#
Comparison of Soil EC Values from Methods Based on 1:1 and 1:5 Soil to Water Ratios and EC_{e} from Saturated Paste Extract Based Method

^{*}

## Abstract

**:**

_{1:1}, EC

_{1:5}). On the same soil samples, also the electrical conductivity of the saturated paste extract (EC

_{e}) was determined and the relationships between EC

_{e}and each of the three of EC

_{1:1}and EC

_{1:5}values were examined. The soil samples used were collected from three areas over Greece (Laconia, Argolida and Kos) and had EC

_{e}values ranging from 0.611 to 25.9 dS m

^{−1}. From the results, it was shown that for soils with EC

_{e}< 3 dS m

^{−1}the higher EC values were obtained by the method where the suspension remained at rest for 23 hours and then shaken mechanically for 1 h. On the contrary, no differences were observed among the three methods for soils with EC

_{e}> 3 dS m

^{−1}. Also, in the case of EC

_{1:5}, the optimal times for equilibration were much longer when EC

_{e}< 3 dS m

^{−1}. Across all soils, the relationships between EC

_{e}and each of three methods of obtaining EC

_{1:1}and EC

_{1:5}were strongly linear (0.953 < R

^{2}< 0.991 and 0.63 < RMSE < 1.27 dS m

^{−1}). Taking into account the threshold of EC

_{e}= 3 dS m

^{−1}, different EC

_{e}= f(EC

_{1:5}) linear relationships were obtained. Although the linear model gave high values of R

^{2}and RMSE for EC

_{e}< 3 dS m

^{−1}, the quadratic model resulted in better R

^{2}and RMSE values for all methods examined. Correspondingly, in the 1:1 method, two of the three methods used exhibited similar slope values of the linear relationships independent of EC

_{e}value (EC

_{e}< 3 or EC

_{e}> 3 dS m

^{−1}), while one method (23 h rest and then shaken mechanically for 1 hour) showed significant differences in the slopes of the linear relationships between the two ranges of EC

_{e}.

## 1. Introduction

_{e}); this has been established as the standard method [2,3]. Saline soils are considered to be the soils where the saturated paste extract has EC

_{e}values greater than 4 dS m

^{−1}. However, this method is laborious and time consuming especially in the case of EC

_{e}determination for a large number of soil samples. Additionally, the method appears to be more difficult and requires skills and expertise to obtain saturation point for clay soils.

_{e}. The most widely used soil over water mass ratios, (soil:water), are the 1:1 and the 1:5. The ratio of 1:5 is used for soil salinity assessment (EC

_{1:5}) in Australia and China [4,5], while the ratio 1:1 (EC

_{1:1}) is commonly used in the United States [6]. Therefore, different methods for EC assessment are applied between different regions and organizations.

_{e}and EC

_{1:1}or EC

_{1:5}[7], (Table 1). However, the coefficients of the linear relationships are different and vary according to the area of interest. These coefficients are affected, among other factors, by the soil texture [8,9,10], the presence of gypsum and calcite in the soil [3,11], the chemical composition of the soil solution, the cation exchange capacity, etc. It has been documented that in the case of coarse-textured soils the slopes of the abovementioned linear relationships is greater than those of fine-textured soils [8].

_{1:1}or EC

_{1:5}are probably additional factors that have led to the observed differences among various models [6,12]. It is worth to know that the equations EC

_{e}= f(EC

_{1:5}) and EC

_{e}= f(EC

_{1:1}) presented in Table 1 are often compared without taking into account these factors even though the equations have been obtained by different methods and at different ranges of EC

_{e}values. More specific, Aboukila and Norton [13] and Aboukila and Abdelaty [14] have used the NRCS method [15], Khorsandi and Yazdi [11] have shaken the suspension for 1 h, Sonmez et al. [10] have used the USDA method [16], while Visconti et al. [3] have applied mechanical shake for 24 h (Table 1). As regards to the EC

_{e}values range, Aboukila and Norton [13] presented their equation for EC

_{e}values up to 10.26 dS m

^{−1}, while Zhang et al. [17] and Khorsandi and Yazdi [11] for EC

_{e}values up to 108 and 170 dS m

^{−1}, respectively (Table 1). Noted that such extreme EC

_{e}values are related to very specific cases (e.g., dumping of saline water as waste from the oil industry or saline areas for large scale halophyte production). Overall, to obtain the equations EC

_{e}= f(EC

_{1:5}) and EC

_{e}= f(EC

_{1:1}) both different methods have been applied to measure EC

_{1:5}and EC

_{1:1}and different ranges of EC

_{e}values.

