Decomposition of Litters of Agroforestry Tree Legumes Suitable for
Soil Productivity in Niger Delta Region of Nigeria.
P. O. Anegbeh1*, M. A. Amakiri2 , T. A. T. Wahua2 and E. E Opuwaribo2
*
Corresponding Author
World Agroforestry Centre (International Centre for Research in Agroforestry ICRAF),
International Institute of Tropical Agriculture (IITA),
IITA High Rainfall Station, Onne, Port Harcourt
P. M. B. 008, Nchia, Rivers State, Nigeria. Tel: 002348036686093
Email: P.Anegbeh@cgiar.org or anegbehpaulo@yahoo.com
1
2
Rivers State University of Science and Technology
P. M. B. 5080, Port Harcourt
Rivers State, Nigeria
ABSTRACT
Decomposition of leafy biomass was performed using litterbags at the International
Institute of Tropical Agriculture, Onne, Rivers State to determine the decomposition rate
of three Agroforestry tree legumes in order to understand the specific food crops to be
grown between the biologically different tree species in Niger Delta Region.
Enterolobium cyclocarpum decomposed faster than Millettia laurentii and Inga edulis.
Overall, a lineal downward trend is indicated, representing exponential decay of the
litters. For E. cyclocarpum the decomposition apparently slowed down when about 2 %
of the original amount was left. For M. laurentii, this happened when 36 % was left and
for I. edulis when 75 % was left. The time required for 50% loss of dry weight for the
litters was about one week for E. cyclocarpum, twelve weeks for M. laurentii and over
sixteen weeks for I. edulis. The relative rate of decomposition of the three tree species
was Enterolobium > Millettia > Inga. Enterolobium cyclocarpum litters are
recommended for maize and vegetable cropping. Millettia laurentii is recommended for
Pineapple and I. edulis for cassava, yam, plantain, edible fruit and medicinal trees.
INTRODUCTION
The key to sustainability and to increasing soil productivity is resource management of
land where soil fertility levels have been severely depleted during the cropping cycle.
Current and future needs for the production of food, fodder, fuelwood and for soil fertility
improvement in Niger Delta necessitate studying the decomposition rate (rate of dry
matter loss) of leaves of Agroforestry tree species. This is part of the efforts to enhance
sustainability and to restore degraded land of Niger Delta to its former productivity
status. The productivity of such lands and subsequently, the yields of the food crops
increased with additions of organic matter as prunings or as mulch. The mulch is
decomposed by soil organisms under the influence of the soil physico-chemical
environment, other soil conditions, and resource quality to release adequate nutrients to
the soil for sustainable production.
High salt concentration in the soil is a serious problem in vast areas of otherwise
productive agricultural lands in Nigeria (Opuwaribo and Odu, 1978), particularly in
Niger Delta Region of Nigeria. Establishment of salt tolerant Agroforestry species such
as Enterolobium cyclocarpum, Inga edulis and Millettia laurentii could be an effective
way of ameliorating this problem (Anegbeh and Tchoundjeu, 2002).
In view of the current food shortages in most parts of Nigeria (especially Niger Delta),
the question most often asked is how biochemical properties of soil in tropical
environments can be sustained. Anegbeh (1997) was of the view that improving
earthworm activities, maintaining favourable levels of organic matter and soil
biochemical properties, preventing soil erosion, and replenishing plant nutrients leached
out or removed by crops using tested Agroforestry species are required in sustaining high
biological properties and hence soil productivity.
The age-old practice of Agroforestry, which combines the cultivation of trees with
Agricultural crops and livestock can help solve problem of land degradation by
preserving soil quality and preventing soil erosion. Soil erosion has rendered
unproductive vast areas of Nigeria especially Niger Delta. Agroforestry trees tap
nutrients deep in the soil and draw them back to crop root zones through fallen leaves,
mulching and surface root decay.
