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Soil properties of termite mounds under different land uses in a Typic Kandiudult of southern Cameroon
Agriculture, Ecosystems and Environment, 43 ( 1993 ) 69-78
69
Elsevier Science Publishers B.V., Amsterdam
Soil properties of termite mounds under different land uses in a Typic Kandiudult of southern Cameroon N.R. Hulugalle and J.N. Ndi International lnstitute of Tropical Agriculture, Humid Forest Zone Station, B.P. 2008, Messa, Yaounde, Cameroon (Accepted 14 April 1992 )
ABSTRACT Hulugalle, N.R. and Ndi, J.N., 1993. Soil properties of termite mounds under different land uses in a Typic Kandiudult of southern Cameroon. Agric. Ecosystems Environ., 43: 69-78. The effect of land use, i.e. 3-4 years of cropping, 2- to 3-year-old Chromolaena odorata fallow and 10- to 15-year-old secondary forest, on soil properties of Microtermes termite mounds in Typic Kandiudults was studied in the humid forest zone of southern Cameroon from November 1990 to March 1991. Termite mound populations increased in the following order: secondary forest greater than fallow greater than cropping. Soil sampled from mound surfaces, mound perimeters (interface of mound and surrounding soil) and surrounding soil was analyzed for various physical and chemical features. Sand and clay contents of soil sampled from the surrounding soil and mound surfaces were primarily influenced by sampling location. The surrounding soil and that from mound surfaces consisted of 58.5% and 39.9% sand, respectively, and 25.6% and 47.9% clay, respectively. Particle size distribution in mound perimeters was, however, dependent on land use. With respect to other soil properties measured, both absolute values and spatial variation between sampling locations were, in general, primarily affected by land use. Bulk density particle size distribution, soil water retention at potentials less than or equal to - 4 . 8 kPa, organic C, total N, pH, exchangeable cations (except total acidity ) and effective cation-exchange capacity contributed significantly to the interactions in spatial variation between sampling locations and land uses.
INTRODUCTION
Detailed studies of termite mounds in tropical soils have shown that in relation to surrounding soil, mound soil can have either higher or lower values of organic carbon, total nitrogen, Bray-l-P, exchangeable Ca, Mg and K, effective cation-exchange capacity, bulk density, aggregate stability, waterholding capacity and water infiltration rates (Trapnell et al., 1976; Kang, 1978; Moormann and Kang, 1978; Roose, 1981; Lal, 1987, 1988; Okwakol, 1987, Correspondence to: N.R. Hulugalle, Agricultural Research Station, N.S.W. Department of Agriculture, PMB, Myall Vale Mail Run, Wee Waa Road, Narrabri, N.S.W. 2390, Australia.
© 1993 Elsevier Science Publishers B.V. All rights reserved 0167-8809/93/$06.00
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N.R. HULUGALLE AND J.N. NDI
1988; Lobry de Bruyn and Conacher, 1990; Brouwer et al., 1991 ). With respect to particle size distribution, however, a consistent pattern emerges with mound soils having higher values of silt and clay, and lower values of sand in relation to bulk soil (Kang, 1978; Lal, 1987, 1988; Okwakol, 1988; Lobry de Bruyn and Conacher, 1990; Brouwer et al., 1991). The contradictions reported in the literature may be caused by variations in site characteristics, termite species and genera, land use at the sampling site and sampling location (Trapnell et al., 1976; Lal, 1987; Dangerfield, 1990; Lobry de Bruyn and Conacher, 1990 ). Water infiltration, for example, is lower on mound surfaces in relation to bulk soil, but higher above the feeding galleries constructed away from the mound (Lal, 1987, 1988). It is, therefore, difficult to generalize on mound characteristics. A better approach is to describe the properties of mound soil for a particular soil type, site and land use, and evaluate them in the context of soil variability and the effects on subsequent crop growth and yield (Kang, 1978; Kang and Moormann, 1978; Lal, 1987). The objective of the present study, therefore, was to quantify the properties of termite mound soils in Typic Kandiudults under three land uses: cropping, fallow and secondary forest, in the humid forest zone of southern Cameroon. MATERIALS AND METHODS
The study was conducted on three adjacent 4-ha (200 m X 200 m) blocks at the Humid Forest Zone Station of the International Institute of Tropical Agriculture located at M'Balmayo, 60 km south of Yaounde (3°51'N, 11 °27'E) in southern Cameroon. M'Balmayo is located in the forest zone of southern Cameroon and has an annual rainfall of 1522 ram. The rainfall pattern is bimodal with rains occurring from March to June followed by a short dry spell of approximately 1 month, which in turn is followed by a second rainy season from August to November. The dry season lasts from November to March. The soil at the experimental site is a clayey, kaolinitic, isohyperthermic, Typic Kandiudult with a sandy clay loam (59% sand, 16% silt, 25% clay) topsoil overlying a clay (29% sand, 8% silt, 63% clay) subsoil. Average depth of topsoil was 0.09 m (range 0.03-0.12 m ). Land use in the three adjacent blocks was (a) 3- to 4-year-old cropped fields consisting primarily of mixtures of cassava (Manihot esculenta Crantz.), maize ( Zea mays L. ), cocoyam ( Xanthosoma sagittifolium L. ), banana and plantain (Musa×paradisiaca L.), oil palm (Elaeis guianensis Jacq.), kolanut ( Cola nitida L. ), cacao ( Theobroma cacao L. ) and papaya ( Carica papaya L.); (b) 2- to 3-year-old natural fallow dominated by Chromolaena odorata L.; (c) 10- to 15-year-old secondary forest. The blocks were delineated, taking care to avoid overlapping of land-use systems, following a land survey of the site (Tchenkoua and Moormann, 1990). The cropped block was cleared manually with a combination of chainsaws, axes and machetes fol-
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
7!
