Model based evaluation of cover crops for banana cropping systems

There is actually a surge for reintroducing biodiversity in agricultural systems in order to reduce chemical inputs, suppress pests, and close biogeochemical cycles. The use of cover-crops is a promising way to reintroduce biodiversity into the fields. Cover-crops have the potential to decrease chemical use against weeds (by competition) and pests (by increasing in natural enemies). To decrease herbicide use, suitable plants must be able to grow in appropriate conditions, to do not compete the cultivated crop for nutrients or water, but should compete weeds for light and space. There is a trade-off between these objectives. Banana is a semi-perennial crop, each plant develops at its own rhythm leading to an unsynchronized plant population in three years; canopy and nitrogen demand of the crop follow this unsynchronized pattern. Banana cropping systems remain based on bare soil management and a large amount of herbicides is used. In tropical environment, the growth of weeds and cover-crop is complex because it is not constrained by seasons; a constant growth is possible due to relatively constant climate. In these conditions, variation in radiation due to canopy closure is one of the major drivers of their growth. We developed a model based method to assess the suitability of cover crop for a given cropping system context. This method first relies on early measurements of cover crop performed on the field. Then, we used a simulation model to contextualize the growth of cover crops and to assess their capacity to control weeds, to compete the cultivated plant, and to sustain on the long term under the shade of the main crop. This approach allows an early selection of cover crops that should be tested in real intercropping in the field. We present results of this evaluation for 11 species intended to banana intercropping. (Texte intégral

Coupling of cropping system models with the AEGIS platform [S4-O.04]

Introduction Agroecological studies dealing with genotype by environment by management interactions generate heterogeneous datasets difficult to gather, store, share and analyse. Modelling is an essential tool for designing and evaluating innovative sustainable cropping systems. Data integration, sharing and reusing for crop modelling need a good data management. CIRAD has developed the AEGIS (AgroEcological Global Information System) platform, which aims to sustain the data value chain {Curry, 2015) for agroecological studies. This paper present the platform overall organisation and the approach used to ensure the data-model continuum. Materials and Methods Good data management is based on two key principles. The first is Data Lifecycle Management (DLM), which consists of managing data throughout its life cycle from production to use. The second is the FAIR data principles that aim to make data findable, freely accessible, interoperable and increase data reuse. Compliant with these standards, the AEGIS platform is organized into four pilars that focus on the steps of data acquisition, processing, sharing and enhancement. Data acquisition is a process of gathering, describing and harmonizing data. AEGIS integrates a generic ®ECOFI database (Auzoux et al., 2017) using metadata technology that allows any type of data to be easily imported according to a collection process and uses a variable dictionary to facilitate the annotation of data making them understandable to all. Data processing is about making the raw data acquired easily usable for analysis and modelling. Through integrated dashboards, AEGIS offers a real-time overview of all stored data, ranging from raw data to indicators for assessing the sustainability and performance of agroecosystems. It provides homogeneous datasets for crops models simulations and capitalizes processed data, which can be simulation parameters and outputs, analysis results and performance indicators. AEGIS proposes data visualisation tools that highlight patterns and correlations inaccessible from the raw data. In the context of open data, AEGIS ensures data sharing increasing the impact and visibility of agroecological studies, promoting potential data reuse for modelling. Interoperability is considered as a necessity for data sharing and involves four levels of data exchange: system, syntactic, structural and semantic. AEGIS uses ontologies dedicated to the plant, pest, environment and cultural practices to ensure compatibility with data from other platforms that comply with these ontologies. Datasets provided comply with metadata standards such as Darwin Core, MIAPPE and EML. AEGIS is able to export data using the standard open Breeding Application Programming Interface (BrAPI). By ensuring data standardization, optimization and curation, AEGIS enhance data in term of publishing quality, accuracy in decision-making and financial value creation. Results and Discussion Such coupling of cropping system models allows performing three kinds of fundamental works in the present agroecological studies: (i) model validation, (ii) parameters estimation, and (iii) cropping system models comparison. In the first work {Chaput et. al 2019), that aims to test the ability of a crop growth model {STICS) to simulate the sugarcane growth response to different climates, soils and nitrogen management. The STICS model was calibrated using the observed data provided by AEGIS that illustrates more than 10 years of sugarcane trials in Reunion. In the second work {Christina et. al, 2019) that aims to model the annual variability of sugar cane yield in Reunion Island, AEGIS is the scheduler of the estimation process until the RMSE error is minimized. It asks to a simulated annealing algorithm to generate a new set of input parameters. These parameters are used to set up simulations of cane growth MOSICAS model thanks to the generic ®ECOFI database and output variables are compared to observed values stored within AEGIS. In the third work, that aims to study on sugarcane dealing with genotype, environment and management interactions as part of the "International Consortium for Sugarcane Modelling" {ICSM), AEGIS has been used to setup, launch simulations of STICS, MOSICAS, and DSSAT models, and compare simulations regarding observed values stored within AEGIS. Conclusions AEGIS is a platform that participates in the construction of a data repository characterizing agroecosystems for integrated multi-scale analysis and ensures data consistency through harmonized reference systems and procedures. It provides all the features of the data value chain paradigm. It ensures a formal coupling (parametrization and output analyse) with the most well-known and ad hoe cropping systems models. It has been used in European and international projects involved in the agro-ecological transition as a steering and decision-making tool

