Monitoring nutrient flows and economic performance in African farming systems (NUTMON)

Bosch, H. van den; Jager, A. de; Vlaming, J.

doi:10.1016/s0167-8809(98)00131-5

Cited by 106 publications

(31 citation statements)

References 6 publications

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“…As illustrated by Ramisch ͑1999͒, different assumptions about the magnitude and direction of 'black box' parameters and processes and their extrapolation over time will strongly affect the outcome of balance calculations. Even if the same system components and processes are considered, differences may still exist in details easily overlooked: while Stoorvogel and Smaling ͑1990͒, Van der Pol ͑1992͒ and Smaling et al ͑1996͒ refer to nutrient balances in the root zone of individual crops, Shepherd and Soule ͑1998͒ calculated their balances for the soil depth of 0-2 m. In addition, many studies conducted at the farm level do not account for differences in resource endowment but consider an average farm ͑Shepherd and Soule 1998; Struif Bontkes 1999͒, while others criticize this standardizing approach ͑Smaling et al 1996; Scoones and Toulmin 1998;Van den Bosch et al 1998͒. Secondly, nutrient fluxes observed at a lower spatial scale are either internalised 2 completely ͑Krogh 1997͒ or partially ͑Ramisch 1999͒ when upscaling. Alternatively, weighted averages that account for different nutrient balances of individual lower-scale units are calculated to determine the balance at a larger geographical scale ͑Stoorvogel and Smaling 1990͒.…”

Section: Nutrient Flows and Balances: The Divergent Results Of Case Smentioning

confidence: 99%

Beyond adding up inputs and outputs: process assessment and upscaling in modelling nutrient flows

Schlecht¹,

Hiernaux

2004

Nutrient Cycling in Agroecosystems

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Departing from the historical background of scientific interest in soil fertility and sustainable agricultural production in sub-Saharan Africa, a review is conducted of nutrient budget studies carried out in semi-arid West Africa at scales ranging from individual fields to the sub-continent. For both, nitrogen and phosphorus, the comparison discloses largely diverging balances calculated for similar agro-ecosystems. In a first step, the modes of calculation of the nutrient budgets are examined. It is demonstrated that the calculations used in the different studies differ by the variables and biophysical processes taken into account, and by the choice of spatial scales as well as related time scales. One important discrepancy between approaches is whether and to which extent nutrient flows are internalized when upscaling. The extent to which the impact of individual and communal management, especially of pastoral and forestry resources, on nutrient flows is accounted for is a second cause of divergence. Moreover, it was observed that nutrient budgets tend to be increasingly negative as the spatial scale of the study increases from farm to sub-continent. This unexpected trend is traced back to the lack of internalization of nutrient flows when upscaling. The complexity of the scale patterns of nutrient flows and that of the interactions and the tradeoffs in the effects of management calls for the use of models to calculate nutrient budgets. Therefore, in a second step, examples of a static model, a multiple-goal linear programming model and a decision rules model were reviewed, all of which include the calculation of nutrient flows and balances and which were applied to West-African farming systems. The models are analyzed for their way of dealing with the critical issues of spatial and temporal scales and the impact of resource management on nutrient flows, taking into account that they have different objectives and were designed for different spatio-temporal scales. To conclude, suggestions were made for strengthening the use of models as tools enabling ex-ante testing of alternative agricultural technologies and policies that could improve soil nutrient balances in semi-arid sub-Saharan Africa.

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Section: Nutrient Flows and Balances: The Divergent Results Of Case Smentioning

confidence: 99%

Beyond adding up inputs and outputs: process assessment and upscaling in modelling nutrient flows

Schlecht¹,

Hiernaux

2004

Nutrient Cycling in Agroecosystems

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“…In cases of negative balances where net nutrient outputs exceed the inputs, stocks of soil nutrients are probably declining, endangering agricultural production which may trigger land degradation (Stoorvogel 1993;De Koning 1999;Van den Bosch et al 1988;Priess et al 2001). On the other hand, if the balance is strongly positive, nutrient enrichment may lead to eutrophication in rivers and downstream in coastal areas.…”

Section: Nutrient Balances and Agricultural Practicesmentioning

confidence: 99%

“…At the subwatershed level there is a positive balance in most of the watersheds suggesting that N and P inputs introduced into the systems by farming practices introduce external inputs to offset nutrient removal in exported crops. If no losses had occurred, these basins may qualify as sustainable with respect to soil fertility, at least by these criteria (Stoorvogel 1993;De Koning 1999;Van den Bosch et al 1988;Priess et al 2001). However, direct assessments of soil fertility should be conducted to verify that nutrients are retained in the soil.…”

