WATER RETENTION AND AVAILABILITY IN SOILS OF THE STATE OF SANTA CATARINA-BRAZIL : EFFECT OF TEXTURAL CLASSES , SOIL CLASSES AND LITHOLOGY ( 1 )

The retention and availability of water in the soil vary according to the soil characteristics and determine plant growth. Thus, the aim of this study was to evaluate water retention and availability in the soils of the State of Santa Catarina, Brazil, according to the textural class, soil class and lithology. The surface and subsurface horizons of 44 profiles were sampled in different regions of the State and different cover crops to determine field capacity, permanent wilting point, available water content, particle size, and organic matter content. Water retention and availability between the horizons were compared in a mixed model, considering the textural classes, the soil classes and lithology as fixed factors and profiles as random factors. It may be concluded that water retention is greater in silty or clayey soils and that the organic matter content is higher, especially in Humic Cambisols, Nitisols and Ferralsol developed from igneous or sedimentary rocks. Water availability is greater in loam-textured soils, with high organic matter content, especially in soils of humic character. It is lower in the sandy texture class, especially in Arenosols formed from recent alluvial deposits or in gravelly soils derived from granite. The greater water availability in the surface horizons, with more organic matter than in the subsurface layers, illustrates the importance of organic matter for water retention and availability.


INTRODUCTION
Simulation models that evaluate water movement in the soil-plant-atmosphere system are an important tool in agriculture and in environmental management.Nevertheless, the use of these models is limited due to the need for a large number of soil properties as input variables, such as water retention and availability in the soil for plants (Wösten et al., 1999), and these properties are strongly affected by soil texture, mineralogy, organic matter content and management (Hillel, 1998).
Generally soils with finer particle sizes retain more water; nevertheless, as moisture increases in both field capacity (FC) and in the permanent wilting point (PWP), this does not always result in greater available water content (Rawls et al., 1982;Gaiser et al., 2000;Al Majou et al., 2008;Reichert et al., 2009).Furthermore, it is important to consider that there are confounding factors in the relation between texture and water retention in the soil.This occurs because in more clayey soils, the chemical and physical protection of organic matter is generally greater (Oades, 1988;Dieckow et al., 2009), especially in soils of colder and wetter regions (Tate, 1992;Chen & Chiu, 2000;Dalmolin et al., 2006).This condition raises the organic matter content and, consequently, water retention, especially at low tensions (Rawls et al., 2003).Another soil property that affects water retention and availability is mineralogy.In soils with predominance of 2:1 clay minerals water retention and availability are higher than in kaolinitic soils (Gaiser et al., 2000).
Since the soil particle size, mineralogical composition and organic matter content are rather variable according to the lithology, altitude and climate, studies must adress the relation of water retention and availability to the other soil properties for each location of interest.In such studies, one tries to group the different profiles according to other soil properties.Generally, use is made of the soil textural class (Rawls et al, 1982;Al Majou et al., 2008), the soil class using different taxonomic systems (Batjes, 1996) or soil lithology (Bastet, 1999) as a criterion for grouping the soil profiles or horizons.In developed countries, the relation between soil properties and water retention and/or availability is evaluated using large databases, such as the NRCS (Soil Survey Staff, 1995) and the HYPRES (Wösten et al., 1999), while in the other countries these studies are generally lacking, which impedes the use of simulation models (Hodnett & Tomasella, 2002).
In the soils of Santa Catarina, few studies have been carried out to determine soil water retention and availability for plants (Veiga et al., 2008;Costa et al., 2009;Morales et al., 2010).As the lithology, relief and climate of the soils of this state are highely variable, various soil classes were formed (containing from sandy textured to very clayey textured soils) (Embrapa, 2004).Thus, in more clayey soils, such as Latossolos (Ferralsols) and Nitossolos (Nitisols) derived from extrusive igneous rocks, the moisture content at field capacity and the permanent wilting point should be higher, raising the available water content for plants in comparison to sandy soils derived from alluvial sediments.In addition, the differentiated climate of Santa Catarina, which is constantly moist, associated with high altitudes in some regions of the State, results in a climate ranging from humid subtropical to temperate, favoring the predominance of 1:1 clay minerals (kaolinite) and a greater accumulation of organic matter in the soil, mainly in more clayey highland soils, in comparison to soils of the same lithology and textural class as in other states of Brazil.The predominance of kaolinite may result in low available water contents in the soils of Santa Catarina, which may be attenuated by the effect of the high contents of organic matter in the surface horizons.
Nevertheless, so far, these hypotheses cannot be confirmed by the quantity of information available on soils of the State of Santa Catarina.Thus, the purpose of this study was to evaluate and compare water retention and availability in soils of different textural classes, soil classes and lithologies located in the state of Santa Catarina, in the southern region of Brazil.
Lithology was determined for each soil based on the rocks found in the profile, considering the geological map and the lithostratigraphic column of the State of Santa Catarina, as presented by Zanini et al. (1997).The horizons A, AB, BA and B, when present, and their subdivisions (A1, A2, B1 and B2) were studied in each profile, and horizons A and C of Neossolos Quartzarênicos (Arenosols).In the middle part of each horizon, undisturbed samples were collected with stainless steel cylinders (diameter 6.0 cm, height 2.5) pushed into the soil, in quadruplicate, as well as composite disturbed samples.
The undisturbed samples were saturated by capillarity and stabilized at water tensions of 1, 6 and 10 kPa in a sand suction column (Reinert & Reichert, 2006) and at tensions of 33, 100, 300, 500 and 1,500 kPa in Richards' chambers (Richards, 1949).Field capacity (FC) was considered as the volumetric soil moisture at a tension of 10 kPa (pore diameter = 30 µm); permanent wilting point (PWP) as the volumetric moisture at 1,500 kPa (pore diameter = 0.2 µm); and the available water content (AW) as the volume of water retained between 10 and 1,500 kPa.
The following properties were determined in the disturbed samples: soil particle size by the pipette method according to Day (1965), to classify the soil according to the textural classes (Santos et al., 2005); and organic matter (OM) content by multiplication with the factor 1.724 of the total organic carbon content determined by the Walkley-Black method modified by Tedesco et al. (1995).
Statistical analysis was carried out after the creation of two soil groups because the surface horizons differed from the subsurface horizons in OM content.The database was thus divided into two groups: horizons O, A, AB, AC and their subdivisions were grouped as "surface" horizons, and horizons BA, B, C and their subdivisions were grouped as "subsurface" horizons.The grouping of horizons by their position in the profile generally reduces the standard error in the estimation of water retention and availability in the soil (Bruand, 2004a).
The effects of the textural class (13 classes), of the soil class at the suborder level (according to Embrapa, 2006) and of the lithology with regard to FC, PWP and AW were analyzed for each group of horizons.For this purpose, univariate statistical analysis was used in a mixed model with the "PROC GLIMMIX" procedure of the SAS 9.2 program (Schabenberger, 2007).In this analysis, the soil class, the textural class or the lithology were considered as a fixed effect and the profiles as a random effect.Due to the different number of horizons in each soil profile, which were separated into "surface" and "subsurface" horizons, the effect of the order of position of each horizon in the soil profile was included using the "random residual" option in the statistical model.For example, all B1 horizons (including Bt1, Bw1, Bi, and Bt) were denominated by a single name.
The mean values of FC, PWP and AW in each textural class, soil class or lithology were compared by the least significant difference (LSD) test.Due to the use of a mixed statistical model, similar mean values may have different letters.This occurs because the comparison method calculates a standard error for the mean value of each one of the levels of fixed effect.Consequently, a level with greater variability in its replications will be statistically similar to a greater number of levels.