Can legume crop residues contribute to sustainable intensification of rainfed rice production in Madagascar?

Rainfed agriculture on smallholder farms across the tropics is crucial for food security and livelihoods when availability of irrigated land is limited. Coarse-textured soils with low organic carbon and poor inherent fertility prevail in these systems (Tittonell and Giller,2013). In the absence of sufficiently remunerative market, small holders cannot afford mineral fertilizers so that nutrient inputs are generally limited to manure. Integrated soil fertility management, e.g. integration of legumes combined with additional supply of mineral fertilizers, is required to sustainably increase rainfed agriculture productivity (Vanlauwe et al. 2014). In Madagascar, most small holders do not use mineral fertilizer under rainfed agriculture. Incorporation of Nitrogen (N) rich crop residues could increase nutrient supply and improve N use efficiency(Aggarwal et al.,1997). Nutrient supply from residues is a complex process related to decomposition rates of residue, which is impacted by residue type and climate variability, e.g increased temperatures can accelerate residue decomposition while intense rainfall can increase the loss of the precious mineralized N through leaching. The potential contribution of N rich crop residues to increase staple crop productivity is therefore complex to anticipate. Soil-crop models can account for such complexity. This study aims at(i) calibrating the STICS crop model for rice yield modeling in the smallholder context of cool humid uplands in Madagascar and (ii) use the model to explore the effect of incorporation of rice and legume residues for low (25kgN ha-1) and high (160kg N ha-1) fertilizer inputs with a variable climate. The soil-crop model STICS (Brisson et al., 2003) was chosen for its capacity to account for soil water and nutrient dynamics during crop cycle for various climates and crop management. Rice experiments (cultivar NERICA 4) carried out in 2016-2017 and 2017-2018 cropping season in Ivory(19°33'S, 46°24'E, 950 m a.s.l)on Ferral sols were used for model calibration and testing. Two previous crops were compared: (i) rice and (ii)Mucuna cochinchinensis-Crotalaria spectabilis intercropping, combined with two levels of nutrient input, i.e. manure only (25kgN ha-1) or manure and mineral fertilizer (160kg N ha-1). Residues were incorporated at plowing. Measured data include rice phenology, above ground biomass and plant N, grain yield and in-season soil moisture and soil N. The calibrated STICS model reproduced adequately rainfed rice emergence, flowering and maturity, with on average an error of less than four days. Simulated in-season soil N and rice biomass agreed with the observations with a relative Root Mean Square Error from 33% to 36% (see Figure 1for rice residues with high N input treatment). The model could reproduce the additional mineral N supply and plant uptake associated with the incorporation of N rich legume residue for the two fertilizer treatments. Calibration for grain yield and scenario analysis using historical climate (1980-2010) are on-going and will allow to determine the profitability and risk associated with the different simulated options. This study will contribute to gain new insights on the relevancy of legume residue for sustainable intensification of cropping systems in a tropical smallholder context

Crop rotation and fertilization effects on weeds in rice based cropping systems in Madagascar

