Abstract
The objective of this study was the investigation of the combined water and osmotic stress effectson water uptake, growth and yield of corn plants, under full and deficit irrigation with saline waters, infield conditions. The prediction of crop response to soil water and soil salinity requires determination ofsalt and water movement through the soil profile. For this purpose a mathematical model was developedfor the prediction of soil water flow and mass transport. A root water uptake reduction function due towater and osmotic stress was incorporated in the model. The multiplicative approach was used todescribe the combined matric and osmotic effects on plant water uptake. The actual and relative yield ofcorn is estimated by the model as the sum of the actual water uptake divided by the sum of themaximum water uptake.A very important approach was incorporated in the model, to account for the toxic effects of Na+and Cl- salts on plant water uptake reduction. The excess concentrations of ...
The objective of this study was the investigation of the combined water and osmotic stress effectson water uptake, growth and yield of corn plants, under full and deficit irrigation with saline waters, infield conditions. The prediction of crop response to soil water and soil salinity requires determination ofsalt and water movement through the soil profile. For this purpose a mathematical model was developedfor the prediction of soil water flow and mass transport. A root water uptake reduction function due towater and osmotic stress was incorporated in the model. The multiplicative approach was used todescribe the combined matric and osmotic effects on plant water uptake. The actual and relative yield ofcorn is estimated by the model as the sum of the actual water uptake divided by the sum of themaximum water uptake.A very important approach was incorporated in the model, to account for the toxic effects of Na+and Cl- salts on plant water uptake reduction. The excess concentrations of Na+ and Cl- in the soilsolution can cause accumulation of these salts to toxic concentrations in the old leaves of plants, thesubsequent wilting and reduced water uptake. This ion specific phase of plant response to salinity wasadded in the osmotic phase, in the form of an ionic pressure.For the calibration, validation and evaluation of the model to describe soil water content,concentrations of individual ions (Ca2+, Mg2+, Na+, K+ and Cl-) and the overall salinity given by theECsw, field experiments were carried out in maize treatments for three consecutive years under full anddeficit irrigation with saline waters of four levels of water salinity (0.8, 1.6, 3.2 και 6.4 dSm-1). Themodel was calibrated using the data sets of 2009 and 2010 and was validated with the data of 2011.The measurements of plant development indices (leaf area index, dry matter production andyield) revealed that the application of irrigation water with ECiw = 1.6 dSm-1 had no effect on cornplants during the three years. The application of irrigation water with ECiw = 3.2 dSm-1 had no effects oncorn plants during the first year but the reduction in corn yield was significant during the second andthird years, because of the accumulation of salts in the soil and the osmotic and ionic effects on plantwater uptake. The application of irrigation water with ECiw = 6.4 dSm-1 reduced growth and corn yieldsignificantly during the first and second year.The model calculates electrical conductivity and the concentrations of individual ions in the soilsolution. Therefore, in order to compare calculated and measured values, ion concentrations and ECewere converted from saturated paste extract to soil water, with the use of the factor fSP which wasderived from the saturation percentage. Visual inspection and the obtained RMSE values suggestrelatively good overall correspondence between measured data and model results of the soil watercontent, the soil solution electrical conductivity and the concentration of soluble Ca2+, Mg2+, Na+ and Cl-. Cation K+ concentration was not predicted satisfactorily. The model predicted that the use of salineirrigation waters with ECiw = 3.2 dSm-1 and 6.4 dSm-1 caused severe soil salinization but not sodificationof the treatments.Passive cation uptake mechanism was also described successfully by the model. The model wasalso able to describe successfully the significant reduction in corn yield after the incorporation of theionic stress. The reduction in water uptake and corn yield could not be explained by osmotic stress asthe reduction in transpiration was not significant due to osmotic stress.The parameters of seven different root water uptake reduction functions were adjusted to themeasured corn yield data. Sensitivity analysis revealed that three out of seven were able to describesatisfactorily the reduction in root water uptake and the subsequent reduction in corn yield. Crop yieldresponse functions were used for the estimation of the threshold Cl- and salt values above which cornyield declines and the percent yield decrease per 100 mg in Cl- and salt soil concentration increase.Model SWANS proved to be a useful tool for predicting the effects of irrigation water quality onsoil and water uptake by plants. The model was able to predict water and salt movement in the soilprofile up to 120 cm, the root water and cations uptake under water, osmotic and ionic stress. The modelΠερίληψη - Abstractvican predict the possible soil salinization and alkalization risks and the reduction in crop yields underlong term use of saline irrigation water. This model can be used for irrigation management in regionswith scarce water resources and low quality water available for irrigation.
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