The effect of land uses on soil properties

1

Title

The effect of land uses on soil properties in and around Mabira Forest

2

CHAPTER ONE

1.0 INTRODUCTION

Land-use changes are environmentally significant in their own right. They degrade or enhance the

land's capacity for sustained use and ability to regain its original cover. In some cases land-cover

changes, or their impacts, can become so large or widespread that they are identified as global

change in themselves. Elsewhere this kind of change has been referred to as globally cumulative

change [Turner, Clark et al. 1990].

Land use patterns in the South Pacific are immensely varied between the various groups of

countries. However, countries of similar size and with a similar degree of development tend to

exhibit similar patterns in their broad land use. The large developed countries, Australia and New

Zealand, have both cleared substantial areas of natural forest to establish pastoral agricultural

systems. The Australian Resource Assessment Commission (1991) notes that since European

settlement approximately half Australia's forests have been cleared or severely modified, while

New Zealand has cleared one-third of its forests in the same period, and a further third in the

preceding millennium of Maori settlement.

Soil structural deterioration has occurred in the over-cultivated and heavily populated districts of

Kisoro, Kabale, Mbale, Kapchorwa, Bushenyi, Mukono and Arua. The main causes of soil

degradation in Uganda include degradation of organic matter content, depletion of vegetative

cover, climate, land form and soil characteristics, land fragmentation, improper farming systems,

soil compaction, overgrazing, deforestation, residual effects of agro-chemicals, bush fires,

population pressure, poverty, illiteracy and lack of awareness and the considerable pressure on

woodlands, forest areas and agricultural lands as sources of fuel wood (NEMA, 2001).

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1.1 STATEMENT OF THE PROBLEM

The different land uses in and around Mabira forest affect soil properties differently. The population

increase has greatly impacted on the forest environment in form of subsistence, commercial

agriculture, logging, grazing, charcoal burning and infrastructural development. This scenario has

greatly impacted on the soil properties (chemical, physical and biological) of Mabira forest.

Therefore with the inadequate knowledge among the population on the impacts of different land

uses on the soil properties, this study will contribute greatly in identifying the effects of land uses on

the soil properties in and around Mabira Central Forest Reserve.

1.2 DEFINITION OF KEY TERMS

Soil is a natural body synthesized over time from a mixture of inorganic and organic parent

materials, now supporting living plants. Soils with depth have natural horizons (layers) that give

them their properties. Such properties include texture, color, structure, and bulk density.

Land use refers to the degree to which the land reflects human activities (such as residential and

industrial development, roads, mining, timber harvesting, agriculture, grazing). Land use describes

how a piece of land is managed or used by humans

1.3 OBJECTIVES

Overall Objective:

To determine the effect of land uses on soil properties in and around Mabira Forest.

Specific Objectives:

i To determine the soil properties under the forestry land use.

ii To determine the soil properties under the agricultural land use.

1.4 JUSTIFICATION OF THE STUDY

The report is set to promote sustainable land management which will recognize the limits of human

consumption and harmonize the complementary goals of society and the economy while

maintaining environmental quality on the soil properties.

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The report will aid the decision makers in monitoring agricultural land uses which tends to encroach

on fragile ecosystems and forests since the process requires close coordinating and policy

measures to be introduced.

The research report will be important in determining how fertility can be maintained in the

agricultural land-use systems to obtain high yields.

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CHAPTER THREE

3.0 MATERIALS AND METHODS

3.1 Area of study

Mabira Forest Reserve lies in the counties of Buikwe and Nakifuma in the administrative district of

Mukono. It was established under the Buganda Agreement in 1900 and occupies an area of 306

km2 with an altitudinal range of 1070-1340m situated between 32 520 – 33 070 E and 0 24 – 0 350

N. It is found 54km east of Kampala and 26km west of Jinja.

The soils of the Mabira Catena are generally ferralitic sandy clay loams with black waterlogged clays in

the valley bottoms. The Mabira catena is characteristic of the entire Mabira Forest Reserve and the

adjacent villages of Najjembe and Kawolo. The general relief of this series is somewhat steeper and the

hills themselves are more ridge-like in appearance with long and generally rounded crests than the

catenas previously described. In this series the upland soil sequence is derived from two different

bands of parent material. The summit and upper slopes are developed over relic ironstone and the

pediment soils from weathering products of phyllite with minor occurrences of aphibolite, which give rise

to red or yellow clays. The red associates of the Mabira Catena are strongly laterized and contain well-

developed murram horizons. The soil has high clay content (well over 60 percent in the lower horizons)

and generally a good nutrient status, particularly in respect of organic matter (4 to 6 percent carbon)

and exchangeable bases (Pallister, 1957).

