Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol53.Issue1.Nov1999:
Soil & Tillage Research 53 (1999) 59±70
Soil quality effects of accelerated erosion and management
systems in three eco-regions of Tanzania
F.B.S. Kaihuraa, I.K. Kullayab, M. Kilasarac,
J.B. Auned, B.R. Singhe, R. Lalf,*
a
Ukiriguru Agriculture Research Institute, PO Box 1433, Mwanze, Tanzania
Agricultural Research Institute Lyamungu, PO Box 3004, Moshi, Tanzania
c
Sokoine University of Agriculture, Soil Science Department, PO Box 3008, Morogoro, Tanzania
d
Centre for International Environment and Development Studies-Noragric, NLH, Aas, Norway
e
Department of Soil Science, NLH, Aas, Norway
f
School of Natural Resources, Ohio State University, 2021 Coffey Road, Columbus, OH 43210-1085, USA
b
Received 27 May 1999; received in revised form 8 July 1999; accepted 15 July 1999
Abstract
Soil erosion can adversely in¯uence soil quality, especially in tropical soils. Thus, a multi-location ®eld experiment was
conducted on eight major agricultural soils with different degrees of erosion, in three eco-regions in Tanzania. The objective
was to assess the impact of topsoil depth (TSD) and management on soil properties. Three eco-regions comprising of humid at
Kilimanjaro, sub-humid at Tanga and sub-humid/semi-arid at Morogoro were selected. There were a total of eight locations
within three eco-regions comprising two at Kilimanjaro (e.g., Kirima Boro and Xeno Helena), two at Tanga (Mlingano 1 and
Mlingano 2) and four at Morogoro (Misu®ni 1, Misu®ni 2, Misu®ni 3, and Mindu). The soil management treatments consisted
of farmyard manure (FYM), N and P fertilizer, tie-ridging and farmers' practice. Plant nutrient content was generally lowest
on severely eroded and the highest on least eroded soil classes. Soil pH decreased with increasing severity of erosion on soils
with higher content of Ca2 in the sub-surface. In general, there occurred a decline in soil organic carbon (SOC) and P with
the decrease in TSD. The SOC content decreased on severely eroded soil class by 0.16%, 0.39% and 0.13% at Misu®ni 1,
Mlingano 1 and Kirima Boro, respectively, compared to slightly or least eroded soil class. Corresponding decline in available
P at these sites was 41%, 62% and 61%, respectively. Application of FYM signi®cantly increased soil pH at some sites. Soil
content of SOC, N, P, K and Mg were signi®cantly increased by FYM application. Signi®cant effects of N and P fertilizers on
SOC and P were observed at most sites. In comparison with farmer's practice, FYM application increased SOC by 0.55%, N
by 0.03%, P by six-fold and K by two-fold. Nitrogen and phosphorus fertilizers had comparable effects for SOC and P only at
some sites. The results indicate that FYM is a better soil input than N and P fertilizers in improving soil quality. The data show
that SOC, N and P are most adversely affected with accelerated erosion and that FYM fertilizer applications have the potential
to improve fertility of eroded soils. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Soil degradation; Tropical soils; Maize; Cowpeas; Sub-Saharan Africa; Erosion and productivity
*
Corresponding author. Tel.: 1-614-292-2265; fax: 1-614-292-7432
E-mail address: [email protected] (R. Lal)
0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 7 7 - X
60
F.B.S. Kaihura et al. / Soil & Tillage Research 53 (1999) 59±70
1. Introduction
Soil erosion is a major threat to sustainable use of
soil and water resources (Lal, 1998). The threat is
more serious for the soils of the tropics that are highly
susceptible to erosion and other degradative processes.
Erosion in¯uences several soil properties, e.g., topsoil
depth (TSD), soil organic carbon (SOC) content,
nutrient status, soil texture and structure, available
water holding capacity (AWC) and water transmission characteristics that regulate soil quality and
determine crop yield. Lal (1988) indicated that low
levels of N, P, K, and low cation exchange capacity
(CEC) are among the most important chemical and
nutritional constraints accentuated by soil erosion. Soil
erosion also decreases the AWC (Nizeyimana and
Olson, 1988) and SOC content (Rhoton and Tyler,
1990) and increases soil bulk density (Frye et al.,
1982).