RESULTS AND DISCUSSION
Water retention and availability in the soil versus textural classes In the surface horizons, the field capacity (FC) and permanent wilting point (PWP) were similar for most textural classes.This was the result of the large variability in FC and PWP observed within a single textural class, which raised the standard error of the estimate.Consequently, soils had mean values with differences of up to 0.14 cm 3 cm -3 for FC and 0.10 cm 3 cm -3 for PWP that were considered statistically similar (Table 1).In the subsurface horizons, the variability among soils with a similar textural class was lower, resulting in a clearer distinction among textural classes by soil water retention (Table 1).The greater variability in water retention in the surface horizons occurred by the more intense weathering effect through the activity of microorganisms, of plants, of wetting and drying cycles, and also of the anthropic effect through soil use and management.The combination of these effects resulted in a high standard error of the estimate of OM contents in surface horizons of soils of the same textural class.This variability of the OM contents, associated with the different uses of the soils of Santa Catarina, results in changes in soil structure, which alters the distribution of pores, water adsorption and water retention in the soil at lower suctions (Braida et al., 2011).In contrast, alteration in the OM contents in soils with the same particle sizes also modifies the water retention capacity at high suctions due to alteration in the specific surface area of the soil and in the quantity of water adsorbed by chemical bonds (Resurreccion et al., 2011).In addition to the OM contents, as the soils of Santa Catarina are derived from distinct materials of origin (Embrapa, 2004) which underwent different pedogenetic processes, the high standard error of PWP in soils of similar particle size may also be related to the variations in the mineralogy of the soils evaluated due to its effect on the specific surface area of the soil and on water retention (Bruand, 2004b).
In the surface horizons, FC was greater (0.41-0.55 cm 3 cm -3 ) in soils with predominance of particles with diameter less than 0.53 µm, including the clayey and loamy soils and their variations (Table 1).The FC values (0.26 cm 3 cm -3 ) were intermediate in the sandy loam soils, and lowest (0.16 cm 3 cm -3 ) in soils of the sandy class.The PWP was also greater in the clayey and/or silty soils and lower in the sandy soils.In the subsurface horizons, moisture values in FC and PWP were higher in horizons with silty clay texture, very clayey texture and clayey texture soils (Table 1), all with high clay, silt and OM contents (Table 2).Intermediate values of FC and PWP occurred in horizons with clayey loam, sandy clay loam and loam texture, which are characterized by a balanced distribution of the particle size fractions (about one third each of clay, silt and sand).Lower FC and PWP occurred in soils with sandy loam, loamy sand and sandy texture.
The increase in FC and PWP in soils with higher clay and silt contents was also observed in Rio Grande do Sul, RS (Reichert et al., 2009), the USA (Rawls et al., 1982), France (Al Majou et al., 2008), and in soils of a semiarid tropical climate in the northeastern region of Brazil and in the Southeast of Nigeria (Gaiser et al., 2000).Lower water retention in the sandier soils occurs due to the predominance of large diameter pores (>30 µm), which are drained at low suctions, while in soils with a more clayey texture, smallerdiameter pores predominate (<0.2 mm), which favor the increase of water retention <30 µm high suctions and water availability in the soil (Petersen et al., 1968).The variations in water retention and availability in soils of Santa Catarina were also similar to those of the theoretical model developed by Buckman & Brady (1964).