lowed by in situ burning of vegetation residues (Hulugalle, 1992). Before sampling the numbers and location of all termite mounds in each 4 ha block were determined by mapping on a 5 m X 5 m grid. The height of each termite m o u n d was recorded at the same time. Termites obtained from the mounds were identified as belonging to the genus Microtermes. Sampling for soil physical and chemical properties was done from all m o u n d s during the dry season of 1990-1991. Composite samples were obtained at random from five locations in the 0.00-0.10 m depth of m o u n d surfaces, m o u n d perimeters (the interface of the m o u n d and surrounding soil) and the surrounding soil at least 2 m away from the m o u n d perimeter. Airdried, ground subsamples were passed through a sieve with aperture diameters of 2 m m and analyzed for particle size distribution using the hydrometer m e t h o d (Klute, 1986 ), pH ( in water), total N ( Kj eldahl digestion ), Bray- 1 P and 1 N a m m o n i u m acetate-extractable Ca, Mg, K, Mn and Na, and 1 N KCl-extractable total acidity (AI + H) (Page et al., 1982 ). Soil organic carbon was determined by dichromate oxidation (Walkley/Black m e t h o d ) of air-dried, ground subsamples which had been passed through a sieve with aperture diameters of 0.5 m m (Page et al., 1982 ). Soil water retention was determined at saturation and at a potential of - 4 . 8 kPa with a sand box apparatus, and at potentials of - 1 0 , - 3 0 , - 1 0 0 , - 3 0 0 and - 1 5 0 0 kPa with a pressure plate apparatus on disturbed subsamples (not ground) which had been passed through a sieve with aperture diameters of 2 m m and saturated by capillarity for 48 h (Klute, 1986). Five soil cores, 51 m m in length and 50 m m in diameter, were obtained at the same location in the 0.00-0.05 m and 0.05-0.10 m depths. Bulk density of the same cores was determined following oven-drying at 105 ° C. Data were analyzed by analysis of variance using a randomized complete block design model for multiple sites (Federer, 1955; Michigan State University, 1991 ). RESULTS
AND DISCUSSION
Distribution of termite mounds The n u m b e r of termite m o u n d s per unit area increased from cropping to fallowing to secondary forest (i.e. as length of fallow period increased) (Table 1 ). Similar results have been reported for a wide range of environments and termite species, and attributed to increased availability of litter and soil water, and cooler air and soil temperatures with increasing length of fallow (Lal, 1987). In addition, soil C / N ratios may also have contributed to the differing m o u n d populations in the various land uses (Lal, 1987). Soil C / N ratio increased such that values of 10.5, 14.6 and 15.5 ( ___SE = 0.74, P < 0.001 ) were observed with cropping, fallowing and secondary forest, respectively.
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N.R. HULUGALLEAND J.N. NDI
TABLE 1 Numbers and heights of termite mounds under cropping, fallow, and secondary forest Land use
Numbers per 4 ha
Mound height (m) (x_+ SD )
Cropped Fallow Forest
8 16 25
0.84 _+0.45 0.81 + 0.38 0.82 + 0.44
Average height of termite mounds, however, was similar in all three land uses (Table 1 ).
Soil physical properties Soil bulk density in the 0.00-0.05 m depth was greatest on m o u n d surfaces with cropping and fallowing, but did not differ significantly between sampiing locations under forest (Table 2 ). Bulk density in the 0.05-0.10 m depth differed significantly between sampling locations only under forest and was lowest on m o u n d surfaces. Bulk density of m o u n d surfaces for both depths was, in general, lowest under forest and may be due to greater quantity and quality of organic materials incorporated into the forest m o u n d s in comparison with those in cropped and fallowed fields. Bulk density averaged over 0.00-0.05 m and 0.05-0.10 m depths was related primarily to soil organic carbon thus:
BD= 1.12-0.03C, r=0.65"**, n = 147 where BD is bulk density (Mg m - 3 ) and C is soil organic carbon content (%) in the 0.00-0.10 m depth. Soil organic matter improves soil structure and porosity (Campbell, 1985; Lal, 1987). Sand and silt contents were lower, and clay content was higher on m o u n d surfaces than in the surrounding soil (Table 2). Preferential transport and incorporation of clay particles into termite mounds is a feature of all termite species (Lal, 1987 ). At m o u n d perimeters, however, particle size distribution was determined by land use. Sand and silt contents at the m o u n d perimeter were similar to that of surrounding soil under cropping, intermediate to those of the m o u n d surfaces and surrounding soil under fallow and similar to the m o u n d surfaces under forest. Silt content at the m o u n d perimeter under cropping and fallow was similar to that of surrounding soil, whereas under forest it was lower. However, both m o u n d and surrounding soil in the forested plot had significantly higher and lower levels of sand and clay, respectively, in comparison with m o u n d s in cropped and fallow fields. These differences may reflect the degree of vegetation cover, both spatial and temporal, in each land use. The land use with least cover, i.e. cropping, suffers most soil erosion .(Lal,
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
73
TABLE 2
Effect of land use and sampling location on bulk density ( Mg m - 3) in the 0.00-0.05 m and 0.05-0.10 m depths and particle size distribution (PSD) in the 0.00-0.10 m depth Land use
Cropped
Location
M o u n d surface M o u n d perimeter
Surrounding soil Mean Fallow
Mound surface M o u n d perimeter
Surrounding soil Mean Forest
M o u n d surface M o u n d perimeter Surrounding soil
Mean
Bulk density
PSD ~
Sand
Silt
Clay
0.00-0.05 m
0.05-0.10 m
(%)
(%)
(%)
1.11 0.91 0.99 1.00
0.96 1.01 1.09 1.03
37.3 47.0 48.8 44.3
11.3 16.0 16.0 14.4
51.4 37.0 35.2 41.2
1.19 0.99 1.04 1.07
1.11 1.04 1.10 1.08
37.1 55.6 65.5 52.7
12.5 16.0 16.0 14.8
50.4 28.5 18.5 32.5
0.85 0.93 0.93 0.91
0.78 1.02 1.11 0.97
45.2 44.5 61.2 50.3
13.0 12.5 15.8 13.8
41.9 43.0 23.1 36.0
0.042 0.028 0.048
0.043 0.028 0.049
* * *
NS ** **
+SE Between land uses Between locations Between locations for same or different land uses
1.48 1.02 1.77
0.51 0.36 0.62
1.69 1.08 1.87
Analysis of variance Land uses
Locations Locations × land uses
** *** ***
NS *** **
** *** ***
' Sand, silt and clay have particle diameters of 50-2000/zm, 2-50/tin, and less than 2/tm, respectively.
