Derived crop coefficients for winter wheat using different reference evpotranspiration estimates methods

This paper reports the results of using three empirical methods (Makkink, Priestley-Taylor and Hargreaves) for estimating the reference evapotranspiration (ET0) in the semi-arid region of Tensift Al Haouz, Marrakech (center of Morocco). The Penman-Monteith equation, standardized by the Food and Agriculture Organization (FAO-PM), is used to evaluate the three empirical methods. The obtained ET0 data were used to estimate crop water requirement (ET) of winter wheat using the crop coefficient (K-c) approach and results were compared with ET measured by the Eddy Covariance technique. The result showed that using the original empirical coefficients a, alpha and C-m in Hargreaves, Priestley-Taylor and Makkink equations, respectively, the Hargreaves method agreed fairly well with FAO-PM method at the test site. Conversely, the Priestley-Taylor and Makkink methods underestimate the ET by about 20 and 18 %. After adjustment of the original values of two parameters alpha and C-m coefficients in Priestley-Taylor and Makkink equations, the underestimation of ET was reduced to 9% and 4% for the Priestley Taylor and Makkink methods, respectively, which led to an improvement of 55% and 76% of the obtained values compared with the original values

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

Agrometerological study of semi-arid areas : an experiment for analysing the potential of time series of FORMOSAT-2 images (Tensift-Marrakech plain)

Earth Observing Systems designed to provide both high spatial resolution (10m) and high capacity of time revisit (a few days) offer strong opportunities for the management of agricultural water resources. The FORMOSAT-2 satellite is the first and only satellite with the ability to provide daily high-resolution images over a particular area with constant viewing angles. As part of the SudMed project, one of the first time series of FORMOSAT-2 images has been acquired over the semi-arid Tensift-Marrakech plain. Along with these acquisitions, an experimental data set has been collected to monitor land-cover/land-use, soil characteristics, vegetation dynamics and surface fluxes. This paper presents a first analysis of the potential of these data for agrometerological study of semi-arid areas

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

Performance assessment of AquaCrop model for estimating evapotranspiration, soil water content and grain yield of winter wheat in Tensift Al Haouz (Morocco) : application to irrigation management

Crop growth simulation models have become important tools to assess and develop deficit irrigation strategies especially in arid and semi-arid regions. In this study, we tested the ability of the FAO developed AquaCrop model (V 4.0) to simulate canopy cover (CC), actual evapotranspiration (ETcact), total soil water content (TWC) and grain yield (GY) for winter wheat under flood irrigation in the semi-arid region of Tensift Al Haouz, Marrakech (center of Morocco). The simulation was performed at a daily time step, using thermal units, i.e., growing degree days (GDDs) during two successive growing seasons: 2002/2003 and 2003/2004. Firstly, the calibration of the model was performed on three fields during 2002/2003 cropping season. Various parameters affecting CC, ETcact,TWC and GY have been calibrated based on the comparison between measurements and the results of simulations. Afterward, the validation was done on six fields during the 2003/2004 cropping season. The results showed that the model simulates reasonably well CC, ETcact, TWC and GY over two growing seasons. The average values of the Mean Bias Error (MBE) between observed and measured CC, ETcact,TWC and GY were -4.6%, -0.23 mm/day, 17.56 mm and 0.05 t/ha for the calibration fields, and 7.89%, -0.01 mm/day, 0.5 mm and 0.06 t/ha for the validation fields, respectively. Additional statistical parameters like the root mean square error (RMSE) and the Nash-Sutcliffe efficiency (NSE) showed also that the model gives acceptable estimates of CC, ETnct, TWC and GY. After accurate calibration and validation of the AquaCrop model, it was used for irrigation scheduling based on the threshold of the root zone water depletion (D-r,D-threshold) over two fields with contrasted sowing dates. The various simulations (irrigation scenarios) showed that early sowing is more adequate than late sowing in saving water and obtaining adequate grain yield. It has been also shown that the value 0.6 of D-r,D- threshold can be used as an appropriate threshold of water depletion to improve the wheat irrigation management. Consequently, the AquaCrop model can be considered as a potentially useful tool for planning irrigation schedules on an operational basis in the arid and semi-arid regions

Development of maize internode under drought stress

International audienc

Estimation of soil evaporation and infiltration losses using stables isotopes, fluxmeter and eddy-covariance system for citrus orchards in a semi-arid region (Morocco)

In arid and semi-arid regions water scarcity is one of the main limiting factors for economic growth. In the context, an experimental setup was conceived to monitor seasonal water consumption of citrus plant irrigated by drip irrigation system in Agafay station, middle of Morocco. For that, an Eddy-Covariance system, meteorological station, fluxmeter, as well as measurements of soil moisture and temperature were continuously operated during experimentation. The stable isotope was used to partition Evapotranspiration (ET) components. By using the water balance equation, the results showed that about 37% of total irrigation and rainfall is lost by infiltration and runoff. Additionally, the partitioning of evapotranspiration using the stable isotope showed that soil evaporation is very small compared to the transpiration at least during tow sampling days. This result confirms that the irrigation method applied by the farmer was very appropriate for the orchard but it is necessary to re-examine amount of water applied and timing of irrigation in order to minimise the loss by infiltratio