Greater FC and PWP were observed for most textural classes of the soils of Santa Catarina (SC) in comparison to soils of RS, the USA, France and other regions of a semiarid tropical climate.The cause of the greater water retention may be associated with the high OM content observed in the soils of Santa Catarina, promoting the increase in water retention, regardless of the soil texture (Rawls et al., 2003).The mean OM content of the soils of Santa Catarina was 47 g kg -1 in the surface horizons and 17 g kg -1 in the subsurface horizons (mean of 30 g kg -1 ), which is greater than the mean contents of the databases used by Reichert et al. (2009), Rawls et al. (1982), Al Majou et al. (2008) and Gaiser et al. (2000).The greater OM content of the soils of SC is a consequence of the climatic conditions and of lithology.The accumulation of OM in the soil is favored in regions with a cold and wet climate (Tate, 1992;Chen & Chiu, 2000;Dalmolin et al., 2006) and in soils with a predominance of clay (Almeida et al., 1997(Almeida et al., , 2003;;Corrêa, 2003;Embrapa, 2004).These factors reduce microbial activity and protect the organic matter chemically and physically by their interaction with soil clay minerals (Oades, 1988;Dieckow et al., 2009).
In the soils of SC, the OM contents had a positive linear relationship to the clay+silt contents for the surface and subsurface horizons (Figure 1a, b), with a greater angular coefficient in the surface horizons, confirming the interaction observed by Oades (1988) and Dieckow et al. (2009).This interaction results in an additive effect of the fine soil particles with the OM in the sense of increasing the available water content (AW) since the AW varied little among the textural classes in the subsurface horizons (Figure 2).
In regard to AW content, greater amplitude was observed in the surface horizons (0.08 cm 3 cm -3 ) in relation to the subsurface horizons (0.04 cm 3 cm -3 ) (Figure 2).In the surface horizons, AW is greater in soils with greater silt as well as OM contents (Table 2), including soils of silty clay loam, loam, clayey loam and silty clay texture, with variation from 0.15 to 0.17 cm 3 cm -3 (Table 1).Intermediate contents of AW occurred in the clayey, very clayey, sandy loam and sandy clay loam classes (variation 0.10-0.13cm 3 cm -3 ).Lower AW contents occurred in soils with a sandy texture, with a mean value of 0.09 cm 3 cm -3 .In percentage, the surface horizons of the soils with silty clay loam, loam, clayey loam and silty clay textures have a 44 and 78 % greater AW content than the very clayey and sandy-textured soils, respectively.
In the subsurface horizons, although water retention is greater in clayey texture soils (Figure 2b), the AW content of most textural classes was similar (0.09-0.13 cm 3 cm -3 ), differing only among the horizons with silty clay and very clayey texture (Table 1).The greater water availability observed in the surface horizons in loamy to clayey soils in comparison to that observed in the subsurface horizons is due to greater OM content (Braida et al., 2011) and to the soil structure in the surface horizons.
Thus, among the main textural classes evaluated, highest water contents are available to plants in soils with loamy texture and high silt and clay levels, as similarly observed in the south of Brazil, the USA and France (Rawls et al, 1982;Al Majou et al., 2008;Reichert et al., 2009).In the subsurface horizons of the soils of SC, the textural class has little influence on water availability.
A similarity was observed in the AW content in most textural classes of the soils of SC and RS (Reichert et al., 2009) and of the region near Paris, France (Al Majou et al., 2008), mainly in the soil surface horizons.This may be atrributed to the clay type in the soil, since the climate types Cfa and Cfb are somewhat similar (Köppen & Geiger, 1928), which favors the formation of 1:1 type clay minerals and, to a lesser extent, 2:1 type clay minerals.Nevertheless, the soils of the USA have greater AW content in most textural classes, compared to the soils of SC.This difference is probably due the predominance of soils with high activity clay of the 2:1 type (Nettleton et al., 1983;Rawls et al., 2003), while in SC soils with kaolinite, 2:1 type clay minerals with hydroxyaluminum interlayers and iron oxides predominate (Almeida et al., 1997(Almeida et al., , 2003;;Corrêa, 2003;Paes Sobrinho et al., 2009;Bringhenti, 2010).The increase in water availability provided by the 2:1 type clay minerals has not been studied in detail (Bruand, 2004b); nevertheless, the studies of Gaiser et al. (2000) and Reichert et al. (2009) indicate a positive relation between these soil properties.

