Publications of Benoît Mercatoris
Bookmark and Share    
Full Text
See detailImaging Wheat Canopy Through Stereo Vision: Overcoming the Challenges of the Laboratory to Field Transition for Morphological Features Extraction
Dandrifosse, Sébastien ULiege; Bouvry, Arnaud ULiege; Leemans, Vincent ULiege et al

in Frontiers in Plant Science (2020)

Stereo vision is a 3D imaging method that allows quick measurement of plant architecture. Historically, the method has mainly been developed in controlled conditions. This study identified several ... [more ▼]

Stereo vision is a 3D imaging method that allows quick measurement of plant architecture. Historically, the method has mainly been developed in controlled conditions. This study identified several challenges to adapt the method to natural field conditions and propose solutions. The plant traits studied were leaf area, mean leaf angle, leaf angle distribution, and canopy height. The experiment took place in a winter wheat, Triticum aestivum L., field dedicated to fertilization trials at Gembloux (Belgium). Images were acquired thanks to two nadir cameras. A machine learning algorithm using RGB and HSV color spaces is proposed to perform soil-plant segmentation robust to light conditions. The matching between images of the two cameras and the leaf area computation was improved if the number of pixels in the image of a scene was binned from 2560 × 2048 to 1280 × 1024 pixels, for a distance of 1 m between the cameras and the canopy. Height descriptors such as median or 95th percentile of plant heights were useful to precisely compare the development of different canopies. Mean spike top height was measured with an accuracy of 97.1 %. The measurement of leaf area was affected by overlaps between leaves so that a calibration curve was necessary. The leaf area estimation presented a root mean square error (RMSE) of 0.37. The impact of wind on the variability of leaf area measurement was inferior to 3% except at the stem elongation stage. Mean leaf angles ranging from 53° to 62° were computed for the whole growing season. For each acquisition date during the vegetative stages, the variability of mean angle measurement was inferior to 1.5% which underpins that the method is precise. [less ▲]

Detailed reference viewed: 37 (6 ULiège)
Full Text
See detailChlorophyll a fluorescence in response to phosphorus deficiency and heat stress
El-Mejjaouy, Yousra ULiege; Zeroual, Youssef; El Gharous, Mohamed et al

Poster (2020, January 31)

Photosynthesis and particularly photosystem II (PSII) is considered sensitive to high temperature. Our main objective in this study is to understand the role of phosphorus in heat treatment effects ... [more ▼]

Photosynthesis and particularly photosystem II (PSII) is considered sensitive to high temperature. Our main objective in this study is to understand the role of phosphorus in heat treatment effects alleviation in tomato plant. In this work, the influence in three levels of phosphorus concentration (15, 31 and 60 ppm) assured by two forms of fertilisers (Mono-Ammonium Phosphate (MAP) (11-52-0) and NPK (15-15-15)) on tomato plants growth and heated-leaves treatment responses was investigated. Tomato plants were grown in hydroponic conditions and the effects of different P levels in change of chlorophyll content index, leaves dry weight and total P in root and shoot ratio were analysed. Results present that plants grown in low phosphorus concentration in hydroponic medium showed a decrease in chlorophyll content index, leaves dry weight and total root P/total shoot P ratio. Furthermore, heat treatment at 40 °C for 30 min significantly affects chlorophyll a fluorescence transient shape and photosynthetic performance index parameter (PIABS). We observed that the two forms of fertilisers positively alleviated the detrimental effects of high temperature on leaves of plants grown at high level of phosphorus. According to these results, the role of phosphorus in the alleviation of the effects of temperature on the electron transfer chain is observed. However, the mechanism by which P acts in this protection remains unclear. It is possible that P has a significant action at the level of the PSI, but further studies are necessary to elucidate the direct or indirect actions of P in this heat effect alleviation. Also, a combined action of P, N and other mineral elements is very likely in this protection against the negative effects of high temperatures. [less ▲]

Detailed reference viewed: 105 (4 ULiège)
Full Text
See detailExperimental and Numerical Investigation of the Drying of an Agricultural Soil
Ralaizafisoloarivony, Njaka Andriamanantena ULiege; Tran, Duc Kien ULiege; Degré, Aurore ULiege et al

in E3S Web of Conferences (2020)

Due to climate change, soil desiccating became a serious concern in the agricultural area of Belgium. Knowing soil evaporation kinetic can help to elucidate and predict: the soil moisture regime, soil ... [more ▼]