Section: Nutrient Balances and Agricultural Practicesmentioning

confidence: 99%

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Nitrogen and phosphorus budgets for a tropical watershed impacted by agricultural land use: Guayas, Ecuador

et al. 2006

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Large-scale changes in land use are occurring in many tropical regions, with significant impacts on nitrogen and phosphorus biogeochemistry. In this study we examine the relationships between land use, anthropogenic nutrient inputs, and riverine nutrient exports in a major agricultural watershed of the Pacific coast of South America, the Guayas River basin of Ecuador. We present comprehensive nutrient budgets for nitrogen (N) and phosphorous (P) for the Guayas River basin and 10 sub-watersheds. We quantify the four major anthropogenic nutrient fluxes into and out of the region: N and P fertilizer application, N fixation by leguminous crops, net import/export of N and P in agricultural products (food and feed), and atmospheric deposition. We also estimate inputs of N from biological N fixation in forests and of P from weathering sources in soils and bedrock. The sum of these sources represents net inputs of N and P to each watershed region. Overall, synthetic fertilizers are the largest input to the Guayas Basin for N (53%) and P (57%), and the largest outputs are N and P in crops. Losses of N and P in river export account for 14-38% of total N and P inputs, and there is significant accumulation of N and P, or unmeasured forms of N and P export, in most of the sub-basins. Nutrient balances are indicative of the sustainability of land use practices in a region, where a negative balance of N or P indicates nutrient depletion and subsequent loss of soil fertility, yield, and economic viability. Although the nutrient balance of the entire Guayas Basin is positive, there are negative or near zero balances in two sub-watersheds with extensive banana, coffee and permanent crops. In these basins, degradation of soil quality may be occurring due to these net nutrient losses. Our data show that nutrients are leaving the basin primarily as export crops, with riverine losses of nutrients smaller than crop exports. Nonetheless, there is a direct relationship between nutrient inputs and river outputs, suggesting that agricultural management practices in the basin may have direct impacts on N and P delivery to the highly productive Guayas estuary.

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“…As a result, and due to permanent cropping, nutrients are mined from the plots. Studies in Africa have shown that nutrient mining in rural areas can be substantial, which on the long run is detrimental to productivity (Elias et al, 1998;Folmer et al, 1998;van den Bosch et al, 1998). In this study, the nitrogen mined is defined as follows for each process and for the system as a whole:…”

Section: Indicatorsmentioning

confidence: 99%

Resource Potentials and Limitations of A Nicaraguan Agricultural Region

Pfister¹,

Baccini²

2005

Environ Dev Sustain

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Food resources become scarcer on a global scale. Should this trend continue, prices for food would inevitably start to rise and, on the long run, importing any significant proportion of staples must be regarded as impracticable for many developing countries. For nations with a rapidly growing population, considerable agricultural improvement and development will be indispensable if sufficient food of satisfactory quality and the energy to prepare it is to be provided. The understanding of the main agricultural regions as entities with specific resource endowments and constraints, characteristic socioeconomic patterns and cultural values is therefore crucial.This study aims at answering the following key questions: 1.How can an agrarian region in a developing country be investigated and modeled to grasp the essential properties in its physical resource management? 2.What are the ecological constraints of such a region for survival on a long term?3. How can we get insight into ecological and economic factors limiting different farming systems in developing countries?The study area chosen is the agricultural region of San Dionisio in the Central Highlands of Nicaragua, which consists of 15 communities.The method chosen was Material Flux Analysis (MFA). Due to the limited amount of published data an original field study was performed. In one community of San Dionisio, semi-structured interviews were carried out with randomly sampled farmers of four socioeconomic strata.In a first step, the status quo was analyzed with a quasi-stationary model on farm level for each stratum and on a regional level. Indicators chosen were nitrogen, staple and VI energy self-sufficiency 1 . Moreover, the coverage of the basic consumer basket was assessed on household level.The results of the quasi-stationary model show that nitrogen is mined primarily from the soils of the staple and the coffee & forest plots. This is mainly caused by the burning of crop residues for field preparation, the surface application of urea fertilizer and the high firewood consumption. A clear link exists between self-sufficiency as well as the coverage of the basic consumer basket and access to land. On a regional scale, current staple production is adequate to supply the population. Yet, the actual problem is firewood supply, which, for a steady state system without Hinterland, lies at roughly 70%.Analysis of the status quo was supplemented with two scenarios. The first Scenario describes the region after a population growth of 3% for the next 25 years. Land is distributed by partible inheritance. No emigration takes place. In the second scenario people adopt a new diet based mainly on animal products. These are produced entirely on the farm. A population threshold is assessed and the land is distributed evenly among the farmers. The surplus families leave the area.In the first scenario energy lacks in 80% of the households, nitrogen is mined and hunger prevails. For the second scenario, the population has to be reduced to half the density of the st...

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Monitoring nutrient flows and economic performance in African farming systems (NUTMON)

Cited by 106 publications

References 6 publications

Beyond adding up inputs and outputs: process assessment and upscaling in modelling nutrient flows

Beyond adding up inputs and outputs: process assessment and upscaling in modelling nutrient flows

Nitrogen and phosphorus budgets for a tropical watershed impacted by agricultural land use: Guayas, Ecuador

Resource Potentials and Limitations of A Nicaraguan Agricultural Region

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