•Alfalfa yield was reduced in the shade of walnut trees, but BNF was significantly increased.•The light use efficiency of alfalfa increased by 35% in the shade.•BNF increase may result from N ...competition or mineralization inhibition under the trees.
While intercropping annual non nitrogen-fixing crops with deciduous hardwood species is now well documented, there is a need to investigate if nitrogen-fixing intercrops may succeed in agroforestry systems. Intercropping with trees usually leads to a decline in crop yield, and could in addition possibly reduce the biological N fixation (BNF) over time due to the competition for resources. In a Mediterranean experimental site, 17 year-old hybrid walnut trees (Juglans nigra x Juglans regia L.) planted in East-West oriented lines were intercropped with alfalfa (Medicago sativa L.) to assess the impact of competition for light and water on alfalfa yield and BNF. Alfalfa yield and shoot δ15N values (a proxy for the proportion of N derived from the air, %Ndfa) were measured during one year at different distances from the tree row in two directions (north and south). Alfalfa yield was reduced close to the tree row (−28% and −22% on the northern and southern sides respectively), but less than the reduction of irradiation (−59% and −33% respectively). Shading improved by 35% the apparent light use efficiency (LUE: aboveground biomass produced per unit of global radiation) of alfalfa, indicating that alfalfa was shade tolerant at this Mediterranean site. Alfalfa shoot δ15N values were lower close to the tree rows than at mid inter-row: BNF was stimulated close to the trees. Compensative and facilitative mechanisms between trees and alfalfa plants led to a rise in LUE and%Ndfa in shaded areas. These results contradict the frequent assumption that N fixation is reduced in the shade of trees. Appropriate tree canopy management may help maintain light competition between trees and alfalfa to a level that still enhance complementary, which would further improve the sustainability of the use of alfalfa as an intercrop in Mediterranean regions.
Alternative agricultural systems, such as organic farming (OF), are promising options to sustain both agriculture productivity and environmental health. However, the adoption of OF by farmers is ...occurring more slowly than is advocated. A key factor limiting farmers is an inability to predict socio-economic consequences of converting to OF. To overcome this, we developed a novel method of integrated assessment of agricultural systems (IAAS) and applied it to scenarios of development of OF in the Camargue region, South of France. In collaboration with the local stakeholders, we characterized the agricultural systems at different spatial scales and defined scenario related to the future of agriculture and to OF. We then used agent-based modeling with farmers and bio-economic modeling with local stakeholders for scenario assessment. We examined the effects on the development of OF systems of key factors such as the ongoing reform in the European Common Agricultural Policy and the effects of regulations for decreased use of pesticides. The policy reform implied trends towards a diversification of crops and greater possibility for conversion to OF. Development of OF at the regional level led to improved environmental performance, but caused a decrease in profitability of the rice supply chains. In light of the observed trade-off between rice production and OF development, objectives and options towards more sustainable agricultural systems were discussed with farmers and local stakeholders. Stakeholders' assessment of the framework provided insights on the positive and specific aspects of the IAAS methodology requiring improvement. The complementarities of agent-based and bio-economic modeling provide stakeholders with a better-informed assessment of diverse scenarios, for the development of more sustainable agricultural systems.
•We target the participatory integrated assessment of agricultural systems.•Scenarios related to organic farming were assessed with local stakeholders.•We combined agent-based and bio-economic modeling to assess scenarios.•The case study in Camargue reveals the complementarities between the models.
Organic viticulture is an effective cultivation method that can reduce the environmental impacts of grape growing while maintaining profitability. For some vineyards, simple adjustments can suffice ...to make the conversion to organic farming; however, for most, major changes in system structure and management must be implemented. Here, we showed for the first time that converting to organic viticulture impacts vineyard complexity. We used six complexity indicators to assess modifications to cropping system structure and management: number of fields, number of difficult-to-manage fields, vineyard area, number of field interventions, number of technical management sequences, and number of management indicators. These six indicators were assessed through interviews carried out with winegrowers from 16 vineyards between 2008 and 2012. Changes in vineyard performances during conversion were also measured. We demonstrate that conversion to organic viticulture increased the complexity of vineyard structure and management for the 16 vineyards surveyed. While this increase allowed agronomic performances in all vineyards to be maintained, it also came with an increase in labor requirements (of up to 56%) compared to conventional agriculture. We conclude that the six indicators are appropriate for assessing changes in vineyard complexity and could be extended to all agricultural systems to better anticipate the implications of organic farming conversion for a farm’s biophysical, technical, and decisional subsystems.
