ISSN 1330-7142 UDK = 631.422
SOIL BULK DENSITY AS RELATED TO SOIL PARTICLE SIZE DISTRIBUTION
AND ORGANIC MATTER CONTENT
T. Aşkin
(1), N. Özdemir
(2)Original scientific paper Izvorni znanstveni članak
SUMMARY
Soil bulk density is a dynamic property that varies with the soil structural conditions. The relationships between some soil physical and chemical properties such as, clay content (C), silt content (Si), sand content (S), very fine sand content (Vfs) and organic matter content (OMC) with soil bulk density (ρb) were studied
using path analysis on 77 surface soil samples (0-20 cm). Soil bulk density showed positive relationships with S and Vfs and negative relationships with Si, C and OMC. It was determined that the direct effects of some soil properties on ρb were in the following order; S>C>Si>OMC>Vfs. On the other hand, the indirect effects
of soil particle size distribution varied among soil bulk densities. The indirect effects of the soil particle size distribution generally occured through sand content. Sand content was the most effective soil property that affected bulk density in soils.
Key-words: soil bulk density, clay content, silt content, sand content, organic matter content
INTRODUCTION
Soil bulk density is defined as the ratio of oven-dried mass weight to its bulk volume depends on the soil particles densities such as sand, silt, clay and organic matter and their packing arrangement. Bulk density values are required for converting gravimetric soil water content to volumetric and to calculate soil porosity which is the amount pore space in the soil (Blake and Hartge, 1986). Researchers often need a bulk density value to use in models, characterize field conditions, or convert to volumetric measurements (Reinsch and Grossman, 1995). Soil bulk density is a basic soil property influenced by some soil physical and chemical properties. Bulk density is a dynamic property that varies with the structural condition of the soil. This condition can be altered by cultivation, trampling by animals, agricultural machinery, weather, i.e. raindrop impact (Arshad et al., 1996). Knowledge of soil bulk density is essential for soil management, and information on the soil bulk density of soils is important in soil compaction and structure degradation as well as in the planning of modern farming techniques. If both, bulk density and particle density are known, the total porosity can be calculated by using these values (Hillel, 1982). Soil bulk density should be used as an indicator of soil quality parameter. Akgül and Özdemir (1996) studies on relationships between soil bulk density and some soil properties explained that these constants can be estimated by means of developed regression models. A unit increases in organic matter and clay content caused a relatively larger decrease in soil bulk density. A soil system can be thought as a network of soil properties. Path analysis may be used to investigate the relationships among these soil properties. The path diagram gives a picture of network of relations among the characters, as quantitative evaluation is possible from the data (Wright, 1968).
The objective of this study was to determine relationships between soil particle size distribution and organic matter content and soil bulk density by using path analysis.
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2 MATERIAL AND METHODS
Samples of seventy-seven surface soils (0-20 cm depth) were taken from grassland in Samsun district in Turkey. This area has a brown forestry soil. Annual mean of precipitation is 670.4 mm and mean temperature is 14.2 0C (Anonymous, 2002). Bulk soil samples were air dried and then crushed to pass through a 2 mm sieve.
Soil organic matter content was measured by a modified Walkley-Black method (Nelson and Sommers, 1982); soil particle size distribution was determined by the hydrometer method (Gee and Bauder, 1979); lime content was measured by Scheibler Calcimeter (Soil Survey Staff, 1993); soil pH was measured by using a 1:2.5 (w/v) soil-water ratio by pH-meter with glass electrode (Black, 1965). Bulk density was determined by means of the clod method (Blake and Hartge, 1986).
The soil bulk density was selected as dependent variables to determine statistical relationships between soil particle size distribution and organic matter content (C, Si, S, Vfs, and OMC) and soil bulk density. Also, direct and indirect effects of the variables were determined with path analysis (Wright, 1968), using TARIST computer package program.
RESULTS AND DISCUSSION Soil Properties
Some descriptive statistical results for some soil physical and chemical properties are given in Table 1.
