J. Agronomy & Crop Science, 156, 193—196 (1986)© 1986 Paul Parey Scientific Publishers, Berhn and HamburgISSN 0044-2151

Indian Institute of Technology, Kharagpur-721 302

Physical Properties Affecting Water Entryin some Humid Tropical Soil

P. B. S.BHADORIA and C. P. GUPTA

Authors' addresses: Dr. P. B. S. BHADORIA, Rural Development Centre, Indian Institute ofTechnology, Kharagpur-721 302 (India), and Prof. Dr. C. P. GuPTA, Agricultural Engineering

Department, Indian Institute of Technology, Kharagpur-721 302 (India).

With two tables

Received July 22, 1985; accepted September 1, 1985

Abstract

Field and laboratory experiments were conducted to study the effect of physical properties onwater entry in three soils, differing appreciably in texture. The results indicate that the saturatedhydraulic conductivity (K) of lateritic soil was manifold higher than the alluvial soil. In lateriticsoil the value of K was 10"' cm/hr and it ranged from 10"̂ to 10"̂ cm/hr in alluvial soil. In general,the conductivity decreases in the sub surface layers and may be attributed high bulk densityresulting from compact blocky structure of the soil. The infiltration rate of lateritic soil wasfound to be 4 times more as compared to the alluvial soils.

Introduction

The research information on physical characteristics of the soil of tropical regions inrelation to their management is inadequate, so the planners must give importance to soilphysical properties in maintaining the productivity of tropical soils. Some tropical soils arenaturally compacted and have low total porosity (BRIDGE et al. 1975, HONISCH 1974). Insurface, it is often expressed by the formation of crust, which decreases water entry,increased run off, soil erosin and poorer seedling emergence. In the sub-surface, it may beexpressed by the formation of hard pan or impervious layer. This leads to decreased waterstorage and decreased water mobility and also hinders the development of plant roots. Themost common soils of tropical areas are alfisols, ultisols and oxisols. These soils exhibit apronounced argillic horizon, indicating that the clay particles could move easily within thesoil profile. With the objective of studying the role of physical properties of soils in watermovement, studies were carried out at three locations which largely comprises of Vindhya-alluvial, Laterite, and Old alluviam soils.

Materials and Methods

After opening the profile, the layers were demarcated and soil samples were collected in fourreplications for the determination of particle size distribution, bulk density and hydraulicconductivity.

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194 P. B. S. BHADORIA and C. P. GUFTA

Hydraulic conductivity

Undisturbed soil cores collected for the determination of bulk density were utilized forevaluation of hydraulic condictivity (K) by using constant head method (KLUTE 1965) andcalculated according to

K = (O/A.T)/(L/AH)where 0 is the volume of air free tap water passing through a core of cross sectional area A intime t, and AH is the difference in hydraulic head across the sample length, L.

Infiltration

Cylinder infiltrometers used in the experiment were made of iron 30 cm dia, and 25 cmlength. A 15 cm steel tape was cemented inside the cylinder to measure the change in head ofwater during infiltration. The cylinder was driven into the soil upto the depth of 7 cm in amanner described by WILKINSON (1975 a). An earthen dike was built around the cylinder to givea buffer zone of about 60 cm diameter. The infiltration run was started by quickly filling thecylinder to a level on the tape, which was immediately recorded alongwith time of waterapplication. The buffer was simultaneously filled to the same depth as that inside the cylinder.Reading of water level was taken up to 5 hours. When the water level in the cylinder droppedabout 10 cm, the level and time was noted and then the cylinder and buffer were quickly refilledto the original level.

Results and Discussion

It is evident from the data (Table 1) that texturally different soils of Kharagpur,Matiberua and Mohanpur were characterized by a marked variation in the content of claydown the profile. The clay content of all the profile increases with increase in soil depthexcept Matiberua, where it decreases within 90—220 cm. This shows that the thickness ofthe argillic horizon varies in these soils.

Table 1 Mechanical composition and physico-chemical properties of different soil profile

Depth,cm pH Ec Organic Mechanical composition Bulk density Hydraulic conductivityjLxmmh matter. g/cc cm/hrcm/hr per cent Sand Silt Clay

0/ 0/ O//o /o /o

Kharagpur, sandy loam

6.00 X 10"'

4.10 X 10'^

1.63 X 10"^

3.94 X

0 - 2 0

2 0 - 505 0 - 75

75-100100- lAO

0 - 15

15- ^5A5- 95

95 - 220

0 - 20

2 0 - 60

60- 9090-220

5.5

5.85.3

5.65.7

5.8

7.67.7

8.0

4.5

5.86.0

6.1

7.3

28.022.6

23.827.4

33.0

32.136.A76.2

63.0

40.0

40.3

200.0

0.45

0.260.2 2

0.100.06

0.68

0.200.150.06

1.20

0.420.37

0.32

59.75

52.5050.81

48.004 3.10

22.60

21.2020.30

25.7024.23

17.65

26.3028.89

27.3032.67

Matiberua, clay loam

30.50

31.0726.50

33.20

33.20

30.0829.93

25.20

36.30

38.0543.57

40.80

Mohanpur,clay

25.25

24.35

26.25

18.80

25.10

19.6020.50

23.00

49.65

56.0553.25

58.20

1.641.541.55

1.701.71

1.53

1.501.471.37

1.10

1.30

1.421.24

1.35 X 10'^

8.84 X 10"''

1.20 X 10"^

1.93 X 10'^

5.01 X 10'^

2.01 X 10'^

5.81 X 10"*

3.50 X 10"*

3.90 X 10"*

Physical Properties Affecting Water Entry in some Humid Tropical Soil 195

The soils are high to moderately acidic at the surface ranging from 4.4 to 5.5 pH. ThepH of agrillic horizon remained at higher level in all the soil. At Matiberua the pH of thesub-surface layers in the depth interval of 95—220 cm was relatively high because ofaccumulation of bases.