_{1:5}was affected by both agitation method and agitation time. Specifically, significant differences existed within three agitation methods when EC

_{e}values ranged between 0.96 and 21.2 dS m

^{−1}. Equilibration times were significantly greater for soils having EC

_{e}< 4 dS m

^{−1}compared to soils having EC

_{e}> 4 dS m

^{−1}. The agitation method of shaking plus centrifuging showed the greatest values of EC

_{1:5}while the stirring method showed the smallest ones for the same soil examined. Also, Vanderheynst et al. [12], conducting an experiment with compost using various dilutions, found that as agitation time increased the EC values increased—especially when agitation time increased from 3 to 15 h. The above results showed the important role of agitation time among the different agitation methods on EC measurement, irrespective of the porous medium (e.g., soil, compost).

_{1:1}, although different methods have been used on the EC

_{1:1}measurement [16,17].

_{e}and (ii) the investigation of the relationship between EC

_{e}and EC values derived from the three methods.

## 2. Materials and Methods

#### 2.1. Sample Collection Areas

#### 2.2. Methods of Determining the Soil Properties

_{3}equivalent percentage was estimated by measuring the eluted CO

_{2}following the addition of HCl (calcimeter Bernard method).

#### 2.3. Methods of Various Soil Extraction and Measurements

#### 2.3.1. EC_{e} Method

_{e}was measured by a conductivity meter (WTW, Cond 315i). For the saturation percentage (SP) determination, a subsample of each paste was oven dried at 105 °C for 24 h.

#### 2.3.2. EC_{1:5} Method

_{e}values of 0.793 and 13.78 dS m

^{−1}, respectively, the EC

_{1:5}values were measured after the suspensions were agitated with mechanical shaker for times 1, 2, 3, 4, 6, 24 and 48 h. After each agitation time the extraction was obtained, and the EC was determined. This process can better evaluate the role of shaking time on the EC

_{1:5}values for the two very different EC

_{e}values.

#### 2.3.3. EC_{1:1} Method

#### 2.3.4. Statistical Analysis

_{e}= f(EC

_{1:1}) and EC

_{e}= f(EC

_{1:5}), a least-squared linear regression was applied and the coefficient of determination R

^{2}was evaluated. The R

^{2}coefficient is used to assessing the correlation between two independent methods. Also, the values of root mean square errors (RMSE) were determined. Analysis of variance (ANOVA) was applied to test the significant difference among the applied EC

_{1:5}or EC

_{1:1}methods using SPSS Statistical Software v. 17.0 (SPSS Inc., Chicago, IL, USA); the means of each method were compared using t-test at a probability level P = 0.05.

## 3. Results and Discussion

#### 3.1. Soil Properties

_{3}, samples from Laconia presented a content lower than 2.5%, from Argolida 5–8% and from Kos 8.5–11%. The pH values ranged from 7.69 to 8.06 for soil samples from Laconia and from 7.5 to 7.7 for soil samples from Argolida and Κos.

_{3}content was 0.2% and 7.66% and pH values were 7.75 and 7 for sample L and A, respectively.

#### 3.2. Estimation of Soil Salinity

_{e}values ranged from 0.611 to 25.9 dS m

^{−1}. It should also be noted that the EC

_{e}variation range of the soil samples from Laconia is much lower than that of the other two regions (Argolida and Kos). Specifically, EC

_{e}values of the samples from Laconia ranged from 0.611 to 1.664 dS m

^{−1}, while in the other two regions they ranged from 2.32 to 25.9 dS m

^{−1}. From the measured EC

_{e}values, it appears that a relatively wide range in salinity levels was obtained for both comparing the different EC

_{1:5}and EC

_{1:1}methods, as well as evaluating the relationship between the EC

_{e}and each of EC

_{1:5}or EC

_{1:1}methods.

#### 3.3. Comparison of 1:1 and 1:5 Soil to Water Extract Electrical Conductivity Methods

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}and R

^{2}are presented.

^{2}of the linear relationship between 1:1 soil to water extract electrical conductivity methods for EC

_{e}< 3 dS m

^{−1}and EC

_{e}>3 dS m

^{−1}are presented in Table 3.

_{1:1}and EC

_{1:5}when EC

_{e}< 3 dS m

^{−1}. Analysis of variance (ANOVA) showed that the three methods are significantly different at a probability level P = 0.05. Furthermore, the t-test analysis (P = 0.05) showed that the NRCS and Loveday methods as well as the USDA and Loveday methods resulted in significantly different EC

_{1:5}values, while EC

_{1:5}values between NRCS and USDA were not significantly different. The mean value with standard deviation for NRCS, USDA and Loveday methods were 0.177 ± 0.029, 0.169 ± 0.029 and 0.151 ± 0.027 dS m

^{−1}, respectively. In the case of 1:1 ratio, the EC values between NRCS and USDA as well as NRCS and Loveday methods were also significantly different (P = 0.05). The mean value with standard deviation for NRCS, USDA and Loveday methods were 0.5 ± 0.070, 0.43 ± 0.100 and 0.423 ± 0.086 dS m

^{−1}, respectively.