Table 1. Descriptive statistics for some soil physical and chemical properties of soil samples (n=77) Tablica 1. Deskriptivna statistika za neka fizikalna i kemijskih svojstva uzoraka tla (n=77)
Soil properties – Svojstva tla Mean
Prosjek Min. Max. Sd Se
Sand – Pjeskovito (S), % 25.7 14.8 45.0 5.59 0.640
Very fine sand – Vrlo fino pjeskovito (Vfs), % 8.9 2.2 12.4 1.60 0.180
Silt – Muljevito (Si), % 27.4 22.1 32.7 1.96 0.220
Clay – Glinasto (C), % 46.9 32.0 55.9 4.69 0.530
pH (1:2.5 soil: water suspension – tlo: vodena suspenzija) 7.1 6.1 7.7 0.44 0.050
Electrical conductivity – Električna provodljivost (EC),
dS.m-1 0.21 0.09 0.46 0.06 0.007
Lime content – Sadržaj vapnenca (LC), % 2.35 0.00 15.94 3.59 0.410
Organic matter content – Sadržaj organske tvari (OMC),
% 4.65 2.67 7.27 0.86 0.100
Bulk density - Volumna gustoća (ρb), g cm-3 1.57 1.35 1.70 0.07 0.009
Sd; standard deviation – standardna devijacija, Se = standard error – standardna greška
The results can be summarized as; soil samples have mostly fine in texture, neutral in pH, high in organic matter (average of 4.65 %), low in lime content (average of 2.35 %), and alkaline problem free (ESP<15 %) (Soil Survey Staff, 1993) (Table 1).
Relationships Between Some Soil Properties and Soil Bulk Density
Correlation coefficients between soil particle size distribution and soil organic matter content and the soil bulk density are given with direct and indirect effects of the variables on the bulk density in Table 2.
3 direct effect of clay content on bulk density (43.82 %) was higher than the other fractions. The clay content and organic matter content gave significant negative relations with soil bulk density. Soil bulk density decreases with increasing organic carbon concentration (Bauer and Black, 1992). Also Gupta and Larson (1979), proposed a model for predicting the dry bulk density of soil. The particle size distribution and organic matter content are used in the model. Organic matter content showed the very significant negative correlation (r=-0.59**) with the soil bulk density (Table 2). The clay content had higher direct effects on soil bulk density after sand content. The silt content was adversely related with soil bulk density as non significantly. Also, the silt content had higher indirect effects through sand content (49.44 %) on the soil bulk density (Table 2). Behavior of particle size distribution of Si in soils might be the similar to clay fractions of soil texture. Therefore increasing of silt content may decrease soil bulk density. Thus, silt content did not give highly significant correlate with soil bulk density according to clay content. Statistically non significant relation was determined between the very fine sand content of soil and soil bulk density. Wagner et al. (1994) suggested using soil texture parameters along with organic carbon content values to estimate soil bulk density.
Table 2. Path analysis results on soil bulk density and relationships with some soil properties Tablica 2. Path analiza rezultata volumne gustoće tla i odnos između nekih svojstava tla
Soil properties
Svojstva tla r
Direct effect Direktni učinak, %
Indirect effect - Indirektni učinak, %
S Vfs Si C OMC
S 0.25* 50.21 - 0.05 10.72 38.78 0.24
Vfs 0.04 6.42 39.53 - 43.08 3.18 7.79
Si -0.16 29.30 49.44 0.27 - 20.17 0.82
C -0.23* 43.82 50.41 0.01 5.68 - 0.08
OMC -0.59** 23.14 37.18 1.64 27.98 10.06 -
**p<0.01; *p<0.05
CONCLUSION
Soil bulk density gave the significant positive correlation with S and negative correlation with C at p<0.05. Also, bulk density achieved the significant negative correlation with OM at p<0.05. Sand and clay contents showed higher direct effects on soil bulk density. Indirect effect of the soil properties were generally occured through sand and clay content. Sand content was found to be the most effective soil fraction that influenced soil bulk density. It was determined that the direct effects of some soil particle size distribution and organic matter content on ρb were in the following order; S>C>Si>OMC>Vfs. It was suggested that the sand fraction of soils should also be assessed in soil management.