3.2. SAMPLING PROCEDURE

Three replications were considered randomly in each land use type. Three points were considered

in each replicate. The soil samples from the three points were then mixed to represent one sample

for a replicate. Samples were taken from two depths: 0-15cm and 15-30cm respectively.

3.3 FIELD METHODS

3.3.1 Physical properties

For bulk density the Core Method was used where the metal cores were pushed into the soil

horizons using a hammer and a hoe to obtain samples with specific volumes. After bringing the soil

samples back from the field, cores were covered with a piece of cloth to prevent the soil from falling

6

out of the cores. The cores were also labeled with a regime number. The soil was saturated to

remove air and the wet mass of the soil was placed in an oven to dry for 48 hours. Bulk density

was calculated from the mass of a given volume of dry soil, including the air spaces, but excluding

materials larger than soil, such as rocks or materials with dimensions greater than 2.0 mm. In the

lab, soil samples were dried in order to obtain the dry mass of the soil using AE ADAM machine.

The cores that were used for collecting the soil samples were massed and their volumes by

diameter and height measured with results recorded in a notebook to get the size of the core in

relation to the volume of the soil.

Plate 1. Shows how bulky density was determined using the core method

Source: Photograph taken by the research in the field

The falling head method was used to measure the saturated hydraulic conductivity of the cores

using water and a piece of cloth tired at the bottom. Cores were first submersed in a basin with

water for a night for saturation. After that any empty core was tired to the saturated one with sole

tape and placed in between block for easy measurements and water flow. The cores were filled

with water for the purpose of hydraulic conductivity and measurements were taken in terms of time

using stop watches and a ruler used for height determinations of the cores.

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Plate 2. Shows how hydraulic conductivity was determined using the falling head method


Structure was got through the mesh/sieve set up method. With structure the buyoucos hydrometer

meter was used in determining the soil texture. The Munsell Soil Color Chart was used to identify

soils. Each color chip in the Munsell book represents a combination of hue (color), value (lightness

or darkness), and chroma (purity) that reflects the degree of wetness in the soil.

Plate 3. Shows how soil structure was got to be determined by mesh set up method


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3.3.2 Chemical properties

For soil pH the pH meter was used in determining the alkalinity, acidity and neutrality of the soil.

For the available phosphorus the bray and Kutz No1 method was used in the phosphorus

assessment in the soil. Organic Matter the Black and Walkley (1934) method was used and

kjeldhal method was used to determine the availability of nitrogen in the soil. The slope positions

were also taken using a suttoo to determine the degrees and centimeters.

3.3.3 Biological properties

The monolith method was used to identify the macro-fauna composition in the different forest and

agricultural regimes in and around Mabira forest. Sampling for macro-fauna was done using a

monolith of size 30cm x 30cm x 30 cm, samples were taken from each regime for example sugar

mechanized, banana, sugar manual, 0-30 years,10 – 20 years,40 – 50 years and above 55 years

at two different depths 0 – 15 cm and 15 – 30 cm.

Sample sites were randomly selected from the different regimes. A hand hoe, basins, a ruler and a

panga were the main tools of importance in activities such as digging the monolith, measuring the

area coverage and depths of the monolith and chopping the monolith respectively. From the two

different levels were put in different basins labeled 0 – 15cm and 15 – 30 cm before the organisms

could be manually counted by breaking the soil laps and any visible organism could be counted

and recorded.

Plate 3. Shows the monolith method used to identify macro-fauna


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3.4 DATA ANALYSIS

All the data collected from the field was edited and coded in Microsoft Excel. The transformed data

were subjected to analysis of variance (ANOVA) using Genstat for Windows program. The least

significant difference was used to determine difference between the treatments and depth.

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Map of Mabira Central Forest Reserve

Source: National Forestry Department

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Map of Mabira Central Forest Reserve showing the sampling sites


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#

#

##

##

#

#

10 - 20 yearsSample sites

0 - 3 yearsSample sites

Metha (NO)Sample sites

Kitigoma

175

Bugule

KITIGOMA

KKONKO

510000

510000

510500

510500

511000

511000

511500

511500

512000

512000

45000 45000

45500 45500

46000 46000

MABIRA CENTRAL FOREST RESERVELocation of Soil Sampling Sites¶

0 0.1 0.2 0.3 0.40.05

Kilometers

1:10,000

Legend

# Sampling Points

Roads

All Weather Road, Bound Surface

All Weather Road, Loose Surface

Dry Weather Road

Motorable Track

GPS Track Log

Rivers

Main

Small Permanent

Seasonal

Management Zonation

Production (Low Impact

Recreation/Buffer Zone

Strict Nature Reserve

##

#

#

#

#

#

#

#

#

#

#

#

##

#

#

#

#

#

Location Map Of Sample site in and near Bugule Compartment (175) in Mabira CFR

Map of Mabira Central Forest Reserve showing the location of soil sampling sites


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CHAPTER FOUR

4.0 RESULTS

4.1 THE FOREST LAND USE ON SOIL PROPERTIES

4.1.1 Chemical Properties

4.1.1.1 Organic Matter

Figure 1: Shows the average organic matter in the forest land use

There was a very highly significant effect of treatment (P<0.001) on the quantities of organic matter

in the soil. The highest being the 10-20 year treatment and the lowest the 0-3 years treatment.

