Cereal–legume intercropping can promote plant growth (i.e. facilitation) through an increase in the amount of phosphorus (P) taken up, especially in low P soils. The aim of this study was to test the ...hypothesis that these positive interactions are supported by rhizosphere processes that increase P availability, such as root-induced pH changes. In neutral and alkaline soils legumes are assumed to increase inorganic P availability by rhizosphere acidification due to N
2 fixation which benefit to the intercropped cereal. Growth, P uptake, changes in inorganic P availability and pH in the rhizosphere of intercropped species were thus investigated in a greenhouse pot experiment with durum wheat and chickpea either grown alone or intercropped. We used a neutral soil from a P fertilizer long-term field trial exhibiting either low (−P) or high (+P) P availability. Phosphorus availability was increased in the rhizosphere of both species, especially when intercropped in −P. Such increase was associated with alkalization. Rhizosphere pH changes could not fully explain the observed changes of P availability though. Low rates of N
2 fixation may explain why no rhizosphere acidification was observed. Increases in P availability did not lead to enhanced P uptake but growth promotion was observed for durum wheat intercropped with chickpea in −P soil. Our hypothesis of an increase in inorganic P availability in intercropping as a consequence of root-induced acidification by the legume was not validated, and we suggested that root-induced alkalization was involved instead, as well as other root-induced processes. Thus, the cereal through rhizosphere alkalization may also enhance P uptake and growth of the intercropped legume. Facilitation can thus occur in both ways.
► Both durum wheat and chickpea increase P availability in their rhizospheres. ► P availability was enhanced especially when species were intercropped in a low P soil. ► Increases in P availability occurred even with root-induced alkalization in a neutral soil. ► Other rhizosphere processes than root-induced pH changes were involved in increasing P availability. ► Chickpea facilitated durum wheat in a low P soil, and vice versa.
We used of a set of mechanistic adsorption models (1-pK TPM, ion exchange and Nica-Donnan) within the framework of the component additive (CA) approach in an attempt to determine the effect of ...repeated massive application of inorganic P fertilizer on the processes and mechanisms controlling the concentration of dissolved inorganic phosphorus (DIP) in soils. We studied the surface layer of a Luvisol with markedly different total concentrations of inorganic P as the result of different P fertilizer history (i.e. massive or no application for 40
years). Soil pH was made to vary from acid to alkaline. Soil solutions were extracted with water and CaCl
2 (0.01
M). The occurrence of montmorillonite led us to determine the binding properties of P and Ca ions for this clay mineral.
Satisfactory results were obtained using generic values for model parameters and soil-specific ones, which were either determined directly by measurements or estimated from the literature. We showed that adsorption largely controlled the variations of DIP concentration and that, because of kinetic constrains, only little Ca-phosphates may be precipitated under alkaline conditions, particularly in the P fertilized treatment. The mineral-P pool initially present in both P treatments did not dissolve significantly during the course of the experiments. The adsorption of Ca ions onto soil minerals also promoted adsorption of P ions through electrostatic interactions. The intensity of the mechanism was high under neutral to alkaline conditions. Changes in DIP concentration as a function of these environmental variables can be related to changes in the contribution of the various soil minerals to P adsorption. The extra P adsorbed in the fertilized treatment compared with the control treatment was mainly adsorbed onto illite. This clay mineral was the major P-fixing constituent from neutral to alkaline pH conditions, because the repulsion interactions between deprotonated hydroxyl surface sites and P ions were sufficiently counterbalanced by Ca ions. The drastic increase of DIP observed at acid pH was due to the effect of the lower concentration of surface sites of Fe oxides and kaolinite.
In addition to confirming the validity of our approach to model DIP concentrations in soils, the present investigation showed that adsorption was the predominant geochemical process even in the P fertilized soil, and that Ca ions can have an important promoting effect on P adsorption. However the influence of the dissolution of the mineral-P pool under field conditions remained questionable.