_{e}(EC

_{e}< 3 dS m

^{−1}) the rest time seems to play an important role since the difference between the NRCS and the Loveday method is only in the duration of rest time. As regards to the NRCS and USDA methods, the slope of the linear regression between the NRCS and USDA at 1:5 ratio is 1.047, while at 1:1 is 1.161.

_{1:5}values of the soil sample L (with EC

_{e}= 0.793 dS m

^{−1}< 3 dS m

^{−1}) obtained by mechanical shaking for 1, 2, 3, 4 and 6 h was approximately 0.142 dS m

^{−1}while EC

_{1:5}values for 24 and 48 h were 0.218 and 0.274 dS m

^{−1}, respectively. Practically, after 48 h shaking the EC

_{1:5}value was approximately doubling. The corresponding EC values obtained by the three methods used were 0.141, 0.127 and 0.158 dS m

^{−1}for USDA, Loveday and NRCS methods, respectively. Therefore, it appears that the agitation time plays a dominant role to obtain equilibrium since the difference between the NRCS method (EC

_{1:5}= 0.158 dS m

^{−1}) and the method with 24 h shaking (EC

_{1:5}= 0.218 dS m

^{−1}) is in the shaking time. These results are similar to those of He et al. [6] in terms of the long shaking time required to equilibration but differ in the fact that in our experiments did not show differences in EC values obtained by shaking of at least up to 6 h. He et al. [6] explained that the higher values of EC obtained by the long shaking time method compared to other methods may be due to the fact that the mechanical shaking destroys micro-aggregates, as well as increase dissolution of salts because the dynamic concentration gradient between solid and liquid phases. Also, Vanderheynst et al. [12] found that differences occur for shaking time greater than a threshold value of 3 h.

_{e}> 3 dS m

^{−1}there is no significant differences between agitation methods since all methods gave almost the same results and the slope of the linear relationship is almost 1 (Table 2 and Table 3). In addition, it is noted that the R

^{2}values for soils with EC

_{e}> 3 dS m

^{−1}are higher for all methods examined, in both 1:5 and 1:1 ratios, compared to R

^{2}values for EC

_{e}< 3 dS m

^{−1}(Table 2 and Table 3).

_{1:5}values of the soil sample A (with EC

_{e}= 13.8 dS m

^{−1}> 3 dS m

^{−1}) obtained by mechanical shaking for 1, 2, 3, 4, 6, 24 and 48 h ranged from 1.683 to 1.751 dS m

^{−1}. It is obvious that for soils with EC

_{e}> 3 dS m

^{−1}the shaking times required to obtain equilibration are significantly lower compared to soils with EC

_{e}< 3 dS m

^{−1}

_{e}value shows that the solid and liquid phases is far from considered a simple system where the only process carried out is dissolution and that the concentration of ions is inversely proportional to dilution. Such situations may exist only in sandy or sandy loam soils in semi-arid areas with high salinity [25]. However, the soils are characterized by a cation exchange capacity value depending on the type and quantity of clay, the presence of slightly soluble minerals but also ion exchanges between solid and liquid phase. In the present experimental work, the existence of a relatively high clay percentage combined with the existence of slightly soluble minerals may be led to different EC values among various methods, especially when EC

_{e}< 3 dS m

^{−1}. This phenomenon may be even more pronounced in the case of clay soils where there are high content of slightly soluble minerals but less pronounced in the coarse-textured soils without slightly soluble minerals.

#### 3.4. Relationship between EC_{e} and 1:5 Soil to Water Extract Electrical Conductivity Methods

_{e}and EC

_{1:5}, for all soil samples, determined by the three different methods are presented. Analysis of the results showed that each 1:5 soil to water extract electrical conductivity method is strongly related with EC

_{e}since R

^{2}values are high (0.953 < R

^{2}< 0.972) and RMSE are low (1.02 dS m

^{−1}< RMSE < 1.27 dS m

^{−1}). It also appears that the linear equations showed small differences regardless of the EC

_{1:5}methods for all soils examined. These data confirm the existence of a strong linear relationship when the range of EC

_{e}is relatively great (Table 1).

_{e}= fEC

_{1:5}using the USDA method is similar to the corresponding one reported by Kargas et al. [7], (Table 1) for Greek soils since both the two equations have almost the same slope (6.61 and 6.53, respectively).