Experiments conducted on Ultisols in Nigeria
showed that maize (Zea mays L.) yield reductions
were 95%, 95% and 100% with 5, 10 and 20 cm removal of TSD, respectively (Mbagwu et al., 1984). For
the same TSD removals on an Al®sol, yield reductions
were 31%, 74% and 94%, respectively. The corresponding yield reductions on an Al®sol at Ilora in
Nigeria were 73%, 83% and 94%, respectively. In all
cases no fertilizer combination was effective in restoring maize yield when TSD was reduced by 10 or
20 cm (Mbagwu et al., 1984). Experiments relating
effects of natural erosion on crop yield have indicated
that the effects are even more severe than that of
arti®cial topsoil removal. Lal (1981) observed that
over a ®ve-year period, the grain yield of maize and
cowpeas (Vigna unguiculata L. Walp.) decreased at
the rate of 9 and 0.7 kg Mgÿ1 of soil loss, respectively.
In another experiment, Lal (1985) observed that maize
yield was reduced 16 times more due to topsoil loss
from natural erosion compared to mechanical topsoil
removal. In some cases, soil quality degraded by
erosion can be improved by judicious use of inputs
and improved soil management practices. Gajri et al.
(1994) observed that application of farmyard manure
(FYM) improved AWC and root growth in soils with
unstable structure and low SOC content. Conventional
or no-tillage plus mulching improved the soil hydrothermal regime, resulting greater root growth, nutrient
uptake and grain yields of maize and wheat (Triticum
aestivum L.) on a Typic Hapludalf in India (Acharya
and Sharma, 1994).
In Tanzania, accelerated erosion has occurred since
the pre-colonial period, but the severity and magnitude
of damage had not been adequately assessed. Most of
the work done so far concentrated on assessment of the
amount of soil loss. Ahn (1977) reported that the
Kondoa and Uluguru mountains in central and eastern
Tanzania, respectively, were severely affected by erosion. Ngatunga et al. (1984) observed that soil loss was
greatest on bare fallow soil compared to plowed,
mulched or natural grass conditions. Soil loss ranged
from 38 to 88 Mg haÿ1 on 10% to 22% slope under
bare fallow conditions as compared to 0.08 to
0.10 Mg haÿ1 under natural grass cover for the same
slopes. Recent studies conducted on eight major agricultural soils in Kilimanjaro, Tanga and Morogoro
ecological regions of Tanzania indicated that decrease
in TSD adversely affected a number of soil properties
including SOC, CEC, pH, total soil N (TSN), available
P, AWC, and water saturation percentage (Kaihura et
al., 1996). It was also observed that maize grain yield
was positively and signi®cantly correlated with TSD,
SOC, TSN, CEC, and AWC. Maize yield declined at
38.5, 55 and 87.7 kg cmÿ1 decrease in TSD in Kilimanjaro, Tanga and Morogoro eco-regions, respectively.
Despite numerous world wide reports on the magnitude and extent of soil erosion and its adverse effects
on soil quality and crop yields, little research has been
done in sub-Saharan Africa on soil management techniques to restore productivity of eroded soils. Therefore, this study was conducted to evaluate the potential
of selected soil management practices on improving
soil physical and chemical qualities of eroded soils in
three eco-regions of Tanzania.
2. Materials and methods
2.1. Identification of erosion classes
The experiments were conducted on eight major
agricultural soils with different degrees of erosion in
three ecological regions in Tanzania. Eco-region characteristics, as described by De Pauw (1984), and
antecedent soil properties for each soil type are presented in Table 1. Recognizing that TSD can be
61
F.B.S. Kaihura et al. / Soil & Tillage Research 53 (1999) 59±70
Table 1
Eco-regions, soil types and selected topsoil properties for each soil type at the beginning of the experiment in 1992
Eco-region
Soil type
Location
pH
(H2O)
SOC
(g kgÿ1)
N
(g kgÿ1)
Av-P
(mg kgÿ1)
Taxonomy
FAO
Kilimanjaro (humid)
Umbric Hapludalfs
Umbric Hapludalfs
Humic Nitisols
Humic Nitisols
Kirima Boro
Xeno Helena
7.0
6.0
24
20
2.1
1.4
38.0
7.6
Tanga (sub-humid)
Tropeptic Haplustox
Typic Rhodustalfs
Rhodic Ferralsols
Haplic Lixisol
Mlingano 1
Mlingano 2
6.6
6.5
27
23
2.2
1.9
4.0
4.0
Morogoro
(sub-humid/
semi-arid)
Lithic Eutrochrepts
Typic Eutrochrepts
Typic Rhodustalfs