Sustainability is a holistic and complex multi-dimensional concept encompassing economic, social and environmental issues, and its assessment is a key step in the implementation of sustainable ...agricultural systems. Realistic assessments of sustainability require: (1) the integration of diverse information concerning economic, social and environmental objectives; and (2) the handling of conflicting aspects of these objectives as a function of the views and opinions of the individuals involved in the assessment process. The assessment of sustainability is therefore increasingly regarded as a typical decision-making problem that could be handled by multi-criteria decision-aid (MCDA) methods. However, the number and variability of MCDA methods are continually increasing, and these methods are not all equally relevant for sustainability assessment. The demands for such approaches are also rapidly changing, and faster ex ante assessment approaches are required, to address scales currently insufficiently dealt with, such as cropping system level. Researchers regularly carry out comparative analyses of MCDA methods and propose guidelines for the selection of a priori relevant methods for the assessment problem considered. However, many of the selection criteria used are based on technical/operational assumptions that have little to do with the specificities of ex ante sustainability assessment of alternative cropping systems. We attempt here to provide a reasoned comparative review of the main groups of MCDA methods, based on considerations related to those specificities. The following main guidelines emerge from our discussion of these methods: (1) decision rule-based and outranking qualitative MCDA methods should be preferred; (2) different MCDA tools should be used simultaneously, making it possible to evaluate and compare the results obtained; and (3) a relevantly structured group of decision-makers should be established for the selection of tool variants of the choosen MCDA methods, the design/choice of sustainability criteria, and the analysis and interpretation of the evaluation results.
Assessing the diversity of sustainability performances of cropping systems in a given regional context is interesting for several reasons, whether for public decision-making or advice to farmers. ...This article presents a multicriteria analysis of organic arable cropping systems in the Midi-Pyrenees region of France. The work, performed with a group of extension agents, required adapting a generic assessment model (MASC) to the particular characteristics of organic systems. Forty-four cropping systems from 19 farms were assessed. The indicators of economic, social and agronomic sustainability show high variability. The economic dimension is the most difficult to secure, since profitability is scored low and economic autonomy is scored medium or low in most cases. The agronomic dimension is frequently considered medium but also rather low in one out of five cases. Problems are associated mainly with nutrient management at the crop-rotation scale. Higher scores are observed for the environmental dimension, even if weak points were identified regarding the use of energy and water resources or the risk of nitrate leaching. Social acceptability scores better for farmers than for society as a whole, given the frequent low production levels of organic cropping systems and their small contribution to local employment. The comparison of irrigated and non-irrigated systems shows that the level of intensification chosen by farmers influences the performance profile of their cropping systems. Irrigated systems have higher economic performance but lower agronomic and environmental performances. In both cases, poor crop productivity levels observed for some systems may impinge on their overall sustainability.
L’analyse de la diversité des performances en durabilité des systèmes de culture dans un contexte régional particulier présente plusieurs sources d’intérêt, que ce soit pour l’aide à la décision publique ou le conseil aux agriculteurs. Cet article présente une évaluation multicritère des systèmes de grandes cultures biologiques spécialisés de la région Midi-Pyrénées. L’entreprise, conduite avec un groupe de conseillers agricoles, a nécessité l’adaptation d’un modèle d’évaluation générique (MASC) aux spécificités de l’agriculture biologique. L’évaluation a porté sur 44 systèmes de culture provenant de 19 exploitations. Les indicateurs de durabilité économique, sociale, et agronomique montrent une variabilité importante. La dimension économique est la plus difficile à assurer, en raison d’une rentabilité jugée le plus souvent faible et d’une autonomie économique moyenne ou faible dans la majorité des cas. La dimension agronomique est fréquemment jugée moyenne mais aussi assez faible dans un cas sur cinq. Les difficultés sont associées essentiellement à la gestion des nutriments à l’échelle des rotations. La dimension environnementale est très favorablement notée, même si des points faibles ont été identifiés concernant l’utilisation des ressources en énergie et en eau, ou les risques de lixiviation de l’azote. L’acceptabilité sociale est favorablement notée, mais cela tient plus à l’acceptabilité pour les agriculteurs que vis-à-vis de la société globale, compte tenu d’un niveau de productivité souvent peu élevé et d’une faible contribution à l’emploi. La comparaison des systèmes irrigués et non irrigués démontre que le niveau d’intensification choisi par les agriculteurs influence le profil de performances des systèmes de culture. Les premiers sont plus performants du point de vue économique, mais moins du point de vue agronomique et environnemental. Dans les deux cas, le niveau de productivité des cultures peut être insuffisant et influer défavorablement sur la durabilité totale des systèmes.