_{e}< 3 dS m

^{−1}showed that a percentage of 70% of experimental EC

_{e}values were lower than those calculated by the equations presented in Table 4. For this reason, the data were separated into two ranges based on the threshold value EC

_{e}= 3 dS m

^{−1}to evaluate whether the relationship EC

_{e}= fEC

_{1:5}is described by different equations as reported by other researchers [26,27].

_{e}and EC

_{1:5}determined by three different methods, as well as the R

^{2}and RMSE for all soil examined for EC

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}, are presented in Table 5.

_{e}< 3 dS m

^{−1}, the slope of the linear equation between EC

_{e}and EC

_{1:5}has different value depending on EC

_{1:5}determination method used with the smallest and the highest values obtained by the NRCS and Loveday method. Also, the values of the slopes of linear relationships, for both EC

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}, differ significantly from each other since in the case of EC

_{e}< 3 dS m

^{−1}these values ranged from 4.68 to 5.46, while they ranged from 6.60 to 6.71 in the case of EC

_{e}> 3 dS m

^{−1}. In addition, for EC

_{e}< 3 dS m

^{−1}R

^{2}values are lower (0.537 < R

^{2}< 0.718) than those ones (0.917 < R

^{2}< 0.942) observed for EC

_{e}> 3 dS m

^{−1}indicating a strong linear relation between EC

_{e}and each EC

_{1:5}determination method.

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}showed a difference between slopes ranging from 18.5% to 28.9%. Thus, in order to compare various equations describing the relationship between EC

_{e}and EC

_{1:5}, both the agitation method of EC

_{1:5}determination and the range of EC

_{e}for which the equation has been proposed should be taken into account. Specifically, as shown in Table 5 and Figure 1, the relationship between EC

_{e}and EC

_{1:5}determined by the NRCS method has a slope of 4.68 for EC

_{e}< 3 dS m

^{−1}and 6.60 for EC

_{e}> 3 dS m

^{−1}. The differences among the methods may be even greater if the soil contains gypsum or larger amounts of calcite than those observed in the soil samples examined.

_{e}and the gypsum content on equation describing the relationship between EC

_{e}and EC

_{1:5}have been presented by other researchers [3,26,27].

_{e}and EC

_{1:5}when EC

_{e}values are lower than 4 dS m

^{−1}. The fitting of a quadratic equation to the data of this study for EC

_{e}< 3 dS m

^{−1}gave R

^{2}values of 0.74, 0.57 and 0.66 and RMSE values 0.096 (NRCS), 0.124 (USDA) and 0.115 dS m

^{−1}(Loveday method), respectively. A comparison between these RMSE values and those of the linear relationships presented in Table 5, showed a significant improvement only in the case of the NRCS method. It should be noted that there is a significant difference in RMSE values presented in Table 4 compared to RMSE values whether we use the linear equation or quadratic equation to EC

_{e}estimation for EC

_{e}< 3 dS m

^{−1}.

#### 3.5. Relationship between EC_{e} and 1:1 Soil to Water Extract Electrical Conductivity Methods

_{e}and the three methods of determining EC

_{1:1}for all soil samples examined. The results showed that the relationship is strongly linear in all methods examined (R

^{2}> 0.986) and RMSE values are low (0.63 < RMSE < 0.74 dS m

^{−1}). The values of both R

^{2}and RMSE indicate that this linear relationship reliably estimates the EC

_{e}. However, EC

_{e}= fEC

_{1:1}linear relationships have different f coefficient for each method.

_{e}and EC

_{1:1}determined by three different methods are presented taking into consideration the threshold of EC

_{e}value 3 dS m

^{−1}. The results showed that the same trends were observed for R

^{2}and RMSE values as in the case of the results of 1:5 ratio presented in Table 5. As regards to differences observed in the slope of linear relationships between the two areas of EC

_{e}values, a notable difference was observed in the NRCS method since it resulted to a slope 1.65 for EC

_{e}< 3 dS m

^{−1}and 2.08 for EC

_{e}> 3 dS m

^{−1}. Furthermore, the quadratic equation for the NRCS method, for EC

_{e}< 3 dS m

^{−1}, resulted almost to the same RMSE values (0.099 dS m

^{−1}) with those of linear equation. Therefore, for this method with EC

_{e}<3 dS m

^{−1}the simple linear equation gave quite reliable results to EC

_{e}estimation. The other two methods showed similar slope values regardless of the EC

_{e}value. In particular, the EC

_{e}-USDA relationship had almost the same slope value regardless of the EC

_{e}.

_{e}and EC

_{1:1}determined by the NRCS method taking into consideration the threshold of EC

_{e}value 3 dS m

^{−1}are also presented in Figure 2.

