Water balance of apricot trees (Prunus armeniaca L. cv. Búlida) under drip irrigation

The water balance of drip irrigated apricot trees (Prunus armeniaca L. cv. Búlida grafted onto “Realfino” apricot rootstock) was determined during a 30-month-period. Two irrigation regimes based on the reduction coefficients of Class A pan evaporation (1 and 0.5) were used to determine the water consumed. The water balance parameters for these treatments are shown and discussed in detail. Overall, the trees receiving less water showed 35% less evapotranspiration. Crop coefficients calculated on the basis of the water balance over a 30-month-period led to a saving of almost 14% water, since the coefficients were slightly below those used in other apricot orchards in the same area.     

Interactive responses to water deficits and crop load in olive (Olea europaea L., cv. Morisca). II: Water use, fruit and oil yield

To understand the relations between water use and yield in response to crop load, two experiments were conducted in olive (cv. Morisca), during six consecutive years (2002-2007) in an experimental orchard located in Badajoz, Southwest Spain. Experiment 1, assessed the responses during the early years of the orchard (2002-2004) using four irrigation treatments that applied fractions of the estimated crop evapotranspiration (ET_c) (125%, 100%, 75% and 0%) and three crop load levels (100%, 50% and 0% of fruit removal, termed Off, Medium and On treatments). Experiment 2 assessed the response of more mature trees (2005-2007) to three irrigation treatments (115%, 100%, and 60% of ET_c) and the natural crop load which were Off, On, and Medium in 2005, 2006 and 2007, respectively. Yield was reduced by water deficits and so did the estimated tree transpiration which was linearly related to yield (y = 1.2302x − 21.15, R² = 0.8864), showing the high sensitivity of cultivar Morisca to water deficits. The relations between fruit number and fruit weight showed that high crop loads had lower fruit weights and oil yield, a decrease that was more pronounced as water deficits increased. The yield response to water supply in the control and excess treatments, and the observations on the water relations of these two treatments suggest that the calculations made using the FAO method (Doorenbos and Pruit, 1974) with the crop coefficient proposed by Pastor et al. (1998) and the reduction coefficient (Fereres et al., 1982) to apply 100% of ET_c in the control treatment, underestimated the ET_c of the orchard. The results indicate that, although the absence of fruits lead to reduced water use as compared to situations of medium and high crop loads, canopy size was much more determinant of orchard water requirements than crop load.     

Water and salt balance at irrigation scheme scale: A comprehensive approach for salinity assessment in a Saharan oasis

Salt balance methods are generally applied in the root-zone and at local scales but do not provide relevant information for salinity management at irrigation scheme scales, where there are methodological impediments. A simple salt balance model was developed at irrigation scheme and yearly time scales and applied in Fatnassa oasis (Nefzaoua, Tunisia). It accounts for input by irrigation, export by drainage and groundwater flow, and provides novel computation of the influence of biogeochemical processes and variations in the resident amount of salt for each chemical component in the soil and shallow groundwater. Impediments were overcome by limiting the depth of the system so that the resident amount of salt that remained was of the same order of magnitude as salt inputs and allowed indirect and reliable estimation of groundwater flow. Sensitivity analyses as partial derivatives of groundwater salinity were carried out according to non-reactive salt balance under steady-state assumption. These analyses enabled the magnitude of the salinization process to be foreseen as a function of hydrological changes linked to irrigation, drainage, groundwater flow and extension of the irrigated area. From a salt input of 39 Mg ha⁻¹ year⁻¹ by irrigation, 21 Mg ha⁻¹ year⁻¹ (54%) and 10 Mg ha⁻¹ year⁻¹ (26%) were exported by groundwater flow and drainage, respectively. 7 Mg ha⁻¹ year⁻¹ (18%) were removed from groundwater by geochemical processes, while a non-significant 2 Mg ha⁻¹ year⁻¹ were estimated to have been stored in the soil and shallow groundwater where the residence time was only 2.7 years. The leaching efficiency of drainage was estimated at 0.77. With a water supply of 1360 mm by irrigation and 90 mm by rainfall, drainage, groundwater flow and actual evapotranspiration were 130, 230, and 1090 mm, respectively. The current extension of date palm plantations and salinization of groundwater resources are expected to significantly increase the salinity hazard while the degradation of the drainage system is expected to be of lesser impact. The approach was successfully implemented in Fatnassa oasis and proved to be particularly relevant in small or medium irrigation schemes where groundwater fluxes are significant.     