► We propose a guide to compare assessment methods of agricultural systems. ► The guide consists of six categories (e.g. type of system, target users). ► We tested the guide with advisors involved in ...a participatory action project. ► The guide helped advisors to choose the method adapted to their expectations.
Modern agriculture must meet new challenges such as production of healthy food, adaptation to climate change, protection of natural resources, and conservation of landscape. These challenges require changes in current agricultural systems and therefore, environmentally-friendly agricultural systems must be designed and their sustainability assessed. Over the past several years, various methods have been developed for making such assessments (e.g. the Balancing and Ranking Method, MEACROS, MODAM, the modelling framework of Pacini et al., ROTAT+FarmImages, MASC, and ROTOR) but few studies put forward simple solutions for selecting one method over another. In this paper, we propose a simple guide to distinguish methods one from another. Categories of the guide include the type of systems to assess, the spatial and temporal scales at which systems are assessed, the dimensions of sustainability for which systems are assessed, the type of visualisation for comparing options, the target users, and the ability to generate alternative systems. The guide was developed and tested with a group of farm advisors involved in a three-year project called RotAB, which aimed to assess the sustainability of organic arable farming systems: the advisors looked for a method for sustainability assessment of cropping systems. We presented seven recent assessment methods as well as the guide to advisors. The guide’s key points allowed them to clearly express their requirements: the method they looked for had to evaluate cropping systems and helped advisors to propose new ones; it had to evaluate multiple sustainability criteria that are easily understandable by farmers; indicators had to be scientifically based, without the need for many input data; the method had to be easy to use and produced graphical output that can be discussed with farmers. Finally, the guide helped advisors to choose one of the seven methods (in that case they chose MASC). This guide can help decision-makers distinguish assessment tools from one another using simple categories and choose the one best adapted to their expectations.
Realistic assessments of sustainability are often viewed as typical decision-making problems requiring multi-criteria decision-aid (MCDA) methods taking into account the conflicting objectives ...underlying the economic, social and environmental dimensions of sustainability, and the different sources of knowledge representing them. Some MCDA-based studies have resulted in the development of sustainable agricultural systems, but the new challenges facing agriculture and the increasing unpredictability of their driving forces highlight the need for faster ex ante (‘
Before-the-event
’) assessment frameworks. These frameworks should also (i) provide a more realistic assessment of sustainability, by integrating a wider range of informal knowledge,
via
the use of qualitative information; (ii) address alternative scales, such as cropping system level, improving granularity for the handling of sustainability issues and (iii) target a larger panel of decision-makers and contexts. We describe here the MASC model, which is at the center of a framework addressing these objectives. The MASC model has at its core a decision tree that breaks the sustainability assessment decisional problem down into simpler units as a function of sustainability dimensional structure (economic, social and environmental), generating a vector of 32 holistic ‘mixed’ (quantitative and qualitative) elementary criteria rating cropping systems. The assessment process involves the calculation of these criteria, their homogenization into qualitative information for input into the model and their aggregation throughout the decision tree based on ‘
If-Then
’ decision rules, entered by the user. We present the model and describe its first implementation for the evaluation of four cropping systems generated from expert knowledge, and discuss its relevance to the objectives cited above. The MASC model has several advantages over existing methods, due to its ability to handle qualitative information, its transparency, flexibility and feasibility.