1987 ), exposing the clay-rich subsoil (Hulugalle, 1991 ). Tillage operations during cropping also exacerbate erosion (Lal, 1987), in addition to bringing up clay-rich subsoil Which at the present site occurs at depths as shallow as 0.07 m.
Soil water content at saturation did not differ significantly between either sampling locations or land uses (Table 3 ). Soil water retention at potentials less than or equal to - 4 . 8 kPa was, however, affected both by land use and sampling location. Significant differences did not occur at any potential under cropping, but under fallow and forest, soil water retention at potentials less than or equal to - 4 . 8 kPa was in the order of mound surfaces greater than mound perimeters greater than surrounding soil. Among land uses, soil water retention at potentials of - 4 . 8 , - 1 0 and - 3 0 kPa increased in the
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N.R. HULUGALLE AND J.N. NDI
TABLE 3 Effect of land use and sampling location on soil water content ( m 3 m -3) at given potentials ( - k P a ) in the 0.00-0.10 m depth Land use
Cropped
Location
Soil water content (%) 0
4.8
10
30
100
300
1500
M o u n d surface M o u n d perimeter Surrounding soil
59.6 64.9 63.6 62.7
33.5 34.4 33.7 33.9
28.4 26.3 26.1 26.9
21.6 20.6 20.6 20.9
18.1 15.7 16.2 16.7
16.7 14.4 14.8 15.3
15.7 13.6 14.1 14.5
M o u n d surface M o u n d perimeter Surrounding soil
59.3 57.7 55.0 57.4
48.9 40.2 37.2 42.1
24.7 19.1 18.4 20.8
23.9 17.9 14.0 18.6
22.0 17.6 14.1 17.9
18.2 16.2 13.0 15.8
15.9 13.5 10.5 13.3
M o u n d surface M o u n d perimeter Surrounding soil
59.6 62.0 58.8 60.1
36.9 34.7 32.9 34.8
20.2 18.6 16.1 18.3
19.9 16.5 13.5 16.6
19.6 16.4 13.3 16.4
18.5 15.3 12.8 15.5
17.7 13.5 10.5 13.9
Mean Fallow
Mean Forest
Mean
+_SE Between land use Between locations Between locations for same or different land uses
1.92 1.19 2.06
2.03 0.94 1.64
0.91 0.52 0.89
0.89 0.45 0.77
0.86 0.39 0.67
0.77 0.39 0.68
0.75 0.41 0.71
Analysis of variance Land uses Locations Locations × land uses
NS NS NS
* ** **
*** *** *
** *** ***
NS *** ***
NS *** *
NS *** **
order o f cropped greater than fallow greater than forest, whereas that at - 100, - 300 and - 1500 kPa did not differ significantly. The occurrence o f significant differences only at potentials less than or equal to - 4.8 kPa suggests that particle size distribution was a major determinant o f the soil water content values observed (Campbell, 1985; Lal, 1987). Soil water retention at potentials less than or equal to - 4.8 kPa was primarily related to the fine soil component, i.e. clay plus silt, thus:
- 100 kPa:
0=26.47+0.22(Si+Cl), r=0.39"**, n = 147 ; 0 = 9 . 7 2 + 0 . 2 2 (Si+ Cl), r=0.50***, n = 147 ; 0 = 1.89 (Si+ CI) °58, r=0.61***, n = 147 ; 0 = 2 . 7 7 (Si-~-Cl) 0"46,r=0.52"**, n = 147;
- - 3 0 0 kPa:
0=3.04
- 4 . 8 kPa: - 10 kPa: - - 3 0 kPa:
- 1500 kPa: 0 = 1.37
(Siq-Cl) °'41, r=0.60***,
n = 147 ;
(Si+CI) °58, r=0.63"**,
n = 147 ;
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
75
where 0 is soil water content (m 3 m - 3, % ) Si is silt content (%) and CI is clay content (%) in the 0.00-0.10 m depth. Soil organic carbon was not related to soil water retention at any potential. The relatively high levels of soil organic carbon observed in all land uses and sampling locations (see Table 5) may have ensured that it played a minor role in the comparative soil water retention characteristics observed in this study. At this site it was found that where soil organic carbon levels are greater than or equal to 1.5%, large increases in soil organic carbon are accompanied only by small increases in soil water retention. For example, soil water content at saturation, 0 (%) and soil organic carbon content, C (%) were related such that: 0 = 4 9 . 1 6 C °-16, r=0.57"**, n=336.