Due to climate change, soil desiccating became a serious concern in the agricultural area of Belgium. Knowing soil evaporation kinetic can help to elucidate and predict: the soil moisture regime, soil water retention and soil water content. Those parameters are vital for water use efficiency and sustainable agriculture. This research analysed the mechanism of soil evaporation both under laboratory experiment and numerical modelling. Soil samples (Luvisol) were collected from the agricultural field in Gembloux-Belgium, and processed in a small drying chamber. Sensors measured the chamber temperature and humidity, while digital camera monitored the soil surface throughout the experiment. HYPROP device recorded the water change, soil suction, and soil water retention curve. During three evaporation experiments, four periods were observed rather than three according to the common theory. The modelling considered thermo-hydro-mechanical framework for predicting the drying process of Luvisol. The model used the finite element code LAGAMINE created at the University of Liege. The Software aims at assessing the mechanism of water transport between soil and atmosphere. The results of the simulation showed major domination of Darcean flow during desiccating, while some short vapour diffusion occurred only after the soil surface began to de-saturate. [less ▲]

Detailed reference viewed: 98 (15 ULiège)
Full Text
See detailIn-field proximal sensing of septoria tritici blotch, stripe rust and brown rust in winter wheat by means of reflectance and textural features from multispectral imagery
Bebronne, Romain ULiege; Carlier, Alexis ULiege; Meurs, Rémy ULiege et al

in Biosystems Engineering (2020), 197

During its growth, winter wheat (Triticum aestivum L.) can be impacted by multiple stresses involving fungal diseases that are responsible for high yield losses. Enhancing the breeding and the ... [more ▼]

During its growth, winter wheat (Triticum aestivum L.) can be impacted by multiple stresses involving fungal diseases that are responsible for high yield losses. Enhancing the breeding and the identification of resistant cultivars could be achieved by collecting automated and reliable information at the plant level. This study aims to estimate the severity of stripe rust (SR), brown rust (BR) and septoria tritici blotch (STB) in natural conditions and to highlight wavebands of interest, based on images acquired through a multispectral camera embedded on a ground-based platform. The severity of the three diseases has been assessed visually in an agronomic trial involving five wheat cultivars with or without fungicide treatment. An acquisition system using multispectral imagery covering the visible and near-infrared range has been set up at the canopy level. Based on spectral and textural features, estimations of area under disease progress curve (AUDPC) were performed by means of artificial neural networks (ANN) and partial least squares regression (PLSR). Supervised classification was also implemented by means of ANN. The ANN performed better at estimating disease severity with R2 of 0.72, 0.57 and 0.65 for STB, SR and BR respectively. Discrimination in two classes below or above 100 AUDPC reached an accuracy of 81% (κ = 0.60) for STB. This study, which combined the effect of date, cultivar and multiple disease infections, managed to highlight a few wavebands for each disease and took a step further in the development of a machine vision-based approach for the characterisation of fungal diseases in natural conditions. © 2020 [less ▲]

Detailed reference viewed: 40 (14 ULiège)
Full Text
See detailUse of precision farming practices and crop modelling for enhancing water and phosphorus efficiency
El-Mejjaouy, Yousra ULiege; Mamassi, Achraf ULiege; Chtouki, Mohamed ULiege et al

Poster (2019, October 07)

In a context of climate change, African agriculture aims at developing new approaches to face multiple constraints related to water scarcity, soil degradation or nutrients depletion. Nonrenewable ... [more ▼]

In a context of climate change, African agriculture aims at developing new approaches to face multiple constraints related to water scarcity, soil degradation or nutrients depletion. Nonrenewable resources such as phosphorus are of concern. Precision farming, as a new alternative to conventional agriculture, aims to improve crop productivity through the optimization of water and nutrients use efficiency. It considers the spatiotemporal variability of fields related to soil heterogeneity, plant nutrient needs and meteorological conditions through the growing season. For an effective management of soil and crop system, several new technologies have emerged, including soil-plant sensing, innovative crop management practices, and crop growth simulation and yield forecasting models. Regarding phosphorus management, use efficiency can be improved through the accurate assessment of phosphorus status in soil and plant. Proximal sensing based on visible near-infrared spectroscopy seems to be a promising alternative to manage soil fertility, understand phosphorus dynamics and enhance crop productivity. These aims can be also achieved by adopting hyper-frequent drip fertigation as an efficient agricultural practice, combined to hydrogeophysics to monitor water and nutrient fluxes in the soil-plant continuum. In addition, based on the interactions between meteorological conditions, soil properties and crop management, the use of agrometeorological models in simulation of crop growth parameters and forecasting crop production levels may allow assessing soil fertility and potential, ensuring an optimal future exploitation of farmland through the improvement of fertilization practices in an integrated management cropping system. [less ▲]