Water retention and availability versus soil classes
The grouping of the profiles according to the soil classes of the Brazilian Soil Classification System (Sistema Brasileiro de Classificação de Solos -SiBCS) (Embrapa, 2006) at the level of suborders indicated differences in water retention, mainly in the surface horizons (Table 3).Nevertheless, FC and PWP in the surface horizon were statistically equal among soils, with differences in the mean values of up to 0.15 cm 3 cm -3 , indicating great variability in water retention among soils of the same class at the suborder level.
Greater water retention in the surface horizons of the Cambissolos Húmicos (Humic Cambisols) is associated with their clayey loam texture and greater OM content, which is greater in this soil class than in the other classes evaluated (18 to 47 g kg -1 ) (Table 4).The high FC and PWP of the Latossolos (Ferralsols) and Nitossolos (Nitisols) are also associated with the high clay and OM contents.Lower water retention in the Neossolos Quartzarênicos (Arenosols) (Table 3), however, is due to their high sand content (more than 900 g kg -1 ) (Table 4), resulting in the predominance of macropores.
The AW content in the surface horizons of the soils of SC differed up to 0.10 cm 3 cm -3 (Table 3) among the suborders.It was highest in the Cambissolos Húmicos (Humic Cambisols) and Neossolos Litólicos (Leptosols) (0.16-0.19 cm 3 cm -3 ) and lowest in the other classes, which did not differ from each other (0.09-0.14 cm 3 cm -3 ).In the subsurface horizons, the AW differed among few soil classes since the amplitude of AW was only 0.05 cm 3 cm -3 .Among the classes, the Cambissolos Húmicos (Humic Cambisols) had greater AW contents, and the Nitossolos Brunos (Nitisols) had lower contents.In regard to the other classes, AW had intermediate contents, not differing from each other (Table 3).The greater water availability in the surface horizons of the Cambissolos Húmicos (Humic Cambisols) and Neossolos Litólicos (Leptosols) occurred due to the additive effect of two properties, greater OM contents, and clay, silt and sand contents near the 1/3 ratio of each fraction.At this proportion, the macropores formed by the sand fraction may be occupied by the silt and clay fractions, forming intermediate diameter pores, responsible for the retention of the available water.Batjes (1996) evaluated the AW content (33-1,500 kPa) of soils that form the "World Inventory of Soil Emission Potentials (WISE)" database, consisting of 4,352 profiles and used to create the Soil Map of the World of the FAO-Unesco.Similalry as in the soils of SC, Batjes (1996) observed greater AW in the Humic Cambisols (FAO, 1991), which correspond approximately to the order of the Cambissolos Húmicos in the SiBCS (Embrapa, 2006).In relation to the classes of Argissolos, Latossolos and Nitossolos of the SiBCS (Embrapa, 2006), which correspond approximately to the classes of Acrisols, Ferralsols and Nitisols, respectively, by the FAO (1991) classification, the AW was approximately 0.04 cm 3 cm -3 greater in the Acrisols (mean of 0.12 cm 3 cm -3 ) in comparison to the Ferralsols and Nitosols (mean of 0.08 cm 3 cm -3 ), i.e., a difference of 50 % in the AW content (Batjes, 1996).Batjes (1996) attributed the effect of soil mineralogy as a cause of lower water availability in the Ferralsols and Nitisols, since 1:1 type clay minerals and oxides predominate in these soils, while 2:1 type clay minerals predominate in the Cambisols and Acrisols.In the soils of SC, this difference was not observed, since the AW contents of these three soil classes was medium 0.12 cm 3 cm -3 in the surface horizons and 0.10 cm 3 cm -3 in the subsurface horizons.
Another difference observed was in regard to the class of the Neossolos Quartzarênicos (Arenosols), which had AW contents in the surface and subsurface horizons similar to other classes, such as in the Latossolos (Ferralsols), Nitossolos (Nitisols), Chernossolos (Chernozems) and Argissolos (Acrisols).
In contrast, Batjes (1996) observed that the soils corresponding to this class, called Arenosols in the FAO (1991) classification, have AW contents of around 50 % (AW = 0.04 cm 3 cm -3 ) of those in the Neossolos Quartzarênicos Arenosols of SC.This greater water availability in the sandy soils of Santa Catarina may be mainly related to the fine sand contents of these soils, which ranged from 681 to 783 g kg -1 (Table 4), and have a positive relation to water availability (Costa, 2012).