## 4. Conclusions

_{1:5}was affected by both agitation method and time, especially for EC

_{e}values lower than 3 dS m

^{−1}. Generally, the NRCS method resulted in the highest EC values compared to the other two methods examined. The differences among agitation methods are essentially eliminated for EC

_{e}values greater than 3 dS m

^{−1}. For soil having EC

_{e}values lower than 3 dS m

^{−1}, equilibration time was very greater than the soils having EC

_{e}values above 3 dS m

^{−1}. The most appropriate equation for EC

_{e}estimation using EC

_{1:5}values for soils having EC

_{e}< 3 dS m

^{−1}is a quadratic equation—especially in the case of the NRCS method—while for soils having EC

_{e}> 3 dS m

^{−1}is the linear equation. However, if soils have a wide range of salinization levels, the linear model are recommended.

_{e}estimation by EC

_{1:5}. Therefore, in order to select each time, the appropriate method and equilibration time for measuring EC

_{1:5}, during laboratory studies, the EC

_{e}value of some samples, as well as the soil characteristics (e.g., gypsum and calcium carbonate content) should be examined in advance.

_{1:1}was affected by EC

_{e}values only in the case of the NRCS method where the estimation of the EC

_{e}can be conducted by simple but different linear relationships whose slopes depend on EC

_{e}values. In the other two methods, the linear relationship EC

_{e}= f(EC

_{1:1}) was not affected by EC

_{e}values.

_{1:1}or EC

_{1:5}and the range of EC

_{e}in order to properly evaluate and compare the proposed equations of EC

_{e}= f(EC

_{1:5}). Additionally, the study of soils with different characteristics than those of the group of soils examined in this work is needed.