Figure 2: Shows the organic matter in the forest land use with depth

Organic matter

0

2

4

6

8

0-3yrs 10-20yrs 40-50yrs >55yrs

Treatment

%

0-15cm

15-30cm

There was a very highly significant effect of depth (P<0.001) on the quantities of organic matter in

the soil. Generally the 0-15cm soil layer had significntly more organic matter than the 15-30cm soil

layer.

Organic matter

4.215.848

4.748 4.748

02468

0-3yrs 10-20yrs 40-50yrs >55yrs

Treatment

%Forest land use

14

4.1.1.2 Phosphorous

There was a very highly significant effect of treatment (P<0.001) on the quantities of Phosphorous

in the soil. Maximum was in treatment 10-20 years (12.09 mg/kg) and minimum was in treatment 0-

3 years (4.19 mg/kg). Treatment 10-20 years had the highest amount of phosphorus.

Figure 3. Shows the average phosphorous in the forest land use

phosphorous

0

5

10

15

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

mg/k

g

forest

Figure 4: Shows the available phosphorous in a forest land use with depth

There was a very high significant effect of depth (P<0.001) on the quantities of Phosphorous in the

soil. Generally 0-15cm soil layer had significntly more phosphorus than the 15-30cm soil layer.

4.1.1.3 Nitrogen

There was no significant effect of treatment (P<0.168) on the quantities of nitrogen in the soil. The

Maximum was in treatment 10-20 years (0.2550%) and minimum was in treatment 0-3 years

(0.1983%).

Phosphorous

0

5

10

15

20

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

mg/k

g 0-15cm

15-30cm

15

Nitrogen

0

0.1

0.2

0.3

0.4

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

%

0-15cm

15-30cm

Figure 5. Shows the average available Nitrogen in the forest land use

Nitrogen

0

0.1

0.2

0.3

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

% forest

Figure 6. Shows the average nitrogen in the forest land use with the depth

There was a very high significant effect of soil depth (P<0.001) on the quantities of nitrogen in the

soil. Generally 0-15cm soil layer had significntly more nitrogen than the 15-30cm soil layer.

4.1.1.3 Soil pH

There was a very highly significant effect of treatment (P<0.001) on soil pH values. The 0-3 year

treatment was the most acidic while the 10-20 year was the least acidic.

Figure 7. Show the average soil pH for the forest land use

soil pH

0

2

4

6

8

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

ph v

alu

es

forest

16

There was a significant effect of depth (P<0.005) on soil pH values. This was attributed to the

decreasing organic matter gradient with depth.

Figure 8. Show the average soil pH for the forest land use

Soil pH

0

2

4

6

8

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

pH

valu

es

0-15cm

15-30cm

4.1.2 Biological Properties

4.1.2.1 Macro fauna – Monolith method

The trend in macro-fauna population decreased with the forest age. The macro-fauna was highest

in the 0-3 years and lowest in the 10-20 years in both 0-15 cm and 15-30 cm depth.

Figure 9. Shows the macro fauna of the forest land use with depth in numbers

333

16.01

302.6 302.6

877.99

20.01

413.8 413.8

0

200

400

600

800

1000

0-3yrs 10-20yrs 40-50yrs >55yrs

0-15cm

15-30cm

17

4.1.3 Physical soil Properties

4.1.3.1 Bulky density

Figure 9. Shows the average bulky density of the forest land use

Bulk density

0

0.5

1

1.5

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

g/c

m3

forest

There was a very significant effect of treatment (P<0.023) on soil bulk density There was an

observer positive trend of bulk density with forest age (minimum 0-3 up to >55 years) treatment.

Statistically, there was no significant effect of depth (P >0.203) bulk density.

Figure 10. Shows the average bulky density of the forest land use with depth

Bulky density

0

0.5

1

1.5

0-3yrs 10-

20yrs

40-

50yrs

>55yrs

treatment

g/c

m3 0-15cm

15-30cm

The 15-30 cm soil layer consistently had a higher bulk density; with a lower conductivity which

made the 0-15 cm layer more conductive. As bulky density increase soil strength increased, pore

space decreased and soils became more compact.