A rigorous approach of determining FAO56 dual crop coefficient using soil sensor measurements and inverse modeling techniques

Accurate estimation of crop coefficients for evaporation and transpiration is of great importance in optimizing irrigation and modeling water and solute transfers in the soil-crop system. In this study we used inverse modeling techniques on soil sensor measurements at depths from the soil-crop system to estimate crop coefficients. An inverse model was rigorously formulated to infer the crop coefficients and the lengths of growth stages using the measured soil water potential at depths during crop growth. By applying a micro-genetic algorithm to the formulated inverse model, the optimum values of the crop coefficient and the corresponding length of growth stage were successfully deduced. It has been found that the lengths of both the initial and development growth stages of cabbage were 5 d shorter than those from the FAO56 (Irrigation and Drainage Paper by the FAO). The deduced crop coefficient for transpiration at the initial growth stage was 0.11; slightly smaller than 0.15 recommended by the FAO56, while at the mid-season growth stage, the deduced value of 0.95 was identical with the recommended value. Results show that the predictions of soil water potential using the obtained values of crop coefficients agreed well with the measurements throughout the entire growing period, indicating that the deduced crop coefficients were credible and appropriate for cabbage grown under the specific conditions of location and climate. It follows that the strategy presented in the study can enable accurate estimates of crop coefficients to be obtained from soil sensor measurements and inverse modeling techniques.     

Water and nutrient use efficiency of a low-cost hydroponic greenhouse for a cucumber crop: An Australian case study

The Australian greenhouse industry is primarily dominated by low-cost hydroponic greenhouses for delivery of water and nutrients to plants to grow a variety of vegetable crops including cucumber and tomato. The nutrient rich drainage water from these greenhouses is generally released into the local environment causing pollution concerns. This study was initiated to investigate the opportunities in recycling drainage water to increase water and nutrient-use efficiency of hydroponic greenhouses and reduce the environmental impact of the drainage water discharge. Results indicated that a total of 4.15 ML/ha of irrigation water was applied during the 13 weeks crop growing period of which 2.56 ML/ha was drained off and 1.59 ML/ha was used to meet the crop evapotranspiration demand. The study showed that the recycling of the drainage water resulted in a 33% reduction in potable water used for irrigation in cucumber production. The drainage water contained 59% applied N, 25% applied P and 55% applied K and illustrated the potential for nutrient recovery and production cost savings through the reuse of drainage water. This case study demonstrates that some relatively simple changes in irrigation practices within greenhouse systems to recycle drainage water can considerably improve sustainability of low-cost hydroponic greenhouses and help minimise the environmental footprint of the greenhouse industry.     

基于主题模型的南水北调东线工程学术关注点研究

通过搜集从2003年到2016年与南水北调东线工程相关的1 405篇中文文献,借助LDA主题模型总共识别出13个有效主题,分别为“工程施工”“泵站运行优化”“水泵性能研究”“工程成本研究”“水环境模型”“河流水污染”“信息自动化”“湖泊富营养化”“水体污染物”“水泵结构计算”“水泵水力计算”“生态学”和“生态环境治理”,并对各主题的内容进行了分析,揭示出其内在的知识结构.然后使用了2个文献计量指标(主题占比和主题演变趋势)来描述南水北调东线工程的学术关注情况,发现“工程施工”为最热门主题,其次是“泵站运行优化”和“水泵性能研究”.而“水环境模型”和“湖泊富营养化”正逐渐成为研究热点.结果反映了学术界的关注情况,也为南水北调东线工程的后评价提供了决策依据.     

