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Uncertainty in technical coefficients for future-oriented land use studies: A case study for N-relationships in cropping systems
Abstract
Engineering of land use systems for policy-oriented future studies and the development of new farming systems requires various information sources. Often, both process knowledge and data are subject to uncertainty that affects quantification of land use systems in their inputs and outputs. This paper analyzes the effects of uncertainty in three important N-relationships relevant for quantification of future-oriented cropping systems: (i) N-leaching as function of crop characteristics, (ii) N-concentration as function of yield level, and (iii) the recovery of crop residue-N. Based on verifiable assumptions, uncertainty in these three N-relationships is specified in terms of N-loss and production costs of cropping systems. Data and process knowledge as applied in LUCTOR, a summary model to design and quantify inputs and outputs of cropping systems for the northern Atlantic zone of Costa Rica, are used as a case study. All three relationships and their uncertainty have a major impact on N-loss of cropping systems, while effects on costs are limited and depend on the share of costs for fertilizer management in total production costs. Analyses as presented explicitly specify uncertainty of process knowledge and data used in future-oriented studies. Therefore, such analyses enable a better management or reduction of uncertainty through the identification of cropping systems with smaller uncertainty margins, and identification of research aimed at a more complete understanding of involved processes.
... mathematical formulation) inputs factors like biomass or bush control, chemicals, etc. actually influence the product level. Especially, in those land use studies (Hengsdijk and van Ittersum 2001), which focus on alternative or new technologies, no such data is hardly available. This causes problems to estimate production functions. ...
... However, since the fixed points of input-output ratios are introduced, directly, in a mathematical programming framework, there is no need to specify a production function (Kruseman 2000). According to (Kruseman 2000), (Hengsdijk and van Ittersum 2001) Leontief techniques (i.e. technology or activity choices) can be generated with Technical Coefficient Generator (TCG). ...
This paper deals with bio-economic modelling of potentially degraded range land in Namibia. It outlines the methodological background, presents a modelling approach in GAMS and offers first results. We show how bush encroachment can be modelled and how various factors, like interest rates and costs of combating bushes, impact on farm behaviour and the environment. In particular the prevalence of bush and range quality decline are a focus of the paper . 1 Introduction Due to overuse of natural resources, especially over-grazing and the application of non-suitable management practices, such as low recognition of prevalent natural vegetation cycles in grass and thorn bush savannahs, the range quality of many commercial farms has declined. A visually decreased appearance of natural composition of grass and bush cover, bush encroachment, and a decreased biodiversity indicate lower stocking potentials for domestic livestock on large tracks of farm lands. Range degradation has become a threat to the continuation of viable commercial farming strategies in many semi-arid grass lands of Southern Africa. Furthermore, reconsidering long-term degradation processes and seeking of cures for environmental degradation are requests and challenges to professions of range land economists, ecologists and farm extension service. One the side farms seek to increase size and decrease intensity which leads to a declining number of farmers and labourers who can make a living from acquiring wealth through farming naturally exposed areas. On the other hand political pressure is increasing to encourage intensity of farming and to create job opportunities for a growing population.
... Climatic conditions and fertilization affected variations in NO 3 -N leaching by ±65%, crop rotations by ±20-25% (Krysanova and Haberlandt, 2002), fertilizer inputs alone affected variations in NO 3 -N leaching by ±40% (Mertens and Huwe, 2002), and agricultural land management affected variations in N leaching by ±48% (Schmidt et al., 2008). Hengsdijk and van Ittersum (2001) showed the uncertainties associated with future modeling of NO 3 -N leaching losses as functions of crop characteristics, yield levels, and crop residuenitrogen to be -36% and +70%, -30% and +40%, and -64% and +67%, respectively. A study done by David and Gertner (1987) to identify the sources of variation in soil solution collected by tension plate lysimeters, found that the CV for volume of leachate and NO 3 -N concentration measured during the study was 122% and 218% respectively. ...
... For bell pepper production on plasticulture system, leaching by ±48% (Schmidt et al., 2008). Hengsdijk and van Ittersum (2001) showed the uncertainties associated with future modeling of NO 3 -N leaching losses as functions of crop characteristics, yield levels, and crop residue-nitrogen to be -36% and +70%, -30% and +40%, and -64% and +67%, respectively. The potential for leaching might also be influenced by the NUE of the crop. ...
... Generated output data need to be carefully evaluated on the basis of the various assumptions made about the agricultural production systems in question. The rapid evaluation of land-use systems with TechnoGIN is of great benefit in land-use studies that often rely on secondary data and assumptions with a wide range of uncertainty (Hengsdijk and Van Ittersum, 2001). TechnoGIN allows rapid identification of outliers and the consequences of assumptions for input–output relationships of land-use systems. ...