Therefore, by growing mixtures of selected trees and crops, and using short fallow
cycles of one to three years, farmers are able to improve soil quality and increase their
crop yields. Anegbeh (1997) experimented nodulation and fixation by Enterolobium
cyclocarpum, Indigifera zollingeriana, Inga edulis, Millettia laurentii and reported that
the four tree legumes in hedgerow intercropping system increase yields of maize and
cassava. Although the amounts of nitrogen fixed biologically by leguminous trees are
still a matter of investigation, 40 Kg N ha-1 yr-1 for Inga trees in coffee fields in
Mexico is considered an acceptable figure [Roskoski, 1982].
MATERIALS AND METHODS
The study was carried out from 1994 to 1997 at the High Rainfall Station of the
International Institute of Tropical Agriculture (IITA) Onne, Nigeria (040 51' N Latitude
070 03' E Longitude). Mean annual rainfall is 2,300 mm (Tables 1 and 2) in a
monomodal distribution falling in one season (March - November). Elevation is 30 m.
The Field of the station consists mainly of flat land (level topography). Soils are Ultisols
derived from coastal sediments. They are strongly acid (pH 4.4) and of low fertility. They
are classified as loamy, siliceous, isohyperthermic, typic paleudult (coarse-loamy)
(Hulugalle et al., 1989). These soils are deep, well drained with good physical properties
but chemically poor. Temperature varied from 280 C in February and March (warmest
months) to 250 C in July (coolest month). Relative Humidity varied from 70 % in
February (driest month) to 84 % in July (rainy month) (Anegbeh, 1997). Sunshine also
varied from 2 hrs per day (September) to 6 hrs per day (February).
Trees of the three Agroforestry species were established in hedgerows in1994 using a
spacing of 4 m x 0.5 m. In 1995, the trees were cut back to prevent shading of associated
food crops in the Agroforestry system. From 1996 to 1997, decomposition of biomass
was performed using litterbags. In the field, mulch materials for the experiment were
obtained by collecting leaves from the different species. Prior to deposition of litter bags
on the soil surface, air-dried samples of the different species were collected and oven
dried until constant weight was achieved. The dry weight samples were re-weighed to
determine the dry matter contained in each of the air-dried samples of the species.
Stainless litterbags, each measuring 90 cm x 50 cm with a mesh size of 2 mm, were filled
with 2.3 kg of the oven-dried leaves (0.75kg leaves from each of the species). The
litterbags were placed on the soil surface in the field during the rainy season (June to
September, each year).
After deposition in the field, three randomly selected litterbags per species were sampled
and retrieved weekly. The samples were collected in replicates of three and taken to the
laboratory where they were sorted out to remove live weeds growing into the samples,
other materials such as roots, soil and cassava leaves that were not part of the original
samples. The litter samples were put in paper bags, oven dried at 650 C until constant
weights were achieved and the dry weights were determined using a mettler balance.
Observations on decomposition rates were made by observing how long it took for
mulch, once applied on the soil surface to decompose into humus. Comparison was made
based on the weights difference. Analysis was done using statistical analysis system
(SAS, 1996).
The decomposition rate constant (K) was determined from the negative exponential
decay model of Olson (1963) as follows:
Wt / Wo = Wo e -kt
where, Wo is the initial weight and Wt is the remaining weight at time exponential
function.
The negative exponential model of Olson 1963 is a predictive equation, which expresses
the relationship between time and decomposition of plant residues.
The equation describes the pattern of decomposition. The exponential equation could be
linearized by log transformation as InYt = InP-Kt and fit to data. One of the advantages
of the mathematical approach is that the exponential decline coefficient (k) can be
compared between substrates and sites when the coefficient is calculated on a relative
basis (litter remaining/initial litter) and the unit of time are the same. The objective of the
trial was to collect litter and determine the decomposition rate of the three Agroforestry
species in order to understand the specific food crops to be grown in association with the
different tree species.
