Pedotransfer functions of the Rye island – Southwest Slovakia

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Chapter 25 PEDOTRANSFER FUNCTIONS OF THE RYE ISLAND – SOUTHWEST SLOVAKIA V. Sˇtekauerova´ and J. Sˇu´tor Institute of Hydrology, Slovak Academy of Sciences, Racˇianska 75 83102 Bratislava, Slovak Republic

Water retention is an important characteristic used in water movement models in vadose zone in order to evaluate such factors as the impact of anthropogenic activity on soil water balance factors, groundwater pollution, water storage in vadose zone, and global changes influence. However, water retention measurements require special experimental equipment and are time consuming, while project timing often does not allot enough time and resources to perform an exhaustive determination of soil water retention by traditional methods in the laboratory (Kutı´lek and Nielsen, 1994). To avoid this problem, a common methodology has been used in the literature where water retention is determined from available soil characteristics, e.g., grain size distribution, bulk density, organic C content, etc. That is, the water content in soil is assumed to depend on characteristics of its structure, bulk density, organic matter content or organic C content, and so on, via relationships described by what are known as pedotransfer functions (PTFs). PTFs not only forgo the difficulty of measuring water retention, but also allow us to use the pedological researches of an area that has been carried out in the past (Pachepsky et al., 1982; Rajkai et al., 1996). Several methods have been devised in soil physics to determine soil hydraulic characteristics from basic soil parameters and to estimate functional forms of PTFs. Originally only the particle-size distribution was used (Brooks and Corey, 1964; Husz, 1967; Renger, 1971). Later dependence on the grain size distribution was expanded to include organic matters contents and bulk density (Gupta and Larson, 1979; Rawls et al., 1982). Three approaches have been developed to estimate water retention. The first approach is based on a regression predicting water retention at several soil water potentials (Cosby et al., 1984; Pachepsky et al., 1982; Puckett et al., 1985; Vereecken et al., 1989, 1990; Wo˝sten et al., 1995; Wiliams et al., 1983; Bastet et al., 1998). The second approach is based on the following physical model of the soil – water system (Arya and Parys, 1981; Haverkamp and Parlange, 1986; Tietje and Tapkenhinrichs, 1993; Zeiliguer et al., 2000): (a) size distribution of soil pores is determined from the grain size distribution or from water retention of separate textural fractions; (b) water content in soil is calculated from the size distribution of soil pores; (c) soil water potential is estimated as the moisture potential, which is in turn calculated from the size distribution of soil pores using a mathematical quantification of capillary phenomena in the soil –water system. DEVELOPMENTS IN SOIL SCIENCE VOLUME 30 ISSN 0166–2481/DOI 10.1016/S0166-2481(04)30025-5

q 2004 Elsevier B.V. All rights reserved.

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The third approach uses an analytical expression of the water retention curve, i.e., a dependence u ¼ FðcÞ; e.g., according to Van Genuchten (1980). The individual parameters in the expression are obtained using a regression of the parameter values on basic soil characteristics such as the grain size distribution, porosity, organic carbon content, bulk and particle density. One of the central questions in PTF development is searching for the PTF expression with general validity for all soils (Tietje and Tapkenhinrichs, 1993; Bastet et al., 1998; Van den Berg et al., 1997; Singh, 1998). However, in the present study, we concentrate on the soils of the Rye Island and develop PTFs using physical and hydrophysical characteristics of the soils of the Rye Island which we consider to be applicable with the presented accuracy only for this region.