Agricultural research in East and Southeast Asia is increasingly challenged by the search for land-use options that best match multiple development objectives of rural societies (e.g., increased income, food security, and reduced environmental pollution). In order to support the identification of sustainable land-use options and to support decision making with respect to land use, a tool was developed for quantifying inputs and outputs of cropping systems at the field level. TechnoGIN, the tool described in this paper, integrates systems analytical and expert knowledge and different types of agronomic data enabling the assessment of inputs and outputs of a broad range of cropping systems and the evaluation of their resource use efficiencies. By using methods of spatial aggregation in combination with linear programming, results can also be used to explore trade-offs in resource-use efficiencies at higher levels such as the farm household, municipality and province. New features in TechnoGIN compared with similar tools include the annual rotation of up to three crops, the distinction between aerobic and anaerobic growing conditions of crops, and the procedure for estimating crop nutrient uptake. TechnoGIN is illustrated with results from the Tam Duong district in North Vietnam. The design of TechnoGIN enables easy access to its data, parameters and assumptions, and rapid generation and evaluation of input–output relationships of cropping systems in order to add new information and to improve data. TechnoGIN raises awareness about the assumptions incorporated and thus supports data collection and setting of the research agenda with respect to agro-ecological processes for which knowledge is incomplete, and is relevant for showing trade-offs between production, economic and environmental impacts of different land-use systems.
... Simulations in scenarios where P is non-limiting suggest that NCE can be maintained at high levels over a wide range of N availability and yields. Using a summary model LUCOR, Hengsdijk and van Ittersum (2001) showed that when P and K were optimized for the target yield, N was utilized in the most efficient way, and constant N-use efficiencies were feasible up to fairly high yield levels, provided that water was not limiting. The three broad soil conditions summarizing NCE as a function of N availability and soil P status are presented inFig. ...
The efficiency with which applied resources are utilized in sub-Saharan African cropping systems is especially critical as the resources are generally scarce. Research efforts to improve farm productivity increasingly focus on resource interactions and trade-offs operating at farm-scale. Farm-scale models that integrate summary models of the various subsystems (crops, livestock, household) are proposed to analyse the complexity of management systems. NUANCES-FIELD is a summary model of the crop/soil system that calculates seasonal crop production based on resource availability, capture and utilization efficiencies. A detailed mechanistic crop growth model, APSIM, was used to generate parameters and variables that can be introduced as descriptive functions in NUANCES-FIELD. To such end, we first parameterized and tested APSIM based on several field experiments carried out on different soil types in western Kenya farms where nitrogen and/or phosphorus were applied. The model was further configured to generate nitrogen and phosphorus response curves as a function of soil condition (carbon content, clay content, phosphorus-sorption characteristics) and the effects of alternative weed management scenarios in relation to labour availability. Nitrogen, phosphorus and rainfall capture efficiencies ranged between 0.22–0.85 kg kg−1, 0.05–0.29 kg kg−1 and 0.10–0.53 mm mm−1, respectively, depending on soil nutrient and physical conditions. Variation in the integrated seasonal fraction of radiation intercepted (intFRINT) with plant density was adequately described by the function y = 0.058x + 0.11 within a range of 1.5–5.5 maize plants per m2. Investigation of weed management using the APSIM model identified a weed-free period of at least five weeks from maize emergence for minimum yield loss from weed–crop competition. The simulation exercises confirmed that resource-use efficiencies sharply decrease on moving from relatively fertile fields ‘close’ to the homestead towards degraded ‘remote’ fields within the same farm, giving impetus to expedite the search for better targeted management strategies for spatially-heterogeneous farms.
... Rapid evaluation of land use systems with TCGs is of great benefit in land use studies that often rely on secondary data and assumptions with a wide range of uncertainty (Hengsdijk and Van Ittersum, 2001). Therefore, TCGs are important tools for the integration of different types of data enabling well-balanced decision-making with respect to resource use. ...
Simulation studies play an important role in predicting the effects of agri-environmental policies. Management plans for the Water Framework Directive, for example, show how policy measures can be based on both the absolute effects and the probability of the achievement of objectives. Here, comprehensive uncertainty analysis is a valuable modern tool.In the context of the six most important uncertainties in this study, the article explains the overall uncertainties of a nitrate leaching model for agricultural land use. Although the primary input data are ‘natural conditionś and ‘land management́, there are also variances caused by model description and upscaling.The management options in a large number of small farming systems are described as adapted in a particular region. A variance analysis of the simulated nitrate leaching-rates by means of the H-test shows significant differences between locations, meaning that the distribution of results often allows no discrimination between two or several locations in terms of simulation objects. These locations, similar in nitrate leaching behaviour, are summarised to so-called Nitrogen Response Units (NRUs). Within these NRUs, a multiple regression analysis, with the dependent variable ‘nitrate leaching-rate,’ and the independent variables ‘percentage of cereals in the crop rotation’ and ‘livestock,’ shows the regression coefficients of each NRU.A calculation of the mean, or theoretically most probable, nitrate leaching-rate follows: all distribution patterns of livestock and cereals are combined, and the regression equations are applied for each NRU. This reveals the range of the possible nitrate leaching-rates in the area. The mean value, like the average of all possible land use patterns, of this distribution is taken as the most probable figure. The minimum and maximum values set the limits for the management distribution of the uncertainty analysis. The overall uncertainties of the results are determined by the sum of the variances that are calculated by all effects, which are classified as important. The first application of this new approach was a study region of about 1000km2 in Germany. The nitrate leaching losses were 63kg NO3/ha on average with a range of uncertainty of +59% and −79%.
