Calibration and validation of the STICS crop model for managing wheat irrigation in the semi-arid Marrakech/Al Haouz Plain

In the first part of this work, the shoot growth module and grain yield of the STICS crop model were calibrated and validated by using field data which was collected from irrigated winter wheat fields in the Haouz plain near Marrakech. The calibration was performed on the thermal units between the four phenological stages that control the dynamics of leaf area index and the thermal unit between emergence and the beginning of grain filling. The plant phenology was calibrated for three fields monitored during the 2002/03 season. Evaluation of the grain yields and the temporal evolution of leaf area index were done for six validation fields during 2003/04. The results showed the significant accuracy of the model in simulating these variables, and also indicated that the plants mainly suffered from lack of nitrogen. The results in the second part show the potential of crop modeling to schedule irrigation water, on the assumption that the plants were growing under optimal conditions of fertilization. In this case, the model was used to manage the time of irrigation according to a threshold for water deficit. Various simulations displayed logical trends in the relationship between the grain yield and both the amount and timing of irrigation water. These results were finally compared with those obtained from real irrigation practices. For the particular climate of 2003/04, the comparison showed that 70 mm and 40 mm of water could be saved in case of early and late sowing, respectively

Role of rhizospheric microbiota as a bioremediation tool for the protection of soil-plant systems from microcystins phytotoxicity and mitigating toxin-related health risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L−1. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This project has received funding from the European Union?s Horizon 2020 research and innovation program under the Marie Sk?odowska-Curie grant agreement No. 823860 and co-sup-ported by the strategical funding from FCT UIDB/04423/2020 and UIDP/04423/2020

Development and validation of model of heat diffusion in maize ear

To calculate the variations of ear temperature, a two-dimensional numerical model of heat transfer within the different parts of the ear was developed and tested. It is based on a heat conduction equation. The ear being considered as a cylinder form with a variable section consisting of three concentric layers: cob, kernels and husk. The heat transfer between two adjoining layers was assumed to be purely conductive and at the external boundary of the ear, free convective heat transfer was assumed. Temperature response curves obtained from cooling and heating experiments were compared with those obtained by the model developed and a simpler model treating the ear as a single cylindrical layer. The average difference between the observed and calculated temperatures was 0.4 and 1 degrees C, respectively for our model and the simple model (ear temperature varied between 5 and 25 degrees C). The delay (lag) of response of ear temperature to air temperature was clearly larger in the deeper layers (center of cob and grains) than just under the husk. The proposed model was used to determine the overall thermal properties of maize ears. Conductivity k*, heat capacity c* and thermal diffusivity a* of each layer within the ear were determined using the model fitting method i.e. their values were obtained fitting a model of heat diffusion in the ear by the least squares method. The values of k* and c* obtained for the kernel layer were respectively significantly higher and lower than those for husk layer. (C) 1999 Elsevier Science B.V. All rights reserved

Development and validation of model for estimating temperature within maize ear

We present a three-dimensional computer model that simulates ear temperatures under field conditions for both daytime and night-time. The meteorological data used are total and diffuse radiation, wind speed, air temperature and humidity (or wet bulb temperature). The model is based on the energy variation of volume elements on ear surface. It takes into account, net radiation, sensible and latent heat exchange and heat diffusion within the ear. The model performs a radiation balance that separates direct, diffuse and scattering components. The husk stomatal resistance was parameterised as a function of water vapour deficit and solar radiation deduced from our experimental data. The model was tested in two stages: first, the calculated flux of downward and upward all wave radiation, at ear level, was compared with real measurements. Second, the calculated grain temperatures were compared with air temperature, and with data collected, for different polar positions around the cob, in two experiments conducted in 1997, in Morocco, and 1998, in Belgium. The agreement was satisfactory; the average difference between the model estimates and measurements of grain temperature were 0.5 degreesC in Belgium and 0.6 degreesC in Morocco, whereas using air temperature as the simplest estimate of the grain temperature gave average differences against the measured grain temperature of 1.1 and 1.8 degreesC, respectively. (C) 2001 Elsevier Science B.V. All rights reserved

Maize ear temperature

An experimental study of ear temperature was made in Morocco (June, 1997) and in Belgium (September, 1998). Measurements were made at mid-length of ear in the centre of cob and at different points in the middle of grains. The results showed that temperature in the middle of the grains: depends significantly on the position of grain around the ear axis, especially in Morocco, between 13 and 16 h (UT). The result obtained shoed that, because of the considerable ear thermal inertia and non-isotropic direction of the direct solar radiation, the average temperatures in the middle of the grain and in the centre of the cob were similar. The difference between grain and air temperature was shown to be clearly more affected by solar radiation than by wind speed. The protection of ear against direct solar radiation led to an average temperature reduction of about 2.1 degreesC in ear protected compared with normal ears. Also, the important role played by the canopy on ear temperature was underlined. A temperature difference of up to 8.5 degreesC was observed between the temperature of ears exposed to direct radiation and other (normal) ears. The effects of the differences observed between grain temperatures on both final weight grain and kernel growth rate were calculated using CERES-Maize functions. These effects were shown unlikely to affect drastically grain yield. (C) 2001 Elsevier Science B.V. All rights reserved

Moment dipolaire de CH

Le moment dipolaire de l'acétonitrile (CH3CN) a été déterminé par spectroscopie millimétrique à absorption saturée et effet Stark. La méthode des moindres carrés corrélés et la méthode de la médiane ont été utilisées pour vérifier la validité du résultat de l’estimation du moment dipolaire. Sa valeur est : μ = 3,92197 (13) D