Soil chemical properties Fertility of surrounding soil under cropping was, in general, superior to that of mound surfaces, with that in the mound perimeter being intermediate (TaTABLE4 Effect o f land use and sampling location on soil pH, organic C, total N and Bray-I-P in the 0.00-0. I 0 m depth L a n d use
Location
pH
Organic C (%)
Total N (%)
Bray- 1-P (mg kg-')
Cropped
M o u n d surface Mound perimeter Surrounding soil
5.8 7.1 6.8 6.5
1.38 2.87 2.33 2.19
O. 172 0.243 0.205 0.207
5.1 8.7 7.6 7.2
Mound surface M o u n d perimeter Surrounding soil
6.1 6.8 5.8 5.7
3.36 3.50 2.91 3.26
0.246 0.243 0.214 0.234
9.2 6.7 5.9 7.3
Mound surface Mound perimeter Surrounding soil
6.2 6.2 5.1 5.8
9.30 3.26 2.42 5.00
0.416 0.221 0.189 0.276
5.7 4.2 2.8 4.2
0.16 0.13 0.22
0.624 0.580 1.004
0.0271 0.0186 0.0323
0.81 0.68 1.18
** ** ***
* * **
NS * ***
* NS NS
Mean Fallow
Mean Forest
Mean
+_SE Between land uses Between locations Between locations for same or different land uses
Analysis of variance L a n d uses Locations Locations × land uses
N.R. HULUGALLE AND J.N. NDI
76 TABLE 5
Effect of land use and sampling location on exchangeable cations and effective cation exchange capacity ( E C E C ) in the 0 . 0 0 - 0 . l0 m d e p t h ( T A - - t o t a l acidity ) Land use
Cropped
Fallow
Forest
Location
Mound surface Mound perimeter Surrounding soil Mean Mound surface Mound perimeter Surrounding soil Mean Mound surface Mound perimeter Surrounding soil Mean
Exchangeable cations and ECEC ( m m o l ( + ) k g - ~) Ca
Mg
K
Na
Mn
TA
ECEC
101,1 112,5 203, 5 139,0 60.0 112, 5 73.2 81.9 l 0 I. 7 92.2 74.8 89.6
17.5 13.8 28.6 20.0 14.0 19.8 15.5 16.4 17.9 19.0 17.4 18.1
3.4 3.0 6.3 4.2 3.4 3.4 2.5 3.1 11.2 2.3 1.9 5.1
2.7 3.7 4.7 3.7 2.0 1.6 1.6 1.8 6.0 1.7 1.5 3.1
1.8 1.9 1.6 1.7 2.0 1.6 1.6 1.8 3.7 1.4 3.0 2.7
4.2 0.5 1.2 2.0 6.9 4.5 4.2 5.2 6.9 6.0 3.9 5.6
130.7 135.3 245.8 170.6 89.3 144.4 99.0 110.9 147.3 122.5 102.6 124.1
+_SE Between land uses Between locations Between locations for same or different land uses
15.32 10.24
2.01 1.36
0.97 0.96
0.49 0.47
0.21 0.23
2.19 0.63
16.4 11.4
17.74
2.35
1.66
0.81
0.39
1.10
19.7
NS NS **
** * *
NS ** NS
Analysis of variance Land uses Locations Locations X land uses
* NS **
NS NS •*
NS NS **
* NS ***
bles 4 and 5 ). This may be because of the release of nutrients from burning of the vegetation residues during land clearance (Hulugalle, 1991 ). With fallowing, however, soil fertility was, in general, highest in the mound perimeter. Erosion of mound surfaces may be the major contributory factor in this instance. Under fallow, erosion and run-off in surrounding soil is low compared with mound surfaces (Lal, 1987). Therefore, lateral movement of nutrients would be negligible, and nutrients washed down from mound surfaces would accumulate at the mound perimeter. Under forest, fertility was greatest on mound surfaces, because erosion losses are negligible under forest.
CONCLUSION
Numbers of termite mounds increased in the order of forest greater than fallow greater than cropping. With respect to all the soil parameters measured during this study, both absolute values and spatial variation among sampling
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
77
l o c a t i o n s w e r e generally strongly i n f l u e n c e d b y l a n d use a n d past h i s t o r y o f the sites. It is, t h e r e f o r e difficult to d e f i n e a ' t y p i c a l ' t e r m i t e m o u n d in t e r m s o f soil p r o p e r t i e s p e r se, a n d in p r a c t i c e t e r m i t e m o u n d s s h o u l d be specified in t e r m s o f p r e s e n t l a n d use a n d past h i s t o r y o f the site in a d d i t i o n to o t h e r e n v i r o n m e n t a l p a r a m e t e r s such as soil type, rainfall, v e g e t a t i o n a n d d e p t h to water-table. A m o n g the soil p a r a m e t e r s m e a s u r e d , t h o s e w h i c h c o n t r i b u t e d significantly to the i n t e r a c t i o n s in spatial v a r i a t i o n b e t w e e n s a m p l i n g locat i o n s a n d l a n d uses w e r e b u l k density, silt a n d clay c o n t e n t s , soil w a t e r retent i o n at p o t e n t i a l s less t h a n o r e q u a l to - 4 . 8 kPa, o r g a n i c C, total N, p H , exc h a n g e a b l e c a t i o n s ( e x c e p t total a c i d i t y ) a n d effective c a t i o n - e x c h a n g e capacity. ACKNOWLEDGMENTS T h e assistance o f Dr. J.B. Suh o f the I n t e r n a t i o n a l I n s t i t u t e o f T r o p i c a l Agriculture, Ibadan, Nigeria, in identifying the t e r m i t e s is greatly appreciated.
REFERENCES Brouwer, J., Geiger, S.C. and Vandenbeldt, R., 1991. Likely positive effects of termites on soil fertility and tree and crop growth near Niamey, Niger: Would tillage reduce these? In: Abstracts of 12th International Conference of International Soil Tillage Research Organization, 8-12 July 1991, Ibadan, Nigeria, OHSU Press, Columbia, OH, p. 82. Campbell, G.S., 1985. Soil Physics with BASIC. Elsevier, Amsterdam, 150 pp. Dangerfield, J.M., 1990. Abundance, biomass and diversity of soil macrofauna in savanna woodland and associated managed habitats. Pedobioiogia, 34:141-150. Federer, W.T., 1955. Experimental Design: Theory and Application. McMillan, New York, 544 PP. Hulugalle, N.R., 1992. Contributory factors to soil spatial variability in an Ultisol. I. Burning vegetation residues in heaps during land clearing. Commun. Soil Sci. Plant Anal., 23: in press. Kang, B.T., 1978. Effect of some biological factors on soil variability in the tropics. II1. Effect of Macrotermes mounds. Plant Soil, 50:241-251. Klute, A. (Editor), 1986. Methods of Soil Analysis, Part 1: Physical and Mineralogical Methods. Am. Soc. Agron., Madison, WI, 1188 pp. Lal, R., 1987. Tropical Ecology and Physical Edaphalogy. John Wiley, Chichester, 732 pp. Lal, R., 1988. Effects of macrofauna on soil properties in tropical ecosystems. Agric. Ecosystems Environ., 24: 101-106. Lobry de Bruyn, L.A. and Conacher, A.J., 1990. The role of termites and ants in soil modification: A review. Aust. J. Soil Res., 28: 55-93. Michigan State University (MSU), 1991. MSTAT-C: A Microcomputer Program for the Design, Management and Analysis of Agronomic Research Experiments. MSU, East Lansing, MI, 408 pp. Moormann, F.R. and Kang, B.T., 1978. Microvariability of soils in the tropics and its agronomic implications with special reference to West Africa. In: Diversity of Soils in the Tropics. ASA Special Publication No. 34. Am. Soc. Agron., Madison, WI, pp. 29-43.