New tools for land use analysis including detailed cost–benefit assessments are needed to integrate resource management for enhancing farmers’ income and mitigating greenhouse gas (GHG) emissions. The paper comprises an assessment of GHG emissions and economic returns under different mitigation technologies in three rice growing regions in Asia, i.e., Ilocos Norte province (Philippines), Zhejiang province (China) and Haryana state (India). Site-specific data on soil, climate and socio-economics were integrated in the previously developed spreadsheet model TechnoGAS (Technical Coefficient Generator for Mitigation Technologies of Greenhouse Gas Emissions from Agricultural Sectors). Three baseline technologies that differed in terms of inorganic/organic N supply have been compared to different mitigation technologies in form of Marginal Abatement Cost Curves (MACCs). For the baseline technology of inorganic N (urea) fertilization, amendment with phosphogypsum and nitrification inhibitors are the most promising mitigation options resulting in shadow prices of less than US$10 per ton of carbon dioxide equivalent (CE). Assuming a mix of urea and farm yard manure for the baseline, we have tested several options including different irrigation patterns and husk used as fossil fuel. Mid-season drainage had a better cost–benefit ratio (ca. US$20 per t CE) than alternate flooding, but was less profitable than husk utilization (ca. US$4 per t CE). Assuming high organic inputs, biogas technology is, in most cases, the preferable option (ca. US$10 per t CE). Finally, we compiled regional abatement cost curves for selected administrative units using the outcome from regional optimization models. Implementing the three most promising technologies required US$6000 for Dingras municipality, Ilocos Norte, in the Philippines (ca. 103 ha of rice land potentially providing emission savings of ca. 3000 t CE), US$50,000 for Pujiang county in China (ca. 104 ha providing ca. 27,000 t CE), and US$1.2 million for Karnal district in India (ca. 105 ha providing ca. 220,000 t CE).
Increasingly, model-based approaches play a role in the design and development of new land use systems. Simulation modeling may play a role in the generation of land use systems for land units, and optimization modeling (e.g. linear programming ¿ LP) may be used in the upscaling to farm and region. In the quantification of new land use systems for land units, often equilibrium conditions with respect to soil resources are assumed, following a so-called target-oriented approach. This facilitates ex ante computation of inputs and emissions of nutrients and allows their use in static optimization models based on LP. The condition of equilibrium in soil resources is often not met, nor is it the ultimate aim. Hence, the dynamics in new systems are insufficiently dealt with. This paper presents an approach for the design of land use systems (crop rotations) and their quantification in terms of input and output coefficients, using particular yields and dynamics in soil resources as targets. Interactions between N input and output of succeeding crops are explicitly taken into account. A simple N-balance model is used describing major processes affecting soil N-dynamics. For the Koutiala region in Mali five crop rotations are evaluated that differ in target crop yield, crop choice, crop residue management and external N source. Modeled crop rotations aiming at high yields, in combination with incorporation of crop residues and legumes, result in depletion of soil N stock. Only in crop rotations aiming at high yields and with incorporation of crop residues combined with a supply of large quantities of animal manure, soil N depletion can be prevented. Four approaches are presented of how to use the dynamic input¿output coefficients of these systems in land use studies using LP: (i) use of average coefficients, (ii) use of discounted coefficients, (iii) use of pessimistic estimates of coefficients in an optimization of the land use allocation followed by a recalculation of the objective values for the optimized land use with optimistic coefficients, and (iv) a combined use of systems characteristics, i.e. cumulative N-inputs of land use systems over the time horizon and the magnitude of the soil N pool at the end of the time horizon, which can be used as filters for land use systems. Though none of the approaches completely captures the dynamics in input¿output coefficients, they enable a well-founded consideration of the consequences of dynamics in, for instance, soil N stocks in static optimization approaches for farm and regional studies.
Between 10 and 14 May 1993, a workshop was organized in Leusden, the Netherlands, in which the concepts and performance of 18 models were discussed. These models were generally aimed at the analysis of effects of acid atmospheric deposition on forest and forest soils. Model concepts were analysed by means of a questionnaire. Model performance was analysed by application of the models to a common dataset for the F1 Norway spruce site, at Solling, for the period 1970–1990. The nature of the participating models varied widely, but all models were process-oriented and dynamic. Included were hydrological models, soil chemistry models as well as integrated models for calculation of forest growth. Overall, average annual hydrology, soil solution chemistry and forest growth of the spruce site between 1970–1990 could be reproduced. Differences between models were attributable more to different parameterizations than to differences of model concepts. Short-term temporal dynamics of soil solution chemistry were not reproduced very well, particularly for nitrate. Models also gave different predictions of the response of the Norway spruce to maintained or reduced fluxes of atmospheric deposition, however, confirming a key role for Mg and N. Complex models did not give better results than more simple models. Integrated models were also judged unbalanced, with respect to description of the hydrologic, soil chemical and forest subsystems. Therefore, it was recommended to improve this balance and to work towards less complex models for prediction of the long-term behaviour of forest stands. Our knowledge about nutrient uptake by forests in nutrient-limited acidified soil systems, and also about the interaction of various forest stresses is still inadequate. Future research should therefore emphasize a better integration of model development and experimental research, e.g., as presently is the case for experimental field manipulations.
