M. Mohammadi; B. Ghahraman; K. Davary; H. Ansari; A. Shahidi
Abstract
Introduction: FAO AquaCrop model (Raes et al., 2009a; Steduto et al., 2009) is a user-friendly and practitioner oriented type of model, because it maintains an optimal balance between accuracy, robustness, and simplicity; and it requires a relatively small number of model input parameters. The FAO AquaCrop ...
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Introduction: FAO AquaCrop model (Raes et al., 2009a; Steduto et al., 2009) is a user-friendly and practitioner oriented type of model, because it maintains an optimal balance between accuracy, robustness, and simplicity; and it requires a relatively small number of model input parameters. The FAO AquaCrop model predicts crop productivity, water requirement, and water use efficiency under water-limiting and saline water conditions. This model has been tested and validated for different crops such as maize, sunflower and wheat (T. aestivum L.) under diverse environments. In most of arid and semi-arid regions water shortage is associated with reduction in water quality (i.e. increasing salinity). Plants in these regions in terms of water quality and quantity may be affected by simultaneous salinity and water stress. Therefore, in this study, the AquaCrop model was evaluated under simultaneous salinity and water stress. In this study, AquaCrop Model (v4.0) was used. This version was developed in 2012 to quantify the effects of salinity. Therefore, the objectives of this study were: i) evaluation of AquaCrop model (v4.0) to simulate wheat yield and water use efficiency under simultaneous salinity and water stress conditions in an arid region of Birjand, Iran and ii) Using different treatments for nested calibration and validation of AquaCrop model.
Materials and Methods: This study was carried out as split plot design (factorial form) in Birjand, east of Iran, in order to evaluate the AquaCrop model.Treatments consisted of three levels of irrigation water salinity (S1, S2, S3 corresponding to 1.4, 4.5, 9.6 dS m-1) as main plot, two wheat varieties (Ghods and Roshan), and four levels of irrigation water amount (I1, I2, I3, I4 corresponding to 125, 100, 75, 50% water requirement) as sub plot. First, AquaCrop model was run with the corresponding data of S1 treatments (for all I1, I2, I3, and I4) and the results (wheat grain yield, average of soil water content, and ECe) were considered as the “basic outputs”. After that and in the next runs of the model, in each step, one of the inputs was changed while the other inputs were kept constant. The interval of variation of the inputs was chosen from -25 to +25% of its median value. After changing the values of input parameters, the model outputs were compared with the “basic outputs” using the sensitivity coefficient (Sc) of McCuen, (1973). Since there are four irrigation treatments for each salinity treatment, the model was calibrated using two irrigation treatments for each salinity treatment and validated using the other two irrigation treatments. In fact, six different cases of calibration and validation for each salinity treatment were [(I3 and I4), (I2 and I4), (I1 and I4), (I2 and I3), (I1 and I3), and (I1 and I2) for calibration and (I1 and I2), (I1 and I3), (I2 and I3), (I1 and I4), (I2 and I4), and (I3 and I4) for validation, respectively]. The model was calibrated by changing the coefficients of water stress (i.e. stomata conductance threshold (p-upper) stomata stress coefficient curve shape, senescence stress coefficient (p-upper), and senescence stress coefficient curve shape) for six different cases. Therefore, the average relative error of the measured and simulated grain yield was minimized for each case of calibration. After calibrating the model for each salinity treatment, the model was simultaneously calibrated using six different cases for three salinity treatments as a whole.
Results and Discussion: Results showed that the sensitivity of the model to crop coefficient for transpiration (KcTr), normalized water productivity (WP*), reference harvest index (HIo), θFC, θsat, and maximum temperature was moderate. The average value of NRMSE, CRM, d, and R2 for soil water content were 11.76, 0.055, 0.79, and 0.61, respectively and for soil salinity were 24.4, 0.195, 0.72, and 0.57, respectively. The model accuracy for simulation of soil water content was more than for simulation of soil salinity. In general, the model accuracy for simulation yield and WP was better than simulation of biomass. The d (index of agreement) values were very close to one for both varieties, which means that simulated reduction in grain yield and biomass was similar to those of measured ones. In most cases the R2 values were about one, confirming a good correlation between simulated and measured values. The NRMSE values in most cases were lower than 10% which seems to be good. The CRM values were close to zero (under- and over-estimation were negligible). Based on higher WP under deficit irrigation treatments (e.g. I3) compared to full irrigation treatments (e.g. I1 and I2), it seems logical to adopt I3 treatment, especially in Birjand as a water-short region, assigning the remaining 25% to another piece of land. By such strategy, WP would be optimized at the regional scale.
Conclusion: The AquaCrop was separately and simultaneously nested calibrated and validated for all salinity treatments. The model accuracy under simultaneous case was slightly lower than that for separate case. According to the results, if the model is well calibrated for minimum and maximum irrigation treatments (full irrigation and maximum deficit irrigation), it could simulate grain yield for any other irrigation treatment in between these two limits. Adopting this approach may reduce the cost of field studies for calibrating the model, since only two irrigation treatments should be conducted in the field. AquaCrop model can be a valuable tool for modelling winter wheat grain yield, WP and biomass. The simplicity of AquaCrop, as it is less data dependent, made it to be user-friendly. Nevertheless, the performance of the model has to be evaluated, validated and fine-tuned under a wider range of conditions and crops.