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4.1.3.2 Hydraulic conductivity

Figure 11. Shows the average bulky density of the forest land use with depth

Ksat

0

0.5

1

1.5

0-3yrs 10-20yrs 40-50yrs >55yrs

treatment

cm

/hr

forest

Statistically, there was no significant effect of treatment (P >0.22) on hydraulic conductivity.

Hydraulic conductivity showed a decrease with increase of forest age. The maximum was in the 0-

3 years treatment and minimum was in the >55 year treatment. Statistically, there was no

significant effect of depth (P >0.090) on hydraulic conductivity. Generally, the 15-30 cm layer had

lower hydraulic conductivity.

Figure 12 . Shows the average bulky density of the forest land use with depth

Ksat

02000400060008000

0-3yrs 10-

20yrs

40-

50yrs

>55yrs

treatment

cm

/hr

0-15cm

15-30cm

4.1.3.3 Soil Colour

0-3 years

The 0-15 cm in Rep 1, Rep 2 and Rep 3 had very dark brown and black color soils. The 15-30 cm

in Rep 1 and Rep 2 had reddish brown due to the moderate amounts of iron oxides in the soil and

Rep 3 had dark brown colour.

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Table 1. Shows the soil colour of 0-3 years for forest land use

Treatment Sample Ref Depth colour

0 - 3 years Rep. 1 0 - 15 Very dark brown

15 - 30 Reddish brown

Rep. 2 0 -15 Very dark brown


Rep. 3 0 -15 Black

15 - 30 Dark brown

10-20 years

Table 2. Shows the soil color of 10-20 years for forest land use


10 - 20 years Rep. 1 0 - 15 Dark brown

15 - 30 Dark reddish brown

Rep. 2 0 -15 Dark brown




The 0-15 cm depth had dark brown soils in all the sample replications and the 15-30 cm also had

dark reddish brown soils.

40-50 years

The 40-50 years with the depth of 0-15 cm in Rep 1 had black soil colour. The very dark brown

colours were in Rep.2 and Rep 3 in all replications of 0-15 cm layer. The 15-30 cm layer had a very

dark brown colour in all the three sample replications.

Table 3. Shows the soil colour of 40-50 years


40 - 50 years Rep. 1 0 - 15 Black

15 - 30 Very dark brown




15 - 30 Dark brown

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>55 years

The 0-15 cm depth in all the three sample replications had very dark brown soil color. The 15-30

cm depth Rep.1 and Rep.2 had dark reddish brown soil colour while the Rep.3 had very dark

brown color.

Table 4. Shows the colour of 40-50 years for forest land use


Intact (>55 years) Rep. 1 0 - 15 Very dark brown






4.1.3.4 Soil Texture

The 0-3 years and >55 years had coarse textured soils which were sandy loam. The 10-20 years

had fine textured soils which were sandy clay loam. These could be organic matter which

increased permeability by increasing the stability of soil aggregates.

4.2 THE AGRICULTURAL LAND USE ON SOIL PROPERTIES

4.2.1 Chemical Properties

4.2.1.1 Organic Matter

Figure 13: Shows the average organic matter in the agricultural land use

There was a very highly significant effect of treatment (P<0.001) on the quantities of organic matter

in the soil. The highest being the banana treatment and the lowest was sugar treatment.

Organic matter

4.2

4.4

4.6

4.8

5

Sugar_mech Banana sugar

treatment

% agric. Land use

21

Figure 14: Shows the organic matter in the agricultural land use with depth

There was a very highly significant effect of depth (P<0.001) on the quantities of organic matter in

the soil. Generally 0-15cm soil layer had significantly more organic matter especially the banana

treatment than the 15-30cm soil layer of sugar mechanised which had the lowest.

4.2.1.2 Phosphorous

There was a very highly significant effect of treatment (P<0.001) on the quantities of Phosphorous

in the soil. Maximum was in sugar mechanised treatment (4.49 mg/kg) and minimum was in sugar

treatment (3.22 mg/kg).

Figure 15. Shows the average phosphorous in the agricultural land use

Figure 16: Shows the available phosphorous in a agricultural land use with depth

Organic matter

0

2

4

6


treatment

%

0-15cm

15-30cm

Phosphorous

0

2

4

6


treatment

mg

/kg

Agric. Land use

Phosphorous

0

2

4

6


treatment

mg

/kg 0-15cm

15-30cm

22

There was a very high significant effect of depth (P<0.001) on the quantities of Phosphorous in the

soil. Generally 0-15cm soil layer had significntly more phosphorus than the 15-30cm soil layer.

4.2.1.3 Nitrogen

There was no significant effect of treatment (P<0.168) on the quantities of nitrogen in the soil. The

Maximum was in sugar (0.2367%) and minimum was in sugar mechanised (0.2233%). Sugar had

the highest amount of nitrogen in the soil.