REFERENCES
1. Akgül, M., Özdemir, N. (1996): Regression models for predicting bulk density form measured soil properties. Tr. J. Of Agriculture and Forestry, 20:407-413.
2. Anonymous (2002): Samsun Meteorology Bulletin Reports. Samsun, Turkey.
3. Arshad, M.A., Lowery, B., Grossman, B. (1996): Physical tests for monitoring soil quality. In: J.W. Doran and A.J. Jones(eds.) Methods for assessing soil quality, Soil Sci. Soc. Am. Spec. Publ. 49:123-142, SSSA, Madison, WI, USA.
4. Bauer, A., Black, A.L.(1992): Organic carbon effects on available water capacity of three soil textural groups. Soil Sci. Soc. Am. J., 56:248-254.
5. Black, C.A. (1965): Methods of Soil Analysis. Part 1, American Society of Agronomy, No 9. 6. Blake, G.R., Hartge, K.H. (1986): Bulk Density. Methods of Soil Analysis, Part 1, Soil Sci. Soc.
4 7. Gee, G.W., Bauder, J.W. (1979): Particle size analysis by hydrometer: A simplified method for routine textural analysis and a sensitivity test of measured parameters. Soil Sci. Soc. Am. J., 43:1004-1007.
8. Gupta, S.C., Larson, W.E. (1979): A model for predicting packing density of soils using particle size distribution. Soil Sci. Soc. Am. J. 43:758-764.
9. Hillel, D. (1982): Introduction to Soil Physics. Academic Press Limited, 24-28 Oval Road, London.
10. Nelson, D.W., Sommers, L.E. (1982): Total Carbon, Organic Carbon and Organic Matter. In: A. L. Page(ed.) Methods of Soil Analysis, Part 2, Chemical and Microbiological Properties, Agronomy Monograph No. 9, p. 539-580, ASA Inc., SSSA Inc., Madison, WI, USA.
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12. Wagner, L.E., Ambe, N.M., Ding, D. (1994): Estimating a Proctor density curve from intrinsic soil properties. Trans. Am. Soc. Agric. Eng. 37:1121-1125.
13. Wright, S. (1968): Path Analysis: Theory, Evolution and The Genetics of Populations, Volume:1, 299-324, The University of Chicago Press.
14. …………. Soil Survey Staff , 1993. Soil Survey Manuel. USDA Handbook No:18, Washington, USA.
POVEZANOST VOLUMNE GUSTOĆE TLA S DISTRIBUCIJOM VELIČINE ČESTICA TLA
I SADRŽAJEM ORGANSKE TVARI
SAŽETAK
Volumna gustoća tla je dinamičko svojstvo koje varira sa stanjem strukture tla. U radu je istražena
povezanost nekih fizikalnih i kemijskih svojstava tla, kao što su sadržaji gline (C), mulja (Si), pijeska (S), vrlo
finog pijeska (Vfs) i organske tvari (OMC), s volumnom gustoćom tla (ρb) pomoću path analize na 77
površinskih uzoraka tla (0-20 cm). Volumna gustoća tla pokazala je da postoji pozitivna korelacija sa S i Vfs i
negativna korelacija sa Si, C i OMC. Utvrđeno je da su direktni učinci nekih svojstava tla na ρb bili sljedeći:
S>C>Si>OMC>Vfs. Nasuprot tome, indirektni učinci distribucije veličine čestica tla varirali su kod volumne
gustoće tla. Indirektni učinci distribucije veličine čestica uglavnom su se javljali ovisno o sadržaju pijeska . Sadržaj pijeska bilo je najučinkovitije svojstvo tla koje je utjecalo na volumnu gustoću tala.
Ključne riječi: gustoća tla, sadržaj gline, sadržaj mulja, sadržaj pijeska, sadržaj organske tvari