A system is described for a quantitative evaluation of the native fertility of tropical soils, using calculated yields of unfertilized maize as a yardstick. The system is applicable to well drained, deep soils, that have a pH(H20) in the range 4.5–7.0, and values for organic carbon, P-Olsen and exchangeable potassium below 70 g/kg, 30 mg/kg and 30 mmol/kg, respectively (0–20 cm). Soil fertility is interpreted as the capacity of a soil to provide plants with nitrogen, phosphorus and potassium, but the methodology allows for including other nutrients.
The role of roots in obtaining high crop production levels as well as a high nutrient use efficiency is discussed. Mathematical models of diffusion and massflow of solutes towards roots are developed for a constant daily uptake requirement. Analytical solutions are given for simple and more complicated soil-root geometries. Nutrient and water availability in soils as a function of root length density is quantified, for various degrees of soil-root contact and for various root distribution patterns. Aeration requirements of root systems are described for simultaneous oxygen transport outside and inside the root.Experiments with tomato and cucumber are discussed, which were aimed at determining the minimum root surface area required in an optimal root environment. Experiments on P-uptake by grasses on various soils were performed to test model calculations. Model calculations on the nitrogen balance of a maize crop in the humid tropics suggested practical measures to increase the nitrogen use efficiency.
A generic methodology is presented for exploration of sustainable land use options at the regional level by quantifying trade-offs between socioeconomic and biophysical sustainability objectives. The methodology is called SOLUS (Sustainable Options for Land USe), and was developed over a ten year period of investigation in the Northern Atlantic Zone of Costa Rica. SOLUS includes a linear programming model, technical coefficient generators for livestock and cropping activities and a geographic information system. The linear programming model maximizes regional economic surplus subject to a flexible number of resource and sustainability constraints. Economic sustainability indicators are economic surplus and labor employment, and biophysical ones include soil N, P and K balances, pesticide use and its environmental impact, nutrient losses and a proxy for trace gas emissions. The capabilities of the methodology are illustrated for the Northern Atlantic Zone of Costa Rica. Though ample scope exists for reducing environmental effects and introducing sustainable production systems separately, pursuing both objectives simultaneously, considerably reduces economic surplus and agricultural employment. Agricultural area can be decreased and forested area increased without severely affecting the regional economic surplus.
In a field of mature bananas, plants can be seen at all stages of vegetative growth and fruit maturity, providing a fascination for anyone who has an interest in growing crops. Banana farmers in the tropics can harvest fruit every day of the year. The absence of seasonality in production is an advantage, in that it provides a continuity of carbohydrate to meet dietary needs as well as a regular source of income, a feature that perhaps has been under-estimated by rural planners and agricultural strategists. The burgeoning interest in bananas in the last 20 years results from the belated realization that Musa is an under-exploited genus, notwithstanding the fact that one genetically narrow group, the Cavendish cultivars, supply a major export commodity second only to citrus in terms of the world fruit trade. International research interest in the diversity of fruit types has been slow to develop, presumably because bananas and plantains have hitherto been regarded as a reliable backyard source of dessert fruit or starch supplying the needs of the household, and in this situation relatively untroubled by pests, diseases or agronomic problems.
The identification of optimal crop management strategies at farm and enterprise levels presents special difficulties — in particular, the nature of the farm itself, operating in an environment defined by biophysical, socioeconomic, and politico-cultural variables, the often intractable effects of human agency, and, in an eco-regional context, the problems of defining appropriate spatial and temporal scales for analysis; these all combine to form a perplexing problem domain. We illustrate the potential use of simulation models in addressing some of these problems with respect to two case studies: season-specific enterprise management in the mid-altitude maize ecology of central Malawi and an analysis of management options facing a hillside smallholder induced to move out of coffee production in the lower Andes of central Colombia. The first case study shows that simple analyses can provide season- and region-specific management recommendations on input use that could improve productivity and stabilise economic returns. The second highlights the importance of price and weather risk in analysing management options and their impact on farm viability.
