Relationships between saturated paste and 1:1 or 1:5 soil/water extract sodium adsorption ratios

This study investigates the relationship between the sodium adsorption ratio acquired by the saturated paste extract (SAR(e)) method and those acquired by 1:1 and 1:5 soil/water extracts (SAR(1:1) and SAR(1:5)) by using 122 surface soil samples from 5 agricultural areas of Greece. The soil samples are classified as medium to fine textured with negligible gypsum content and low organic carbon content. The United States Department of Agriculture (USDA) method was used to obtain all extracts. The results showed that the relationships between SAR(e) and SAR(1:1), as well as SAR(e) and SAR(1:5), are strongly linear, with a higher coefficient of determination (R-2) observed in the case of the SAR(e)-SAR(1:1) relationship. The linear regression equations were SAR(e) = 1.21 center dot SAR(1:1) (R-2 = 0.954) and SAR(e) = 2.22 center dot SAR(1:5) (R-2 = 0.828). The linearity of the SAR(e)-SAR(1:5) relationship was stronger when the calcium carbonate content of soils was greater than 4%. Linear relationships were also observed between the electrical conductivity (EC) relationships ECe-EC1:1 and ECe-EC1:5 and between the concentrations of ions Na+, Ca2+ and Mg2+ derived from saturated paste extract and each of the 1:1 and 1:5 extracts. The 1:1 method was more effective than the 1:5 method in the prediction of EC, SAR and ion concentrations of the preferred index of the saturated paste extract method.