Figure 17. Shows the average available Nitrogen in the agricultural land use

Figure 18. Shows the average nitrogen in the agricultural land use with the depth

Nitrogen

0

0.1

0.2

0.3


treatment

%

0-15cm

15-30cm

There was a very high significant effect of soil depth (P<0.001) on the quantities of nitrogen in the

soil. Generally 0-15cm soil layer had significntly more nitrogen than the 15-30cm soil layer.

4.2.1.4 Soil pH

There was a very highly significant effect of treatment (P<0.001) on soil pH values. Generally the

soil had low pH implying that it was acidic. The sugar treatment was the most acidic while the

sugar mechanised was the least acidic.

Nitrogen

0.21

0.22

0.23

0.24


treatment

% Agric. Land use

23

Soil pH

4.5

5

5.5


treatment

va

lue

s

Agric. Land use

Figure 19. Shows the average soil pH for the agricultural land use

There was significant effect of depth (P<0.005) on soil pH values. This was attributed to the

decreasing organic matter gradient with depth. The sugar mechanised had the highest pH and

lowest was the sugar manual.

Figure 20. Shows the average soil pH for the agricultural land use

4.2.2 Biological Properties

4.2.2.1 Macro fauna – Monolith method

Figure 21. Shows the macro fauna for the agricultural land use

Soil Ph

44.5

55.5

6


treatment

va

lue

s 0-15cm

15-30cm

Macro-fauna

101.01 144.01

918.98

223441 507

0

500

1000


treatment

co

un

t

0-15cm

15-30cm

24

The macro-fauna abundance was highest in the sugar manual treatment with the depth of 0-15 cm

and lowest in the sugar mechanized. For the depth of 15-30 cm, sugar manual still had the highest

macro-fauna abundance and lowest in the sugar mechanized.

4.2.3 Physical soil Properties

4.2.3.1 Bulky density

Figure 20. Shows the average bulky density of the agricultural land use

There was a very significant effect of treatment (P<0.023) on soil bulk density. There was a positive

trend of bulk density with agricultural land use, sugar mechanised being the lowest and sugar

manual the highest in bulky density. Statistically, there was no significant effect of depth (P >0.203)

on the bulk density because it was affected by both the nature of solids and the volume of pores.

Figure 21. Shows the average bulky density of the agricultural land use with depth

The 15-30 cm soil layer consistently had a higher bulk density with a lower conductivity. The

process builds upwards towards the soil surface hence making the 0-15 cm layer more conductive.

Bulky density

0.850.9

0.951

1.051.1


treatment

g/c

m3

Agric. Land use

Bulky density

0

0.5

1

1.5


treatment

g/c

m3

0-15cm

15-30cm

25

4.2.3.2 Hydraulic conductivity

Figure 22. Shows the average hydraulic conductivity of the agricultural land use

There was no significant effect of treatment (P>0.22) on hydraulic conductivity. Hydraulic

conductivity showed a decrease with the agricultural land uses. The maximum was in the sugar

mechanised and minimum was in the sugarcane treatment. There was no significant effect of

depth (P >0.090) on hydraulic conductivity. The 15-30 cm layer had big pore spaces with sugar

mechanised had the highest rendered conductivity higher followed by sugar manual.

Figure 23 . Shows the average hydraulic conductivity of the agriultual land use with depth

4.2.3.3 Soil Texture

Both sugar mechanized and banana had sandy loam, sugar manual had sandy clay loam.

4.2.3.4 Soil Colour

Sugar mechanized

Table 5. Shows the colour of No regeneration sugar mech. for agricultural land use

Treatment Sample Ref Depth Colour

No Regeneration Rep. 1 0 - 15 Very dark brown

(Sugar Mehta) 15 - 30 Brown


15 - 30 Brown



The sugar mechanized in Rep.1 had very dark brown color and Rep. 2 and Rep. 3 had dark brown.

The 15-30 cm Rep.1 and Rep.2 had brown colours and reddish brown in Rep 3 which implied

heavy presence of iron oxides in the soil.

Ksat

0

0.5

1

1.5


treatment

cm

/hr

Agric. Land use

Ksat

0

2000

4000

6000


treatment

cm

/hr 0-15cm

15-30cm

26

Banana

Table 6. Shows the soil colour of Banana


Banana Rep. 1 0 - 15 Dark brown






In banana Rep 1 had dark brown colour and Rep.2 and Rep.3 had very dark brown colours. With

the depth of 15-30 cm all the three replications had dark reddish brown colours.

Sugar manual

Table 7. Shows the colour of Sugar for agricultural land use


Sugar Rep. 1 0 - 15 Dark brown






The sugar treatment with the depth of 0-15 cm had dark brown soil color. The 15-30 cm had dark

reddish brown in all the 3 replications.

