段来建立水环境中污染变化的规律。文章对水环境评价模型进行了概述。主要分为两大类,一类是确定性水质模型,包括:QUAL水质模型、WASP模型、MIKE模型、非点源污染模型、SWMM模型、HSPF模型、SWAT模型;另一类是不确定性水质模型,包括:马尔可夫模型、灰色模型、人工神经网络模型、层次分析模型。水环境评价模型的综述主要为环评工作者提供水质环评方法做参考。     

Intra-basin spatial approach on pollution load estimation in a large Mediterranean river

In order to find the segments of Pinios River which lack the retention capacity of the BOD and nutrient input, the difference of the estimated input and output pollution loads was compared at upstream and downstream clustered areas of a total of 73 segments. Catchment areas ranged from 1 to 11,300 km². Emissions were always higher than the actual transport, therefore retention was assumed to take place. Specific runoff, percentage of the surface water area and the calculated input of pollution loads (BOD, P, N) varied between the different Pinios River basin catchment areas. The transport to the emission load ratio was different between large and small catchments. The rate of retention among consecutive segments revealed that four lowland segments lacked in their relative retention capacity.     

Machine learning-based canola yield prediction for site-specific nitrogen recommendations

An effective crop yield prediction is critical for making precise nitrogen (N) management decisions. A multi-site-year study was conducted across eastern Canada with the objectives to (1) construct machine-learning random forest regression (RFR) models for canola yield prediction; and (2) develop site-specific N recommendations using the RFR modelling approach. Soil characteristics, weather, plant growth and spectral index data collected from 2013 to 2015 were used to train the RFR models and the 2016 data for model validation in terms of making N decisions. Results showed that canola yields responded positively to N application rates in 16 out of the 18 site-year environments, with sometimes higher yields and an average of 8% higher N use efficiency for the split-N strategy than for the same amount of N applied only at preplant. Heat stress and precipitation distribution were identified as of critical importance in total yield variation. The RFR model by combining weather, soil and plant growth features with the spectral indices displayed highly improved prediction reliability, up to 85%, with 53–57% lower root mean square errors, compared with the model based only on leaf chlorophyll or normalized difference vegetation index. Based on the RFR algorithm, an average economic optimum N rate of 150 kg N ha^?1 was recommended for most canola production scenarios in the test year. This study demonstrated that the machine learning-based RFR modelling approach can be used to implement optimal nutrient management strategies for sustainable crop production, which is sensitive and better adapted to environment-induced abiotic stresses.

     

Benefits of integrated soil fertility and water management in semi-arid West Africa: an example study in Burkina Faso

The synergistic effect of soil and water conservation (SWC) measures (stone rows or grass strips) and nutrient inputs (organic or mineral nutrient sources) was studied at Saria station, Burkina Faso. The reduction in runoff was 59% in plots with barriers alone, but reached 67% in plots with barriers + mineral N and 84% in plots with barriers + organic N, as compared with the control plots. Plots with no SWC measure lost huge amounts of soil (3 t ha⁻¹) and nutrients. Annual losses from eroded sediments and runoff reached 84 kg OC ha⁻¹, 16.5 kg N ha⁻¹, 2 kg P ha⁻¹, and 1.5 kg K ha⁻¹ in the control plots. The application of compost led to the reduction of total soil loss by 52% in plots without barriers and 79% in plots with stone rows as compared to the losses in control plots. SWC measures without N input did not significantly increase sorghum yield. Application of compost or manure in combination with SWC measures increased sorghum grain yield by about 142% compared to a 65% increase due to mineral fertilizers. Yields increase did not cover annual costs of single SWC measures while application of single compost or urea was cost effective. The combination of SWC measures with application of compost resulted in financial gains of 145,000 to 180,000 FCFA ha⁻¹ year⁻¹ under adequate rainfall condition. Without nutrient inputs, SWC measures hardly affected sorghum yields, and without SWC, fertilizer inputs also had little effect. However, combining SWC and nutrient management caused an increase in sorghum yield.     