Compared a high-input and two reduced-input farming systems with a rotation of winter wheat-sugar beet-spring barley-potatoes on a calcareous silt loam soil. Nitrogen balance sheets for the growing seasons of 1986-1988 showed N deficits of 0-170 kg ha-1, suggesting substantial N losses to the environment. Periods with much rainfall in 1987 and 1988, inappropriate use of animal manure and soil compaction may partly account for the heavy N losses in all systems. To increase the efficiency of mineral and organic N inputs, and to decrease N losses, soil inorganic-N concentrations should be kept low, especially in periods when losses are likely to occur. -from Authors
Publisher Summary This chapter elaborates the genotypic variation in crop plant root systems. Genetic improvement of crop species, however, requires knowledge of intraspecies variability in significant root parameters and its genetic control. Ecological studies provide many examples of plant root systems, adapted to cope with variability in major edaphic environmental factors such as temperature and water. Vertical distribution of root dry matter illustrated that some species were better adapted to rooting in the shallow soil near the surface while others exploited crevices in the underlying limestone. It is found that many landraces of rice adapted to rain-fed culture exhibit substantially larger root systems with some large-diameter roots extending into the plow pan and deeper soil levels. Rain-fed agricultural ecosystems range from no-input mixed cropping of shifting cultivators on marginal soils to complex soil, water, and fertility management systems rivaling irrigated areas in production. It is found that when root pruning was performed in the field to simulate stress or mechanical damage to nodal roots, the inbreds with early vigorous seminal root development showed less reduction in height and ear weight. The analysis of means and variances indicated considerable heritable variation from crosses between tall and semidwarf height groups.
The important role of sensitivity and uncertainty analysis in the mathematical modelling process is indicated, and guidelines are given for these analyses. The main features are presented of the software package UNCSAM, which applies efficient Monte Carlo sampling in combination with regression and correlation analysis to perform sensitivity and uncertainty analyses on a large variety of simulation models. The use of UNCSAM is illustrated by an environmental application study.
Direct measurements of fertilizer-derived N2O emission data from 104 field experiment reported in agriculture and soil science literature that were obtained between 1979 and 1987 were summarized and used to estimate woldwide fertilizer-derived N2O emissions. Although without statistical determination, there appears to be a trend between emissions and type and quantity of fertilizer applied; the available data does not indicate a trend between emissions and a particular soil type or agriculture system. Using the fraction of the N fertilizer evolved as N2O and fertilizer consumption estimates for five fertilizer types, 0.1 to 1.0 Tg N2O-N (avg. 0.3;median 0.2) were estimated to be released during the 'sampling period.' If these estimates are doubled to account for emissions after the sampling period and emissions from fertilizer lost in drainage water and groundwater, the expected rage would be 0.2 to 2.1 Tg N2O-N (avg. 0.7; median 0.5) emitted into the atmosphere in 1984. The magnitude of this estimate is in agreement with recent global estimates. If 100 Tg N fertilizer are consumed worldwide in the year 2000, the global release of fertilizer-derived emissions into the atmosphere will probably not exceed 3 Tg N2O-N in the year 2000. It is estimated that 23 to 315 Gg N2O-N were emitted into the atmosphere from fields of culivated leguminous crops in 1986. Future research needs were suggested.
Use of nitrogen fertilizer is thought to contribute significantly to the increase of atmospheric nitrous oxide (N2O) and nitric oxide (NO). While the current increase of fertilizer use is concentrated in tropical areas, nearly all studies of nitrogen oxide emissions have been conducted in agricultural systems in temperate areas. We measured N2O and NO fluxes from a fertilized banana plantation in the humid tropics of Costa Rica, where 360kgNha-1yr-1 is applied. Using chamber techniques, we sampled an Andisol and an Inceptisol on a monthly basis. Twice on each soil type, we sampled intensively in time following fertilizer applications. There is a strong spatial and temporal dependence of nitrogen oxide emissions on place and time of fertilizer application. We find greater mean N2O and NO emissions from the Andisol (31.4 ng N2O-Ncm-2h-1 and 55.6ngNO-Ncm-2h-1) than from the Inceptisol (9.3ngN2O-Ncm-2h-1 and 41.1ngNO-Ncm-2h-1) under the plants where fertilizer is typically applied. The percentages of applied fertilizer-N that are converted into nitrogen oxide (``yield'') are between 1.26 and 2.91% for N2O and between 5.09 and 5.66% for NO depending on soil type. We consistently calculate higher nitrogen oxide yields based on intensive sampling versus monthly sampling. Temporal variation in nitrogen oxide emissions probably causes monthly sampling to underestimate mean annual fluxes. Our results suggest that in some tropical systems a higher percentage of applied nitrogen may be lost in gaseous form than in temperature agriculture. Current global estimates of N2O and NO sources from tropical agriculture are based on information from temperate areas and may cause an underestimate of the contribution of tropical agriculture to the budgets of these trace gases.
A multiple goal linear programming model has been used to explore the impact of inorganic fertilizer availability on land use, crop and livestock production in the Fifth Region of Mali. Three scenarios have been examined with restricted, intermediate and unrestricted inorganic fertilizer availability. Marketable crop production was maximized under various restrictions and limiting values of other goals, such as a minimum regional gross revenue, and on the basis of sustainable agricultural activities. Results are discussed at both regional and subregional levels.
Unrestricted inorganic fertilizer availability allows a substantial increase in crop production. In normal years, the food needs in 8 of 11 agro-ecological zones distinguished in the region are met, whereas this holds for 7 out of 11 in the other two scenarios. In dry years, food needs can only be met if, in addition to unrestricted inorganic fertilizer availability and emigration, some sacrifices (e.g. lower regional gross revenue) are accepted.