WaLIS—A simple model to simulate water partitioning in a crop association: The example of an intercropped vineyard

The introduction of cover crops in vineyards is being tested as it mitigates some undesirable environmental impacts of these cropping systems, such as surface runoff and soil erosion. In some cases, it could even reduce an excessive vegetative vigour of grapevine. However, most of time, wine growers are worried that severe competition for soil resources between the intercrop and grapevines could impair grape yield and quality. WaLIS (Water baLance for Intercropped Systems), a simple model simulating the water resource partitioning in such an association was designed to evaluate and optimize the water regime in intercropped systems.The model is presented and evaluated in this paper in three situations: the same grapevine cultivar (cv. Aranel) with either bare soil, or a temporary intercrop (barley) or a permanent intercrop (tall fescue). All three situations are located in the south of France. It is based on an existing model, designed to simulate the water regime of a bare soil vineyard, which was adapted to take into account the specific features of intercropped systems. Hence it includes a two-compartment representation of the soil particularly adapted to row crops. The simulation of a grass cover growth and its transpiration were added. Finally, particular importance was dedicated to the simulation of surface runoff which was the main source of the original model deviation during the winter period and made difficult multi-year simulations. Now, the model appears to be able to evaluate perennial cropping systems and provide decision support.The WaLIS model simulated the water available for both grapevine and intercrop well, and it proved to be efficient in most of the tested situations and years. The modelling of the water stress experienced by both crops was also generally good and all water fluxes simulated by the model were realistic. The main observed deviation in the simulation of the water soil content occurred during winter, i.e. outside the grapevine growth period. It was very likely due to the use of a constant parameter value for the surface runoff which did not take into account of changes in the soil surface and their effects on water infiltration.Finally, the analysis of sensitivity made on the WaLIS model showed that it is robust and sensitive to a few parameters, which drive the maximal grapevine transpiration and soil evaporation or are linked to the surface runoff simulation. The work also revealed how a good estimate of the total soil water available for each crop is crucial. This model, easy to use and parameterise, can provide sound management advice for designing valuable intercropped cropping systems.     

Hydrological impact of biofuel production: A case study of the Khlong Phlo Watershed in Thailand

This study evaluates the potential impact of increased biofuel production on the hydrology of a small watershed, Khlong Phlo, in the eastern part of Thailand. The water footprint of biofuel energy was estimated for three crops in order to identify the most water-efficient crop. The Soil and Water Assessment Tool (SWAT) model was used to evaluate the impact of land use change (LUC) caused by the expansion of biofuel crops on the components of water balance and water quality in the studied watershed. Several LUC scenarios consisting of oil palm (biodiesel), cassava and sugarcane (bio-ethanol) expansion were evaluated. The water footprint results indicated that cassava is more water-efficient than the other two crops considered. Simulation results revealed that although oil palm expansion would have negligible alteration in evapotranspiration (0.5 to 1.6%) and water yield (−0.5 to −1.1%), there would be an increased nitrate loading (1.3 to 51.7%) to the surface water. On the contrary, expansion of cassava and sugarcane would decrease evapotranspiration (0.8 to 11.8%) and increase water yield (1.6 to 18.0%), which would lead to increased sediment (10.9 to 91.5%), nitrate (1.9 to 44.5%) and total phosphorus (15.0 to 165.0%) loading to surface water. Based on the results, it can be concluded that land use change for biodiesel production would affect water quality, while both the water balance components and water quality would be affected by the expansion of bio-ethanol crops. Overall, the study indicates that biofuel production would have a negative impact on the water quality of the studied watershed. Further research at large scale (e.g. basin level) and on the economic aspect is recommended, in order to contribute to developing suitable land use and energy policies.     