Water retention and availability versus soil lithology
The physical properties related to water retention also differed according to the soil lithology (Table 5).In the surface horizons, greater FC and PWP occurred in the soils derived from extrusive igneous rocks from the Serra Geral Formation (basaltic andesite, basalt, amygdaloidal basalt, dacite, rhyodacite), which give rise to soils with clayey or very clayey textural classes (Embrapa, 2006) and with mean OM contents (above 50 g kg -1 ) (Table 6); intrusive igneous (hornblendite, except for granite), metamorphic rocks (muscovite garnet schist, mafic  granulite, migmatite, parametamorphic); and fine texture sedimentary rocks (Shales or siltstones), which gave rise to medium texture soils (Embrapa, 2006) and medium OM contents (35 to 50 g kg -1 ) (Table 5).Soils with intermediate FC and PWP moisture contents were those derived from sedimentary rocks, which gave rise to soils with loam texture (Embrapa, 2006), but with clay contents of approximately 170 g kg -1 and with medium OM contents (approximately 35 g kg -1 ).The moisture contents of FC and PWP were lowest in soils derived from rocks or quartz-rich sedimentary deposits (Botucatu sandstone and recent alluvial deposits), which gave rise to soils with a sandy texture (Embrapa, 2006) and medium OM contents (20 to 25 g kg -1 ); and also in the soils derived from granite, which gives rise to soils with sandy texture with medium OM contents (35 g kg -1 ), differing from the other soils in the high gravel (186 g kg -1 ) and coarse sand (356 g kg -1 ) contents (Table 5).
In the subsurface horizons, the decreasing order of FC and PWP according to the soil lithology was very similar to that observed in the surface horizons (Table 5), while the OM content was lower and clay content higher (Table 6).Nevertheless, the rate of OM reduction and of the increase in clay content according to soil depth varied among the soils of different lithologies.
The effect of increased density and clay contents increased FC and to a greater extent, PWP for most of the subsurface horizons, with a mean value of 0.04 cm 3 cm -3 in FC and of 0.07 cm 3 cm -3 in PWP.The greatest moistures in FC and in PWP were observed in the soils derived from the following lithologies: muscovite garnet schist, siltstones and fine sandstones, parametamorphic, amygdaloidal basalt and mafic granulite, in which FC and PWP increased up to 0.13 and 0.18 cm 3 cm -3 , respectively, in relation to those observed in the surface horizons.This difference is principally due to the increase in the clay content (192 to 417 g kg -1 ) (Table 6).Using lithology as a fixed effect, large differences were observed in FC and in PWP among soils with different lithologies.In the surface horizons, FC ranged from 0.16 cm 3 cm -3 in the soils of recent alluvial deposits to 0.54 cm 3 cm -3 in the soils derived from Basaltic Andesite, while PWP ranged from 0.07 to 0.38 cm 3 cm -3 among these lithologies (Table 5).In the subsurface horizons with these same lithologies, FC ranged from 0.20 to 0.55 cm 3 cm -3 , and PWP from 0.10 to 0.44 cm 3 cm -3 .These differences result in an amplitude of 0.38 cm 3 cm -3 in FC and of 0.31 cm 3 cm -3 in PWP in the surface horizons and 0.35 cm 3 cm -3 in FC and 0.34 cm 3 cm -3 in PWP of the subsurface horizons (Table 5).This amplitude shows the importance of determination of water retention in soils that occur in a certain region when simulation models are used that involve soil physical-water processes.

