Biological Agriculture and Horticulture, 2000, Vol....
Biological Agriculture and Horticulture, 2000, Vol. 17, pp. 329-338
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C~mm4 8
Fish By-Product as a Soi1
p
Amendment for Millet and
P35 5
Groundnut Cropping Systems /$) 1
in Senegal
Mamadou Ndiaye ‘*, Charles F. Yamoah* and
Richard P. Dick3
lNational Center of Agronomie Research of Bambey, ISRA CNRA, BP 53,
Bsmbey, Senegal. *Courtcil for Scientific & IndustriaI Research (Soi/
Institute) Accra Centre, P.O. Box 32, Accra, Ghana. 30regon State
University, Corvallis, Oregon, U.S.A.
ABSTRACT
Soils of the groundnut (Arachis hypogaea) L. basin of Senegal are impovetished with low fertility
and organic matter content. Previously, farmers maintained yields of millet (Pennisetum gluucum
(L.) R. Br. and groundnut with subsidized inorganic fertilizers and fallow periods to restote soifs.
Fish meal or by-product in various forms is a commercial commodity worldwide, but in Senegal
the non-edible portion of dsh (intestines, bottes, scales and gilfs) are often discarded after
processing. A three-year study was conducted on processed fkh by-products as a soi1 amendment
for millet and groundnut productivity. Chemical anaiysis showed that the processed fish by-
products are high in major nutrients such as N, 5.35%; P, 4.17%; K, 0.92%; Ca, 9.‘77%; and Mg,
0.36% Consequently, the application of the processed fïsh by-products significantly (p < 0.05)
increased millet grain from 0.29 Mg ha-’ in the control plot (no tïsh by-producr) to 2.50 Mg
ha-t with 6 Mg ha-’ fïsh by-product. Millet stover yield was ako increased. Groundnut yielda.
increased (p < 0.01) from 0.23 Mg ha-’ in the control plots to about 1.00 Mg ha-’ with 2 Mg
ha-’ fish by-product. Response curves for millet and groundnut were curvilinear with the
incorporated fïsh remains explaining 98 and 99% of variability in yields of millet and groundnut
respecfively. Residual effect
of fïsh by-product after one year signifïcantly (p < 0.05) improved
yields of millet and groundnut compared with inorganic fertilizer and equalled yields of the same
crops with inorganic fertilizer after two years. However, stability analysis indicated that millet
yieids with tïsh by-product were less stable (se. = 0.31) than yields with inorganic fertilizer (se.
= 0.16‘~ reflecting the non-unifonnity of the by-products and processing methods across villages
*Correspcmding author
329
_
L.
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J
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i
330
MAMALI~II N»IA~ ANI)CITHERS
INTRODUCTION
Low trop yie](js in thc semi-arid region of 5encpal arc attributcd primarily to
increasing droughl frequency and low soil rcrtilitk (Picri. 1986). In the past.
farmers counted on prolonged fallow periods. to huild soi1 nutricnt reserves and
organic matter. Today, this is not feasible in thl: arable areas of Senegal becausc
of an increase in both human and animal populations. Farmers know about the
benefîts of minera1 fertilizers but the majority of Senegalese farmers have small
land holdings and are unable to purchase adequate levels of minera1 fertilizers.
Traditionally, for economic and logistic r$easons. African farmers rarely use
inorganic fertilizer; instead, they apply organic methods such as animal manure,
green manure, and agroforestry.-related
practices to restore fertility of their
farmlands (Gillier, 1960; Lemoine, 1967; Pieri, 1986). Although, farmers
recognize that trop yields are sub-optimal when fertilized solely with organic
amendments, they continue to use them because sources of organic inputs are
sustainable locally. Furthermore, several audits have documented
positive
results with the use of organic amendments in cropping systems, both in the
temperate and tropical environm.ents
(Gillier, 1960; Hamon, 1967; Lemoine,
1967; Pieri, 1986).