RESULTS AND DISCUSSION
Considerable variation in decomposition rates of the different litter types was found. The
dry weight remaining in the litter-bags sampled over a period of 16 weeks is shown in
Fig. 1. At two weeks after placement of litter, Enterolobium cyclocarpum leaf mulch
decomposed faster than other woody species as there was less litter remaining for E.
cyclocarpum than for other species. From week four to eight, the most rapid
decomposition litter occurred in E. cyclocarpum. At final assessment time (16 weeks
after litter decomposition), the rate of decomposition was most rapid for E. cyclocarpum
(Fig. 1). The most rapid decomposition recorded for Enterolobium pruning was in
agreement with its high N-content. Inga residues with a low N-content had a relatively
slow decomposition. Interestingly, the combination of a high N-content and a slow
decomposition, as observed in Millettia laurentii, leads to both a considerable
contribution to crop N-nutrition and a large residue adding to the organic matter content
of the soil. Millettia litter might thus form a good compromise between the two functions
of litter inputs.
The litter-bag technique remains one of the most convenient methods for comparing
decomposition process among woody species. For example, working on some tropical
legumes, Fox et al., (1990) and Palm and Sanchez (1991) stated that leaves of woody
species decomposed and released N at different rates and that the rate of decomposition
depended on the polyphenolic, lignin and N content of the leaves. Crop benefits from the
nitrogen and other nutrients supplied when the leaves are applied as mulch to the soil
(Read et al., 1985; Gichuru, 1991; Mulongoy and Gasser, 1993). Also, Amakiri and
Nwoboshi (1988) studied the microbial biomass and the nutrient dynamics of a managed
teak plantation in Nigeria. They stated in their results that high microbial population
occurred between May and October as a result of litter quality and soil moisture content
during the period. By supplying biologically fixed nitrogen, the woody species especially
if nitrogen-fixers, therefore have the potential to reduce the nitrogen requirement of the
companion food crops for inorganic fertilizer nitrogen.
Many factors are known to influence the rate of decomposition of plant materials and
various workers have confirmed these. For example, Tian et al., (1992) studied the
decomposition and nutrient release of prunings of Gliricidia sepium, Leucaena
leucocephala, Acioa barteri (Dactyladenia barteri Hook ex Olw), maize stover and rice
straw in the field. They explained that Gliricidia sepium had low C : N ratio, lignin, silica
and polyphenol content while Leucaena leucocephala prunings had similar results but for
its high polyphenol content. Rice straw had high silica content. They observed that
nutrient immobilization occurred with N in maize stover and rice straw, P in Leucaena
prunings and rice straw, Ca in rice straw, maize stover, Gliricidia and Leucaena
prunings. They concluded that plant residue with low C : N ratio, lignin and polyphenol
content, decomposed and released nutrient faster. Woody species with high nitrogen
content, ash and acid detergent cell wall decomposes rapidly (Gupta and Sing, 1981).
Similarly, changes in nitrogen concentration with time, weather and shade (Wahua and
Miller, 1978) are factors known to influence the rate of decomposition of plant material.
For example, Swift et al., (1981) reported that rapid decomposition of leaf litter occurred
during the rainy season when microbial population was increased. The work of Okeke
and Omaliko (1991), at Ozala in southeastern Nigeria showed that nutrient accretion to
the soil via throughfall was higher in macroelements, except Mg, than open-fall and leaf
litter. The development of agroforestry systems and procedures for biological
manipulation of organic matter offers potential for introducing environmentally friendly
and economic management practices that can provide significant reductions in
requirements for application of polluting and costly agro-chemicals such as inorganic
fertilizers to Niger Delta Region of Nigeria.
CONCLUSION
Farmers should be encouraged to use organic residues to supply nutrient to crops in order
to expect results in the short term. In light of the decomposition of the three litter types,
Enterolobium would be a better soil amendment in the short term than Inga and Millettia,
hence Enterolobium is preferred to Inga and Millettia litter for maize and vegetable
production. Inga and Millettia, due to their slow decomposition, would be a better source
of organic matter than Enterolobium litter and are suitable for cassava, yam, Banana and
Plantain, and perennial crops production. It appears that Inga with slow decomposition
rate contain high tannins in its leaves which may inhibit microbial decomposition. This
requires further study.