In the Mediterranean area, the introduction of cover crops in vineyards is hampered by the risk of severe competition for water. Belowground interactions are still not very clear in this ...perennial-herbaceous association. This work was aimed at characterizing the development of the root systems of associated crops and the soil water dynamics. It also investigated whether water competition could be the cause of vine vigour and yield reductions. Experiments were conducted in a 4-year-old association (vine – tall fescue) and in a weed controlled vineyard. Water transfers in the soil were estimated on the basis of the soil water potential and soil hydrodynamic properties. The vine root system was concentrated in the soil under the row, whereas the intercrop highly colonized a soil compartment under the inter-row to a depth of approximately 1 m. Despite this spatial complementarity in root distribution, intercropping reduced the amount of soil water available for the vine crop. The low soil water content reduced soil water conductivity thereby limiting water transfers, despite a significant gradient in the soil water potential. This conductivity did not differ significantly between treatments but the intercrop enhanced the infiltration of winter rainwater, probably by limiting surface runoff. There was temporal complementarity in this association since the period of intense water uptake by the intercrop occurred earlier than noted for the vine under bare soil conditions. Nevertheless, the competition for water was limited by better refilling of the soil water profile during winter in the intercropped treatment. The intercrop clearly interacted with the vine and decreased its vegetative vigor. Since predawn leaf water potential and stomatal conductance did not differ among treatments, mechanism(s) other than competition for water (e.g. nutrient competition, allelopathy) may be responsible.
Agriculture and agri-food systems of the highly vulnerable Middle East and North Africa (MENA) region needs a radical transformation under a changing climate. Based on a two-year effort, initially we ...developed a mega hypothesis on how to achieve climate-smart agri-food transformation in the region. In the study, we hypothesized that “Climate-Smart Lifts” implemented in the enabling environments can rapidly facilitate agri-food transformation in the region. In order to gather the stakeholders’ perception about this, we organized a collective conversation among ~400 stakeholders that represent various scales and sectors within the agriculture sector in MENA. These “listening cum learning consultations” were conducted through a survey followed by a series of webinars. The webinar discussions were strategically guided based on our hypothesis, the responses from the surveys and the regional needs. These discussions provided a forum to bring-out the stakeholders’ perspective on what new knowledge, partnerships, instruments and projects were needed in the MENA. The deliberation focused on the opportunities of public–private partnerships focusing in all the four major agroecosystems in MENA (irrigated, rainfed, rangelands, and deserts). In result, we developed an effective framework for strategic resource mobilization in the region, keeping in view the strong regional needs for climate actions and the requisite long-term commitments for the SDGs implementation.
•Crops had lower yields in agroforestry whatever the water regime.•Agroforestry limited crop growth and reduced the number of grains per unit area.•Agroforestry improved individual grain weight but ...not grain yield.•Agroforestry enhances the protein content of grains and straw.•Agroforestry had LER > 1 in most cases but wasn’t clearly affected by water regimes.
Agroforestry systems can be an effective means of stabilizing or even enhancing crop yields under climate change. Although trees compete with crops for soil resources in agroforestry,they can also improve crops' growing conditions, especially, by providing shade under drought. They can promote higher crop yields and higher harvest quality in the drylands. However, the beneficial effect of tree shade may depend on the seasonal pattern of rainfall, which determines the compensation between yield components. In this study, we evaluated two annual crops (durum wheat and faba bean) in olive agroforestry in northern Morocco. We manipulated water supply in a field experiment to span the high inter-annual rainfall variability at the site and tested whether olive trees reduce or improve crop yields. We assessed the effect of water addition on crop growth, yield components, and final yields and estimated the land equivalent ratio of olive agroforestry. Agroforestry limited crop growth and yield whatever the water regime. The magnitude of grain yield reduction was around 50 % for both crops in 2018, probably due to shade. The number of grains per unit area was the most impacted yield component in both 2018 and 2019. In contrast, water addition only had limited effects on faba bean yield, although it enhanced wheat grain yield by 11 % and the number of wheat spikes by 13 %. Agroforestry improved individual grain weight by 39 % for wheat and 17 % for faba bean, and enhanced the protein content of wheat grains and straw by 4 % and 9 %. However, improvements in grain weight and in protein content were not sufficient to compensate for yield loss due to shade. Despite lower crop yields, we show that agroforestry systems are still more land productive than sole crops and trees, even under arid conditions. We show how changing water supply may impact the performance of olive agroforestry in a drier future.
•Regulated Deficit Irrigation was applied on young peach trees after plantation.•An original method was created to hierarchize processes sensitivity to water deficit.•Photosynthesis is less sensitive ...than shoot growth to soil water deficit.•Early soil water deficit irrigation+grass drastically reduces tree growth.