Generally, fish meal in various forms is traded internationally. In Senegal,
however, parts of the fish like the intestines, bones, scales, fins and gills are not
eaten and are discarded after processing. The present study is to determine the
effect of these fish by-products on yields of millet and groundnut. Prier to the
agronomie field work, socioeconomic surveys were condacted KO ascertain
adequacy, availability and farmers’ perception of t.he fïsh by-product for farming
(Ndiaye et al., 1994). This study was the first attempt to evaluate the use of fish
by-products in cropping systems in Senegal (Annnymous,
1993).
MATERIALS AND METHODS
Site characteristics and fish processing
The study was conducted in two villages, Gandtigal and Ndianda, in the semi-
arid zone of Senegal. Reasons for the: choice of these villages were (1) proximity
to the ocean where the fish are processed and (2) experience of the farmers in
organic farming. Rainfall for the study period ranged fmm 300 to 620 mm
yr-’ which was recorded at both villages. Mean annual temperature is 27.6”C.
Soi1 and plant analyses were determined using standard lahoratory techniques
developed at IITA (1977). The soils are Alfi~sols with thc following pre-plant
chemical propertics. cation exchange capacity 1.2--7.8 cm01 kg.-‘: organic carbon
0.23-0.X%: pH 5.8-6.5; exchangeable calcium + mapnesium 0.76 cmol
kg-‘; and sand 93.5%. The vegetation is woodcd Ciuinea rsavanna comprising
predominantly Comhretum sp.
FISH BY-PRO&JCT AS SOIL AMENDMENT
231
r
The fïsh (Sardinella orira) by-products were obtained from the fishing
villages of Joal and Mbour. The fish were fïrst smoked and then processed by
cleaning and removing the by-products which were made up of intestines, bonrs,
scales, fins and gills. The by-products were then placed into compost pits for 4--
6 weeks depending on location and farmer. Prior to planting, the contents of thc:
pits were removed, broadcast, and applied to the field, usually by incorporatitin.
Table 1 gives chemical content of the fïsh by-product at the time of field
application as determined hy standard analytical procedures
(IITA, 1977).
There were three field experiments from 1994 to 1996; two on the direct
effects of fish by-product on yields of millet and the third on the residual effects.
Fertilizer rates commonly recommended by ISRA (21 N, 4 P and 9 K kg
ha-’ as NPK + 46 N kg ha-’ as urea) were used (M. Ndiaye, persona1
communication, 1999).
Experiment I
The fïrst experiment was designed to test the effect of 0, 2, 4 or 6 Mg ha-’ fish
remains on the millet variety Souna 3 at Gandigal. Plot size was 4.5 by 9.0 rn
with six rows of millet spaced 0.9 m between rows and 0.9 m (thinned to three
plants per hill) within rows. Also, the effect of 0, 0.5, 1 .O, 1.5 or 2 Mg ha-’ fish
by-product on the groundnut variety 55437 at Ndianda was tested. Smaller
plots, 2.0 by 5.0 m, consisting of six groundnut rows were used; spacing was 0.4
m between rows and 0.2 within rows. Both millet and groundnut had a 90 day
growth cycle.
Seed bed preparation was done with a no-till method in conformity with
prevailing farmers’ practices in the Sahelian region of West Africa (Lai, 1987)‘.
Fish by-product was incorporated followed by seeding with a local disk planter;
the disk of thc planter was adjusted to deliver seeds at recommended plant
TABLE 1
Chemical analysis of processed fïsh by-product.
-
P H
C N P K Ca Mg Na
s,02 CI s
-
w a t e r KCI
IS)
Mcan
6.6
6 . 5
2 7 . 3
5.35
4.17
0.92
9 . 7 7
0.36
7.99 1 9 . 2
2 87
0.37
s.e
0.10
0.10
0.10
0.80
0.90
0.10
1 . 2 0
0.10
0.30
0.80
0.30
0.10
A I
Mn Fe
Zn
CU
(mg kg ‘)
Mean
tr
3 5
1493
8 4
30
SS?.