Adapting to intersectoral transfers in the Zhanghe Irrigation System, China: Part II: Impacts of in-system storage on water balance and productivity

This paper investigates the impacts of farm ponds in a context of declining supplies in a major canal command within the Zhanghe Irrigation System (ZIS), in Central China. As dam supplies have been diverted to higher-valued uses (hydropower, cities and industry), farmers have responded by constructing small storages within their fields. These farm ponds have given them sufficient flexibility in water supply to practice varying forms of alternate wetting and drying irrigation for rice without compromising yields and incomes. Ponds are recharged by a combination of return flows from irrigation and runoff from catchment areas within the irrigated perimeter. Various scenarios of water supply incorporating the main reservoir, in-system reservoirs, farm ponds and irrigation practices were simulated using the OASIS model. OASIS integrates surface and groundwater flows, and contains a crop growth module to aggregate the impacts of different water management regimes. The modelling and sensitivity analysis show that further reductions in main reservoir supplies will have a negative effect on rice production in dry and average years, and that ponds have played a crucial role in adapting agriculture to reduced canal supplies. The flexibility allowed by the ponds has resulted in increased water productivity, except in high rainfall years, but net depletion has not decreased, as local supplies have substituted for water from the main reservoir. The study demonstrates the importance of properly accounting for return flows and the necessity to understand crop production in relation to the actual depletion of water (as evapotranspiration) within an irrigation system.     

A universal agro-hydrological model for water and nitrogen cycles in the soil-crop system SMCR_N: Critical update and further validation

Agro-hydrological models have widely been used for optimizing resources use and minimizing environmental consequences in agriculture. SMCR_N is a recently developed sophisticated model which simulates crop response to nitrogen fertilizer for a wide range of crops, and the associated leaching of nitrate from arable soils. In this paper, we describe the improvements of this model by replacing the existing approximate hydrological cascade algorithm with a new simple and explicit algorithm for the basic soil water flow equation, which not only enhanced the model performance in hydrological simulation, but also was essential to extend the model application to the situations where the capillary flow is important. As a result, the updated SMCR_N model could be used for more accurate study of water dynamics in the soil-crop system. The success of the model update was demonstrated by the simulated results that the updated model consistently out-performed the original model in drainage simulations and in predicting time course soil water content in different layers in the soil-wheat system. Tests of the updated SMCR_N model against data from 4 field crop experiments showed that crop nitrogen offtakes and soil mineral nitrogen in the top 90 cm were in a good agreement with the measured values, indicating that the model could make more reliable predictions of nitrogen fate in the crop-soil system, and thus provides a useful platform to assess the impacts of nitrogen fertilizer on crop yield and nitrogen leaching from different production systems.     

南水北调中线干线工程安全监测自动化系统

介绍了南水北调中线干线工程基本情况,对该工程管理模式和输水特点进行了说明,从工程安全监测的必要性出发,阐述了安全监测自动化系统设计思想,重点对系统功能、网络结构等内容进行了详细说明。     

Constraints to farmers’ adoption of direct-seeding mulch-based cropping systems: A farm scale modeling approach applied to the mountainous slopes of Vietnam

Substantial initiatives are under way in the tropical world to develop and promote direct-seeding mulch-based cropping systems (DMC) in order to reduce soil erosion and improve crop nutrient and water balances. DMC have been adopted by large-scale mechanized farmers, especially in America and Australia, but seldom by resource-poor farmers in the developing world. This study was conducted in Vietnam with the aim of evaluating the feasibility of farmers’ implementing DMC in a mountainous area. The method involved simulation of rational households maximizing their income subject to food security constraints and availability of resources. It generated insight into why farmers of a small region were reluctant to adopt DMC due to the extra labor and input required to implement these techniques during the first years, which hampers their economic performance. In another region, under different biophysical and economic environmental conditions, the study showed that DMC were more likely to be adopted provided that possible constraints at the community level are overcome. The method also allowed us to discuss the types of technical improvements that would make DMC more attractive to farmers. For most farm types, labor required by mulch establishment would have to be reduced by more than 30%. This would mean spreading much less biomass than the 7 t ha⁻¹ currently necessary, compromising the weed-control function of mulch. This would be technically feasible only by using herbicides but this would not be economically sound since it would increase cash requirements. The study showed that subsidies of 50 to more than 200 USD ha⁻¹ were necessary to enable the conversion of all conventionally managed sloping land into DMC in the simulations. These amounts are high relatively to gross margins (250-750 USD ha⁻¹) under conventional management.     