Lithology
In accordance with the differences observed in FC and in PWP, the AW content ranged from 0.08 to 0.21 cm 3 cm -3 in the surface horizons.Nevertheless, the greater water retention capacity of some soils did not result in greater water availability to plants, since the AW contents were highest in soils derived from siltstones and lowest in those derived from granite and from recent alluvial deposits (Table 5).The AW content in the soils of the other lithologies was intermediate.The greater AW content in soils of Santa Catarina derived from siltstones occurred through more balanced particle size distribution, with clay, silt and sand contents very near the 1/3 ratio of each fraction, and also due to the greater contents of very fine sand (172 g kg -1 ) in comparison to the soils of the other lithologies (5-99 g kg -1 ).The lower AW content in soils of Santa Catarina derived from recent alluvial deposits, however, occurred due to their lower OM and very fine sand content (Table 6).
In the subsurface horizons, the mean AW contents ranged from 0.07 to 0.13 cm 3 cm -3 , but there was no significant difference due to their high variability in soils with the same lithology.Thus, in the subsurface horizons of the soils of SC, the mean AW content is 0.10 cm 3 cm -3 .CONCLUSIONS 1.In the soils of Santa Catarina, water retention is greatest in clayey, silty and loamy soils, which have greater organic matter content, with small differences in water retention between the soil textural classes, due to higher field capacity and permanent wilting point.In contrast, water availability is greatest in the clayey loam and silty loam textural classes, also with highest organic matter contents, and lowest in the sand textural class.In addition, the greater water availability in the surface horizons in comparison to the subsurface horizons proves the importance of organic matter in water retention and availability.
2. Soil moisture at field capacity and at the permanent wilting point is highest in the Cambissolos (Cambisols) (especially in Cambissolos Húmicos), Nitossolos (Nitisols) and Latossolos (Ferralsols); intermediate in the Argissolos (Acrisols), Neossolos Litólicos (Leptosols) and Chernossolos (Chernozems); and lowest in the Neossolos Quartzarênicos (Arenosols).Greater water availability occurs in the Cambissolos Húmicos (Humic Cambisols) and the Neossolos Litólicos (Leptosols) located in the Planalto Serrano of Santa Catarina, mainly due to their high organic matter contents.Nevertheless, it is also important to remember that crops exploit distinct soil layers during their vegetative cycles and, for this reason, the quantity of water available also depends on the thickness of the soil horizons, especially of the surface horizons.
3. Water retention is highest in soils derived from extrusive igneous rocks from the Serra Geral Formation, metamorphic rocks, intrusive igneous rocks and fine-textured sedimentary rocks; it is intermediate in soils derived from medium-textured sedimentary rocks; and lowest retention occurs in soils derived from rocks or quartz-rich sedimentary deposits.The available water content is greatest in soils derived from siltstones and lowest in soils derived from granite and from recent alluvial deposits.