-
0.01
262
8 . 5
3 . 5
--
- - -- -_._ - .._.
332
MAMAIXKI NDIAYE AND O’lXF:RS
populations of 38,000 plants ha- ’ for millet and 125.000 plants ha-* for
groundnut. Two central rows wer’e harvested 1%r biomass and yield analysis.
Experimental design was a randomized complcl~: hlock with four replications.
Experiment II
The second study compared the effect of minera1 fcrtilizer and fish by-product
on millet and groundnut yields. Treatments for millet were (1) control;
(2) 21 kg N, 4 kg P, and 9 K kg h-’ (14-7-7 NPK fertilizer) followed by 46 kg
N ha-’ (urea) as top dressing; and (3) 4 Mg ha-’ fish by-product. Tbe NPK
fertilizer was broadcast at planting and the urca was split in equal proportions,
one half at 25 da,ys after planting and the rest -&30 davs
, later. The treatments for
groundnut were: (1) control; (2) 21 N, 4 P and 9 K kg ha-’ as NPK fertilizer
alone; or (3) 2 Mg ha-l fish by-product at planting. The design was a
randomized complete block with four replications. Planting arrangement and
other cultural practices were the same as Elxperiment 1.
Experiment Ill
Experiment 3 was a millet (variety Souna3)-groundnut
(variety 55-437) rotation
conducted on 13 farmers’ fields at Lagnaer and Mbotile villages from 1995 to
1997. Tbere yere tbree treatments; (1) control; (2) 4 Mg ha-’ fish by-product;
or (3) 21 N, 4 P and 9 K kg ha-’ as NPK fertiljzer followed by 46 kg N ha-’
urea as top dressing. Half of the urea was a.pplied 25 days after planting and the
remaining 20 days later. Groundnut received 12 N, 12 P and 34 kg ha-’ as NPK
(8-18-27) and 2 Mg ha-’ fish by-product. Each farmers’ field was spiit in half
for planting millet or groundnut in each half of the fïeld. ‘IIe two crops and
fertilization treatments are presented sequr:ntially in Table 2. Within each split
treatments were superimposed with plot sires of 4.5 m by 9.0 m. The
experimental design was a randomized completc block with four replications.
TABLE 2
Ckops and fertilization treatment? schcme in Experiment 111
Yeÿr
Plot
Crop
tktilization treatments
-
_-II---.
199.5
1
Millet
Control, fertilizer. fïsh by-product
1995
2
Groundnut
~ontrol, fertilizer. fïsh by-product
1 9 9 6
1
Groundnut
VontroI, no fertilizr. no fïsh by-product
1 9 9 6
2
Millet
CJontwl. fertiliser, no fïsh by-product
1 9 9 7
1
Millet
(‘ontr,,l. krtilizer, no tïsh by-product
1 9 9 7
2,
Groundnut
(‘ontrul. no fertilizer, no fïsh hy-producr
FISH BY-PRODUCT AS SOIL AMENDMENT
333
Data was analysed hy standard ANOVA procedures
with mean separation
(p = 0.05) and second order regression, Y = a+bX+cX2 (where Y = yield and X
= fish by-product are in Mg ha-‘) to estimate optimum level of fish residue for
millet and groundnut yields. Fish by-product N-use efficiency (FNU) was
calculated as the ratio: (yield in Mg ha-’ N)/(Mg ha-’ N in fish by-product) * 100
SPSS (Norusic- 1997) and MSTAT-C software was used for the statistical
analysis.
RESULTS AND DISCUSSION
Nutrient contents of the fish by-product before field application are shown in
Table 1. According to the data, nutrient values for N = 5.35% and P = 4.17%
were relatively high, compared to the NPK fertilizer formula used in this study.
In the course of the study, it was noticed that rainfall was lower and more erratic
at Gandigal than Ndianda. Thus, under normal conditions, yields would be
expected to be higher at Ndianda than Gandigal.