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Okwakol, M.J.N., 1987. Effect of Cubitermes testaceus (Williams) on some physical and chemical properties of soil in a grassland area of Uganda. Afr. J. Ecol., 25:147-153. Okwakol, M.J.N., 1988. The present knowledge on soil fauna in East Africa. Rev. Zool. Afr., 102: 323-331. Page, A.L., Miller, R.H. and Keeney, D.R. (Editors), 1982. Methods of Soil Analysis, Part 2: Chemical and Mineralogical Properties. Am. Soc. Agron., Madison, WI, 1159 pp. Roose, E., 1981. Dynamique Actuelle de Sols Ferrallitiques et Ferrigineux Tropicaux d'Afrique Occidentale, Travaux et Documents de I'ORSTOM No. 130, ORSTOM, Paris, 569 pp. Tchenkoua, M. and Moormann, F.R., 1990. Semi-detailed Soil and Land Use Survey of the Future IITA Humid Forest Substation at M'Balmayo (South Cameroon). IITA, Ibadan, 182 PP. Trapnell, C.G., Friend, M.T., Chamberlain, G.T. and Birch, H.F., 1976. The effects of fire and termites on a Zambian woodland soil. J. Ecol., 64: 577-588.
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Elsevier Science Publishers B.V., Amsterdam
Soil properties of termite mounds under different land uses in a Typic Kandiudult of southern Cameroon N.R. Hulugalle and J.N. Ndi International lnstitute of Tropical Agriculture, Humid Forest Zone Station, B.P. 2008, Messa, Yaounde, Cameroon (Accepted 14 April 1992 )
ABSTRACT Hulugalle, N.R. and Ndi, J.N., 1993. Soil properties of termite mounds under different land uses in a Typic Kandiudult of southern Cameroon. Agric. Ecosystems Environ., 43: 69-78. The effect of land use, i.e. 3-4 years of cropping, 2- to 3-year-old Chromolaena odorata fallow and 10- to 15-year-old secondary forest, on soil properties of Microtermes termite mounds in Typic Kandiudults was studied in the humid forest zone of southern Cameroon from November 1990 to March 1991. Termite mound populations increased in the following order: secondary forest greater than fallow greater than cropping. Soil sampled from mound surfaces, mound perimeters (interface of mound and surrounding soil) and surrounding soil was analyzed for various physical and chemical features. Sand and clay contents of soil sampled from the surrounding soil and mound surfaces were primarily influenced by sampling location. The surrounding soil and that from mound surfaces consisted of 58.5% and 39.9% sand, respectively, and 25.6% and 47.9% clay, respectively. Particle size distribution in mound perimeters was, however, dependent on land use. With respect to other soil properties measured, both absolute values and spatial variation between sampling locations were, in general, primarily affected by land use. Bulk density particle size distribution, soil water retention at potentials less than or equal to - 4 . 8 kPa, organic C, total N, pH, exchangeable cations (except total acidity ) and effective cation-exchange capacity contributed significantly to the interactions in spatial variation between sampling locations and land uses.
INTRODUCTION
Detailed studies of termite mounds in tropical soils have shown that in relation to surrounding soil, mound soil can have either higher or lower values of organic carbon, total nitrogen, Bray-l-P, exchangeable Ca, Mg and K, effective cation-exchange capacity, bulk density, aggregate stability, waterholding capacity and water infiltration rates (Trapnell et al., 1976; Kang, 1978; Moormann and Kang, 1978; Roose, 1981; Lal, 1987, 1988; Okwakol, 1987, Correspondence to: N.R. Hulugalle, Agricultural Research Station, N.S.W. Department of Agriculture, PMB, Myall Vale Mail Run, Wee Waa Road, Narrabri, N.S.W. 2390, Australia.
© 1993 Elsevier Science Publishers B.V. All rights reserved 0167-8809/93/$06.00
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N.R. HULUGALLE AND J.N. NDI
1988; Lobry de Bruyn and Conacher, 1990; Brouwer et al., 1991 ). With respect to particle size distribution, however, a consistent pattern emerges with mound soils having higher values of silt and clay, and lower values of sand in relation to bulk soil (Kang, 1978; Lal, 1987, 1988; Okwakol, 1988; Lobry de Bruyn and Conacher, 1990; Brouwer et al., 1991). The contradictions reported in the literature may be caused by variations in site characteristics, termite species and genera, land use at the sampling site and sampling location (Trapnell et al., 1976; Lal, 1987; Dangerfield, 1990; Lobry de Bruyn and Conacher, 1990 ). Water infiltration, for example, is lower on mound surfaces in relation to bulk soil, but higher above the feeding galleries constructed away from the mound (Lal, 1987, 1988). It is, therefore, difficult to generalize on mound characteristics. A better approach is to describe the properties of mound soil for a particular soil type, site and land use, and evaluate them in the context of soil variability and the effects on subsequent crop growth and yield (Kang, 1978; Kang and Moormann, 1978; Lal, 1987). The objective of the present study, therefore, was to quantify the properties of termite mound soils in Typic Kandiudults under three land uses: cropping, fallow and secondary forest, in the humid forest zone of southern Cameroon. MATERIALS AND METHODS
The study was conducted on three adjacent 4-ha (200 m X 200 m) blocks at the Humid Forest Zone Station of the International Institute of Tropical Agriculture located at M'Balmayo, 60 km south of Yaounde (3°51'N, 11 °27'E) in southern Cameroon. M'Balmayo is located in the forest zone of southern Cameroon and has an annual rainfall of 1522 ram. The rainfall pattern is bimodal with rains occurring from March to June followed by a short dry spell of approximately 1 month, which in turn is followed by a second rainy season from August to November. The dry season lasts from November to March. The soil at the experimental site is a clayey, kaolinitic, isohyperthermic, Typic Kandiudult with a sandy clay loam (59% sand, 16% silt, 25% clay) topsoil overlying a clay (29% sand, 8% silt, 63% clay) subsoil. Average depth of topsoil was 0.09 m (range 0.03-0.12 m ). Land use in the three adjacent blocks was (a) 3- to 4-year-old cropped fields consisting primarily of mixtures of cassava (Manihot esculenta Crantz.), maize ( Zea mays L. ), cocoyam ( Xanthosoma sagittifolium L. ), banana and plantain (Musa×paradisiaca L.), oil palm (Elaeis guianensis Jacq.), kolanut ( Cola nitida L. ), cacao ( Theobroma cacao L. ) and papaya ( Carica papaya L.); (b) 2- to 3-year-old natural fallow dominated by Chromolaena odorata L.; (c) 10- to 15-year-old secondary forest. The blocks were delineated, taking care to avoid overlapping of land-use systems, following a land survey of the site (Tchenkoua and Moormann, 1990). The cropped block was cleared manually with a combination of chainsaws, axes and machetes fol-
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
7!