In all three scenarios, available animal manure has to be utilized completely and supplemented by substantial amounts of imported inorganic fertilizer, largely exceeding current total national imports.
In a post-model analysis aspects are examined that could not be incorporated in the model. To stimulate the use of inorganic fertilizer, a reduction in its farmgate price is recommended. Income generated outside the agricultural sector is required to pay for subsidies on fertilizers and reduce risks in animal marketing.
Current production systems for flower bulbs in the Netherlands employ considerable quantities of pesticides and nutrients per unit area. In 1993, an association of growers and environmentalists set out to design new farming systems that meet environmental objectives in addition to economic objectives. To support the design process, an explorative study was carried out to bring together the fragmented agronomic information and to assess agro-technical options for sustainable flower bulb production with a time horizon of 10 to 15 years. Crop and inter-crop management systems representing the agro-technical components of sustainability at the farm level, were generated with a computer model by systematically varying four system characteristics, three of which represented strategic and tactical aspects of crop protection. Subjective components, one economic and two environmental objectives and various socio-economic constraints, were identified in interaction with the stakeholders. Interactive multiple goal linear programming was used to optimize the objectives at the farm level and determine the exchange value of the economic objective in terms of the environmental objectives. Calculations were carried out for two reference farm types. The results revealed that the negative impact of environment-oriented production systems on farm gross margin is importantly mitigated by strategic choices at the farm level, such as renting land and allowing a soil health improving crop, even though of low gross margin, into the rotation. In contrast, the a priori attention of the growers was focused on improving tactical pest and nutrient management at the crop level, the effect of which on farm gross margin is constrained by the strategic choices. Sensitivity analyses highlighted the need for more insight into the ecology of soil-borne growth reducing factors and their effect on crop yield. The paper describes the approach used, reports results and discusses the usefulness of the approach for the stakeholders and for disciplinary crop protection research.
The simulation results obtained from 19 participants of the workshop “Validation of Agroecosystem Models” were compared and discussed. Although all models were applied to the same data set, the results differ significantly. From the results it can be concluded that the experience of a scientist applying a model is as important as the differences between various model approaches. Only one model simulated all main proceesses like water dynamics, plant growth and nitrogen dynamics with the same quality, the others are able to reproduce the measured dynamic only in parts.
Nutrient depletion may be reduced by effective land use planning using a nutrient balance model and linear programming techniques to optimize the distribution of land use over different land units. This technique plans the geographical distribution of land utilization types and creates a more sustainable basis for agriculture in an area. In contrast with traditional land use planning where land utilization types are matched with land units on the basis of maximizing present agricultural production, this approach focuses on long-term effects.
Soil-plant N dynamics lie at the heart of some of the questions being asked of researchers by farmers, environmentalists and policy makers. Our aim in this paper is to highlight areas in which research is needed to address these questions. Although we have a general understanding of many processes, fundamental understanding of the processes of the soil-plant system is not complete. Improved understanding of crop and soil processes should lead to the continuous improvement of simulation models, which are able to integrate the complex effects of management and environmental factors. However, farmers cannot wait for the achievement of perfect models, but need researchers to put their current knowledge to use. We suggest that for both crops and soils, diagnostic measurements be used in conjunction with the best of, or a combination of, current models. Development work should be carried out with all possible speed to draw suitable models and diagnostics together. We stress the importance of conducting research to understand and improve N efficiency at a range of scales and indicate the need for the involvement of related disciplines, such as statistics, to allow the development of robust guidelines and methodologies for up- and down-scaling measurements and models. Above all, it is essential that our understanding of the processes of soil-plant dynamics continues to underpin the development of strategies for dynamic optimisation and improve simulation models that are used in fertiliser recommendation systems
This paper describes two generic so-called technical coefficient generators, PASTOR (Pasture and Animal System Technical coefficient generatOR) and LUCTOR (Land Use Crop Technical coefficient generatOR), that quantify land use systems in terms of inputs and outputs based on the integration of systems-analytical knowledge, standard agronomic and animal husbandry data and expert knowledge. PASTOR quantifies livestock systems while LUCTOR is geared towards cropping systems. Main inputs quantified include costs, labour requirements, fertiliser use and application of crop protection agents. Outputs are production and a number of associated environmental indicators. Although both PASTOR and LUCTOR were developed to generate input data for land use models, they are also useful as stand-alone tools to explore the technical efficiency of land use systems, to perform cost-benefit analyses and to quantify the trade-off among socio-economic, agronomic and environmental indicators at the field level. PASTOR and LUCTOR are illustrated with data from the Northern Atlantic zone in Costa Rica. Tools such as PASTOR and LUCTOR integrate different types of knowledge, including non-documented knowledge from field experts and make that knowledge transparent and open to critical review and discussion by others.