Experiment
I
Manuring with processed fish by-product significantly (p < 0.05) increased
millet yield (Table 3). The lowest rate of 2 Mg ha-’ by-product increased yield
TABLE 3
Effect of tïsh by-product on yields of millet and groundnut
in Experiment 1.
trop
By-product rate
Yield
(Mg ha-‘)
(Mg ha-‘)
Millet
0
0.29
2
1 . 4 0
4
2.44
6
2.50
Standard error cs.e.)
0.15
Linear effect
0 . 0 5
Quadratic effect
0.10
Groundnut
0
0.23
0.5
0.57
1
0.81
1 .s
0.93
2
0 . 9 5
Standard errer ~s.e.)
0.056
Linear effect
p < 0.ooo1
Quadratic effect
p < 0.ooo1
~~-
- 7
----
---.---.-
..-----.
._
.__~
..__
.-..
.~
_
334
MAMADOU NDIAYE kND OTHERS
of millet by over 350% (frOm 0.292 kg ha-’ to 1, 392 Mg ha-‘) at Gandigal. The
highest yield of 2.50 Mg ha-’ wi’th 6 Mg fïsh by-product ha-’ did net differ frorn
that of 4 Mg ha-.‘. The second order regression. Y = 0.24 .t 0.78 -. 0.07X2
indicated that 4 Mg ha-’ fish hy-product
is ,the optimum rate. ‘T’he Equation
attributcd 98% of the variability of millet yield to fish by-product.
Similarly, fish by-product used as manure increased groundnut yield (Table
3). The lowesr rate of 0.5 Mg ha”* resulted in an increase of 1.50% (from 0.23
Mg ha ’ to 0.57 Mg ha-l) at Ndianda. Groundnut yield did not increase
significantly beyond the use of 1.0 Mg ha-’ manure. The yield data were hest
described by the second order regression function: Y = 0.23 + 0.80 - 0.22X’,
which also explained 99% of the variability of groundnut yield.
In general, FNU decreases with increasing rai.es of N. Fish by-product N-use
effïciency was lO%, and the by-product rate was optimum between 2 and 4 Mg
ha-’ in the millet; FNU in the groundnut system was 4.5% and the rate was
optimum between 0.5 and 1.0 Mg ha-*. Groundnut trop meets part of its N
requirement through atmospheric N fixation and therefore it is less dependent on
N from an external source.
Experiment II
Experiment II assessed the potential value of fish by-product as a fertilizer
amendment (Table 4). Millet grain tid residue yields with the application of 4
Mg ha-’ fish hy-product signilbcantly out-performed the use of the recom-
mended dose of minera1 fertilizer for two consecutive
years. Total N applied as
minerai fertilizer in the recommended dose was 67 kg ha-’ giving N efficiencies
of 11% and 4% respectively in 1995 and 1996 at Ndianda. The same minerai
lèrtilizcr had a N effïciency of 5% at Gandigal in 1996. Generally, N from
TABLE 4
I;ffects of fïsh by-product and inorganic fertilizer on millet (Souna 3) yields at
Ndianda and Gandigai in 1995-1996 in Experiment Il.
-
-
-
Yield (Mg ha-‘)
_--.-_
---_-
Nduanda
Gandigal
- _
199s
1996
1 9 9 5
1996
-
-
-
-
- - - -
l reattnent~
Grain
Stover
Grain
Grain
Stover
Grain
-~-
- - -
-
-
Control
0 . 2 3
1.06
0.5 1
1.52
3.31
0 . 9 3
Fertiliser
I .44
?,.41
0.91
2 . 2 3
4 . 3 3
1 .w
Fish by-product
2 . 2 3
6 . 1 5
1.48
2 . 3 1
5 . 3 8
1.89
Standard errer
0.12
0 . 1 9
0 . 9 2
0 . 0 7
0.14
0.06
-
-
-
-
FISH BY-PRODUCT AS SOIL AMENDMENT
335
inorganic sources is more readily available to crops than N from organic sources
such as green manure and compost (Palm & Sanchez, 1990).