1. AREA DESCRIPTION The Rye Island region and its basic characteristics include the Danube river that flows through a relatively narrow valley along the Austrian – Slovak border. The Danube crosses a strip of mountains connecting the Alps and the Karpatians, passes Bratislava, and divides into two branches just below Slovak capital, the Danube and the Small Danube. The two branches of the Danube flow separately for approximately 100 km and then join each other again near the industrial town of Komarno. The area between the two branches of the Danube river is called Rye Island. Rye Island is part of the Danube Lowland and, because of its favorable climate, soil and morphological conditions, is one of the most productive agricultural areas of Slovakia. The average width of Rye Island is 20 km; its area is approximately 2000 km2, which represents about 4% of the Slovak territory, but about 10% of the most productive arable land. Due to its extreme importance for Slovakia, preservation and improvement of the agricultural production potential of Rye Island is of great interest. The Rye Island area forms a flat plain with only small differences in altitude. The altitude of Rye Island decreases in the South-East direction. Its altitude is between 135 and 136 m above sea level in the Bratislava area, decreasing downstream to 108 m (the town of Komarno). Rye Island is the result of sedimentation of the Danube, with sediments from upstream mountains being spread over its territory. During previous centuries (up to the 19th century), the river branched into multiple streams and frequently changed course within its own alluvial sediments. Remainders of old river branches can still be observed in the territory. The most important environmental factors that contributed to the formation of Rye Island were the Danube river and its water regime, climate changes and the Gabcikovo power station. Soils in Rye Island area are a result of Danube river sedimentation, natural pedogenesis and antropogenic activities. Mollic Gleysols, Mollic Fluvisols and Calcaric Haplic Chernozems developed on alluvial sediments of Rye Island, especially in areas where the groundwater table is not in direct contact with the soil profile and where flooding does not occur regularly. Calcaric Fluvisols and Fluvic Gleysols evolved on young alluvial deposits of the Danubian Lowland. In the South-Eastern part of the Rye Island area many Solonchaks and Solonetz can be found. Due to different pedogenetic conditions across Rye Island, different soils can be found in the area. Close to the Danube and Small Danube rivers, young soils (fluvisols) with different degrees of gley processes can be identified.

Table 1 Statistical characteristics of the soil water content sets measured for different soil moisture potential. upF – water content in soil water potential pF (vol.%) Statistical characteristics

upF¼0.3

upF¼1.75

upF¼2

upF¼2.3

upF¼2.74

upF¼3

upF¼3.48

upF¼4.2

upF¼4.78

Average Standard deviation Median Modus Standard error Variance Kurtosis Skewness Range Minimum Maximum Sample size Coefficient of variation

42.16 0.36 41.31 38.6 5.35 28.58 0.30 0.40 35.73 25.80 61.53 221 0.13

37.00 0.42 36.6 35.09 5.35 28.58 0.22 0.27 32.95 21.22 54.17 159 0.14

36.34 0.61 37.6 37.0 7.50 56.21 1.41 2 1.06 42.54 9.66 52.20 151 0.21

34.76 0.45 35.00 34.9 6.38 40.65 1.19 2 0.44 42.74 10.60 53.34 199 0.18

31.36 0.47 30.59 29.39 5.98 35.77 2 0.04 0.36 33.29 16.32 49.61 159 0.19

27.21 0.55 27.99 27.43 8.19 67.09 0.20 2 0.37 43.43 5.79 49.22 224 0.30

25.11 0.38 24.66 22.93 4.85 23.50 0.51 0.16 28.26 11.07 39.33 159 0.19

13.35 0.54 14.005 4.5 6.10 37.24 2 0.65 2 0.09 7.05 0.40 27.45 128 0.46

12.18 0.37 11.5 7.5 5.61 31.47 0.07 0.57 27.80 2.0 29.80 235 0.40

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In depression areas continuously influenced by stagnant water, a specific catena of hydromorphic soils is found. Chernozems cover the major part of the Rye Island area. These soils have not been subjected to long-term effects by groundwater, and are among the most productive in Slovakia. The soil cover of Rye Island area according to texture is as follows: course-textured soils (sandy soils) – 5%, medium-textured soils (loamy soils) – 66%, fine-textured soils (clayey soils) – 23%, and extremely fine-textured soils (clays) – 6%.

