THE EFFECT OF BUSH BURNING ON CHEMICAL AND PHYSICAL PROPERTIES OF SOIL



CHAPTER FOUR
4.0                                      RESULT AND DISCUSSION
4.1.0   THE EFFECT OF BUSH BURNING ON CHEMICAL PROPERTIES OF SOIL
 4.1.1 Soil pH
The pH of the experimental site revealed that the burnt area was statistically different from the unburnt area when compared with each other. The pH of the unburnt and burnt area was 5.97 and 6.15 respectively. The result shows that the burnt area was 5units more acidic than the unburnt area. This is because during the combustion process, several previously bound nutrients are released in their elemental or radical form.
Certain cations are stable at typical combustion temperature and remain onsite after burning in form of ash. If in the ash form are subsequently leached into the soil where they exchange with H+ ions, the resulting increase in H+ ions in solution increases the pH of the burnt area and ash deposited after burning is composed mostly of salts, these salts can effectively increase soil pH by capturing the salt cations as they leach through the soil profile. The result shows moderately to slightly acidic in the unburnt are and burnt area (Ulery et al., 1993)

4.1.2 Total nitrogen
The result of the effect of bush burning on total N of the soil shows no statistical significance difference when the unburnt and burnt areas were compared with each other. There was 3% slight increase in total nitrogen of the unburnt area. The level of nitrogen recorded low to medium in the unburnt and burnt area. The decrease of nitrogen in burnt area is as a result of heating which causes decrement and because some are lost through volatilization (Fisher and Binkly, 2000).

4.1.3 Calcium
The calcium of the experimental site revealed that there was statistically significant different in calcium level of the unburnt and burnt area when compared with one another. This result revealed that there was an increase in calcium content of the unburnt area when compared with the burnt area. This is because calcium is present in adequate amounts in most soils; calcium is a component of several primary and secondary minerals in the soil. It increases in unburnt area because calcium is not considered a leach able nutrient; however it will move deeper into the soil. Because of this, and the fact that many soils are derived from limestone bedrock, many soils have higher level of Ca. The decrease in calcium level of the burnt area may be caused by environmental factors and it could be removed in particulate form by surface wind transport during and after burning (Goh and Phillips, 1991). The calcium in the soil recorded medium to high level (Landon, 1991).

4.1.4 Available phosphorus
The effect of bush burning on available phosphorus recorded 43.29 and 8.04Cmol/100g for the unburnt and burnt area respectively. This shows that there was statistically significant in difference phosphorus in both areas. The increase of phosphorus in unburnt area may be as a result of phosphate precipitation and dissolution. Phosphate precipitation is a process in which phosphorus react with another substance to form a solid mineral. Dissolution of phosphate mineral occurs when the mineral dissolves and releases phosphorus, the reaction of phosphate with another substance to form a solid mineral aids the increase of phosphorus in the unburnt area. The increase implies that there was no available phosphorus in the unburnt, while there is a decrease of phosphorus in the burnt area due to fire severity which induced losses of available phosphorus through volatilization. This is in line with the findings of Cade-Manun et al, (2000). The result recorded marginal to rich level of phosphorus in critical level for available phosphorus (Serrasolsas and Khanna, 1995).

4.1.5 Magnesium
The magnesium of the experimental site revealed that there was statistically significant difference when the unburnt and burnt areas were compared with one another. The level of magnesium in the unburnt and burnt area recorded 0.69 and 0.47mg/l respectively. The unburnt area is 22% high than that of the burnt area. This may be because magnesium is held on the surface of clay and organic matter particles and the soil pH of the unburnt area is not as high as that of the burnt area (George et al., 1994). The magnesium level recorded low level according to its rating and availability (Simard et al., 2001).

4.1.6 Potassium
The result of the effect of burning on potassium content of the soil showed that there was significant difference when the unburnt and burnt area were compared with one another. The level of potassium in the unburnt and burnt area of Ali-ogo Ekoli soil was 0.26 and 0.36Cmol/100g soil. There was 10% more potassium level of the burnt area when compared with unburnt area. This may be as a result of environmental factors like wind and rainfall which played a major role in the concentration of potassium after burning in the burnt area (Ulery et al., 1993). Generally, the level of potassium is recorded medium classes of potassium availability in the soil (Wild, 1987).

4.1.7 Sodium
The sodium of the research site showed that there was no statistical significant from the unburnt and burnt area when compared together. The sodium of the unburnt and burnt area was 0.15 and 0.10Cmol/100g soil respectively. The slight reduction in sodium of the burnt area may be as a result of leaching since sodium is weakly held by the soil colloid (Simard et al., 2001). The level of sodium in the soil recorded low level according to its classification which is deficient in the unburnt and burnt soils.