Mean yields of groundnut from fish by-product treakd plots and plots
fertilized with NPK were comparable (Table 5). Yields from the two abovc
treatments were significantly
(p < 0.05) better than the control. Fertilizer N use
efficiencies were 4% in 1995 and 6% in 1996. Yieids of millet and groundntrt
did not differ (p > 0.05) between sites.
Experiment III
Direct and residual effects of fish by-product on millet and groundnut yields are
presented in Table 6. Years, fertilization and years by fertilization interaction
were significantly different (p < 0.0001). Yields of both crops in the control
plots decreased slightly with years of cultivation due to decline in native soi1
fertility. Millet yields fertilized with fkh by-product were much higher in 1995
and 1996 than yields in the fertilizer treated and control plots, even though millet
was fertilized with inorganic fertilizer every year. This suggests that fish by-
product may have an added effect on millet yield that goes beyond its nutrient
contribution, because the inorganic fertilizer treatment is high enough to
maximize yields. Perhaps, increased trop biomass after harvest in addition to the
remaining fish by-product improved the soi1 structure to enhance root activity.
Organîc additions provide the important substrates for microbial activity that
stimulates physical enmeshment of soi1 particles and the organic compounds that
bind particles together (Tate, 1987). Although the amount of C added by organic
amendments is low relative to the total organic matter, recent additions cari
signifïcantly
affect aggregation and aggregate stability. As an example, Martin
(1942) showed that various compost amendments increased water stable
aggregates from 26 to 49% over the control even after 200 days on soi1 that was
82% Sand. Subsequent studies havt: found that organic inputs cari affect
TABLE 5
Effects of f%h hy-product and inorganic fertilizer on groundnut yields at
Ndianda and Gandigal in 1995-1996 in Experirnent II.
Yield (Mg ha ‘)
Ndlanda (1995)
Gandigal ( 1996)
-
_-
Treatments
stover
P o d s
Grain
sto\\c1
Pods
Grain
Control
1.62
1.11
0.69
1 . 1 0
0 . 8 8
0.46
Fertilizer
2 . 8 8
1.50
0.90
2.4.T
1.15
0.88
Fish by-product
2 . 9 5
1.22
0.94
227
1 . 1 0
0.75
Standard error
0.10
0 . 0 6
0.04
0.0x
0 . 0 2
0.03
336
MAMAWU NDIAYE AND 0TtIERS
TABLE 6
Effe(:t of direct and residual affects of fish Ihy-pruducts and inorganic
fcnihzer on yields of millet and groundnut in Experimem 111.
-
-
L
Yield (Mg ha-‘)
- ---~-
YGU
Treatmcnt
Millet
Groundnut
199.5 (direct effectf
Control
0.6 I
0.46
Fertilizer
0.90
0.79
Fish by-product
1.13
0.17
1996 (fïrst year effect)
Control
0.59
0.43
Fertiliser
0.80
0.66
Fish by-producl
1.77
0.7 1
1997 (second year effect)
Control
0.57
0.38
Fertiliser
0.83
0.43
Fish by-product
0.82
0.57
Level of significance
Year (Y,,
p < o.ooo1
p < o.ooo1
Treatment (T)
p < o.ooo1
p < o.c@01
YxT
p < 0.0001
p < O.c@OI
aggregation within a growing season (Gilmour et al., 1948; Griffiths & Jones,
196.5; Oades, 1984). More recent studies have shown that recently deposited
organic matter (l-4 years, Buyanovsky st ai., 1994; < 6 years, Puget et al.,
1995) is important in macroaggregate stabilization. Recent organic matter
additions cari also increase a light fraction organic matter, also known as
particulate organic matter which is undecomposed
plant and microbial debris
(Cambardella & Elliot, 1992) which cari also provide structure to soils.