Figure 1 .
Figure 1.Relation between organic matter (OM) contents with the clay+silt contents for the surface (a) and subsurface (b) horizons of the soils of the State of Santa Catarina.** model significant at 1 %.

Figure 2 .
Figure 2. Variation of field capacity (FC), permanent wilting point (PWP) and available water content (AW) according to the textural class of surface (a) and subsurface (b) horizons of the soils of the State of Santa Catarina.

Table 2
. Number of horizons (n), mean contents and standard error (SE) of the estimate for clay, silt, sand and organic matter (OM) in horizons grouped according to the textural classes of the soils of the State of Santa Catarina

Table 3 .
Soil moisture at field capacity (FC), permanent wilting point (PWP), and available water content (AW), in different soil classes in the State of Santa Catarina (1) Embrapa (2006); (2) SE: standard error.Lower case letters compare the soil classes in each horizon by the LSD test (F<0.05).

Table 4 .
Number of horizons (n), mean values and standard error (SE) of the estimate for clay, silt, sand and organic matter (OM) contents in soils grouped by soil classes in the State of Santa Catarina (1) Embrapa (2006).

Table 5 .
Soil moisture at field capacity (FC), permanent wilting point (PWP), and available water content (AW), in soils grouped by lithology in the State of Santa Catarina (1) SE: standard error.Lower case letters compare the lithologies in each horizon by the LSD test (F<0.05).

Table 6 .
Number of horizons (n), mean contents and standard error (SE) of the estimate for clay, silt, sand and organic matter (OM) in soils grouped by lithology in the State of Santa Catarina