4.1.8 Exchangeable cation
The result of the effect of bush burning on exchangeable cation of the soil showed that there was statistically difference when the two areas were compared with one another. There was high increase of exchangeable cation in the burnt area which was in accordance with the findings of Parkinson, 1998. The increase may be as a result of ash deposit in the burnt area that increased the soil pH. This recorded high exchangeable cation value according to the ranking (Kattering et al., 2000).

4.1.9 Effective cation exchange capacity
The effect of bush burning on effective cation exchange capacity revealed the following result 3.49 and 3.88mg/100g in unburnt and burnt area respectively. From the result, there was 39% increase of effective cation exchange capacity in the burnt area. The reason of this increase may be as a result of ash deposit on the burnt area and ash deposited contains Fe³+, Mg²+ which provide exchange site for ion interactions to take place. Soils with large amount of cation exchange capacity are chemically stable (Parkinson, 1998). The effective cation exchange capacity recorded medium ranking according to its classification (Oswald et al. 1999; Badia and Matni, 2003).

4.1.10 Exchangeable Sodium Percentage
The effect of burning on exchangeable sodium of the soil showed that there was significant difference when the unburnt and burnt area was compared with one another. The result of the unburnt and burnt area was 2.86 and 3.23% respectively. There was 37% more exchangeable sodium in the burnt area and this increase may be as a result of ash deposit that leads to cation concentration in the burnt area. This is supported by the findings of Kattering et al., (2000), and Parkinson, (1998).

4.1.11 Exchangeable acidity
The exchangeable acidity of the experimental site showed that there was no statistically significant from the unburnt and burnt area when compared with one another. The value recorded was 0.47 and 0.47Cmol/100g respectively. The unburnt and burnt area recorded low values in ranking according to Landon (1991). Badia et al., (2003).

4.1.12 Base saturation
The result of the effect of bush burning on percentage base saturation of the soil showed that there was statistically difference when the unburnt area was compared with the burnt area of Ali-ogo Ekoli. The percentage base saturation in the unburnt and burnt area was 80.44 and 87.72% respectively. There was about 728% more base saturation in the burnt area. This may be as a result of the proportion of the cation exchange in the burnt area that are occupied by the various cations (H, Ca, Mg, k).The surfaces of soil mineral and organic matter have negative charged cations. Cations with one positive charge (H, K, Na) will occupy one negatively charged site and cations with two positive charges (Ca, Mg) occupied two sites on the burnt area according to the findings of Serrasolsas and Khanna (1995).

4.1.13 Organic carbon
Organic carbon is the amount of carbon bound in organic compound. The effect of burning on unburnt and burnt area of Ali-ogo Ekoli showed that there was significant difference in both the unburnt and burnt area. The result of the unburnt and burnt area was 12.29 and 6.29% when compared with one another. There was difference of about 100% more organic carbon in the unburnt area than that of the burnt area. The reason of high level of organic carbon in the unburnt area may be as a result of leave drop, plant and animal decay and excess litter layer on the soil surface of the unburnt area which are neither disturbed nor altered. The organic carbon content of the unburnt and burnt area recorded medium to high in the rating of organic carbon content according to Landon (1991). Also, the decrease in organic carbon of the burnt area may be as a result of denaturation of organic carbon present in the soil as supported by the findings of Guinto et al., (1999) who found that fire induced a reduction in organic carbon ratio of soil.

TABLE 1:  EFFECT OF BUSH BURNING ON SOIL CHEMICAL PROPERTIES

pH
H2O
EC
(mg/100g)
ESP
(%)
OC
(%)
Total N
(%)
Avail P
(Cmol/100g)
Ca
(Cmol/100g)
Mg
(Mg/L)
K
(Cmol/100g)
Na
(Cmol/100g)

EA
(Cmol/100g)

Bs
(%)
ECEC
(Mg/100g)
Unburnt Area (A)
5.97a
14.00a
2.86a
12.29a
0.12a
43.29a
2.88a
0.69a
0.26a
0.15a
0.47a
80.44a
3.49a
Burnt Area (B)
6.15b
17.00b
3.23b
6.29b
0.09a
8.04b
1.86b
0.47b
0.36b
0.10a
0.47a
87.72b
3.88b
F-LSD
P = 0.05
0.01
0.05
0.12
2.4
NS
6.42
0.12
0.01
0.03
NS
NS
2.14
0.01

Figures with the same super sample are not statistically significant.