Millet yields in 1997 were about half the harvest of 1996, and this may
suggest that positive effect of fish by-product on yield lasts only one year and
has to be renewed thereafter. But, even in 1997, the yiclds were comparable with
inorganic fertilized millet and better than the control.
Groundnut yields in 1995 were higher in the fïsh by-product and inorganic
fertilized plots. Groundnut yields with fertilizer and manure were about equal.
In I996, fish by-product out yielded inorganic fertilizer by 7% and the control
by 62%. Groundnut yield dropped by 20% from 1996 to 1997 with fish by-
product but it still remained superior to inorganic fertilizer and the control.
Yields in the third year (i.e. second year effect) were 0.43 Mg ha-’ for inorganic
fertiiizer as opposed to 0.57 Mg ha-’ with fish by-product, a difference of 34%
with respect to inorganic fertilizer.
Figure 1 presents information on adaptability and stability of millet yields as
affected by fish hy-product, inorganic fertilizer and the control across a11 13
farms in the three experiments. The treatments responded positively and
signifïcantly (p < 0.01) across farms. Clearly, fish by-product produced hrgher
FISH BY-PRODUCT AS SOIL AMENDMENT
331
3000
2500
f - 2 0 0 0
f
g 1500
w
z
h 1000
500
0
200
700
1200
1700
2200
Site mean yield (kg ha-‘)
FIGURE 1. Stability analysis of millet yields as affected by fish by-producr and inorganic
krtilizer treatments.
yields than the inorganic fertilizer and the control treatments, but the yields were
more variable across farms as indicated by large standard error (s.e. = 0.31).
Although inorganic fertîlizer wa$ not as high-yielding as fïsh by-product, yields
were more responsive to fertilizer as shown in Figure 1 with the steepest positive
slope of the three treatments (p < 0.0001) and stable from farm-to-farm
(s.e. = 0.16).
The conclusion from this study is that fish by-product has potential to increase
trop yields but its effect on yields is more variable across farms reflecting the
numerous ways farmers process their lish by-products. There was indirect
evidence that the increase in yield due to fish by-products was not ,solely due to
the nutrient addition because even with adequate applications of inorganic
fertiiizer, the fish by-product caused an additional yield response. The by-
products are currently causing an environmental problem in the communily
because of the bad odour and are free of cost. Storing them in compost pits is
a means to improve the environment and soi1 fertility. By-product is available in
s>Jfficient quantities now to be agronomically important (Ndiaye et al., 1994)
and likely to increase in availability as the population grows and demand for fish
consumption
increases. Mixing the fish by-product with trop residues Will result
in improved compost that could fertilize a greater number of farms or to fertilize
specialized high value crops.
.“.. -
338
MAMA»O~: F~DIAYE AND ,D THfRs
ACKNOWLEDGMENTS
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.
C~mm4 8
Fish By-Product as a Soi1
p
Amendment for Millet and
P35 5
Groundnut Cropping Systems /$) 1
in Senegal
Mamadou Ndiaye ‘*, Charles F. Yamoah* and
Richard P. Dick3
lNational Center of Agronomie Research of Bambey, ISRA CNRA, BP 53,
Bsmbey, Senegal. *Courtcil for Scientific & IndustriaI Research (Soi/
Institute) Accra Centre, P.O. Box 32, Accra, Ghana. 30regon State
University, Corvallis, Oregon, U.S.A.
ABSTRACT
Soils of the groundnut (Arachis hypogaea) L. basin of Senegal are impovetished with low fertility
and organic matter content. Previously, farmers maintained yields of millet (Pennisetum gluucum
(L.) R. Br. and groundnut with subsidized inorganic fertilizers and fallow periods to restote soifs.