Detailed reference viewed: 49 (8 ULiège)
Full Text
See detailAssessing soil crack dynamics during dryings from reduced tillage and conventional tillage fields
Ralaizafisoloarivony, Njaka Andriamanantena ULiege; Degré, Aurore ULiege; Mercatoris, Benoît ULiege et al

Poster (2019, September 02)

Crack formation and development has been a general concern in the agricultural science. Cracks contribute to the soil aeration, aggregate formation, and easy root penetration. However, cracks accelerated ... [more ▼]

Crack formation and development has been a general concern in the agricultural science. Cracks contribute to the soil aeration, aggregate formation, and easy root penetration. However, cracks accelerated the soil desiccation, allowed deep infiltration of pesticides/pollutants through preferential flow, and polluted the shallow water-table in Belgium. Cracks were mostly studied on pure clay or on high clay content soil (Vertisol). Yet in Wallonia, cracks were present even on silt-loam soil (Luvisol). This study tried to cover this gap by analysing crack dynamics and evaporation process, during drying kinetics of the Luvisol found in Gembloux. Soils were collected right from the agricultural field and processed on a small drying chamber in which evaporation test was taking place. Ceramic-IR-emitter heated the chamber while sensors (DHT22) measured the temperature and relative humidity. Digital camera took photos of the soil surface at 30min interval. Balance and tensiometer were linked to datalogger (CR800) and recorded the soil hydraulic properties (evaporation, water retention, etc.). Cracks were assessed from small samples (~5cm x 1cm thick) and big samples (~20cm size x 1.6 cm thick). Three treatments were considered including: disturbed soil, conventional tillage and reduced tillage. For big samples, results showed higher cracks formation on disturbed soil > reduced-tillage > conventional-tillage due to loose of soil cohesion, soil organic content, soil aggregation, biological activities, and soil porosity. The soil evaporation rate was also greater in disturbed soil > reduced-tillage > conventional tillage. Cracks opening exposed profound-soil-water to the atmosphere without passing through the soil matrix. For small samples, the repetitive drying experiments increased cracks length/width, especially for the dense samples. Future study is needed to assess the presence of pre-(micro)-cracks in soil using X-ray microtomography. [less ▲]

Detailed reference viewed: 70 (5 ULiège)
Full Text
See detailCereal morphology through proximal stereovision
Dandrifosse, Sébastien ULiege; Bouvry, Arnaud ULiege; Leemans, Vincent ULiege et al

Conference (2019, July 10)

Detailed reference viewed: 28 (2 ULiège)
Full Text
See detailCharacterisation of fungal diseases on winter wheat crop using proximal and remote multispectral imaging
Bebronne, Romain ULiege; Michez, Adrien ULiege; Leemans, Vincent ULiege et al

in Precision agriculture ’19 (2019, July 08)

Winter wheat fungal diseases, responsible for high yield losses, can be assessed by computer vision to increase phenotyping performance. This study aims to compare multispectral imagery based on remote ... [more ▼]

Winter wheat fungal diseases, responsible for high yield losses, can be assessed by computer vision to increase phenotyping performance. This study aims to compare multispectral imagery based on remote and proximal sensing for disease detection. Wavelength selection was achieved by ANOVA and stepwise regression. Prediction of disease severity was performed by means of an artificial neural network based on proximal sensing data. If septoria requires proximal measurements, stripe and brown rusts can be detected from UAVs and early detection from the ground. Prediction results obtained gave R² of 0.55 and 0.57 for septoria tritici blotch and stripe rust respectively. [less ▲]

Detailed reference viewed: 58 (20 ULiège)
Full Text
See detailEstimation of ear density in winter wheat crop by stereoscopic imaging for crop yield prediction
Bouvry, Arnaud ULiege; Dandrifosse, Sébastien ULiege; Dumont, Benjamin ULiege et al

Poster (2019, July)