4.2.0   THE EFFECT OF BUSH BURNING ON SOIL SELECTED PHYSICAL PROPERTIES       
4.2.1 Bulk density
The effect of burning showed statistically difference in the unburnt and burnt area of Ali-ogo Ekoli. The result recorded 1.53 and 1.69 in unburnt and burnt area respectively. This result shows that there was 16% increase in bulk density in the burnt area; the reason may be due to high clay, silt and sand content in the burnt area (Webster and Wilson, 1980). The bulk density of the unburnt and burnt area recorded low bulk density according to the rating of Landon, 1991. The slight increase of bulk density of the burnt area may also be because of collapse of aggregates and clogging of voids by the ash (Certini, 2005).

4.2.2 Total porosity
The result of the effect of bush burning on total porosity of the unburnt and burnt area was 40.37 and 36.23%. The reason for decrease in total porosity of burnt area may be as a result of destruction of soil structure by fire which also affects pore size distribution in the surface horizons of the burnt soil (DeBano et al., 1998). According to Landon 1991, the two values of unburnt and burnt area are of very high classes in the classification rating.

4.2.3 Hydraulic conductivity
The effect of burning on hydraulic conductivity of soil showed statistically difference in the unburnt and burnt area when compared with one another. The result recorded 30.21 and 31.42Cmhr­‑¹ respectively for unburnt and burnt area. This shows that there was 121% more free movement of liquid in the burnt area. This result may be because the size, shape, and continuity of the pore spaces, structure and the soil texture of the burnt area was altered and tempered with by fire. According to soil permeability classification, the result recorded very rapid hydraulic conductivity according to the classification (Landon, 1991).

4.2.4 Moisture content
The result of the unburnt and burnt area of Ali-ogo Ekoli recorded 12.0 and 16.0% when compared with one another. There was more moisture content in the burnt area. The reason may be due to burning of the organic matter, plant residues that cover the soil surface that may have seal the soil surface and crusting has been burnt off thereby making the soil to be moisture absorber. The moisture content of the unburnt and burnt area recorded high according to the rating of Landon, (1991)

4.2.5 Sand, silt and clay
The percentage sand fraction for the unburnt and burnt area was 56.4 and 62.4% respectively. There was an increase in sand fraction of the burnt area due to high temperature that may lead to breakdown of soil particles causing the soil to be coarse, (Ulery et al., 1993). The fraction of silt and percentage clay fraction has the following results 32.10 and 20.91% for silt fraction of the unburnt and burnt area and 11.5% and 16.7% for clay fraction of the unburnt and burnt area respectively. There was decrease in silt fraction of the burnt area which was as a result of high temperature fusing the silt fractions hence its reduction, (Kattering et al., 2000). The increase in percentage clay of the burnt area shows that the fire severity was high enough to lead to fusion of clay fraction of the soil, (Imeson et al., 1992; and Kattering et al., 2000).
The above results showed that the resultant effect of fire on soil texture could be due to the irregular pattern of fire severities which leads to different types of textural classes. The textural class of the unburnt and burnt area is sandy clay loam according to the textural classification (Imeson et al., 1992; Martin and Moody, 2001). Soil coarsening at some parts of the burnt area occurred which was in accordance with the findings of Mermut et al, (1997) who reported that selective removal of fine fractions could be caused by environmental action of rain through erosion. Also, exposure of the soils to high temperature results in the fusion of clay and silt fraction into sand- size particles (Kattering et al., 2000).   

TABLE 2: EFFECT OF BUSH BURNING ON SOME SOILS SELECTED PHYSICAL PROPERTIES


TP
(%)
BD
(Cm3)
HC
(C mhr-1)
MC
(%)
SAND
(%)
CLAY
(%)
SILT
(%)
TEXTURAL CLASS
Unburnt Area (A)
40.37
1.53
30.21
12.0
56.4
11.5
32.1
SANDY CLAY
Burnt Area(B)
36.23
1.60
31.42
16.0
62.4
16.7
20.91
CLAY LOAM
F-LSD P=0.05
0.41
0.01
0.51
0.28
21.0
21.0
18.1


4.3.0   THE EFFECT OF BUSH BURNING ON SOME SOIL SELECTED HEAVY METALS
4.3.1 Zinc
The result of the effect of bush burning on zinc content of soil showed that there was statistically difference when the unburnt and burnt areas were compared with one another. The zinc level in the unburnt and burnt area of Ali- ogo soil was 0.26 and 0.58Cmol/100g respectively. There was 32% more zinc in the burnt area than the unburnt area. The reason for higher level of zinc in the burnt area may be as a result of breaking down of soil solid particles by fire which help to release the zinc content of the soil because most zinc stays bound to the solid particles.
Generally, the level of zinc in the burnt and unburnt areas recorded low to medium classes of zinc sufficiency. This means that response of zinc application will be high in both unburnt and burnt areas (White, 1987).