All the Agroforestry tree species used in this study are capable of contributing substantial
quantities of organic matter as litter-fall in Niger Delta. Since fertilizer - an essential
input for maize, cassava, yam and vegetables production in Nigeria - is very expensive
and out of reach of the small-scale farmers, available low-cost organic fertilizer (leaves of
Enterolobium, Millettia and Inga.) is recommended to increase food production and to
ward off starvation and malnutrition. This valuable resource must be sourced locally to
minimize the needs for expensive inorganic fertilizer.
Since Agroforestry involves the integration of trees with food crops, farm productivity
and profitability actually increase. If the findings from this work can be adopted on a
larger scale, such an Agroforestry system would have clear potential to improve food and
economic security in rural farming populations of the Niger Delta. From a practical and a
biological point of view, the theoretical potential of Agroforestry system is beyond
dispute as highlighted in this study.
REFERENCES.
Anegbeh, P. O. and Tchoundjeu, Z. (2002). Nodulation in Some Agroforestry Tree and
Shrub Legumes Grown on Acid Soils in Southeast Nigeria. Improvement and
Culture of Nitrogen Fixing Trees 5 (1): 2-3
Anegbeh, P. O. (1997). Evaluation of Selected Woody Species for Agroforestry Systems
on Acid Soils of Onne, Southeast Nigeria. Ph.D Thesis. Department of Crop/Soil
Science and Forestry. Rivers State University of Science and Technology. Port
Harcourt. 260p.
Amakiri, M. A. and Nwoboshi, L. C. (1988). Nutrient cycling in managed teak
plantation. Nigerian Journal of Science 22 (1/2): 9-12.
Fox, R. H., Meyers, R. J. K. and Vallis, I. (1990). The nitrogen mineralization rate of
legume residue in soil as influence by their polyphenol, lignin and N content.
Plant and Soil 129: 251-259.
Gichuru, M. P. (1991). Residual effect of natural bush, Cajanus cajan and Tephrosia
candida on the productivity of an acid soil in southern Nigeria. Plant and Soil.
134: 31-36.
Gupta, S. R. and Singh, J. S. (1981). The effect of plant species, weather variables and
chemical composition of plant materials on decomposition in a Tropical
Grassland. Plant and Soil 59: 99-117.
Hulugalle, N. R., Lal, R. and Gichuru, M. (1989). Effects of five years of no-tillage and
mulch on soil properties and tuber yield of cassava on an acid Ultisol in
southeastern Nigeria. Experimental Agriculture 26: 235-240.
Mulongoy, K. and Gasser, M. O. (1993). Nitrogen supply capacity of leaves of
Dactyladenia barteri (Hook ex Olw) and Leucaena leucocephala (Lam.) de Wit
in two soils of different acidity from Southern Nigeria. Biology and Fertility of
Soils 16: 57-62.
Okeke, A. I. and Omaliko, C. P. E. (1991). Nutrients accretion to the soil via litterfall and
throughfall in Dactyladenia barterii at Ozala, Nigeria. Agroforestry Systems 16:
39-59.
Olson, J. S. (1963). Energy storage and balance of producer and decomposers in
ecological systems. Ecology 44: 322-331.
Opuwaribo, E. E. and Odu, C. T. I. (1978). Ammonium Fixation in Nigerian Soils: 5.
Types of Clay minerals and relationship with ammonium fixation. Soil Science
125 (5): 283-293.
Palm, C. A. and Sanchez, P. A. (1991). Nitrogen release from the leaves of some tropical
legumes as affected by their lignin and polyphenolic contents. Soil Biology and
Biochemistry 23: 83-88.
Read, M. D., Kang, B. T. and Wilson, G. F. (1985). Use of Leucaena leucocephala leaves
as a nitrogen source for crop production. Fertilizer Research 8: 107-116
Roskoski, J. P. (1982). Nitrogen fixation in a Mexican coffee plantation. Plant and Soil
67: 283-291.
SAS, (1996). Statistical Analysis Systems. SAS procedures guide for personal computer,
Release 6.12 edition. SAS Incorporation, Cary NC. USA. 112 p.
Swift, M. J., Smith, A. R. and Perfect, J. J. (1981). Decomposition and mineral nutrient
dynamics of plant litter regeneration bush fallow in sub-humid tropical Nigeria. J.