Performance of CERES-Rice and CERES-Wheat models in rice–wheat systems: A review

Rice–wheat (RW) systems are critical to food security and livelihoods of rural and urban poor in south Asia and China, and to regional economies in southeast Australia. The sustainability of RW systems in south Asia is, however, threatened by yield stagnation or decline, and declining partial factor productivity, soil organic C and water availability. Crop models potentially offer a means to readily explore management options to increase yield, and to determine trade-off between yield, resource-use efficiency and environmental outcomes. This paper reviews the performance of CERES-Rice and CERES-Wheat in Asia and Australia in relation to their potential application towards increasing resource use efficiency and yield of RW systems.

The performance of the models was evaluated using simulated and observed data on anthesis and maturity dates, in-season LAI and growth, final grain yield and its components, and soil water and N balances from published studies across Asia and Australia, and then by computing the statistical parameters for the major characters. Over the four data sets examined for anthesis and six for maturity dates, CERES-Rice predicted those dates fairly well (normalised RMSE = 4–5%; D-index = 0.94–0.95), but over the 11 sets for grain and 4 for biomass yield, the predictions were more variable (normalised RMSE = 23% for both; D-index 0.90 and 0.76, for grain and biomass, respectively). Model performance was poorer under conditions of low N, water deficit, and low temperatures during the reproductive stages. Over the three data sets examined, CERES-Wheat predicted the anthesis and maturity dates quite well (normalised RMSE = 4–5%; D-index = 0.94–0.99), and over eight sets for grain and two sets for biomass yield the model predicted them also reasonably well (RMSE = 13–16%; D-index = 0.86–0.97). Only one study evaluated the DSSAT RW sequence model with fairly satisfactory predictions of rice and wheat yields over 20 years with adequate N, but not the long-term change in soil organic C and N. Predictions of in-season LAI and crop growth, and soil and water processes were quite limited to investigate the robustness of model processes.

Application of models to evaluate options to increase water and N use efficiency requires the ability to perform well at the margin where deficit stress begins. While both models generally perform satisfactorily under water and N non-limiting conditions, the little evidence available suggests that they do not perform well under resource-limiting situations. We recommend that the models’ key processes under the water and N limiting conditions be further evaluated urgently. The DSSAT sequence model also needs to be further evaluated against observations for a range of locations and management using data from long-term experiments in RW systems.     

Effects of planting density on the productivity and water use of tea (Camellia sinensis L.) clones: I. Measurement of water use in young tea using sap flow meters with a stem heat balance method

Sap flow meters based on the stem heat balance method were used to measure the mass flow rates or water use in young potted tea (Camellia sinensis L.) plants of clones AHP S15/10 and BBK35. The meters were constructed on site and installed onto the stem or branch sections of field growing plants in an experiment originally designed to study the effects of plant population density and drought on the productivity and water use of young tea clones. The objective of the study was to use the SHB method as a first attempt to use sap flow meters for determining the water use of young tea growing in the field under well watered conditions in Tanzania. The results are reported and recommendation made for further work on using the technique.     