2. METHODS Water retention curves of the Rye Island soils were determined under laboratory conditions using the pressure apparatus Soil Moisture Equipment, Santa Barbara, California. Soil samples were taken at selected localities of the Rye Island area during years 1990– 1998 to represent relative occurrence of the soil kinds of the area. The data set contained data from 221 soil samples. Soil water potential values, or pF, of 0.3, 1.75, 2.0, 2.3, 2.74, 3.0, 3.48, and 4.2 were chosen to determine PTF from the above-mentioned data set. Water contents upF for pF ¼ 4:78 were obtained by an exicator method on 235 disturbed soil samples (Sˇu´tor and Koma´r, 1984; Sˇu´tor and Majercˇa´k, 1988). Nine data subsets for PTF creation were obtained (one data subset for every pF point). Statistical characteristics of the subsets are presented in Table 1. The PTF input parameters included the content (%) of the category I particles ðd , 0:01 mmÞ; category II particles ð0:01 mm , d , 0:05 mmÞ; category particles III ð0:05  mm , d , 0:1 mmÞ; and category IV particles ð0:1 mm , d , 2 mmÞ and the dry bulk density rd (g cm23). 3. RESULTS AND DISCUSSION Below we present regression equations for the water content in soil, ui , where i is the soil water potential pF:

u0:3 ¼ 0:19396X1 þ 0:10889X2 þ 0:04911X3 þ 0:12254X4 2 29:9873X5 þ 72:2029

ð1Þ

u1:75 ¼ 0:07392X1 þ 0:16894X2 2 0:21362X3 þ 0:03521X4 2 21:3444X5 þ 62:0236 ð2Þ u2:0 ¼ 20:00095X1 þ 0:02568X2 2 0:15271X3 2 0:33344X4 2 7:27798X5 þ 52:5034

ð3Þ

u2:3 ¼ 0:0195X1 þ 0:00195X2 2 0:20661X3 2 0:4705X4 2 21:8808X5 þ 70:3349

ð4Þ

u2:74 ¼ 0:05301X1 þ 0:15938X2 2 0:29316X3 2 0:01822X4 2 23:5785X5 þ 62:5331

ð5Þ

u3:0 ¼ 20:06503X1 2 0:09055X2 2 0:59549X3 2 0:3002X4 2 12:687X5 þ 65:5509

ð6Þ

u3:48 ¼ 20:07141X1 2 0:18031X2 2 0:4179X3 2 0:2657X4 2 15:5787X5 þ 66:4839

ð7Þ

u4:2 ¼ 0:09661X1 þ 0:04884X2 2 0:14197X3 þ 0:26499X4 2 8:84463X5 þ 23:3886

ð8Þ

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u4:78 ¼ 0:229492X1 2 0:26074

ð9Þ

where ui was measured in vol.%; X1, X2, X3, and X4 stand for the contents (%) of particles of the I, II, III, and IV categories; and X5 is the dry bulk density rd (g cm23). Statistics for individual pF values are shown in Table 2. The bulk density rd was not used to develop equation (9) because the data obtained from disturbed soil samples were used. Developed PTFs were tested with data on 24 soil samples from locations of the Rye Island that were not used when creating the PTFs. The accuracy of the calculated retention curve was quantified with the mean difference (MD) and the root of mean squared difference (RMSD). RMSD has been used for testing the closeness between measured and calculated water retention curves in works by Vereecken et al. (1989) and Tietje and Tapkenhinrichs (1993). MD and RMSD are used in the published work to directly compare the obtained PTFs with the data. The MD and the RMSD are calculated using the method of numerical quadrature within an interval of water potentials from 2 74130 to 0 cm: MD ¼