## Author Contributions

## Funding

## Conflicts of Interest

## References

- Libutti, A.; Cammerino, A.R.B.; Monteleone, M. Risk assessment of soil salinization due to tomato cultivation in Mediterranean climate conditions. Water
**2018**, 10, 1503. [Google Scholar] [CrossRef] [Green Version] - USDA-Natural Resources Conservation Service. Soil Survey Laboratory Information Manual; Burt, R., Ed.; Soil Survey Investigations Report No. 45; version 2.0.; Aqueous Extraction, Method 4.3.3.; USDA-NRCS: Lincoln, NE, USA, 2011; p. 167.
- Visconti, F.; De Paz, J.M.; Rubio, J.L. What information does the electrical conductivity of soil water extracts of 1 and 5 ratio (w/v) provide for soil salinity assessment of agricultural irrigated lands? Geoderma
**2010**, 154, 387–397. [Google Scholar] [CrossRef] - Rayment, G.E.; Lyons, D.J. Soil Chemical Analysis Methods-Australia; CSIRO Publishing: Collingwood, Australia, 2011. [Google Scholar]
- Wang, Y.; Wang, Z.X.; Lian, X.J.; Xiao, H.; Wang, L.Y.; He, H.D. Measurements of soil electrical conductivity in Tianjin coastal area. Tianjin Agric. Sci.
**2011**, 17, 18–21. [Google Scholar] - He, Y.; DeSutter, T.; Prunty, L.; Hopkins, D.; Jia, X.; Wysocki, D.A. Evaluation of 1:5 soil to water extract electrical conductivity methods. Geoderma
**2012**, 185–186, 12–17. [Google Scholar] [CrossRef] - Kargas, G.; Chatzigiakoumis, I.; Kollias, A.; Spiliotis, D.; Massas, I.; Kerkides, P. Soil Salinity Assessment Using Saturated Paste and Mass Soil:Water 1:1 and 1:5 Ratios Extracts. Water
**2018**, 10, 1589. [Google Scholar] [CrossRef] [Green Version] - Slavich, P.G.; Petterson, G.H. Estimation the Electrical Conductivity of Saturated Paste Extracts from 1:5 Soil: Water Suspensions and Texture. Aust. J. Soil Res.
**1993**, 31, 73–81. [Google Scholar] [CrossRef] - Franzen, D. Managing Saline Soils in North Dakota; North Dakota State University Extension Service: Fargo, ND, USA, 2003; Available online: https://www.ag.ndsu.edu/publications/crops/managing-saline-soils-in-north-dakota (accessed on 1 April 2020).
- Sonmez, S.; Buyuktas, D.; Okturen, F.; Citak, S. Assessment of different soil to water ratios (1:1, 1:2:5, 1:5) in soil salinity studies. Geoderma
**2008**, 144, 361–369. [Google Scholar] [CrossRef] - Khorsandi, F.; Yazdi, F.A. Gypsum and Texture Effects on the Estimation of Saturated Paste Electrical Conductivity by Two Extraction Methods. Commun. Soil Sci. Plant Anal.
**2007**, 38, 1105–1117. [Google Scholar] [CrossRef] - Vanderheynst, J.S.; Pettygrave, S.; Dooley, T.M.; Arnold, K.A. Estimating electrical conductivity of compost extracts at different extraction ratios. Compost Sci. Util.
**2004**, 12, 202–207. [Google Scholar] [CrossRef] - Aboukila, E.F.; Norton, J.B. Estimation of Saturated Soil Paste Salinity from Soil-Water Extracts. Soil Sci.
**2017**, 182, 107–113. [Google Scholar] [CrossRef] - Aboukila, E.F.; Abdelaty, E.F. Assessment of Saturated Soil Paste Salinity from 1:2.5 and 1:5 Soil-Water Extracts for Coarse Textured Soils. Alex. Sci. Exch. J.
**2018**, 38, 722–732. [Google Scholar] [CrossRef] - NRCS. Method 4.3.3: Aqueous Extraction. In Soil Survey Laboratory Information Manual; Burt, R., Ed.; Version 2.0.; NRCS: Washington, DC, USA, 2011. [Google Scholar]
- United States Department of Agriculture (USDA). Diagnoses and Improvement of Saline and Alkali Soils; Agriculture Handbook No. 60; United States Department of Agriculture: Washington, DC, USA, 1954.
- Zhang, H.; Schroder, J.L.; Pittman, J.J.; Wang, J.J.; Payton, M.E. Soil Salinity Using Saturated Paste and 1:1 Soil to water extract. Soil Sci. Soc. Am. J.
**2005**, 69, 1146–1151. [Google Scholar] [CrossRef] - Loveday, J. Methods for Analysis of Irrigated Soils; Tech. Comm. No.54, Commonwealth Bureau of Soils; Commonwealth Agricultural Bureau: Farnham Royal, UK, 1974. [Google Scholar]
- Rhoades, J.D. Soluble Salts. In Methods of Soil Analysis, Part 2: Chemical and Microbiological Properties, 2nd ed.; Page, A.L., Ed.; Agronomy Monograph No. 9; American Society of Agronomy: Madison, WI, USA, 1982; pp. 167–179. [Google Scholar]
- Chi, M.C.; Wang, Z.C. Characterizing salt affected soils of Songnen Plain using saturated paste and 1:5 soil to water extraction methods. Arid Land Res. Manag.
**2010**, 24, 1–11. [Google Scholar] [CrossRef] - Ozcan, H.; Ekinci, H.; Yigini, Y.; Yuksel, O. Comparison of four soil salinity extraction methods. In Proceedings of the 18th International Soil Meeting on Soil Sustaining Life on Earth, Managing Soil and Technology, Sanlıurfa, Turkey, 22−26 May 2006; pp. 697–703. [Google Scholar]
- Hogg, T.J.; Henry, J.L. Comparison of 1:1 and 1:2 suspensions and extracts with the saturation extracts in estimating salinity in Saskatchewan. Can. J. Soil Sci.
**1984**, 64, 699–704. [Google Scholar] [CrossRef] [Green Version] - Bouyoucos, G.H. A recalibration of the hydrometer method for making mechanical analysis of soils. Agron. J.
**1951**, 43, 434–438. [Google Scholar] [CrossRef] [Green Version] - McLean, E.O. Soil pH and Lime Requirement. Agron. Monogr.
**1983**, 9, 199–223. [Google Scholar] - Nadler, A. Discrepancies between soil solute concentration estimates obtained by TDR and aqueous extracts. Aust. J. Soil. Res.
**1997**, 35, 527–537. [Google Scholar] [CrossRef] - Agarwal, R.R.; Das, S.K.; Mehrota, G.L. Interrelationship between electrical conductivity of 1:5 and saturation extracts and total soluble salts in saline alkali soils of the Gangetic alluvium in Uttar Pradesh. Indian J. Agric. Sci.
**1961**, 31, 284–294. [Google Scholar] - He, Y.; DeSutter, T.; Hopkins, D.; Jia, X.; Wysocki, D.A. Predicting ECe of the saturated paste extract from value of EC1:5. Can. J. Soil Sci.
**2013**, 93, 585–594. [Google Scholar] [CrossRef]

**Figure 1.**Relationship between EC

_{e}and EC

_{1:5}for NRCS extraction method. A: all soil samples, B: soil samples range EC

_{e}< 3 dS m

^{−1}, C: soil samples range EC

_{e}> 3 dS m

^{−1}.

**Figure 2.**Relationship between EC

_{e}and EC

_{1:1}for NRCS extraction method. A: all soil samples, B: soil samples range EC

_{e}< 3 dS m

^{−1}, C: soil samples range EC

_{e}> 3 dS m

^{−1}.