Agronomists need methodologies to assess the sustainability of cropping systems. Few models such as MASC have been recently developed for evaluation. The effective use of those models is still a ...challenge, notably for low-input systems. Here a more specific model entitled MASC-OF was developed and applied to study stockless organic cropping systems. The MASC-OF model is original because it is based on agricultural advisers’ needs and expertises. Two groups of advisers supported by agronomic scientists were involved in a nine-step methodology to progress from preliminary meetings to data analysis. The methodology allowed advisers to design a model including their own views on what is a sustainable organic cropping system. Soil fertility and weed and pest control were integrated as a new branch in the original MASC model. We also developed evaluation criteria for each basic attribute, defining aggregation rules and weighting attributes. Tested case studies were based on 44 real cropping systems identified on 19 farms in the Midi-Pyrenees region of France and on 23 cropping system types developed by the advisers from the Centre, Ile-de-France, Pays de Loire, Poitou-Charentes and Rhône-Alpes regions of France. Our results show that a high score of economic sustainability is the most difficult to achieve. This finding is explained by low productivity of cereal crops and high variability of market prices for organic grain. Further, agronomic viability is also difficult to ensure, as a consequence of poor soil-fertility management practices. The ability to achieve social acceptability for the producer, including workload and health risk, is high. By contrast, acceptability for the society has a medium score due to reduced productivity and contribution to local employment. Environmental sustainability is the easiest dimension to achieve, despite nitrogen-loss risks in some situations and high water and energy consumption in irrigated systems. Overall our findings show that the potential for the development of more sustainable organic cropping systems in stockless farms is high.
New agricultural systems are required to satisfy societal expectations such as higher quantity and quality of agricultural products, reducing environmental impacts, and more jobs. However, ...identifying and implementing more suitable agricultural systems is difficult due to conflicting objectives and to the wide diversity of scientific disciplines required to solve agricultural issues. Therefore, designing models to assess the sustainability of agricultural systems requires multi-criteria decision aid methods. The French agronomist community has recently developed 11 hierarchical and qualitative models to assess sustainability using the DEXi decision aid software. Here, we give guidelines to help designers to build their own specific models. First, we present the principles and applications of the DEXi software. Then, we provide guidance on the following steps of model designing: (1) initial analysis and planning of the design process, (2) selection and hierarchy of sustainability criteria, (3) indicator selection and building, (4) parameterization, (5) evaluation, and (6) model dissemination and uses. We then discuss advantages and drawbacks of this kind of modeling formalism, the role of a participatory approach, and the main properties to consider during the design process.
Fertiliser recommendation systems should aim at a finer tuning of non-renewable P inputs for agronomic, environmental and economic reasons. Modern decision support systems should take into account ...the relevant soil characteristics, the P recycling capabilities of the cropping system, and crop requirements for attainable production in a range of soil/weather conditions. Unfortunately, information is still lacking for low input cropping systems in south-western France. In 1968 INRA Toulouse set up a P experiment, which has been going on for 36 years, on a deep alluvial silty-clay/clay soil with varying CaCO
3. Four P regimes (P0, P1, P2, P4) were arranged in four blocks with periodic changes in the fertiliser dressings. Wheat, maize, sunflower, sorghum and soybean were tested for grain yield (GY) and grain P concentration (GPC) response to soil Olsen P concentration. The highest GY were observed in both P2 and P4, although P1 yields were significantly lower in only 4 years out of 36. P0 resulted 32 times in lower yields than P2–P4 and 27 times in lower yields than P1. Wheat was the crop most sensitive to the absence of P fertilization (GY
P0/GY
Pmax
=
0.72); maize and sorghum were intermediate (0.77) and sunflower was the less sensitive on average (0.83). As the highest GPC values were observed in the P4 treatments, P removal was maximum for P4 (21.9
kg
P
ha
−1
year
−1) and minimal in P0 (11.7
kg
P
ha
−1
year
−1). The critical soil Olsen P values for yield responses were determined using the Cate–Nelson and Mitscherlich approaches. Although the thresholds differ for the two methods (3.3–7.2
mg
P
kg
−1 with Cate–Nelson; 4.4–11.2
mg
P
kg
−1 with Mitscherlich), crops ranked similarly with both methods. Critical soil P values were lowest for maize and highest for sunflower, while wheat, soybean and sorghum had intermediate values. Because of low-input management and frequent water stress, critical values fall within the lower range of published values. Only in the P4 treatment were P-Olsen values potentially hazardous for the environment (>20
mg
P
kg
−1) 8–10 years after the beginning of the experiment. Annual P dressings of 17.5
kg
P
ha
−1
year
−1 (P1) were sufficient to achieve good yields but P dressings of 35
kg
P
ha
−1
year
−1 (P2) were necessary to stabilize soil P around the critical level in the calcareous part of the experiment.
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