Ultic Haplustalfs
Eutric Cambisols
Chromic Cambisols
Chromic Luvisols
Haplic Alfisols
Misufini 1
Misufini 2
Misufini 3
Mindu
6.5
6.6
6.3
5.8
12
11
10
12
1.1
1.2
1.2
1.1
Soil quality effects of accelerated erosion and management
systems in three eco-regions of Tanzania
F.B.S. Kaihuraa, I.K. Kullayab, M. Kilasarac,
J.B. Auned, B.R. Singhe, R. Lalf,*
a
Ukiriguru Agriculture Research Institute, PO Box 1433, Mwanze, Tanzania
Agricultural Research Institute Lyamungu, PO Box 3004, Moshi, Tanzania
c
Sokoine University of Agriculture, Soil Science Department, PO Box 3008, Morogoro, Tanzania
d
Centre for International Environment and Development Studies-Noragric, NLH, Aas, Norway
e
Department of Soil Science, NLH, Aas, Norway
f
School of Natural Resources, Ohio State University, 2021 Coffey Road, Columbus, OH 43210-1085, USA
b
Received 27 May 1999; received in revised form 8 July 1999; accepted 15 July 1999
Abstract
Soil erosion can adversely in¯uence soil quality, especially in tropical soils. Thus, a multi-location ®eld experiment was
conducted on eight major agricultural soils with different degrees of erosion, in three eco-regions in Tanzania. The objective
was to assess the impact of topsoil depth (TSD) and management on soil properties. Three eco-regions comprising of humid at
Kilimanjaro, sub-humid at Tanga and sub-humid/semi-arid at Morogoro were selected. There were a total of eight locations
within three eco-regions comprising two at Kilimanjaro (e.g., Kirima Boro and Xeno Helena), two at Tanga (Mlingano 1 and
Mlingano 2) and four at Morogoro (Misu®ni 1, Misu®ni 2, Misu®ni 3, and Mindu). The soil management treatments consisted
of farmyard manure (FYM), N and P fertilizer, tie-ridging and farmers' practice. Plant nutrient content was generally lowest
on severely eroded and the highest on least eroded soil classes. Soil pH decreased with increasing severity of erosion on soils
with higher content of Ca2 in the sub-surface. In general, there occurred a decline in soil organic carbon (SOC) and P with
the decrease in TSD. The SOC content decreased on severely eroded soil class by 0.16%, 0.39% and 0.13% at Misu®ni 1,
Mlingano 1 and Kirima Boro, respectively, compared to slightly or least eroded soil class. Corresponding decline in available
P at these sites was 41%, 62% and 61%, respectively. Application of FYM signi®cantly increased soil pH at some sites. Soil
content of SOC, N, P, K and Mg were signi®cantly increased by FYM application. Signi®cant effects of N and P fertilizers on
SOC and P were observed at most sites. In comparison with farmer's practice, FYM application increased SOC by 0.55%, N
by 0.03%, P by six-fold and K by two-fold. Nitrogen and phosphorus fertilizers had comparable effects for SOC and P only at
some sites. The results indicate that FYM is a better soil input than N and P fertilizers in improving soil quality. The data show
that SOC, N and P are most adversely affected with accelerated erosion and that FYM fertilizer applications have the potential
to improve fertility of eroded soils. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Soil degradation; Tropical soils; Maize; Cowpeas; Sub-Saharan Africa; Erosion and productivity
*
Corresponding author. Tel.: 1-614-292-2265; fax: 1-614-292-7432
E-mail address: [email protected] (R. Lal)
0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 7 7 - X
60
F.B.S. Kaihura et al. / Soil & Tillage Research 53 (1999) 59±70
1. Introduction
Soil erosion is a major threat to sustainable use of
soil and water resources (Lal, 1998). The threat is
more serious for the soils of the tropics that are highly
susceptible to erosion and other degradative processes.
Erosion in¯uences several soil properties, e.g., topsoil
depth (TSD), soil organic carbon (SOC) content,
nutrient status, soil texture and structure, available
water holding capacity (AWC) and water transmission characteristics that regulate soil quality and
determine crop yield. Lal (1988) indicated that low
levels of N, P, K, and low cation exchange capacity
(CEC) are among the most important chemical and
nutritional constraints accentuated by soil erosion. Soil
erosion also decreases the AWC (Nizeyimana and
Olson, 1988) and SOC content (Rhoton and Tyler,
1990) and increases soil bulk density (Frye et al.,
1982).