27

5.0 DISCUSSIONS

THE FOREST LAND USE ON SOIL PROPERTIES

The high presence of organic matter in the 10-20 years was attributed mainly to the presence of

abundant vegetation litter available from the forest and to a lesser extent dead fauna the lowest the

0-3 years treatment due spatial and limited vegetation cover. Organic matter varied with depth in

that the upper layers of the soil were often high in an organic fraction called humus. Humus was

relatively resistant to further breakdown and decomposition in the 0-15cm layer and then it moved

downwards to the 15-30cm layer by means like leaches and macro fauna activity. Lal, R. [1981]

described that the most dramastic loss of organic matter, soil humic substances, biological activity

and soil physical quality is undoubtedly associated with tropical deforestation and subsequent soil

management techniques.

The high phosphorous levels were due to charcoal burning in the 10-20 years during

encroachment and evidence of kilns was seen to that effect. Also the amount of phosphorus

increased with the age of the forest up to about 30 years and then level off as the forest

approached climax (stable intact forest). This was attributed to the fact that litter on the forest floor

from which the phosphorus comes from, also increased with the forest age. Phosphorus was high

in the 0-15cm layer because it was released by decomposition of organic matter on and then it

moved downwards to the 15-30cm layer by means like leaches and macro fauna activity.

Phosphorus was low in the 0-3years due to limited litter on the soil surface which Nayle [2002]

stated that organic matter has liitle capacity to strongly fix phosphate ions. Soils high in organic

matter especially active fractions of organic matter exhibit relatively low levels of phosphorous

fixation.

Treatment 10-20 years had the highest amount of nitrogen because the forest land use type

contained pools of nitrogen in the plant biomass and when they died they released these into the

soil from the decomposing organic matter and the lowest the 0-3 years treatment due to limited

vegetation cover. The amount of nitrogen increased with the age of the forest and stabilized at 40-

50 years and above (intact forest). This was attributed to litter on the forest floor from which the

nitrogen comes from, also increased with forest age. Nitrogen was released in the 0-15cm layer

28

due to the decomposition of organic matter and then it moved downward to the 15-30cm layer by

means like leaches and macro fauna activity. Boyd [1992] asserts that since the decomposition of

organic matter is caused by living organisms, nitrogen availability in soil is influenced by

temperature, moisture and aeration. Thus, the supply is extremely variable as it could the case with

the 10-29 treatment.

The soil pH was attributed to the presence of organic matter in the soil. Generally the soil had low

pH implying that it was acidic and decreasing organic matter gradient with depth. This could also

be as Miller [1995] reports that ammonia and oxides of nitrogen and sulphur are also deposited dry

on vegetation and soils are washed into the soil by rain where they produce acidity. The depth of

15-30 cm the difference was not significant in that a high pH, nutrients became insoluble and plants

could not readily extract them apart from the 10-20 years treatment.

Macro-fauna decreased with the forest age and this was attributed to the organic matter availability

in the soils, good aeration, structure, the differently adaptability of the different macro-fauna

species to the treatments, macro-fauna was highest in the 0-3 years treatment. In the 10-20 years

treatment, there was charcoal burning in that locality, which limited the survival of many macro-

fauna. Different macro faunal groups might had survival strategies to fit with the varying soil

compactness thereby creating an increase in biomass albeit slightly and a significant decrease in

abundance and species diversity therefore soil compactness seem to impact positively on the

macro faunal biomass but negatively on abundance and diversity.

The positive trend of bulk density was attributed to the gradual pore space clogging by very fine

suspension carried by rain water (run off) and compaction due to lack of disturbance as the forest

established itself. The fine textured soils such as silt loams, clay and clay loams generally have

lower bulk densities than do sandy soils. The fine textured soils tend to be organised in porous

granules, especially if adequate organic matter is present. Also the gradual elimination of herbs

and shrubs from the forest floor whose roots were contributing to soil porosity (as part of forest

succession). The 15-30 cm soil layer consistently had a higher bulk density than 0-15 cm layer

which was more conductive. The surface horizon of most forested soils has rather low bulk

densities. Tree growth and forest ecosystems functions are particularly sensitive to increases in

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bulky density. Conventional timber harvest generally disturbs and compacts 20 to 40% of the forest

floor.

Hydraulic conductivity showed a decrease with increase of forest age and this was because the

recently opened forest (0-3, 10-20 year) soils were more porous due to human activities like

digging, charcoal burning and so on. Also the recently opened forest (0-3, 10-20 year) soils had

spaces left behind by rotting roots of dead trees. To some extent, burrows made by macro fauna

also contributed to the high conductivity of soils (0-3 years). Conductivity decreased with forest age

because of soil compaction due to lack of disturbance and pore space clogging by very fine soil

particles as rain water seeped through it. The 15-30 cm layer had lower conductivity because the

pore space clogging and compaction begins from this layer where the pores are smallest. The

process builds upwards towards the soil surface hence making the 0-15 cm layer more conductive.