Exante assessment of dual-purpose sweet potato in the crop–livestock system of western Kenya: A minimum-data approach

Mixed crop–livestock systems have a crucial role to play in meeting the agricultural production challenges of smallholder farmers in sub-Saharan Africa. Sweet potato is seen as a potential remedial crop for these farmers because of its high productivity and low input requirements, while its usefulness for both food and feed (dual-purpose) make it attractive in areas where land availability is declining. In this paper, we develop and apply a ‘minimum-data’ methodology to assess exante the economic viability of adopting dual-purpose sweet potato in Vihiga district, western Kenya. The methodology uses and integrates available socio-economic and bio-physical data on farmers’ land use allocation, production, and input and output use. Spatially heterogeneous characteristics of the current system regarding resources and productivity are analyzed to assess the profitability of substituting dual-purpose sweet potato for other crops currently grown for food and feed. Results indicate that a substantial number of farmers in the study area could benefit economically from adopting dual-purpose sweet potato. Depending on assumptions made, the adoption rate, expressed as the percentage of the total land under adopting farms, is between 55% and 80%. The analysis shows that the adoption rate is likely to vary positively with the average total yield of dual-purpose sweet potato, the harvest index (the ratio between tuber and fodder yields), the price of milk, and the nutritional value of available fodder. This study demonstrates the usefulness of the minimum-data methodology and provides evidence to support the hypothesis that dissemination of the dual-purpose sweet potato could help improve the livelihoods of smallholder farmers operating in mixed crop–livestock systems in east Africa.     

Livestock water productivity in mixed crop–livestock farming systems of the Blue Nile basin: Assessing variability and prospects for improvement

Water scarcity is a major factor limiting food production. Improving Livestock Water Productivity (LWP) is one of the approaches to address those problems. LWP is defined as the ratio of livestock’s beneficial outputs and services to water depleted in their production. Increasing LWP can help achieve more production per unit of water depleted. In this study we assess the spatial variability of LWP in three farming systems (rice-based, millet-based and barley-based) of the Gumera watershed in the highlands of the Blue Nile basin, Ethiopia. We collected data on land use, livestock management and climatic variables using focused group discussions, field observation and secondary data. We estimated the water depleted by evapotranspiration (ET) and beneficial animal products and services and then calculated LWP. Our results suggest that LWP is comparable with crop water productivity at watershed scales. Variability of LWP across farming systems of the Gumera watershed was apparent and this can be explained by farmers’ livelihood strategies and prevailing biophysical conditions. In view of the results there are opportunities to improve LWP: improved feed sourcing, enhancing livestock productivity and multiple livestock use strategies can help make animal production more water productive. Attempts to improve agricultural water productivity, at system scale, must recognize differences among systems and optimize resources use by system components.     

Evaluation of the water use efficiency of alternative farm practices at a range of spatial and temporal scales: A conceptual framework and a modelling approach

Water is the principal limiting resource in Australian broadacre farming, and the efficiency with which farmers use water to produce various products is a major determinant both of farm profit and of a range of natural resource management (NRM) outcomes. We propose a conceptual framework based on multiple water use efficiencies (WUEs) that can be used to gain insight into high-level comparisons of the productivity and sustainability of alternative farming practices across temporal and spatial scales. The framework is intended as a data aggregation and presentation device. It treats flows of water, biomass and money in a mixed farming system; economic inefficiencies in these flows are tracked as they are associated with a range of NRM indicators.We illustrate the use of the framework, and its place in a larger research programme, by employing it to synthesise the results from a set of modelling analyses of the effect of land use choices on long-term productivity and a range of NRM indicators (frequency of low ground cover, deep drainage, N leaching rates and rate of change in surface soil organic carbon). The analyses span scales from single paddocks and years to whole farms and have been carried out with the APSIM and GRAZPLAN biophysical simulation models and the MIDAS whole-farm economic model.In single wheat crops in one study, different land uses in preceding years affect grain yield primarily by affecting the harvest index. When the scale changes to cropping rotations, the critical factor affecting overall water use efficiency is found to be the proportion of stored soil water that is transpired by crops. When ordinated in terms of their water use efficiencies, a set of 45 modelled rotation sequences at another location are differentiated mainly by the proportion of pasture in the rotation; when rotations are ordinated using key NRM indicators, the proportion of lucerne pasture is the main distinguishing factor. Finally, we show that for whole crop-livestock farms at three different locations across southern Australia, the pattern of water use efficiencies in the most profitable farming systems changes in similar ways as cropping proportion is altered. At this scale, land use choices affect multiple water use efficiency indices simultaneously and commodity prices determine the balance of the resulting economic tradeoffs.Limitations to the use of the WUE framework arising from its relative simplicity are discussed, as are other areas of farming systems research and development to which it can be applied.     