Bulk density

In lateritic soil, the bulk density of surface soil was 1.64 g/cc and decreased in theintermediate layers and again increased in the deeper layers of 75—140 cm, possibly due tothe presence of murrum and other rocky materials. Low density of intermediate layers isascribed to relatively higher fraction of Kaolin and allophane contents. The bulk density ofthe alluvial soil was in the range of 1.10 to 1.53 g/cc at the surface layers and increased by0.03 to 0.20 unit with the inrease in depth and finally decreased to the minimum value of1.24 g/cc. Increase of bulk density in the intermediate layers in alluvial is possibly related toa compact angular blocky structure.

Hydraulic conductivity

The data in Table 1 indicate that in all the soil profiles studied the hydraulic conductivityof lateritic sandy loam soil was manifold higher than the old alluvial soils. In lateritic soil,the value of K was 6 X 10"̂ cm/hr and it ranged from 10"̂ to 10"-* cm/hr in alluvial soil. Theconductivity decreases in the sub-surface layers in all the soil profiles except Matiberua soilwhere K value of 90—220 cm layer was higher than that of the overlying layers. Thedecrease in value of K may be attributed to higher bulk density resulting from compactblocky structure of the soil. The close packing of particles may cause lower total porosity(STAPLE 1975) and reduced mean pore diameter. In the bottom-most layer, of alluvial soils,the bulk density was low because of higher clay content, but also had low K value due todeposited silicate clays, which indicate a condition of impeded internal drainage. In thelower horizons, the difference in K and bulk density between the different textural soilprofiles are related not only due to the difference in soil texture, but also due to theilluviation reorganization of particles within the original pore spaces.

Infiltration Rate

The infiltration rate of water as a function of time was measured and presented in Table2. The initial infiltration rate of lateritic sandy loam was 9.5 cm/hr and decreased to a valueof 0.80 cm/hr after 5 hours. Water intake rate of tropical soil under their natural vegetationcover is high (LAL 1976). The entry of water reveals that the movement of wetting frontwas very fast in the surface layers, which are incidently coarser in texture. The decreasedrate after the lapse of time corresponds to slower movement of wetting front in the lowerlayers, which are relatively finer in texture with less non-capillary porosity. In contrast to

Table 2 Five hours infiltration rate of different soil type

51. No.

1

2

3

Soil type

Kharagpur, sandy loam

Mafiberua , clay loam

Mohanpur, clay

InfiltrationMinimum

cm/hr

0.80

0.35

0.20

rateMaximum

cm/hr

9.5

3.9

0.92

196 P. B. S. BHADORIA and C. P. GUPTA, Physical Properties Affecting Water Entry

higher infiltration rate in lateritic soil, the infiltration rate were in the range of 0.35 and0.20 cm/hr (low) in alluvial clay soils. The final infiltration rate of these alluvial soilssuggest that the internal drainage is quite slow.

The evaluation of infiltration rate and hydraulic conductivity may serve as guide line forland use planners if it is based on texture, bulk density and porosities. But the importanceof soil structure and pore size distribution cannot be neglected, but for routine evaluationit becomes difficult to measure these parameters. Thus the properties like infiltration,conductivity and bulk density would assume greater significance in the field.

Zusammenfassung

Physikalische Eigenschaften mit Wirkungen auf den "Wassereintrittbei einigen humld-tropischen Boden

Es wurden Feld- und Laboratoriumsversuche durchgefiihrt, um den Einflufi physikali-scher Eigenschaften auf den Wassereintritt in drei Boden, die sich deutlich in ihrer Texturunterscheiden, zu untersuchen. Die Ergebnisse weisen darauf hin, dafi die gesattigte,hydraulische Konduktivitat (K) eines lateritischen Bodens vielfach hoher war als einesallivialen Bodens. Im lateritischen Boden betrug der Wert von K 10"̂ cm/h, wahrend er ineinem alluvialen Boden zwischen Werten von 10"̂ bis 10"̂ cm/h lag. Grundsatzlich nimmtdie Konduktivitat in den Unterbodenzonen ab, was auf die hohe Bodendichte zuriickge-fiihrt werden kann, die sich aus der kompakten Blockstruktur des Bodens ergibt. DieInfiltrationsrate erwies sich fiir lateritische Boden vier Mal hoher als fiir alluviale Boden,

References

BRIDGE, B. J., S. BOONYOI, and U, ARROMRATANA 1975: Properties affecting water entry incertain plain soils, Thailand, Thai Journal of Agric. Sci. 8, 177—193.

HoNiscH, O., 1974: Water conservation in three grain crops in the Zambazi Valley, Expl.Agric. 10, 1—8.

KLUTE, A., 1965: Laboratory measurements of hydraulic conductivity of saturated soil. In: C.A. BLACK et al, (editors). Methods of Soil Analysis, I. Agronomy 9, 210—221.

LAL, R,, 1976: No tillage effects on soil properties under different crops in Western Nigeria.Soil. Sci. Soc. Amer. Proc. 40, 762—769.

STAPLE, W. J., 1975: The influence of size distribution on the bulk density of uniformly packedglass panicles. Soil Sci. Soc, Amer, Proc, 39, 404—408.

WILKINSON, G. E., 1975a: Effect of grass fallow rotations on the infiltration of water into asavanna zone soil of Northern Nigeria. Trop. Agric. (Trinidad) 52, 97—103.