**Table 1.**Relationships between soil saturated paste extract electrical conductivity (EC

_{e}) and 1:1 and 1:5 soil to water extract electrical conductivities (EC

_{1:1}, EC

_{1:5}) as proposed by several researchers, as well as the extraction method and the corresponding range of EC

_{e}values.

Reference | Expression | Method | EC_{e} Values Range(dS m ^{−1}) |
---|---|---|---|

USDA [16] | EC_{e} = 3 (EC_{1:1}) ^{f} | ||

Khorsandi and Yazdi [11] | EC_{e} = 7.94 (EC_{1:5}) + 0.27 ^{d}EC _{e} = 9.14 (EC_{1:5}) − 15.72 ^{e} | Shake 1 h | 1.04–170 |

Sonmez et al. [10] | EC_{e} = 2.03 (EC_{1:1}) − 0.41 ^{c}EC _{e} = 7.36 (EC_{1:5}) − 0.24 ^{c} | Rhoades [19] | 0.22–17.68 |

Frazen [9] | EC_{e} = 2.96 (EC_{1:1}) − 0.95 ^{c} | N/A | N/A |

Aboukila and Norton [13] | EC_{e} = 5.04 (EC_{1:5}) + 0.37 ^{c} | NRCS method [15] | 0.624–10.26 |

Chi and Wang [20] | EC_{e} = 11.74 (EC_{1:5}) − 6.15 ^{b}EC _{e} = 11.04 (EC_{1:5}) − 2.41 ^{c}EC _{e} = 11.68 (EC_{1:5}) − 5.77 ^{f} | USDA method [16] | 1.02–227 |

Slavich and Petterson [8] | EC_{e} = f(EC_{1:5}) | Loveday [18] | 0–38 |

Ozcan et al. [21] | EC_{e} = 1.93 (EC_{1:1}) − 0.57 ^{f}EC _{e} = 5.97 (EC_{1:5}) − 1.17 ^{f} | N/A | N/A |

Aboukila and Abdelaty [14] | EC_{e} = 7.46 (EC_{1:5}) + 0.43 ^{a} | NRCS method [15] | 0–18.3 |

Hong and Henry [22] | EC_{e} = 1.56 (EC_{1:1}) − 0.06 ^{f} | Shake 1 h | 0.25–42.01 |

Zhang et al. [17] | EC_{e} = 1.79 (EC_{1:1}) + 1.46 ^{f} | Equilibrate 4 h | 0.165–108 |

Visconti et al. [3] | EC_{e} = 5.7 (EC_{1:5}) − 0.2 | Shake 24 h | 0.5–14 |

Kargas et al. [7] | EC_{e} = 1.83 (EC_{1:1}) + 0.117 ^{c}EC _{e} = 6.53 (EC_{1:5}) − 0.108 ^{c} | USDA [16] | 0.47–37.5 |

**Table 2.**Slopes of the linear equations describing the relation between 1:5 soil to water extract electrical conductivity methods for EC

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}and coefficient of determination R

^{2}.

EC_{1:5} | ||
---|---|---|

Methods | Slope | R^{2} |

EC_{e} < 3 dS m^{−1} | ||

NRCS–Loveday method | 1.166 | 0.872 |

NRCS–USDA | 1.047 | 0.797 |

USDA–Loveday method | 1.108 | 0.812 |

EC_{e} > 3 dS m^{−1} | ||

NRCS–Loveday method | 1.01 | 0.990 |

NRCS–USDA | 1.00 | 0.960 |

USDA–Loveday method | 1.00 | 0.976 |

**Table 3.**Slopes of the linear equations describing the relation between 1:1 soil to water extract electrical conductivity methods for EC

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}and coefficient of determination R

^{2}.

EC_{1:1} | ||

Methods | Slope | R^{2} |

EC_{e} < 3 dS m^{−1} | ||

NRCS–Loveday method | 1.185 | 0.800 |

NRCS–USDA | 1.161 | 0.781 |

USDA–Loveday method | 1.012 | 0.817 |

EC_{e} > 3 dS m^{−1} | ||

NRCS–Loveday method | 1.01 | 0.984 |

NRCS–USDA | 0.97 | 0.945 |

USDA–Loveday method | 1.09 | 0.952 |

**Table 4.**Regression equations describing the relation between saturated paste extracts EC

_{e}and EC

_{1:5}determined by three different methods with the coefficients of determination (R

^{2}) and root mean square errors (RMSE) for all soil samples examined.