1 ðb ðu 2 um ÞdC b2a a p

RMSD ¼



1=2 1 ðb ðu 2 um ÞdC b2a a p

ð10Þ

ð11Þ

where um is the measured water content and up is the water content calculated from PTF. MD values can be positive as well as negative depending on whether the moisture values calculated from the PTF are over or below the measured moisture values. They are equal to zero in the case when the water retention curve from the measured data is identical to the water retention curve calculated using PTF. On the other hand, if MD ¼ 0; it does not mean that the RMSD ¼ 0: RMSD values determine the closeness between the measured values of the water retention curve and its values obtained using PTF. Tietje and Tapkenhinrichs (1993) present results from evaluating 13 PTFs using data from Lower Saxony, Germany. The best five PTFs for this database had the following values of MD and RMSD, respectively: 1.29 and 5.75 (Renger, 1971); 0.95 and 6.11 (Arya and Parys, 1981); 2 0.19 and 6.5 (Cosby et al., 1984); 2 5.27 and 7.51 (Rawls and Brakensiek, 1985); and 2 1.45 and 5.31 (Vereecken et al., 1990). From the equations (1) – (9) obtained using the test dataset in this work, the following average values were obtained: MD ¼ 22:5 and RSMD ¼ 3:6: Compared with the Tietje and Tarpenhinrich’s evaluation, these values show a good applicability of equations (1) – (9). Figure 1 shows the statistical distributions of MD and RMSD values. The distribution of MD is close to normal as the points in Figure 1 lie close to the straight line on the probability scale. The probability distribution of RMSD is far from normal. Small values of RMSD are observed much more frequently as compared to the large values. About 50% of the RMSD values are in the range between 0 and 2.5%, and another half of the points is in the range between 2.5 and 10%. We have also observed a strong relationship between MD and RMSD values as shown in Figure 2. This may indicate that using both MD and RMSD as PTF performance indicators may be excessive.

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Table 2 Statistical characteristics of the representative soil physical properties for measured points of water retention curves pF

Statistical characteristic I

0.3

1.76

2

2.3

2.74

3

3.48

4.2

4.78

Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample Mean Min Max Sample

size

size

size

size

size

size

size

size

size

Content of the particles of the corresponding category (%) II III IV

37.36 16 66 221 35.69 16 60 159 28.00 4.2 77.81 151 37.70 4.48 77.81 199 35.69 16 60 159 29.10 4.2 60 224 35.69 16 60 159 37.99 4.48 77.81 128 12.18 2 29.80 235

36.52 12 52 221 38.65 22 52 159 35.75 8.51 76.2 151 34.63 8.51 52.78 199 38.65 22 52 159 40.52 12.3 76.2 224 38.65 22 52 159 31.84 8.51 52.78 128

17.91 2 39 221 17.62 2 39 159 27.82 2.71 82.32 151 22.44 2 82.32 199 17.62 2 39 159 20.08 2 75.13 224 17.62 2 39 159 25.60 2.71 82.32 128

7.96 0 42 221 7.87 0 41 159 8.27 0.04 59.1 151 4.95 0 41 199 7.87 0 41 159 10.26 0 59.1 224 7.87 0 41 159 4.13 0.04 41 128

Dry bulk density (g cm23)

1.44 0.91 1.72 221 1.44 0.91 1.72 159 1.38 0.97 1.7 151 1.44 0.91 1.72 199 1.44 0.91 1.72 159 1.40 0.91 1.72 224 1.44 0.91 1.72 159 1.44 1.00 1.70 128

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Figure 1. Probability distributions of the MD and RMSD between measured and PTFestimated water retention in the test dataset.

Figure 2. Relationship between the MD and RMSD obtained from the PTF testing. 4. CONCLUSION This study presents a soil PTFs developed for the natural environment of the Rye Island. A data set of water retention curves determined under laboratory conditions was used. Multiple linear regression was used to express the dependency of water content in soil on the particle-size distribution in the ranges d , 0:01 mm; 0:01 mm , d , 0:05  mm; 0:05 mm , d , 0:1 mm; and 0:1 mm , d , 2 mm and on dry bulk density. The obtained PTFs for 9 points of the water retention curve were tested with water retention curves from another data set, also from the Rye Island. Comparison of the water retention curves measured and calculated using PTFs shows a good agreement. We conclude that the developed PTFs may be successfully used as inputs into mathematical models of soil water regime for The Rye Island region.

472

ACKNOWLEDGEMENTS The authors express their gratitude to the project VEGA 2/2003/2002 for the financial support.

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