The effect of fertiliser and grazing on nitrogen export in surface runoff from rain-fed and irrigated pastures in south-eastern Australia

Nutrients, including nitrogen (N), exported from agricultural systems contribute to eutrophication and the development of algal blooms. Understanding the relative effect of farm management on nutrient export will indicate the extent to which farmers can potentially mitigate this process. Six years of monitoring surface runoff from rain-fed and irrigated dairy pastures was carried out in south-eastern Australia. Over the monitoring period, the flow-weighted mean annual total N (TN) concentrations in runoff varied between 8.2 and 29 mg/l for rain-fed pasture and 8.7 and 58 mg/l for irrigated pasture. An additive component model describing N concentrations separated the management (grazing and fertiliser) and year effects from other processes. The model accounted for 40 and 47% of the variation in N concentrations for the rain-fed and irrigated pastures, respectively. While fertiliser application, grazing and year had a significant effect on concentrations, other variables that are not necessarily under management control significantly affected N export. With current knowledge, improved management of pasture-based systems such as improved timing of fertiliser application and grazing relative to runoff may only result in a small decrease in N export. The remainder of the variability was attributed to environmentally mediated changes of N concentrations in runoff water. The collection of more detailed information on environmental parameters including soil moisture and soil temperature is proposed, to enable a better prediction of N concentrations and therefore improved understanding of potential management strategies.     

甘肃省流域环境风险评估模型构建

结合环境风险系统理论理念,从流域基础风险等级、移动源风险等级2个层面提出了适用于甘肃省环境风险现实特点的流域环境风险评估模型,旨在为各级生态环境管理部门有效管控流域环境风险、建立完善风险防控体系提供基础技术支撑。     

Runoff capture through vegetative barriers and planting methodologies to reduce erosion,and improve soil moisture,fertility and crop productivity in southern Orissa,India

Use of perennial grasses as vegetative barriers to reduce soil erosion from farm and non-farm lands is increasing world-over. A number of perennial grasses have been identified for their soil conserving properties, but their effectiveness varies with location and method of planting. Installing vegetative barriers in combination with suitable mechanical measures, like bunds or trenches or both, on the appropriately spaced contours may enhance their conservation potential. Hence, the effect of vegetative barriers, viz., sambuta (Saccharum spp.)—a local grass, vetiver (Vetiveria zizanioides) and lemongrass (Cymbopogon citratus) planted in combination with trench-cum-bund, on runoff, soil loss, nutrient loss, soil fertility, moisture retention and crop yield in the rainfed uplands, was studied in Kokriguda watershed in southern Orissa, India through 2001–2005. However, runoff, soil and nutrient losses were studied for 2002, 2003 and 2004 only. Analysis of the experimental data revealed that on a 5% slope, the lowest average runoff (8.1%) and soil loss (4.0 Mg ha⁻¹) were observed in the sambuta + trench-cum-bund treatment followed by vetiver + trench-cum-bund (runoff 9.8%, soil loss 5.5 Mg ha⁻¹). Lemongrass permitted the highest runoff and soil loss. Further, the conservation effect of grass barriers was greater under bund planting than berm planting. Minimum organic C (50.02 kg ha⁻¹), available N (2.49 kg ha⁻¹) and available K (1.56 kg ha⁻¹) loss was observed under sambuta with bund planting. The next best arrester of the soil nutrients was vetiver planted on bund. Significantly better conservation of nutrients under sambuta and vetiver resulted in the soil fertility build-up. Soil moisture content was also higher in the sambuta and vetiver than lemongrass treated plots. Increase in the yield of associated finger millet (Eleusine coracana (L.) Gaertn.) due to vegetative barriers ranged from 18.04% for lemongrass to 33.67% for sambuta. Further, the sambuta and vetiver treated plots produced 13.23 and 11.86% higher yield, respectively, compared to the plots having lemongrass barrier (1.17 Mg ha⁻¹). Considering the conservation potential, and crop yield and soil fertility improvements, the sambuta barrier with trench-cum-bund is the best conservation technology for treating the cultivated land vulnerable to water erosion. Farmers also showed greater acceptance for the sambuta barrier as it is erect growing and available locally. Vetiver with-trench-cum bund can be the second best option.     

Farm nitrogen flows of four farmer field schools in Kenya

Re-use of nutrients within farming systems contributes to sustainable food production in nutrient limited production systems. Re-use is established when nutrients pass through several farm compartments before they leave the farm via marketable products. In this paper re-use of nitrogen is examined as an indicator for sustainable soil fertility management. Re-use (RU, kg farm⁻¹) was defined as the amount of nitrogen that was translocated within one farm divided by the sum of transitions between farm compartments within a farm. In 2002, a total of 101 farms belonging to 4 farmer field schools in Kenya were analysed using the NUTMON (now known as MonQI) toolbox. The farms were distributed over 4 farmer field schools located in two agro-ecological zones. RU was positively related to the net farm income and to crop yields. However, data were scattered and often local farm conditions veiled the relation between nitrogen management strategies and farm performances. The results of this paper demonstrate that different agro-ecological zones with diverse production constraints have developed different in-farm nitrogen management strategies that are best adapted to the local conditions, but may have different environmental impacts. An erratum to this article can be found at     