Experiments conducted on Ultisols in Nigeria
showed that maize (Zea mays L.) yield reductions
were 95%, 95% and 100% with 5, 10 and 20 cm removal of TSD, respectively (Mbagwu et al., 1984). For
the same TSD removals on an Al®sol, yield reductions
were 31%, 74% and 94%, respectively. The corresponding yield reductions on an Al®sol at Ilora in
Nigeria were 73%, 83% and 94%, respectively. In all
cases no fertilizer combination was effective in restoring maize yield when TSD was reduced by 10 or
20 cm (Mbagwu et al., 1984). Experiments relating
effects of natural erosion on crop yield have indicated
that the effects are even more severe than that of
arti®cial topsoil removal. Lal (1981) observed that
over a ®ve-year period, the grain yield of maize and
cowpeas (Vigna unguiculata L. Walp.) decreased at
the rate of 9 and 0.7 kg Mgÿ1 of soil loss, respectively.
In another experiment, Lal (1985) observed that maize
yield was reduced 16 times more due to topsoil loss
from natural erosion compared to mechanical topsoil
removal. In some cases, soil quality degraded by
erosion can be improved by judicious use of inputs
and improved soil management practices. Gajri et al.
(1994) observed that application of farmyard manure
(FYM) improved AWC and root growth in soils with
unstable structure and low SOC content. Conventional
or no-tillage plus mulching improved the soil hydrothermal regime, resulting greater root growth, nutrient
uptake and grain yields of maize and wheat (Triticum
aestivum L.) on a Typic Hapludalf in India (Acharya
and Sharma, 1994).
In Tanzania, accelerated erosion has occurred since
the pre-colonial period, but the severity and magnitude
of damage had not been adequately assessed. Most of
the work done so far concentrated on assessment of the
amount of soil loss. Ahn (1977) reported that the
Kondoa and Uluguru mountains in central and eastern
Tanzania, respectively, were severely affected by erosion. Ngatunga et al. (1984) observed that soil loss was
greatest on bare fallow soil compared to plowed,
mulched or natural grass conditions. Soil loss ranged
from 38 to 88 Mg haÿ1 on 10% to 22% slope under
bare fallow conditions as compared to 0.08 to
0.10 Mg haÿ1 under natural grass cover for the same
slopes. Recent studies conducted on eight major agricultural soils in Kilimanjaro, Tanga and Morogoro
ecological regions of Tanzania indicated that decrease
in TSD adversely affected a number of soil properties
including SOC, CEC, pH, total soil N (TSN), available
P, AWC, and water saturation percentage (Kaihura et
al., 1996). It was also observed that maize grain yield
was positively and signi®cantly correlated with TSD,
SOC, TSN, CEC, and AWC. Maize yield declined at
38.5, 55 and 87.7 kg cmÿ1 decrease in TSD in Kilimanjaro, Tanga and Morogoro eco-regions, respectively.
Despite numerous world wide reports on the magnitude and extent of soil erosion and its adverse effects
on soil quality and crop yields, little research has been
done in sub-Saharan Africa on soil management techniques to restore productivity of eroded soils. Therefore, this study was conducted to evaluate the potential
of selected soil management practices on improving
soil physical and chemical qualities of eroded soils in
three eco-regions of Tanzania.
2. Materials and methods
2.1. Identification of erosion classes
The experiments were conducted on eight major
agricultural soils with different degrees of erosion in
three ecological regions in Tanzania. Eco-region characteristics, as described by De Pauw (1984), and
antecedent soil properties for each soil type are presented in Table 1. Recognizing that TSD can be
61
F.B.S. Kaihura et al. / Soil & Tillage Research 53 (1999) 59±70
Table 1
Eco-regions, soil types and selected topsoil properties for each soil type at the beginning of the experiment in 1992
Eco-region
Soil type
Location
pH
(H2O)
SOC
(g kgÿ1)
N
(g kgÿ1)
Av-P
(mg kgÿ1)
Taxonomy
FAO
Kilimanjaro (humid)
Umbric Hapludalfs
Umbric Hapludalfs
Humic Nitisols
Humic Nitisols
Kirima Boro
Xeno Helena
7.0
6.0
24
20
2.1
1.4
38.0
7.6
Tanga (sub-humid)
Tropeptic Haplustox
Typic Rhodustalfs
Rhodic Ferralsols
Haplic Lixisol
Mlingano 1
Mlingano 2
6.6
6.5
27
23
2.2
1.9
4.0
4.0
Morogoro
(sub-humid/
semi-arid)
Lithic Eutrochrepts
Typic Eutrochrepts
Typic Rhodustalfs
Ultic Haplustalfs
Eutric Cambisols
Chromic Cambisols
Chromic Luvisols
Haplic Alfisols
Misufini 1
Misufini 2
Misufini 3
Mindu
6.5
6.6
6.3
5.8
12
11
10
12
1.1
1.2
1.2
1.1