Ecol. 69: 981-995.
Tian, G., Kang, B. T. and Brussaard, L. (1992). Biological effect of plant residues with
contrasting chemical composition and nutrient release. Soil Biol. and Biochem. 24
(10): 1051-1060.
Wahua, T. A. T. and Miller, D. A. (1978). Effect of shade on nitrogen-fixation by soybean.
Agron. J. 70: 387-392.
Table 1. Summary of major weather data 1994-1995 at IITA Station, Onne.
__________________________________________________________________________________
Total Rainfall
Rain days
Min temp.
Max temp.
Rel. humidity
0
Month
(mm)
(no.)
...........( C)………
( %)
____________
____________
__________
________
____________
1994 1995
1994 1995 1994 1995 1994 1995
1994 1995
__________________________________________________________________________________
JAN
44.8
1.4
7
2
21.4
20.8 31.7
33.2
74
55
FEB
43.3
78.6
4
5
23.5
22.9 32.8
33.6
75
63
MAR
118.4
196.1
10
10
23.5
23.0 32.1
32.4
76
82
APR
164.9
72.8
16
10
23.0
23.5 31.8
32.6
80
78
MAY
237.0
300.9
22
17
22.8
22.6 30.7
31.0
80
78
JUN
202.1
318.7
21
21
22.1
22.6 28.9
29.9
84
78
JUL
378.7
312.2
30
26
22.2
22.4 27.3
28.4
88
84
AUG
306.2
433.7
27
26
22.5
22.5 27.8
28.3
81
83
SEP
419.1
375.0
25
24
22.4
22.4 28.4
29.4
82
84
OCT
218.8
422.4
25
22
22.4
21.8 29.5
29.8
86
94
NOV
259.3
76.7
13
8
22.3
22.3 31.3
31.8
78
78
DEC
0.0
4.2
0
6
21.3
21.8 32.7
31.8
69
74
__________________________________________________________________________________
ANNUAL
TOTAL: 2392.6
2592.7
200
177
AVERAGE:
22.5
22.4 30.4
31.0
79
78
__________________________________________________________________________________
Table 2. Summary of major weather data 1996-1997 at IITA Station, Onne.
__________________________________________________________________________________
Total Rainfall
Rain days
Min temp.
Max temp.
Rel. humidity
0
Month
(mm)
(no.)
...........( C)………
( %)
____________
____________
__________
________
____________
1996 1997
1996 1997
1996 1997 1996 1997
1996 1997
__________________________________________________________________________________
JAN
0.0
83.2
0
6
21.9
22.6
32.7
32.0
72
72
FEB
43.8
8.2
8
1
22.6
21.6
33.0
34.0
72
60
MAR
158.2
85.7
9
9
22.5
23.9
32.0
32.8
78
73
APR
288.1
116.1
17
17
22.1
23.2
32.4
31.3
76
76
MAY
204.2
314.4
15
21
23.2
23.0
31.5
31.3
78
78
JUN
242.7
340.9
16
24
23.2
23.1
29.8
29.2
80
81
JUL
204.4
423.2
22
22
22.5
22.9
28.2
28.2
82
82
AUG
358.0
321.7
27
22
22.7
23.1
27.4
28.3
85
82
SEP
390.1
198.9
23
18
22.6
23.3
6.3
29.8
84
81
OCT
265.7
423.0
20
18
22.1
23.3
29.7
30.5
80
80
NOV
52.0
120.0
3
19
23.1
23.3
32.0
30.7
70
79
DEC
15.4
28.9
5
23.2
22.6
32.0
32.3
74
70
____________________________________________________________________________________________________
ANNUAL
TOTAL:
2222.6
2464.2
164
182
____________________________________________________________________________________________________
AVERAGE:
22.6
22.9
30.8
30.8
78
76.2
25
Millettia
Enterolobium
Inga
Dry weight of litter remaining
20
15
10
5
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17
Weeks after placement of litter on soil surface
Fig. 1. Litter decay patterns of Enterolobium
Cyclocarpum , Inga edulis and Millettia laurentii