Use of the partial nutrient budget as an indicator of nutrient depletion in the highlands of southwestern Uganda

Agricultural management has its roots in the manipulation of the system to optimise conditions for crop production. It is now widely recognised that this could result in land degradation with subsequent serious impact on crop productivity if the nutrient losses to the agricultural system are not replaced. A nutrient budget is an account of gains and losses of nutrients in an agricultural system, a tool that could be used to develop sound nutrient management and sustainable agriculture. This tool was applied to the annual crop farming system in the highlands of southwestern Uganda to demonstrate (i) within farm nutrient depletion and accumulating zones, and (ii) the extent of nutrient losses at farm and district levels through marketing pathways. Partial nutrient budgets were constructed at field and farm levels using farmer-recorded resource inputs and outputs over a period of one year, and at the district level using annual inventory data of agricultural imports and exports. The computed nutrient balances were highly variable at field and farm levels, but predominantly negative. Nitrogen (N) gains and losses averaged 30.6 and 72.3 kg ha^–1 yr^–1, respectively in the homestead fields; 10.8 and 33.4 kg ha^–1 yr^–1 in the outfields; 15.8 and 17.4 kg ha^–1 yr^–1 at the farm level; and only losses of 5.6 kg ha^–1 yr^–1 at the district level. Potassium (K) gains and losses followed a similar trend, although less in magnitude. The phosphorus (P) balance was positive but only in the homestead fields and at the farm level. Where agricultural produce were marketed, nutrient losses were reflected more at the higher scales (e.g. district level) and became tied up in pools from which recycling back to agriculture was barely feasible, and with quite alarming monetary implications. Such results can be used to influence policies at different scales on nutrient management.     

Toward integrated production and distribution management in multi-echelon supply chains

The effective management of multi-site systems involves the proper coordination of activities performed in multiple factories, distribution centers (DCs), retailers and end-users located in many different cities, countries and/or continents. To optimally manage numerous production and transportation decisions, a novel monolithic continuous-time MILP-based framework is developed to determine the best short-term operational planning to meet all customer requests at minimum total cost. The formulation lies on the unit-specific general precedence concept for the production scheduling problem whereas the immediate precedence notion is used for transportation decisions. To illustrate the applicability and potential benefits of the model, a challenging example corresponding to a supply chain comprising several locations geographically spread in six European countries has been solved to optimality with modest CPU times. Several scenarios with different logistics features were addressed in order to remark the significant advantages of using the integrated approach.     

Land use impact on nitrogen discharge by stream: a case study in subtropical hilly region of China

As a crucial factor of water eutrophication, nitrogen (N) discharge by agricultural non-point sources (NPS) has become a worldwide concern, and so has its relationship to land use. This study was aimed at the quantitative relationships between N discharge by stream and land use. It was conducted in the Meicun watershed of Xuancheng County, Anhui Province, in the subtropical low hilly area of China. The study integrated dynamic monitoring of nutrient discharge by stream water and Geographic Information Systems (GIS) analysis of land use of the watershed. Results showed that NO₃⁻-N discharge ranged between 50 and 60% of the total nitrogen (T-N) and was 2.5–3.0 times as much as NH₄⁺-N. There was a significant difference between forested and mixed sub-watersheds for NH₄⁺-N, NO₃⁻-N and T-N concentrations. Significant correlations existed between NH₄⁺-N, NO₃⁻-N and T-N concentrations in stream water and the area percentages of forest and paddy fields. The study found that the discharges of NH₄⁺-N, NO₃⁻-N and T-N decreased exponentially with forest area increase, but a steep decline for NO₃⁻-N and T-N seemed to occur when the forest percentage surpassed 70% and then there was almost no change. Similarly, the discharges of NH₄⁺-N, NO₃⁻-N and T-N increased exponentially with the paddy fields increase, but a steep augmentation occurred for NO₃⁻-N and T-N when the paddy percentage surpassed 20% and then it remained at a plateau. The study showed that in the subtropical hilly region, paddy fields could increase N discharge due to farming management practices. Thus, primary measures to reduce N in the receiving water body would include a change in farming management and building an ecological interception system for paddy fields.