Hillel [1980] states that hydraulic conductivity is obviously affected by structure as well as by

texture, being greater if the soil is highly porous, fractured or aggregated than if it is highly

compacted and dense.

The 0-3 years 0-15 cm in Rep 1, Rep 2 and Rep 3 had very dark brown and black color soils which

implied that there was organic matter content in the soil. The 15-30 cm in Rep 1 and Rep 2 had

reddish brown colour due to the moderate amounts of iron in the soil and Rep 3 had dark brown

with organic matter. This was due the presence of litter and dead macro-fauna which contributed to

its organic matter content. This could also be as stated by Nayle [2002] that water content of a soil

also influences the level of soil air, and more specifically soil oxygen. Oxygen in turn determines

the oxidation state of several elements and especially of iron in its oxide minerals.

The 0-50 years with the depth of 0-15 cm in Rep 1 had black soil colour. The very dark brown

colours in Rep.2 and Rep 3 showed a high presence of organic matter due the leaf fall and dead

micro organisms in all replications of 0-15 cm. For the 55 years and above in 0-15 cm depth in all

the three sample replications had very dark brown soil color and 15-30 cm depth Rep.1 and Rep.2

had dark reddish brown soil colour attributed to the presence of iron oxides in the soil while the

Rep.3 had very dark brown color.

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The 0-3 years and >55 years had coarse textured soils which were sandy loam. The 10-20 years

had fine textured soils which were sandy clay loam. These could be the organic matter which

increased permeability by increasing the stability of soil aggregates.

The soil structure of 0-3 years and >55 years had coarse textured soils which were sandy loam.

These held low amounts of water and nutrients which necessitated irrigating and fertilizing

frequently, compacted to form a hardpan and also allowed water to infiltrate but less runoff. The

10-20 years had fine textured soils which were sandy clay loam. These also held large amounts of

nutrients and water which also held things too tightly. This could be organic matter which increased

permeability by increasing the stability of soil aggregates. The organic matter decomposed to form

glues and gums that helped cement or stick soil particles together.

THE AGRICULTURAL LAND USE ON SOIL PROPERTIES

Organic matter was high in the banana treatment and the lowest in sugar. The depth of 0-15 cm

sugar mechanised had the highest organic matter and lowest banana. With the 15-30cm depth

banana had the highest organic matter and lowest sugar mechanised. This was attributed to the

presence of vegetation litter in the surface layers. Pushparajah [1990] asserted that the effects of

organic inputs on the soil physical properties depend on the residence time or quality and

placement of the material, thus organic inputs that decompose slowly will have a greater and more

durable effect on soil physical properties than high quality organic resides.

There was a positive trend of bulk density with agricultural land use, sugar mechanised being the

lowest and sugar manual the highest in bulky density. Boyd [1992] states that deeper in the soil

profile, bulk densities are generally higher, probably as a result of lower organic matter contents,

less aggregation, fewer roots and other soil dwelling organisms and compaction caused by weight

of the over laying layers.

The sugar mechanised had the highest amount of phosphorus because of the fertilizer application

and high organic matter due to the litter on the ground. The trend was that the amount of

phosphorus decreased as the litter decreases due to frequent weeding and burning litter which

hinders the presence of organic matter in the soils hence availability of phosphorous. Phosphorus

was released by decomposition of organic matter on and in the 0-15cm layer and then it moves

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downwards to the 15-30cm layer by means like leaches and macro fauna activity. This expalins

why phosphoruos was high in the 0-15cm depth. Ronnell [1994] stated that clay soils often have

large reserves of non exchangeable k+ in minerals which supply some overall of the crop needs

from year to year. However, there are very few soils which have large reserves of phosphorous in

soil minerals

Sugar manual had the highest amount of nitrogen which was released into the soil from the

decomposing organic matter. The trend was that the amount of nitrogen increased with the kind of

agricultural land use practices. The reasons for high nitrogen in the 0-15cm were that nitorgen

was released by decomposition of organic matter on and in the 0-15cm layer and then it moved

downward to the 15-30cm layer by means for example by leaches. Ronnell [1994] attributes to

nitrate leaching in heavy textured soils is more complex, because water moves through large

cracks and channels leaving nitrate behind in the soil aggregates where little water movement

occurs.

The high soil pH was attributed to the presence of organic matter in the soil. This could due to

clearing of natural vegetation which causes accelerated organic matter decomposition, nitrate

leaching and acidity production. This could also explain why the sugar treatment was the most

acidic while the sugar mechanised was the least acidic.