lowed by in situ burning of vegetation residues (Hulugalle, 1992). Before sampling the numbers and location of all termite mounds in each 4 ha block were determined by mapping on a 5 m X 5 m grid. The height of each termite m o u n d was recorded at the same time. Termites obtained from the mounds were identified as belonging to the genus Microtermes. Sampling for soil physical and chemical properties was done from all m o u n d s during the dry season of 1990-1991. Composite samples were obtained at random from five locations in the 0.00-0.10 m depth of m o u n d surfaces, m o u n d perimeters (the interface of the m o u n d and surrounding soil) and the surrounding soil at least 2 m away from the m o u n d perimeter. Airdried, ground subsamples were passed through a sieve with aperture diameters of 2 m m and analyzed for particle size distribution using the hydrometer m e t h o d (Klute, 1986 ), pH ( in water), total N ( Kj eldahl digestion ), Bray- 1 P and 1 N a m m o n i u m acetate-extractable Ca, Mg, K, Mn and Na, and 1 N KCl-extractable total acidity (AI + H) (Page et al., 1982 ). Soil organic carbon was determined by dichromate oxidation (Walkley/Black m e t h o d ) of air-dried, ground subsamples which had been passed through a sieve with aperture diameters of 0.5 m m (Page et al., 1982 ). Soil water retention was determined at saturation and at a potential of - 4 . 8 kPa with a sand box apparatus, and at potentials of - 1 0 , - 3 0 , - 1 0 0 , - 3 0 0 and - 1 5 0 0 kPa with a pressure plate apparatus on disturbed subsamples (not ground) which had been passed through a sieve with aperture diameters of 2 m m and saturated by capillarity for 48 h (Klute, 1986). Five soil cores, 51 m m in length and 50 m m in diameter, were obtained at the same location in the 0.00-0.05 m and 0.05-0.10 m depths. Bulk density of the same cores was determined following oven-drying at 105 ° C. Data were analyzed by analysis of variance using a randomized complete block design model for multiple sites (Federer, 1955; Michigan State University, 1991 ). RESULTS
AND DISCUSSION
Distribution of termite mounds The n u m b e r of termite m o u n d s per unit area increased from cropping to fallowing to secondary forest (i.e. as length of fallow period increased) (Table 1 ). Similar results have been reported for a wide range of environments and termite species, and attributed to increased availability of litter and soil water, and cooler air and soil temperatures with increasing length of fallow (Lal, 1987). In addition, soil C / N ratios may also have contributed to the differing m o u n d populations in the various land uses (Lal, 1987). Soil C / N ratio increased such that values of 10.5, 14.6 and 15.5 ( ___SE = 0.74, P < 0.001 ) were observed with cropping, fallowing and secondary forest, respectively.
72
N.R. HULUGALLEAND J.N. NDI
TABLE 1 Numbers and heights of termite mounds under cropping, fallow, and secondary forest Land use
Numbers per 4 ha
Mound height (m) (x_+ SD )
Cropped Fallow Forest
8 16 25
0.84 _+0.45 0.81 + 0.38 0.82 + 0.44
Average height of termite mounds, however, was similar in all three land uses (Table 1 ).
Soil physical properties Soil bulk density in the 0.00-0.05 m depth was greatest on m o u n d surfaces with cropping and fallowing, but did not differ significantly between sampiing locations under forest (Table 2 ). Bulk density in the 0.05-0.10 m depth differed significantly between sampling locations only under forest and was lowest on m o u n d surfaces. Bulk density of m o u n d surfaces for both depths was, in general, lowest under forest and may be due to greater quantity and quality of organic materials incorporated into the forest m o u n d s in comparison with those in cropped and fallowed fields. Bulk density averaged over 0.00-0.05 m and 0.05-0.10 m depths was related primarily to soil organic carbon thus:
BD= 1.12-0.03C, r=0.65"**, n = 147 where BD is bulk density (Mg m - 3 ) and C is soil organic carbon content (%) in the 0.00-0.10 m depth. Soil organic matter improves soil structure and porosity (Campbell, 1985; Lal, 1987). Sand and silt contents were lower, and clay content was higher on m o u n d surfaces than in the surrounding soil (Table 2). Preferential transport and incorporation of clay particles into termite mounds is a feature of all termite species (Lal, 1987 ). At m o u n d perimeters, however, particle size distribution was determined by land use. Sand and silt contents at the m o u n d perimeter were similar to that of surrounding soil under cropping, intermediate to those of the m o u n d surfaces and surrounding soil under fallow and similar to the m o u n d surfaces under forest. Silt content at the m o u n d perimeter under cropping and fallow was similar to that of surrounding soil, whereas under forest it was lower. However, both m o u n d and surrounding soil in the forested plot had significantly higher and lower levels of sand and clay, respectively, in comparison with m o u n d s in cropped and fallow fields. These differences may reflect the degree of vegetation cover, both spatial and temporal, in each land use. The land use with least cover, i.e. cropping, suffers most soil erosion .(Lal,
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
73
TABLE 2
Effect of land use and sampling location on bulk density ( Mg m - 3) in the 0.00-0.05 m and 0.05-0.10 m depths and particle size distribution (PSD) in the 0.00-0.10 m depth Land use
Cropped
Location
M o u n d surface M o u n d perimeter
Surrounding soil Mean Fallow
Mound surface M o u n d perimeter
Surrounding soil Mean Forest
M o u n d surface M o u n d perimeter Surrounding soil
Mean
Bulk density
PSD ~
Sand
Silt
Clay
0.00-0.05 m
0.05-0.10 m
(%)
(%)
(%)
1.11 0.91 0.99 1.00
0.96 1.01 1.09 1.03
37.3 47.0 48.8 44.3
11.3 16.0 16.0 14.4
51.4 37.0 35.2 41.2
1.19 0.99 1.04 1.07
1.11 1.04 1.10 1.08
37.1 55.6 65.5 52.7
12.5 16.0 16.0 14.8
50.4 28.5 18.5 32.5
0.85 0.93 0.93 0.91
0.78 1.02 1.11 0.97
45.2 44.5 61.2 50.3
13.0 12.5 15.8 13.8
41.9 43.0 23.1 36.0
0.042 0.028 0.048
0.043 0.028 0.049
* * *
NS ** **
+SE Between land uses Between locations Between locations for same or different land uses
1.48 1.02 1.77
0.51 0.36 0.62
1.69 1.08 1.87
Analysis of variance Land uses
Locations Locations × land uses
** *** ***
NS *** **
** *** ***
' Sand, silt and clay have particle diameters of 50-2000/zm, 2-50/tin, and less than 2/tm, respectively.
