Ali Javadi; b m; m sh; m m
Abstract
In order to design or evaluate an irrigation system, the infiltration phenomenon and its variations should be determined accurately. In saline and sodic soil and water conditions, the importance of this issue will become greater. The main objective of this study was to estimate the coefficients of different ...
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In order to design or evaluate an irrigation system, the infiltration phenomenon and its variations should be determined accurately. In saline and sodic soil and water conditions, the importance of this issue will become greater. The main objective of this study was to estimate the coefficients of different infiltration equations (Kostiakov, Kostiakov-Lewis, Horton, Philip, and U. S. Soil Conservation) and to evaluate the performance of these equations under different qualities of irrigation water, initial soil moistures, and constant water head. Using a laboratory method, infiltrations were measured in soil columns for constant water head. Then, by applying the cumulative infiltration and drainage outflow data to HYDRUS-1D model, soil hydraulic parameters were determined by the inverse solution. To determine the coefficients of infiltration equations, the outputs of the HYDRUS-1D model including cumulative infiltration verses time were corrolated. The values of root mean square error (RMSE), standard deviation root mean square error (SDRMSE), normalized root mean square error (NRMSE), percent relative absolute error (AE) and percent relative error (RE), were used to evaluate the performance of each infiltration equation and to rank the equations. The equation that had the highest rank was considered as the best and more stable equation. The Horton equation with RMSE, SDRMSE, NRMSE and AE of 0.043, 0.018, 0.006 and 1 and the Kostiakov equation with the values of 0.234, 0.175, 0.025 and 4, were the most and the least suitable eqations, respectively. The evaluation of the performance of infiltration equations using statistical indicators showed that the Kostiakov-Lewis and the Kostiakov infiltration equations were the best and the worst equations, respectively. Comparison of NRMSE values showed that in most cases, under deficit irrigation, infiltration equations estimate infiltration more accurately. For a given treatment, the errors of Kostiakov-Lewis and Philip infiltration equations increased as the amount of irrigation water increased, and as the end of the season approached. The rest of the equations did not show any especial trends. To measure infiltration, it is necessary to consider the effects of irrigation water quality, initial soil moisture, and water heads, because these parameters influence the coefficients of infiltration equations and, consequently, the irrigation efficiency.
a o; m n; m m; d z
Abstract
Large areas of Iran are affected by salinity and drought. Due to the tolerance of almond (Prunus dulcis) to water stress, this tree is mainly grown in arid and semi-arid regions, where salinity is commonly another agricultural problem at such areas. Sensitivity of almond trees to salinity calls for special ...
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Large areas of Iran are affected by salinity and drought. Due to the tolerance of almond (Prunus dulcis) to water stress, this tree is mainly grown in arid and semi-arid regions, where salinity is commonly another agricultural problem at such areas. Sensitivity of almond trees to salinity calls for special attention to the integrated effect of salinity and water stress on its water relations. This study aimed to evaluate the combined effect of salinity and drought stress on almond water status. The trial was conducted during 2014 based on randomized complete block design with three replications on a loamy sand soil at horticultural station of the Agricultural Research Center of Azarbaijan province. Treatments comprised three irrigation salinity levels viz. 2 (T1), 4 (T2), and 5 (T3) dSm-1. Leaf (Tc) and air (Ta) temperatures, air relative humidity, leaf water potential (LWP) and integrated volumetric soil water content (SWC) at three depths (0˗20, 0˗40, and 0˗70) were measured at midday (12˗14) during the growing season. Results indicated that salinity had significant effect (p<0.0001) on stomatal conductance (gs), Tc, LWP and available water depletion (AWD). Seasonal averages of gs for treatment T1 to T3 were 0.86, 0.59 and 0.44 cm.s-1, respectively, and the corresponding LWP were ˗1.90, ˗1.93 and ˗2.16 MPa. Also, significant correlation was found between gs, LWP, Tc and AWD. Based on the regression equations, threshold value of gs for initiating stress was obtained to be 0.73 cm s-1. Corresponding LWP and AWD for this gs value were ˗1.85 MPa and 64%, respectively. Optimum Tcfor highest gs was determined to be 28.2 oC. Highly significant correlation between Tc and other water status indicators showed that midday canopy temperature may be a useful tool for assessment of water status and irrigation scheduling of almond orchards.