For the depth of 15-30 cm sugar manual still had the highest macro-fauna abundance and lowest

in the sugar mechanized. This was attributed to the quality of the organic input to the soil and the

nature of land use which could have influenced soil compactness and consequently faunal

abundance. Hillel [1980] stated that compaction impedes the movement of water and air through

the soil by reducing the number of large pores. The resulting restriction of aeration and drainage

thus exposes roots to several simultaneous stresses.

Sugar manual had the highest bulky density which was attributed to the gradual pore space

clogging by very fine suspension carried by rain water (run off). The 15-30cm layer had a higher

bulk density with a lower conductivity because the pore space clogging and compaction begins

from this layer where the pores are smallest. The process builds upwards towards the soil surface

hence making the 0-15 cm layer more conductive. Also the improper land clearing or tillage

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reduces the mean diameter of soil aggregates resulting in increases in bulky density and

decreases in aeration, hydraulic conductivity and increased erodibility.

The hydraulic conductivity was high in the sugar mechanised and minimum was in the sugarcane

treatment. This was because the sugar mechanisation had soils which were more porous due to

human activities like digging. Hillel [1980] reported that in a saturated soil of stable structure, as

well as in a rigid porous medium such as sandstone, for instance, the hydraulic conductivity is

characteristically constant. It is order of magnitude is about 10-2-10-3 cm/sec in a sandy soil and 10-

4-10-7 cm/sec in a clayey soil.

In banana Rep 1 had dark brown colour and Rep.2 and Rep.3 had very dark brown colours which

showed high presence of organic matter. With the depth of 15-30 cm all the three replications had

dark reddish brown colours implying high heavy presence of iron oxides in the soil. Nayle [2002]

shows how organic matter to be dark brown to black in colour. Organic coatings tend to darken and

mask the brighter colours from compounds such as iron oxides. The red or brown colours are of

well drained uplands and have the presence of oxidized iron oxides.

6.0 CONCLUSION

The land uses affected the soil properties differently (chemically, physically and biologically). The

forest land use greatly influenced the Soil pH, Organic matter due to the leaf fall and macro-fauna.

The macro-fauna abundance and hydraulic conductivity had been also influenced by the

agricultural land use activities such as burning little and monoculture practices. The land pressure

by the population should be eased to manage the land sustainably for proper determination of soil

properties in and around Mabira Central Forest Reserve.

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ACKNOWLEDGMENT

First and foremost, I would like to thank the Almighty God for the wisdom, guidance, courage and

decisions made whenever I sat down to concentrate on this research report without whom I would

not have completed this report.

I wish to extend my sincere thanks to my parents Mr. and Mrs. Wabwire Geoffrey whose roles have

contributed a lot to my life without their prayers, love and protection; I would not be where I am

now.

I am indeed grateful with the group members who were Catherine, Amos and Edward whose

positive critics and guidance culminated in writing up what constitutes the contents of this report.

I wish to extend my heartfelt gratitude to the MUIENR staff and National Forestry Authority staff

especially Mr. Tonga for their willingness to participate when we were conducting research in

Mabira Central Forest Reserve I am indeed grateful.

A lot of thanks go to my resource personnel DR. MAJALIWA MAJOLOLO for the expert guidance

he rendered to ensure that my report was successfully completed.

MAY GOD BLESS YOU ALL

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REFERENCES

Pushparajah, E. [1989] Soil Management and Small holder development in the Pacific Islands.

International board for soil research and management – Thailand.

Hillel David [1980] Fundamentals of Soil Physics, Harcourt Brace Jovanovich Publishers, New

York. P 179.

Boyd, G. Ellis and Ray L. Cook [1992], Soil Management, Krieger Publishing company Malabar,

Florida. P 61-191

Turner II, B.L., W.C. Clark, R.W. Kates, J.F. Richards, J.T. Mathews, and W.B. Meyer, eds. 1990.

The Earth as Transformed by Human Action: Global and Regional Changes in the Biosphere Over

the Past 300 Years. Cambridge University Press, Cambridge.

National Environmental Management Authority (2001), State of Environment Report.

Ronell. L. David [1994] Soil Science, Published by Pearson Education [pte] Ltd, England, P 153-

160].

Lal, R. [1981] Deforestation of Tropical Rainforest and Hydrological problems, Published by John

Wiley and Sons, p.131-140 Chichester UK.

Pushparajah, E. and Latham. M. [1990] Organic matter management and tillage in Humid and sub

humid Africa. P 176. proceedings of the third regional workshop of the AFRICALAND programme

held at Antananarivo, Madagascar.

Nayle. C. Brady and Ray R. Well [2002] The Nature and Properties of Soils. Thirteenth edition,

Pearson Education ltd. USA.

Miller. W. Raymond and Roy. L. Donahue [1995] Soils in our Environment, Published

by Prentice Hall inc. New Jersery.

The effect of land uses on soil properties

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