Development of an empirical equation for optimum leaching depth (case study in Northern Khuzestan Province, Iran)

Abstract

The primary aim of this study is to evaluate mathematical models of desalinization in two zones of northeastern Khuzestan province (southwestern Iran) with and without the use of a soil amendment (sulphuric acid). At each experimental site, we applied four leaching-depth treatments (25, 50, 75 and 100 cm of water) and two soil-amendment treatments (with and without sulphuric acid), for a total of eight treatments, in one square metre plots. Four replicates of each treatment were established before and after each leaching event. Soil samples were collected every 25 cm from the surface to a depth of 125 cm and electrical conductivity of samples measured for each layer. Eleven mathematical models were developed using SPSS 12.0 software. In all models, the ratio of the net depth of irrigation to soil depth was used as the independent variable (X), while the ratio of the difference between the final electrical conductivity and the equivalent electrical conductivity to the difference between the initial electrical conductivity and the equivalent electrical conductivity was used as the dependent variable (Y). Statistical analysis of these mathematical models indicates that in Zone 1 (with or without sulphuric acid), the cubic equation was the best and the logistic equation was the worst and in Zone 2 (with or without sulphuric acid), the cubic equation was the best and the inverse exponential equation was the worst. The soil texture in Zone 1 was silt loam and silt clay loam. Therefore, the cubic equation obtained here could be generally applied to determine the appropriate leaching depth in the Shavoor plain in northern Khuzestan province, southwestern Iran. Also, validation of the cubic equation in the Shavoor plain shows this model can predict the amount of Y very successfully and agreement between calculated and observed values is more than 70%.

Keywords:

• leaching
• desalinization
• soil amendment
• Khuzestan
• cubic equation

ACKNOWLEDGEMENTS

Authors are grateful to the Khuzestan Water and Power Authority Company and the Research Office of Irrigation and Drainage Networks for their support of this research.