Presentation exploring the added value of 3D information in winter wheat ear detection compared to RGB image based methods. Image acquisition procedure is presented and a processing pipeline is proposed ... [more ▼]

Presentation exploring the added value of 3D information in winter wheat ear detection compared to RGB image based methods. Image acquisition procedure is presented and a processing pipeline is proposed. The poster focuses on potential of the methods and future improvements. [less ▲]

Detailed reference viewed: 35 (4 ULiège)
Full Text
See detailPrediction of organic potato yield using tillage systems and soil properties by artificial neural network (ANN) and multiple linear regressions (MLR)
Abrougui, Khaoula; Gabsi, Karim; Mercatoris, Benoît ULiege et al

in Soil and Tillage Research (2019), 190

Tillage aims to prepare the soil with the adequate treatment to create the ideal and most favorable conditions for cultivation. To evaluate the effect of tillage systems on soil environment, it is ... [more ▼]

Tillage aims to prepare the soil with the adequate treatment to create the ideal and most favorable conditions for cultivation. To evaluate the effect of tillage systems on soil environment, it is mandatory to measure the modifications in physical, chemical and biological properties. In recent decades, artificial intelligence systems were used for developing predictive models to simplify, estimate and predict many farming processes. They are also employed to optimize performance and control risks. These systems have become true virtual helpers, and more so when integrated with predictive analytics. In the present study, the effects of tillage systems on soil properties and crop production and the predictive capabilities of multiple linear regressions (MLR) and artificial neural networks (ANN) are evaluated to estimate organic potato crop yield including soil microbial biomass (MB), soil resistance to penetration, soil organic matter (OM) and tillage system. Potato yield was found to be significantly impacted by tillage and soil properties. The results showed that MLR model estimated crop yield more accuracy than ANN model. Correlation coefficient and root mean squared (RMSE) were 0.97 and 0.077 between the measured and the estimated data by the ANN model, respectively. Generally, the ANN model showed greater potential in determining the relationship between potato yield, tillage and soil properties. [less ▲]

Detailed reference viewed: 46 (1 ULiège)
Full Text
See detailCharacterisation of cereal morphology through proximal stereo vision under contrasting nitrogen inputs
Dandrifosse, Sébastien ULiege; Bouvry, Arnaud ULiege; Leemans, Vincent ULiege et al

in Precision Agriculture '19 (2019)

This study aimed at determining the capacity of a proximal stereo vision system to characterise the architecture of winter wheat and spring barley canopies. Images were acquired by a nadir pair of cameras ... [more ▼]

This study aimed at determining the capacity of a proximal stereo vision system to characterise the architecture of winter wheat and spring barley canopies. Images were acquired by a nadir pair of cameras, in two fields dedicated to fertilisation trials (Gembloux, Belgium). Soil and plants were separated through Support Vector Machines. Dense 3D point clouds were computed, describing canopy height. The study of mean leaf angles and leaf angle distributions revealed different dynamics for wheat and barley but little effect of fertilisation. Due to its low cost and its compactness, such a 3D vision system is suitable for farm applications. [less ▲]

Detailed reference viewed: 30 (10 ULiège)
Full Text
See detailStudying the effect of desiccation cracking on the evaporation process of a Luvisol – From a small-scale experimental and numerical approach
Tran, Duc Kien ULiege; Ralaizafisoloarivony, Njaka Andriamanantena ULiege; Charlier, Robert ULiege et al

in Soil and Tillage Research (2019), 193

Cracking formation due to desiccation of the soil surface is a common phenomenon related to the interaction between soil and the atmosphere. Indeed, during dry seasons, high evaporation of pore water near ... [more ▼]

Cracking formation due to desiccation of the soil surface is a common phenomenon related to the interaction between soil and the atmosphere. Indeed, during dry seasons, high evaporation of pore water near the soil surface leads to a more significant soil suction in this region. The suction results in compressive effective stress on the soil structure and produces shrinkage including cracking. As the crack network forms, the initial soil structure is strongly modified, which provides preferential flow pathways for solute-water and influences the soil hydraulic behaviour in general. The work aims to study the formation of cracks during evaporation process of a Cutanic Luvisol and evaluate how cracking affects the soil hydraulic behaviour. Laboratory experiments were performed on undisturbed soil samples. To do that, a small-scale environmental chamber was designed and equipped with sensors for measuring the ambient temperature and relative humidity, and a digital camera for investigating the initiation and propagation of cracks on the soil surface. By combining with a HYPROP device (UMS GmbH, Munich, Germany), the hydraulic properties and the kinetics of evaporation of soil samples were also determined through the tests. Finally, numerical simulations were carried out by using the finite element code LAGAMINE developed at the University of Liege to emphasize the effect of desiccation cracking on the soil hydraulic conductivity and the moisture transport mechanisms in the soil, as well as exchanges with ambient atmosphere. [less ▲]