Keywords: Biomass, Plant modeling, Sensitivity analysis
vahid Rezaverdinejad; M. Hemmati; H. Ahmadi; A. Shahidi; B. Ababaei
Abstract
In this study, the FAO agro-hydrological model was investigated and evaluated to predict of yield production, soil water and solute balance by winter wheat field data under water and salt stresses. For this purpose, a field experimental was conducted with three salinity levels of irrigation water include: ...
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In this study, the FAO agro-hydrological model was investigated and evaluated to predict of yield production, soil water and solute balance by winter wheat field data under water and salt stresses. For this purpose, a field experimental was conducted with three salinity levels of irrigation water include: S1, S2 and S3 corresponding to 1.4, 4.5 and 9.6 dS/m, respectively, and four irrigation depth levels include: I1, I2, I3 and I4 corresponding to 50, 75, 100 and 125% of crop water requirement, respectively, for two varieties of winter wheat: Roshan and Ghods, with three replications in an experimental farm of Birjand University for 1384-85 period. Based on results, the mean relative error of the model in yield prediction for Roshan and Ghods were obtained 9.2 and 26.1%, respectively. The maximum error of yield prediction in both of the Roshan and Ghods varieties, were obtained for S1I1, S2I1 and S3I1 treatments. The relative error of Roshan yield prediction for S1I1, S2I1 and S3I1 were calculated 20.0, 28.1 and 26.6%, respectively and for Ghods variety were calculated 61, 94.5 and 99.9%, respectively, that indicated a significant over estimate error under higher water stress. The mean relative error of model for all treatments, in prediction of soil water depletion and electrical conductivity of soil saturation extract, were calculated 7.1 and 5.8%, respectively, that indicated proper accuracy of model in prediction of soil water content and soil salinity.
M.H. Najafi Mood; A. Alizadeh; K. Davari; M. Kafi; A. Shahidi
Abstract
This experiment was conducted based upon a factorial split plot design consisting of three factors: salinity with three levels (2.2, 5.5 and 8.3 dS/m), irrigation with four levels (50%, 75%, 100% and 125%), cultivars with two levels (Varamin and Khordad). There were three replicates for each treatment ...
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This experiment was conducted based upon a factorial split plot design consisting of three factors: salinity with three levels (2.2, 5.5 and 8.3 dS/m), irrigation with four levels (50%, 75%, 100% and 125%), cultivars with two levels (Varamin and Khordad). There were three replicates for each treatment combination. Salinity was considered as main plot while the other factors were arranged as sub plots in the experiment. Effects salinity and deficit irrigation on yield for cultivars of cotton studied with Marginal Production(MP), Marginal Rate of Technical Substitution(MRTS) and Value of Marginal Production(VMP) indexes. Also for economics analysis, optimum depth of irrigation for deficit irrigation and complete irrigation depth were determined for tow cultivar. MPI showed That in deficit irrigation condition, yield of Khordad less than Varamin, for 1 centimeter of irrigation depth. But in over irrigation level , decreasing yield of Khordad rather than Varamin. Also MPECw showed, That yield decreased 31.8 Kg/ha on Varamin and 76.5 Kg/ha on Khordad cultivars, by increasing 1 dS/m salinity of irrigation water. MRTS index showed for instant yield, when salinity of irrigation water decrease 1 dS/m, must be increase depth of irrigation, 1.68, 3.85 cm for Varamin and Khordad respectively. So that, in equal situation of irrigation water salinity, optimum irrigation depth for Khordad was rather than Varamin.Also in all of salinity levels, optimum irrigation depth, for Khordad was rather than Varamin.
A. Shahidi; M.J. Nahvinia; M. Parsinejad; A. Liaghat
Abstract
Abstract
Various mathematical water uptake models have been introduced for plants response to combined drought and salinity stress. The reduction functions are classified as additive, multiplicative and conceptual models. In this study six different macroscopic reduction functions, namely; Van Genuchten ...
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Abstract
Various mathematical water uptake models have been introduced for plants response to combined drought and salinity stress. The reduction functions are classified as additive, multiplicative and conceptual models. In this study six different macroscopic reduction functions, namely; Van Genuchten (additive and multiplicative), Dirksen et al., Van Dam et al, Skaggs et al and Homaee were evaluated. The experiment was carried out at Research farm of Birjand University in a factorial split plot design with 3 replicates. The treatments consisted of four levels of irrigation (50, 75, 100 and 120%of crop water requirement), and three water qualities (1.4, 4.5, 9.6 dS/m) and two wheat cultivars. The results indicated that the additive model estimates relative yield less than the actual amount. In other word, the effect of combined stresses on wheat yield was less than the summation of separate effects due to salinity and water stress. The effect of drought stress on yield reduction was more than salinity stress. The results also revealed that reduction function of Skaggs et al and Homaee's models agreed well with the measured data when compared with other functions.
Keywords: Salinity stress, Drought stress, Reduction function, Wheat, Birjand