1987 ), exposing the clay-rich subsoil (Hulugalle, 1991 ). Tillage operations during cropping also exacerbate erosion (Lal, 1987), in addition to bringing up clay-rich subsoil Which at the present site occurs at depths as shallow as 0.07 m.
Soil water content at saturation did not differ significantly between either sampling locations or land uses (Table 3 ). Soil water retention at potentials less than or equal to - 4 . 8 kPa was, however, affected both by land use and sampling location. Significant differences did not occur at any potential under cropping, but under fallow and forest, soil water retention at potentials less than or equal to - 4 . 8 kPa was in the order of mound surfaces greater than mound perimeters greater than surrounding soil. Among land uses, soil water retention at potentials of - 4 . 8 , - 1 0 and - 3 0 kPa increased in the
74
N.R. HULUGALLE AND J.N. NDI
TABLE 3 Effect of land use and sampling location on soil water content ( m 3 m -3) at given potentials ( - k P a ) in the 0.00-0.10 m depth Land use
Cropped
Location
Soil water content (%) 0
4.8
10
30
100
300
1500
M o u n d surface M o u n d perimeter Surrounding soil
59.6 64.9 63.6 62.7
33.5 34.4 33.7 33.9
28.4 26.3 26.1 26.9
21.6 20.6 20.6 20.9
18.1 15.7 16.2 16.7
16.7 14.4 14.8 15.3
15.7 13.6 14.1 14.5
M o u n d surface M o u n d perimeter Surrounding soil
59.3 57.7 55.0 57.4
48.9 40.2 37.2 42.1
24.7 19.1 18.4 20.8
23.9 17.9 14.0 18.6
22.0 17.6 14.1 17.9
18.2 16.2 13.0 15.8
15.9 13.5 10.5 13.3
M o u n d surface M o u n d perimeter Surrounding soil
59.6 62.0 58.8 60.1
36.9 34.7 32.9 34.8
20.2 18.6 16.1 18.3
19.9 16.5 13.5 16.6
19.6 16.4 13.3 16.4
18.5 15.3 12.8 15.5
17.7 13.5 10.5 13.9
Mean Fallow
Mean Forest
Mean
+_SE Between land use Between locations Between locations for same or different land uses
1.92 1.19 2.06
2.03 0.94 1.64
0.91 0.52 0.89
0.89 0.45 0.77
0.86 0.39 0.67
0.77 0.39 0.68
0.75 0.41 0.71
Analysis of variance Land uses Locations Locations × land uses
NS NS NS
* ** **
*** *** *
** *** ***
NS *** ***
NS *** *
NS *** **
order o f cropped greater than fallow greater than forest, whereas that at - 100, - 300 and - 1500 kPa did not differ significantly. The occurrence o f significant differences only at potentials less than or equal to - 4.8 kPa suggests that particle size distribution was a major determinant o f the soil water content values observed (Campbell, 1985; Lal, 1987). Soil water retention at potentials less than or equal to - 4.8 kPa was primarily related to the fine soil component, i.e. clay plus silt, thus:
- 100 kPa:
0=26.47+0.22(Si+Cl), r=0.39"**, n = 147 ; 0 = 9 . 7 2 + 0 . 2 2 (Si+ Cl), r=0.50***, n = 147 ; 0 = 1.89 (Si+ CI) °58, r=0.61***, n = 147 ; 0 = 2 . 7 7 (Si-~-Cl) 0"46,r=0.52"**, n = 147;
- - 3 0 0 kPa:
0=3.04
- 4 . 8 kPa: - 10 kPa: - - 3 0 kPa:
- 1500 kPa: 0 = 1.37
(Siq-Cl) °'41, r=0.60***,
n = 147 ;
(Si+CI) °58, r=0.63"**,
n = 147 ;
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
75
where 0 is soil water content (m 3 m - 3, % ) Si is silt content (%) and CI is clay content (%) in the 0.00-0.10 m depth. Soil organic carbon was not related to soil water retention at any potential. The relatively high levels of soil organic carbon observed in all land uses and sampling locations (see Table 5) may have ensured that it played a minor role in the comparative soil water retention characteristics observed in this study. At this site it was found that where soil organic carbon levels are greater than or equal to 1.5%, large increases in soil organic carbon are accompanied only by small increases in soil water retention. For example, soil water content at saturation, 0 (%) and soil organic carbon content, C (%) were related such that: 0 = 4 9 . 1 6 C °-16, r=0.57"**, n=336.