In the Mid-West region of Madagascar, yields in upland rice remain low due to both low soil fertility and high weed pressure in fields. Increasing managed biodiversity inside crop rotation may be an option to reduce weed pressure in cropping systems. The effect of managed biodiversity was studied in a field experiment carried out in Ivory (19°33'18.90"S, 46°24'53.08"E), with a randomized block design with four replications during two years. Three rainfed rice based rotations (Rice // Groundnut = RA, Rice // Sorghum + Vigna unguiculata =RSV, Rice//Mucuna cochinchinensis + Crotalaria spectabilis = RMC) combined with two levels of fertilization (Low Fertilization = manure vs. High Fertilization = manure + fertilizer) were compared to a rainfed rice monoculture. Each crop or crop mixture in the rotation was grown every year on plots measuring 45.9 m². Each year, weed and rice biomass were measured at each weeding date. Rice biomass was also measured at flowering and harvest. Rice yield and its components were measured at harvest. Weed flora was observed the second year to analyse potential change in weed communities according to fertilization and/or crop rotation. The first year, weed biomass and rice yield were higher in highly fertilized treatments than in lowly ones. In highly fertilized treatments, weeds did not affect yield and weed biomass was positively correlated to rice yield. On contrary, fertilization had no effect on weed biomass the second year. The highest and lowest weed biomass were observed on RA and RMC treatments respectively. Lowest rice yields were observed in RSV and RA treatments, in highly and lowly fertilized treatments respectively. In lowly fertilized treatments, weed biomass reduces significantly rice yield. Finally, rotation had more impact than fertilization on weed flora. Biodiversity may have positive effect on cropping systems performances but it depends largely on the introduced species

Analysis of ecosystem services trade-offs to design agroecosystems with perennial crops

Agroecosystems represent 38 % of global land use. Agroecosystems are located close to human settlements and are managed to produce food and fibers, traded in markets. Agroecosystems also produce other goods and services essential to human beings, such as climate regulation, flood mitigation, and landscape amenity. Economists and ecologists have developed the ecosystem services framework to foster the provision of these non-commercial services. Scientists can therefore help decision makers to develop sustainable ecosystems by studying ecosystem services. Here, we analyze the trade-offs of ecosystem services of farming systems. We discuss case studies of mixed perennial crops. The set of ecosystem services provided by these agroecosystems depends on their composition, structure, and management. Complex rule-based management will be required if winegrowers are to maintain an adequate set of ecosystem services across contrasting climatic years. Innovations including cover crops in banana systems can fulfill most of the objective set but will rely on increased farm labor. We then discuss the advantages, challenges, and opportunities to include the description of relations between ecosystem services in cropping system design. We propose to extend the yield gap analysis to ecosystem services, as a service gap analysis. This extension faces methodological questions about the potential provision of a service in a region. We conclude on the challenges that need to be faced if we want to use ecosystem services trade-offs to improve the contribution of agricultural systems to human well-being. (Résumé d'auteur

Malagasy farmers' view on the use of Stylosanthes guianensis for weed management in no-till rain-fed rice cropping systems

Upland rice-based cropping systems in the Mid-West of Madagascar suffer from low soil fertility, and weed pressure further reduces the already low yields of 1.5 - 2 t/ha. About twelve years ago, an agroecological practice based on a no-till system with Stylosanthes guianensis, a cover crop used as a live mulch, was introduced. This system has been proved to enhance soil fertility but its effect on weed community was not yet studied. Thus this research focuses on the effect of stylosanthes on weed infestation. In the administrative units of Ankazomiriotra and Vinany, interviews and focus groups were performed with 40 farmers. The aim was to map farmers' knowledge of and opinion about weeds and stylosanthes. According to farmers, most dangerous species were Striga asiatica, Richardia scabra, Eleusine indica, Digitaria spp., Cleome hirta and Cyperus spp., due to their capacity to reduce crop yield and the difficulty to eliminate them from the field. The general perception is that weed abundances decreased in the system with stylosanthes. Furthermore farmers feel that S. asiatica problems are less pronounced in this system, which is in line with the general knowledge that this hemi-parasitic weed decreases in more fertile soils