Detailed reference viewed: 62 (17 ULiège)
Full Text
See detailDéveloppement d’un système de vision multispectrale pour le phénotypage de culture
Naiken, Alwin ULiege; Mercatoris, Benoît ULiege

Poster (2018, October)

In the frame of research activities regarding the characterization of crop growth dynamics in a context of precision agriculture, we have developed a multispectral proxidetection system covering a wide ... [more ▼]

In the frame of research activities regarding the characterization of crop growth dynamics in a context of precision agriculture, we have developed a multispectral proxidetection system covering a wide spectrum in the near-infrared and short-wave infrared domains. This part of the spectrum is important for the characterization of vegetation since it includes the reflectance plateau of plants in the near-infrared and the main water absorption bands. Nowadays, the most commonly used tool in this spectral range is the spectrometer, which measures the average reflectance of a scene without any spatial detail. In the infrared range, hyperspectral imaging is ermerging, as a high-potential solution, but remains difficult to implement and process. In this contribution, we propose a solution, based on an optical filter wheel, which provides the spatial dimension in the infrared domain with a simple implementation to study plants at the scale of organs (leaves, stems, ears). The proposed multispectral vision system complements an equivalent tool already developed in the visible and near-infrared field using a monochrome CMOS camera. The particularity of the presented instrument is the use of an InGaAs camera (indium-galllium arsenide sensor) Gold-eye G-007 (Allied Vision) with a bandwidth from 950 nm to 1650 nm. This camera is combined with a wheel composed of 10 optical filters of 100 nm bandwidth and distributed over the camera's bandwidth. The positioning of the filters in front of the camera is automatically controlled by the image acquisition system using a microcontroller (Arduino Uno). The implemented program allows to select successively the filters of interest for the acquisition. This multipectral vision system will allow the selection of wavelength ranges and morphological parameters that explain physiological traits of plants such as water or nitrogen deficiencies. For this purpose, the image characteristics will be correlated with conventional reference measurements. [less ▲]

Detailed reference viewed: 107 (15 ULiège)
Full Text
See detailEffect of desiccation cracking on the fluid transfer process in agricultural soil
Tran, Duc Kien ULiege; Ralaizafisoloarivony, Njaka; Charlier, Robert ULiege et al

Poster (2018, October)

The natural soil structure can be strongly modified and generate heterogeneities during wetting and drying processes. This significantly affects the transfer of fluids and nutrients between the atmosphere ... [more ▼]

The natural soil structure can be strongly modified and generate heterogeneities during wetting and drying processes. This significantly affects the transfer of fluids and nutrients between the atmosphere, the subsoil, the hydrosphere and the biosphere. Experimental observations on a Cutanic Luvisol from agricultural field in Gembloux, Belgium, by using X-ray microtomography coupled with 3D image analysis have shown the cracking phenomenon occurring and leading to preferential flows in the soil sample during a drainage process. In order to better understand the impact of cracks on the behaviour of this soil type, in this study, we have proposed a numerical modelling of soil evaporation process by using the constitutive models implemented in the finite element code LAGAMINE. Considering that the soil we study is a loamy soil, we have chosen to fit the dual model of Durner (Durner, 1994) for the water retention capacity. The drying kinetics is modelled using the boundary layer model (Gerard et al., 2010), assuming that the vapour and heat transfers take place in a boundary layer at the surface of the porous medium. The embedded fracture model is chosen to represent the development of the fractures in porous medium in which fracture opening is activated by a threshold strain parameter (Olivella et Alonso, 2008). The results obtained have shown that an increase in permeability in the fracture zones makes the permeability tensor anisotropic up to one order and thus strongly modifies the drying kinetics of the soil core (e.g., evaporation rate). The results also have suggested that using a simple concept of cracking development, a continuum model is capable of modelling preferential flows developed in a fractured porous medium such as agricultural soil. [less ▲]

Detailed reference viewed: 37 (3 ULiège)