In this paper, a modelling system that integrates various complex model components for the purposes of water balance modelling and crop growth simulation is presented. These components are modules for calculating potential and actual evapotranspiration, crop growth and soil water balance. Two different complex simulation models obtained from the modelling system were tested using field data from two arable test sites. The modelling results show the ability of this modelling system to simulate water balance and crop growth with acceptable precision. Additionally, the impact of a recombination of the two simulation model components on the simulations of the field data was analyzed. These recombinations include an exchange of the soil water balance modules, the crop-growth models and the formulae for calculating potential evapotranspiration. This analysis indicates that the type of soil water model used is the most essential consideration for simulating the dynamics of soil water contents and percolation. The exchange of crop models and the use of different modules for calculating potential evapotranspiration affect evaporation, transpiration and interception. The impact of these rearrangements on soil water dynamics was less significant than the effects from the different soil water models.
This paper illustrates the basic ideas of good crop rotations, adequate crop husbandry and high resource-use efficiencies and some relevant ecological approaches. The use of special crops to prevent the need of high inputs of crop protectants or to reduce losses of nutrients at the level of the cropping system deserves special attention in research. Examples are given for the ecological control of soil-borne fungi, parasitic weeds, nitrogen loss and other sustainable techniques to increase the resource-use efficiency at the cropping system level.
A generic methodology is presented for exploration of sustainable land use options at the regional level by quantifying trade-offs between socio-economic and biophysical sustainability objectives. The methodology is called SOLUS (Sustainable Options for Land USe), and was developed over a ten year period of investigation in the Northern Atlantic Zone of Costa Rica. SOLUS includes a linear programming model, technical coefficient generators for livestock and cropping activities and a geographic information system. The linear programming model maximizes regional economic surplus subject to a flexible number of resource and sustainability constraints. Economic sustainability indicators are economic surplus and labor employment, and biophysical ones include soil N, P and K balances, pesticide use and its environmental impact, nutrient losses and a proxy for trace gas emissions. The capabilities of the methodology are illustrated for the Northern Atlantic Zone of Costa Rica. Though ample scope exists for reducing environmental effects and introducing sustainable production systems separately, pursuing both objectives simultaneously, considerably reduces economic surplus and agricultural employment. Agricultural area can be decreased and forested area increased without severely affecting the regional economic surplus.
The usefulness of water quality simulation models for environmental management is explored with a focus on prediction uncertainty. Ecological risk and environmental analysis often involve scientific assessments that are highly uncertain. Still, environmental management decisions are being made, often with the support of a mathematical simulation model. In the area of pollutant transport and fate in surface waters, few of the extant simulation models have been rigorously evaluated. Limited observational data and limited scientific knowledge are often incompatible with the highly-detailed model structures of the large pollutant transport and fate models. Two examples are presented to illustrate data and knowledge weaknesses that are likely to undermine these large models for decision support. An alternative to comprehensive structured simulation models is proposed as a flexible approach to introduce science into the environmental risk assessment and decision making process.
Intensive agriculture in The Netherlands has a price in the form of environmental degradation and the diminution of nature and landscape values. A reorientation of farming is needed to find a new balance between economic goals and rural employment, and care for clean water and air, animal well-being, safe food, and the preservation of soil, landscape and biodiversity. The search for farm systems that meet such multiple goals requires a systematic combination of (a) agrotechnical, agroecological and agroeconomic knowledge, with (b) the stakeholders’ joint agreement on normative objectives, to arrive at conceptual new designs followed by (c) empirical work to test, adapt and refine these under real commercial farming conditions. In this paper explorative modelling at the whole farm level is presented as a method that effectively integrates component knowledge at crop or animal level, and outlines the consequences of particular choices on scientific grounds. This enables quantitative consideration of a broad spectrum of alternative farming systems, including very innovative and risky ones, before empirical work starts. It thus contributes to a transparent learning and development process needed to arrive at farm concepts acceptable to both entrepreneurs and society. Three case studies are presented to illustrate the method: dairy farming on sandy soils; highly intensified flower bulb industry in sensitive areas in the western Netherlands; and integrated arable farming. Trade-offs between economic and environmental objectives were assessed in all three cases, as well as virtual farm configurations that best satisfy specified priority settings of objectives. In two of the three cases the mutual reinforcement and true integration of modelling and on-farm empirical research appeared difficult, but for obvious reasons. Only in the flower bulb case was the explorative approach utilized to its full potential by involving a broad platform of stakeholders. The other two case studies lacked such formalised platforms and their impact remained limited. Three critical success factors for explorative modelling are identified: to cover a well-differentiated spectrum of possible production technologies; early timing of modelling work relative to empirical farm prototyping; and involvement of stakeholders throughout.
An interactive multiple goal linear programming model has been developed for analysis of agricultural development options in a semiarid region in Mali. Natural and human resources have been quantified, constraints identified and the relations between agricultural activities described explicitly at both regional level and the level of agro-ecological zones. Animal husbandry and cropping system have been defined in a target-oriented way taking into account quantified aspects of sustainability. For crops this implies the requirement that the amounts of the macronutrients N, P and K in the rootable layer of the soil are safeguarded in the long run by nutrient applications. External inputs to realize predetermined target yields have been specified to compile quantitative input-output tables. Goals and goal-variables to be optimized in the model have been defined after consultations with various stakeholders in the region. Goal restrictions have been established through the interactive approach of the model.