GAMEDE: A global activity model for evaluating the sustainability of dairy enterprises Part I – Whole-farm dynamic model

 Crop-livestock farms are complex systems. The interactions operating in such systems involve decisional, biophysical, structural, and environmental factors. Moreover, as farmers face a large range of management options, tools are needed to support their decision-making to enable them to reach production levels meeting their objectives and compatible with their human and physical resources, while controlling their effects on the environment. Gamede, a whole-dairy-farm model, has been developed to explore this complexity and to represent dynamically the effect of management decisions on biomass and nitrogen flows and on numerous sustainability indicators, such as milk and forage crop productivity, labour requirements, nitrogen balance, and nitrogen efficiency.This article describes the integration of six modules accounting for biophysical processes in a dairy farm (forage production; forage conditioning; herd demography; milk, excreta and animal biomass productions; grazing, quality of fertilisers; and nitrogen gaseous emissions) together with a decision system accounting for the farmer’s strategy and technical operations. Most of the six biophysical modules incorporate mathematical models from the literature, but the decision system stems from our own original work.Six commercial farms with different structures, agro-climatic conditions and management strategies were used for validation. The model can explain the differences found in their sustainability indicators at the year scale. The intra-year variability of the main biomass stocks and flows is also well explained. This quantitative validation was completed by a qualitative validation from researcher, adviser and farmer points of view, including simulations of prospective scenarios.     

GAMEDE: A global activity model for evaluating the sustainability of dairy enterprises. Part II – Interactive simulation of various management strategies with diverse stakeholders

GAMEDE is a stock-flow dynamic simulation model designed with farmers to represent dairy farm functioning and the consequences of the farmer’s daily management decisions for whole-farm sustainability. Sustainability is evaluated according to its three pillars: technico-economic viability, respect for environment, and social liveability. The model provides original information for a better understanding of the processes regulating nitrogen dynamics within the farm, and the factors determining farmers’ decisions and practices. Model implementation experiments have revealed that GAMEDE is also a useful tool to support discussions and to generate knowledge exchange among various stakeholders who play an important role in the development of farm sustainability: farmers, extension agents and researchers.While a majority of researchers and advisers are specialised and a majority of farmers fix their attention on specific and narrow themes of farm management, such a comprehensive model can help stakeholders complement their knowledge to gain a holistic view of the farming system. This holistic and integrated view is crucial: (i) for researchers who wish to explain diversity in farming systems and understand decisional and biophysical processes and their interrelated effects operating in such complex agro-ecosystems, (ii) for advisers whose aim is to define alternative management strategies applicable in practice, i.e. taking into account farm specificities, and (iii) for farmers who must choose practices compatible with their resources, assets, constraints and objectives.Holism can also improve versatility and thus the generic character of models. Issues are narrowly specified and greatly vary both among categories of stakeholders (e.g. scientists versus farmers) and within each category (e.g. among farmers). A comprehensive model that: (i) details all farm management operations, and (ii) represents their effects on different spatio-temporal levels and on the three sustainability dimensions, is more likely to respond to the various issues facing different stakeholders. We argue that capacity of models to respond to stakeholders’ questions has to be considered in future evaluations of decision support systems.