EC_{1:5} | |||
---|---|---|---|

Methods | EC_{e} = fEC_{1:5} | R^{2} | RMSE (dS m^{−1}) |

EC_{e}–NRCS | EC_{e} = 6.58 EC_{1:5} | 0.973 | 1.09 |

EC_{e}–USDA | EC_{e} = 6.61 EC_{1:5} | 0.953 | 1.27 |

EC_{e}–Loveday method | EC_{e} = 6.71 EC_{1:5} | 0.971 | 1.02 |

**Table 5.**Regression equations describing the relation between saturated paste extracts EC

_{e}and EC

_{1:5}determined by three different methods with the coefficients of determination (R

^{2}) and root mean square errors (RMSE) for all soil examined for EC

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}.

EC_{1:5} | |||
---|---|---|---|

Methods | EC_{e} = fEC_{1:5} | R^{2} | RMSE (dS m^{−1}) |

EC_{e} < 3 dS m^{−1} | |||

EC_{e}–NRCS | EC_{e} = 4.68 EC_{1:5} | 0.718 | 0.189 |

EC_{e}–USDA | EC_{e} = 4.89 EC_{1:5} | 0.537 | 0.130 |

EC_{e}–Loveday method | EC_{e} = 5.46 EC_{1:5} | 0.647 | 0.123 |

EC_{e} > 3 dS m^{−1} | |||

EC_{e}–NRCS | EC_{e} = 6.60 EC_{1:5} | 0.934 | 1.710 |

EC_{e}–USDA | EC_{e} = 6.60 EC_{1:5} | 0.917 | 1.800 |

EC_{e}–Loveday method | EC_{e} = 6.71 EC_{1:5} | 0.942 | 1.580 |

**Table 6.**Regression equations describing the relation between saturated paste extracts EC

_{e}and EC

_{1:1}determined by three different methods with the coefficients of determination (R

^{2}) and root mean square errors (RMSE) for all soil examined.

EC_{1:1} | |||
---|---|---|---|

Methods | EC_{e} = fEC_{1:1} | R^{2} | RMSE (dS m^{−1}) |

EC_{e}–NRCS | EC_{e} = 2.07 EC_{1:1} | 0.986 | 0.63 |

EC_{e}–USDA | EC_{e} = 1.93 EC_{1:1} | 0.991 | 0.74 |

EC_{e}–Loveday method | EC_{e} = 2.12 EC_{1:1} | 0.988 | 0.68 |

**Table 7.**Regression equations describing the relation between saturated paste extracts EC

_{e}and EC

_{1:1}determined by three different methods with the coefficients of determination (R

^{2}) and root mean square errors (RMSE) for all soil examined for EC

_{e}< 3 dS m

^{−1}and EC

_{e}> 3 dS m

^{−1}.

EC_{1:1} | |||
---|---|---|---|

Methods | EC_{e} = fEC_{1:1} | R^{2} | RMSE (dS m^{−1}) |

EC_{e} < 3 dS m^{−1} | |||

EC_{e}–NRCS | EC_{e} = 1.65 EC_{1:1} | 0.551 | 0.102 |

EC_{e}–USDA | EC_{e} = 1.93 EC_{1:1} | 0.566 | 0.254 |

EC_{e}–Loveday method | EC_{e} = 1.96 EC_{1:1} | 0.624 | 0.091 |

EC_{e} > 3 dS m^{−1} | |||

EC_{e}–NRCS | EC_{e} = 2.08 EC_{1:1} | 0.985 | 1.62 |

EC_{e}–USDA | EC_{e} =1.90 EC_{1:1} | 0.991 | 1.06 |

EC_{e}–Loveday method | EC_{e} =2.12 EC_{1:1} | 0.984 | 1.62 |

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## Share and Cite

**MDPI and ACS Style**

Kargas, G.; Londra, P.; Sgoubopoulou, A.
Comparison of Soil EC Values from Methods Based on 1:1 and 1:5 Soil to Water Ratios and EC_{e} from Saturated Paste Extract Based Method. *Water* **2020**, *12*, 1010.
https://doi.org/10.3390/w12041010

**AMA Style**

Kargas G, Londra P, Sgoubopoulou A.
Comparison of Soil EC Values from Methods Based on 1:1 and 1:5 Soil to Water Ratios and EC_{e} from Saturated Paste Extract Based Method. *Water*. 2020; 12(4):1010.
https://doi.org/10.3390/w12041010

**Chicago/Turabian Style**

Kargas, George, Paraskevi Londra, and Anastasia Sgoubopoulou.
2020. "Comparison of Soil EC Values from Methods Based on 1:1 and 1:5 Soil to Water Ratios and EC_{e} from Saturated Paste Extract Based Method" *Water* 12, no. 4: 1010.
https://doi.org/10.3390/w12041010