Een introduktie in het ontwikkelen van computerprogramma's voor modellen van de plantengroei door dynamische simulatie. Het bestrijkt de disciplines gewasfysiologie, gewas-micrometeorologie, bodemfysica, bodemmicrobiologie en plantenziektekunde. Verschillende hoofdstukken zijn gebaseerd op onderwijsprogramma's van de Vakgroep Theoretische Teeltkunde van de Landbouwhogeschool Wageningen en zijn voorzien van oefeningen
The leaves and crowns from 15N-labelled sugar beets were incubated in either a silty clay loam or sand soil for almost one year. Four additions of fresh, chopped residues mixed with soil were tested: 15N-labelled leaves alone, 15N-labelled leaves plus unlabelled crowns, unlabelled leaves plus 15N-labelled crowns, and 15N-labelled crowns alone; a control with no addition was also incubated. The C:N ratio of the leaves was 11 and that of the crowns 40. Incubations were carried out in pots kept at 20 °C and optimal moisture conditions. The leaves mineralized N from the start of the experiment but the addition of crowns to soil at first caused immobilization of nitrogen followed eventually by mineralization after 6 or 12 weeks depending on soil type. The extra amounts of mineral N found in soil at the end of the experiment where additions were made corresponded to the sum of the background mineralization and the addition; no priming effects were encountered. Very slight differences only were found between the initial rates of mineralization of C in all of the treatments. Although there was also little difference between the sand and silty clay loam soils in the direct mineralization of nitrogen from the sugar beet leaves, where N was first immobilized (i.e. from crowns or a mixture) re-release of N took place more quickly in the sand soil. The total recovery of15 N found in soils after 24 weeks incubation ranged from 70% to 90% with least being lost from the sugar-rich but N-deficient crowns. Where leaves plus crowns were incubated together both residues contributed to the microbial biomass N.
Definitions and concepts of production ecology are presented as a basis for development of alternative production technologies characterized by their input-output combinations. With these concepts the relative importance of several growth factors and inputs is investigated to explain actual yield levels and resource-use efficiencies. Differences between potential and actual levels are analyzed to open ways for improved production technologies. The basis of the analysis is knowledge of basic physical, chemical, physiological and ecological processes at soil, field and crop level. New production technologies and their input-output combinations can be used in studies aimed at the exploration of options for sustainable agricultural production systems and land use. The concepts allow a systematic analysis and quantification of input-output combinations and clearly discriminate between bio-physical possibilities and socio-economic constraints and objectives. They help in defining objectives and means for agricultural production and land use, and may be valuable as aids to communication between various disciplines involved in studying the possibility and feasibility of future production technologies and land use options. The concepts production level, physical environment, target-oriented approach, production technique, production activity, and production orientation are applied to identify new technologies and production systems at various levels of scale, each requiring different types of information. In this paper some examples of applications are given at field, farm and at regional level.
The Netherlands Scientific Council for Government Policy (WRR) has explored possible future developments in rural land use within the European Community (EC) to support strategic policy making. Multiple goal linear programming (MGLP) was applied to evaluate different scenarios based on alternative policy views. For the MGLP-model, WRR needed information on agricultural production systems, specifically quantification of inputs like nutrients, water, pesticides, labour and machinery, and outputs like crop yields and environmental pollution. In this paper, the determination of inputs and outputs is described for a number of pre-defined cropping systems at regional level, using results of a land evaluation study for the EC. All cropping systems defined are based on the assumption that the best available production techniques are being used, taking into account that the explorations aim at possible agricultural developments in the next 25 years.
Trajectories over time of nitrogen use and yield show that the fertilizer is used as efficiently at the high end of the yield range, as at the low end. Apparently, any decrease in marginal returns as predicted by the law of diminishing returns is more or less compensated by the benefits of other technological changes. Main processes that govern such opposing trends are analyzed in this paper to contribute towards more efficient use of resources in agriculture. The analyses elaborate on the optimum law of Liebscher, formulated at the end of the 19th century. This law states that a production factor which is in minimum supply contributes more to production, the closer other production factors are to their optimum. With some reservations regarding the control of pests, diseases and weeds, this law is fully confirmed. Accordingly, no production resource is used less efficiently and most production resources are used more efficiently with increasing yield level due to further optimizing of growing conditions. Whether external means of production are used at all depends of course on their price, but as soon as the farmer can afford them, they should be used in such a way that the production possibilities of all other available resources are fully exploited. It thus appears that with further optimizing of the growing conditions an increasing number of inputs gradually lose their variable character and the number of fixed operations on the farm increase. This makes more and more inputs not a variable cost element, but a complementary cost element of the decision to farm a piece of land. Therefore strategic research that is to serve both agriculture and its environment should not be so much directed towards the search for marginal returns of variable resources, as towards the search for the minimum of each production resource that is needed to allow maximum utilization of all other resources.
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Eco-Regional Approaches for Sustainable Land Use and Food Production
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