4.3.2 Boron
The boron content of the experimental site revealed that there was statistically significant difference in the comparison of the unburnt and burnt areas. Boron level in Ali- ogo Ekoli unburnt and burnt areas were 34.50 and 28.9Cmol/100g soil respectively. There was an increase in Boron level in the unburnt area and decrease of boron level in the burnt area. The reason for the accumulation of boron in the unburnt area may be because boron is present and accumulates in organic matter and is freely available to plants in all except alkaline soils. Also, the level of boron in burnt area decreased as a result of fire severity and volatilization and ash deposition on the burnt soil which will make the soil to be alkaline. The boron content of the unburnt and burnt areas recorded low to medium classes of boron sufficiency in the soil (Ulery, 1993).

4.3.3 Iron
The effect of burning on soil iron content showed that there was difference in iron level of the unburnt and burnt areas. The two areas recorded 105.8 and 191.4Cmol/100g for the unburnt and burnt areas respectively. This showed that there was less than 100% more iron in unburnt area, the reason of higher iron content of the unburnt area may be as a result of iron been immobile and its stickiness to soil solid particles (Webster et al., 1980). The level of iron in unburnt and burnt area recorded medium classes of iron sufficiency and reduction in iron content of the burnt area may be due to long duration of fire that leads to high temperature of the burnt area (Kattering et al., 2000).

4.3.4 Molybdenum
The effect of bush burning on molybdenum showed the following results 56.90 and 35.90Cmol/100g in unburnt and burnt area respectively. This result showed that there was about 58% more molybdenum content in the unburnt area. This high level of molybdenum in the unburnt area may be due to the fact that molybdenum does not occur naturally as a free metal in soil, but rather in various oxidation states in minerals. The level of molybdenum in unburnt and burnt area recorded high classes of molybdenum excessively and a decrease of molybdenum in burnt area is as a result of fire severity and high temperature of the burnt soil (Kattering et al, 2000; Ulery, 1993).

TABLE 3: EFFECT OF BUSH BURNING ON SOIL SELECTED
HEAVY METALS

Zn
(Cmol/100g)
Bo
(Cmol/100g)
Fe
(Cmol/100g)
Mo
(Cmol/100g)
Unburnt Area (A)
0.26
34.50
105.9
56.90
Burn Area (B)
0.58
28.90
101.4
35.90
F-LSD P=0.05
0.02
1.21
1.2
10.1


CHAPTER FIVE
5.0       SUMMARY, CONCLUSION AND RECOMMENDATION
5.1       Summary
 The physico – chemical properties of soils at Ali-ogo Ekoli in Ebonyi state south – east Nigeria have undergone changes due to annual cycles of bush burning. Results from this research work suggested that soil properties vary in their response to burning in the unburnt and burnt area. This work tested three things first, the effect of fire on soil chemical properties showed that pH was favoured by fire in the burnt area but at unburnt area, it was not favoured. Percentage base saturation, exchangeable cation, cation exchange capacity, potassium and magnesium were favoured by burning in the burnt area; total nitrogen, sodium and exchangeable acidity are not statistically significant in the unburnt and burnt area. The effect of bush burning on soil selected heavy metals showed that zinc was favoured by fire; Boron, Iron, and Molybdenum were not favoured by bush burning. Also, bulk density, moisture content, sand and clay fractions were favoured by fire while total porosity and silt fraction were not favoured by bush burning. Hydraulic conductivity have free movement of liquid in burnt area.  
5.2       Conclusion
From the results of my study, the following conclusion could be drawn. Firstly, that burning can significantly alter the chemical properties like pH, exchangeable cation, exchangeable sodium, potassium, cation exchange capacity and percentage base saturation. However, it also alter the physical properties of the burnt area like bulk density, hydraulic conductivity and moisture content but only the sand and clay of the burnt area was increased due to burning while there reduction in silt of the burnt area.

5.3       Recommendation

The use of fire as a management tool in forest agriculture in Ali-ogo Ekoli in Ebonyi state south – east Nigeria is likely to continue since it is cheap to implement and reduce their cost of labour. However, there should be sensitization on the effect of bush burning on forest soil and environment if not adequately controlled.

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