WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail:
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Journal of Food, Agriculture & Environment Vol.11 (1): 748-750. 2013
www.world-food.net
Determination of regression equations to predict soil extract salinity from aqueous soil samples (1:2 and 1:5) for calcareous and non-calcareous loamy soils Gülüzar Duygu Semiz and Ömer Atmaca Department of Farm Structure and Irrigation, Agricultural Faculty, Ankara University, Diskapi, 06190 Ankara, Turkey. e-mail:
[email protected],
[email protected] Received 18 September 2012, accepted 10 January 2013.
Abstract The aim of the study was to reveal regression equations to predict soil extract salinities (ECe) for calcareous and non-calcareous soils. For this purpose, 12 calcareous and 12 non-calcareous soil samples were artificially salinized by 1.0, 5.0 and 10 dSm-1 saline waters which were prepared with NaCl. In order not to disturb the homogeneity of application of each sample, the saline waters were added to unapplied soils by the ratio of 1:1(w/ w), and then oven dried at 105°C until reaching constant weight to prepare the saline soils to analyze. Hence, 3 salinity levels (1.0, 5.0 and 10 dSm-1), 24 soil samples (12 calcareous and 12 non-calcareous) and 3 methods (ECe, EC1:2 and EC1:5), total of 216 analyzes were performed. Saturation percentage of soils were recorded in order to recalculate aqueous soil samples back to soil:water ratio at saturation level. Thus, 8 regression equations were developed for specified conditions such as i) four equations for direct conversion from EC1:2 or EC1:5 to ECe, where there was no data on soil:water ratio at saturation point, for calcareous and non-calcareous conditions and ii) another four equations were calculated by soil:water ratio at saturation point from EC1:2 or EC1:5 to ECe, on where there were data on soil:water ratio at saturation point, for calcareous and non-calcareous conditions. Key words: Calcareous soil, non-calcareous soil, loamy soil, salinity, regression equation, soil:water ratio, soil extract, soil paste, soil water dilution.
Introduction Salt- affected soils are widely distributed in the world 1, especially in arid and semi-arid areas, covering an area of 9500 million hm 2-4. Salinity is a measure of the amount of salts in the soil saturation extracts 5. Customarily, soil salinity has been defined and assessed in terms of laboratory measurements of the electrical conductivity of the extract of a saturated soil-paste sample (ECe). The saturation percentage (SP) is the lowest water/soil ratio suitable for the practical laboratory extraction of readily dissolvable salts in soils. The water content of saturated soil-pastes (the so-called saturation percentage, SP), as well as the water/soil ratio, varies with soil texture 6. The use of saturation extracts as a method of measuring and referencing salinity provides a direct relationship with the field moisture range for most soils. However, soil water suspensions of different ratios, such as 1:1, 1:2, 1:5 and 1:10, can be more easily made and extracted than obtaining saturation extracts7. When the objectives are relative changes rather than absolute solute content, such as the case with soil-salinity monitoring programs, the wider extraction ratios have advantages of speed and greater volume 6 and more information can be gathered about soil salinity with the same amount of labor 8. Soil water salinity is changed depending on the volume of the water in soil. This can easily be explained sample concentration rule. The more water the less salinity or the less water the more salinity. To be useful to the farmer or who may concern about the soil salinity, it needs to be defined at saturation point, depending on where and why to use this information. If the question is plant salt tolerance or there is a need to know exact magnitude of the salinity, 748
one may need salinity at soil saturation point. The aim of the study was to determine equations for loamy soils to convert from EC1:2 and EC1:5 to ECe depending on soil being calcareous or noncalcareous. Material and Methods This study was conducted in the laboratory of Ankara University, Agricultural Faculty, Department of Farm Structure and Irrigation. The experimental soil samples were obtained from an earlier study which was carried out in Anatolia Seyitömer-Kütahya. Calcareous (12) and non-calcareous (12) loamy textured soil samples were selected. Some initial soil properties are shown in Table 1. Calcite percentages of calcareous and non-calcareous soils were 1032.2% and 0.9-3.2%, respectively. Saline waters having 1, 5 and 10 dSm-1 salinities were prepared adding NaCl to tap water. The saline waters were added to intact soils 1:1 w:w ratio, in order to maintain equal treatments. The treated saline soils were oven dried until reaching the constant weight. Saturated paste extracts were prepared by adding distilled water to approximately 250 g soil sample with stirring until it reached a condition of complete saturation. The saturated pastes were allowed to equilibrate for 18-24 h. The extracts were obtained by vacuum 9. The soil water ratios 1:2 and 1:5 were prepared adding 80 and 100 ml distilled water to 40 and 20 g oven dried soils, respectively. The plastic containers having suspensions of 1:2 and 1:5 soil water ratio were shaked on an automatic shaker for 30 min and left for 18-24 h to establish the equilibrium. Journal of Food, Agriculture & Environment, Vol.11 (1), January 2013
Table 1. Initial soil properties. 8.14 0.16 4.01 3 8.13 0.18 1.05 18
7.3 0.11 3.67 1.3 7.73 0.17 4.15 24.4
7.21 0.13 5.55 2.5 8.11 0.20 3.71 22
7.99 0.22 3.02 2.5 7.94 0.18 3.12 16
7.98 0.18 2.08 1.21 7.81 0.17 1.91 12
7.74 0.17 3.56 3.2 8.04 0.16 2.43 10
7.8 0.24 3.73 3.2 8 0.25 2.36 21.3
Equations were developed for two different situations depending on whether there is information on saturation percentage (SP). If SP is known from an earlier study, one can calculate (convert) ECe of saturation extract from EC1:2 and EC1:5, directly. For example, saturation percentage of a sample is 63% (Pw). Water content for the sample at 1:2 and 1:5 soil:water ratios would be 200 and 500% (Pw) respectively. EC1:2 and EC1:5 of the same samples were 0.96 and 0.45 dSm-1, respectively. If we apply the concentration rule to this sample, one can easily calculate ECe like, at 1:2 soil water ratio: 2/0.63 = 3.175 (= concentration factor) then ECe should be 0.96 x 3.175 = 3.048 dSm-1, 1:5 soil water ratio: 5/0.63 = 7.9365 (= concentration factor) then ECe should be 0.45 x 7.9365 = 3.57 dSm-1. Results Calcareous soils: EC of calcareous soil samples were measured for saturation extract, 1:2 and 1:5 soil water ratios. SP of each samples were recorded. Regression analyses revealed that EC1:2 (significant F = 7.54E-22) and EC1:5 (significant F = 1.45E-16) were statistically significant at p