Soil chemical properties Fertility of surrounding soil under cropping was, in general, superior to that of mound surfaces, with that in the mound perimeter being intermediate (TaTABLE4 Effect o f land use and sampling location on soil pH, organic C, total N and Bray-I-P in the 0.00-0. I 0 m depth L a n d use
Location
pH
Organic C (%)
Total N (%)
Bray- 1-P (mg kg-')
Cropped
M o u n d surface Mound perimeter Surrounding soil
5.8 7.1 6.8 6.5
1.38 2.87 2.33 2.19
O. 172 0.243 0.205 0.207
5.1 8.7 7.6 7.2
Mound surface M o u n d perimeter Surrounding soil
6.1 6.8 5.8 5.7
3.36 3.50 2.91 3.26
0.246 0.243 0.214 0.234
9.2 6.7 5.9 7.3
Mound surface Mound perimeter Surrounding soil
6.2 6.2 5.1 5.8
9.30 3.26 2.42 5.00
0.416 0.221 0.189 0.276
5.7 4.2 2.8 4.2
0.16 0.13 0.22
0.624 0.580 1.004
0.0271 0.0186 0.0323
0.81 0.68 1.18
** ** ***
* * **
NS * ***
* NS NS
Mean Fallow
Mean Forest
Mean
+_SE Between land uses Between locations Between locations for same or different land uses
Analysis of variance L a n d uses Locations Locations × land uses
N.R. HULUGALLE AND J.N. NDI
76 TABLE 5
Effect of land use and sampling location on exchangeable cations and effective cation exchange capacity ( E C E C ) in the 0 . 0 0 - 0 . l0 m d e p t h ( T A - - t o t a l acidity ) Land use
Cropped
Fallow
Forest
Location
Mound surface Mound perimeter Surrounding soil Mean Mound surface Mound perimeter Surrounding soil Mean Mound surface Mound perimeter Surrounding soil Mean
Exchangeable cations and ECEC ( m m o l ( + ) k g - ~) Ca
Mg
K
Na
Mn
TA
ECEC
101,1 112,5 203, 5 139,0 60.0 112, 5 73.2 81.9 l 0 I. 7 92.2 74.8 89.6
17.5 13.8 28.6 20.0 14.0 19.8 15.5 16.4 17.9 19.0 17.4 18.1
3.4 3.0 6.3 4.2 3.4 3.4 2.5 3.1 11.2 2.3 1.9 5.1
2.7 3.7 4.7 3.7 2.0 1.6 1.6 1.8 6.0 1.7 1.5 3.1
1.8 1.9 1.6 1.7 2.0 1.6 1.6 1.8 3.7 1.4 3.0 2.7
4.2 0.5 1.2 2.0 6.9 4.5 4.2 5.2 6.9 6.0 3.9 5.6
130.7 135.3 245.8 170.6 89.3 144.4 99.0 110.9 147.3 122.5 102.6 124.1
+_SE Between land uses Between locations Between locations for same or different land uses
15.32 10.24
2.01 1.36
0.97 0.96
0.49 0.47
0.21 0.23
2.19 0.63
16.4 11.4
17.74
2.35
1.66
0.81
0.39
1.10
19.7
NS NS **
** * *
NS ** NS
Analysis of variance Land uses Locations Locations X land uses
* NS **
NS NS •*
NS NS **
* NS ***
bles 4 and 5 ). This may be because of the release of nutrients from burning of the vegetation residues during land clearance (Hulugalle, 1991 ). With fallowing, however, soil fertility was, in general, highest in the mound perimeter. Erosion of mound surfaces may be the major contributory factor in this instance. Under fallow, erosion and run-off in surrounding soil is low compared with mound surfaces (Lal, 1987). Therefore, lateral movement of nutrients would be negligible, and nutrients washed down from mound surfaces would accumulate at the mound perimeter. Under forest, fertility was greatest on mound surfaces, because erosion losses are negligible under forest.
CONCLUSION
Numbers of termite mounds increased in the order of forest greater than fallow greater than cropping. With respect to all the soil parameters measured during this study, both absolute values and spatial variation among sampling
EFFECT OF LAND USE ON SOIL PROPERTIES OF TERMITE MOUNDS
77
l o c a t i o n s w e r e generally strongly i n f l u e n c e d b y l a n d use a n d past h i s t o r y o f the sites. It is, t h e r e f o r e difficult to d e f i n e a ' t y p i c a l ' t e r m i t e m o u n d in t e r m s o f soil p r o p e r t i e s p e r se, a n d in p r a c t i c e t e r m i t e m o u n d s s h o u l d be specified in t e r m s o f p r e s e n t l a n d use a n d past h i s t o r y o f the site in a d d i t i o n to o t h e r e n v i r o n m e n t a l p a r a m e t e r s such as soil type, rainfall, v e g e t a t i o n a n d d e p t h to water-table. A m o n g the soil p a r a m e t e r s m e a s u r e d , t h o s e w h i c h c o n t r i b u t e d significantly to the i n t e r a c t i o n s in spatial v a r i a t i o n b e t w e e n s a m p l i n g locat i o n s a n d l a n d uses w e r e b u l k density, silt a n d clay c o n t e n t s , soil w a t e r retent i o n at p o t e n t i a l s less t h a n o r e q u a l to - 4 . 8 kPa, o r g a n i c C, total N, p H , exc h a n g e a b l e c a t i o n s ( e x c e p t total a c i d i t y ) a n d effective c a t i o n - e x c h a n g e capacity. ACKNOWLEDGMENTS T h e assistance o f Dr. J.B. Suh o f the I n t e r n a t i o n a l I n s t i t u t e o f T r o p i c a l Agriculture, Ibadan, Nigeria, in identifying the t e r m i t e s is greatly appreciated.
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Okwakol, M.J.N., 1987. Effect of Cubitermes testaceus (Williams) on some physical and chemical properties of soil in a grassland area of Uganda. Afr. J. Ecol., 25:147-153. Okwakol, M.J.N., 1988. The present knowledge on soil fauna in East Africa. Rev. Zool. Afr., 102: 323-331. Page, A.L., Miller, R.H. and Keeney, D.R. (Editors), 1982. Methods of Soil Analysis, Part 2: Chemical and Mineralogical Properties. Am. Soc. Agron., Madison, WI, 1159 pp. Roose, E., 1981. Dynamique Actuelle de Sols Ferrallitiques et Ferrigineux Tropicaux d'Afrique Occidentale, Travaux et Documents de I'ORSTOM No. 130, ORSTOM, Paris, 569 pp. Tchenkoua, M. and Moormann, F.R., 1990. Semi-detailed Soil and Land Use Survey of the Future IITA Humid Forest Substation at M'Balmayo (South Cameroon). IITA, Ibadan, 182 PP. Trapnell, C.G., Friend, M.T., Chamberlain, G.T. and Birch, H.F., 1976. The effects of fire and termites on a Zambian woodland soil. J. Ecol., 64: 577-588.