The effects of a moderate soil water deficit on several shoot growth variables (1st and 2nd order shoot growth and final leaves number, final height and final number of 2nd order shoots) and on net photosynthesis were studied in young peach trees during the two years following plantation (January 2014). Trees were either fully irrigated (C), subjected to moderate water deficit (RDI) or subjected to moderate water deficit and associated with a grass-legume mixture on the entire orchard floor (RDI +G). Irrigation was scheduled according to soil water potential target ranges in order to keep C trees above −0.02MPa, i.e. at field capacity, and RDI and RDI+G trees between −0.04MPa and −0.06MPa. The level of water deficit obtained was moderate but yet significantly reduced by 50% overall tree growth in 2014 in RDI. This reduction was enhanced when water deficit lasted longer and when it was associated with grass in RDI+G. No reduction in growth variables occurred in RDI in 2015 due to the shorter duration of water deficit. Overall reduction was observed in 2015 in RDI+G mostly due to a carry-over effect of the previous year. Net photosynthesis was reduced by the longer and more intense water deficit in 2014, but was not reduced during the soil water deficit in 2015. An indicator of plant process sensitivity to water deficit, taking into account the variable reduction with regards to the control, the water deficit intensity and its duration was used to classify shoot growth variables and net photosynthesis according to their sensitivity to water deficit. Variables could be classified according to the following order of ascending sensitivity: net photosynthesis <1st order final leaf number<final tree height <1st order final shoot length <2nd order final leaf number <2nd order final shoot number <2nd order final shoot length. Applying a moderate water deficit combined with full grass cover drastically reduces overall tree size due to grass competition.
Provisioning services, such as the production of food, feed, and fiber, have always been the main focus of agriculture. Since the 1950s, intensive cropping systems based on the cultivation of a ...single crop or a single cultivar, in simplified rotations or monocultures, and relying on extensive use of agrochemical inputs have been preferred to more diverse, self-sustaining cropping systems, regardless of the environmental consequences. However, there is increasing evidence that such intensive agroecosystems have led to a decline in biodiversity as well as threatening the environment and have damaged a number of ecosystem services such as the biogeochemical nutrient cycles and the regulation of climate and water quality. Consequently, the current challenge facing agriculture is to ensure the future of food production while reducing the use of inputs and limiting environmental impacts and the loss of biodiversity. Here, we review examples of multiple cropping systems that aim to use biotic interactions to reduce chemical inputs and provide more ecosystem services than just provisioning. Our main findings are the identification of underlying ecological processes and management strategies related to the provision of pairs of ecosystem services namely food production and a regulation service. We also found gaps between ecological knowledge and the constraints of agricultural practices in taking account of the interactions and possible trade-offs between multiple ecosystem services as well as socioeconomic constraints. We present guidelines for the design of multiple cropping systems combining ecological, agricultural, and genetic concepts and approaches.
•A model simulating the water stress dynamics of bi-specific agrosystems is proposed.•Dedicated modelling concepts were used to provide genericity and to limit input parameters.•The model was tested ...on salads, mono/bispecific vineyards and peach orchards.•RMSE of the water stress index ranged from 0.049 to 0.123.•BISWAT model can contribute to the design of new agro-ecological cropping systems.
The ability to simulate soil and crop processes in many bi-specific systems (vineyards, orchards, silvo-arable agroforestry, strip-intercropping of arable crops…) is one of the major challenge for crop modelling in order to contribute to the design of agro-ecological cropping systems. A typical question is how soil, climate and management would influence the soil water deficit experienced by a plant grown alone or intercropped with a cover crop, with another crop or a tree, in order to improve the resilience of a cropping system to climate change and limit the use of chemical input.
This study introduces BISWAT – Bispecific Intercrop System WATer Stress dynamic model - a new water balance model designed to simulate the dynamic of Soil Water deficit Experienced (SWEP) by two Plants when grown together or separated. BISWAT has been built to simulate a large range of agrosystems (annual and perennial crops, mono- or bi-specific) cultivated in various conditions. The model is primarily based on three modelling concepts: i) a 2D generic pattern for the system’s spatial representation, ii) the use of the Radiation Interception Efficiency (RIE) to drive potential plant transpiration and soil evaporation, iii) the use of the Total Transpirable Soil Water (TTSW) concept coupled with a simple root dynamics representation. These concepts are not new but they allowed us to define a model able to simulate many crops and trees (including vineyards) using a limited number of inputs and without an explicit need for parameter calibration.
The model was evaluated on five reference agrosystems (mono-specific salads, mono-specific vineyards, bi-specific vineyards, mono-specific peach orchards and bi-specific peach orchards). The RMSE of the SWEP variable ranged from 0.049 to 0.123. A combined sensitivity and uncertainty analysis performed on typical farmer’s fields situations stressed the particular importance of model inputs related to the TTSW of the soil-crop system.
We conclude that the genericity of the BISWAT model, its method of parameterization and its performance open the perspective to use the model in a wide range of conditions where the dynamic of water stress between two species grown together is a key variable to be accessed with limited data for parameterization and a large number of fields to simulate.
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