Fish meal or by-product in various forms is a commercial commodity worldwide, but in Senegal
the non-edible portion of dsh (intestines, bottes, scales and gilfs) are often discarded after
processing. A three-year study was conducted on processed fkh by-products as a soi1 amendment
for millet and groundnut productivity. Chemical anaiysis showed that the processed fish by-
products are high in major nutrients such as N, 5.35%; P, 4.17%; K, 0.92%; Ca, 9.‘77%; and Mg,
0.36% Consequently, the application of the processed fïsh by-products significantly (p < 0.05)
increased millet grain from 0.29 Mg ha-’ in the control plot (no tïsh by-producr) to 2.50 Mg
ha-t with 6 Mg ha-’ fïsh by-product. Millet stover yield was ako increased. Groundnut yielda.
increased (p < 0.01) from 0.23 Mg ha-’ in the control plots to about 1.00 Mg ha-’ with 2 Mg
ha-’ fish by-product. Response curves for millet and groundnut were curvilinear with the
incorporated fïsh remains explaining 98 and 99% of variability in yields of millet and groundnut
respecfively. Residual effect
of fïsh by-product after one year signifïcantly (p < 0.05) improved
yields of millet and groundnut compared with inorganic fertilizer and equalled yields of the same
crops with inorganic fertilizer after two years. However, stability analysis indicated that millet
yieids with tïsh by-product were less stable (se. = 0.31) than yields with inorganic fertilizer (se.
= 0.16‘~ reflecting the non-unifonnity of the by-products and processing methods across villages
*Correspcmding author
329
_
L.
-
J
. -
-i
.A- A-
~---.
i
330
MAMALI~II N»IA~ ANI)CITHERS
INTRODUCTION
Low trop yie](js in thc semi-arid region of 5encpal arc attributcd primarily to
increasing droughl frequency and low soil rcrtilitk (Picri. 1986). In the past.
farmers counted on prolonged fallow periods. to huild soi1 nutricnt reserves and
organic matter. Today, this is not feasible in thl: arable areas of Senegal becausc
of an increase in both human and animal populations. Farmers know about the
benefîts of minera1 fertilizers but the majority of Senegalese farmers have small
land holdings and are unable to purchase adequate levels of minera1 fertilizers.
Traditionally, for economic and logistic r$easons. African farmers rarely use
inorganic fertilizer; instead, they apply organic methods such as animal manure,
green manure, and agroforestry.-related
practices to restore fertility of their
farmlands (Gillier, 1960; Lemoine, 1967; Pieri, 1986). Although, farmers
recognize that trop yields are sub-optimal when fertilized solely with organic
amendments, they continue to use them because sources of organic inputs are
sustainable locally. Furthermore, several audits have documented
positive
results with the use of organic amendments in cropping systems, both in the
temperate and tropical environm.ents
(Gillier, 1960; Hamon, 1967; Lemoine,
1967; Pieri, 1986).
Generally, fish meal in various forms is traded internationally. In Senegal,
however, parts of the fish like the intestines, bones, scales, fins and gills are not
eaten and are discarded after processing. The present study is to determine the
effect of these fish by-products on yields of millet and groundnut. Prier to the
agronomie field work, socioeconomic surveys were condacted KO ascertain
adequacy, availability and farmers’ perception of t.he fïsh by-product for farming
(Ndiaye et al., 1994). This study was the first attempt to evaluate the use of fish
by-products in cropping systems in Senegal (Annnymous,
1993).
MATERIALS AND METHODS
Site characteristics and fish processing
The study was conducted in two villages, Gandtigal and Ndianda, in the semi-
arid zone of Senegal. Reasons for the: choice of these villages were (1) proximity
to the ocean where the fish are processed and (2) experience of the farmers in
organic farming. Rainfall for the study period ranged fmm 300 to 620 mm
yr-’ which was recorded at both villages. Mean annual temperature is 27.6”C.
Soi1 and plant analyses were determined using standard lahoratory techniques
developed at IITA (1977). The soils are Alfi~sols with thc following pre-plant
chemical propertics. cation exchange capacity 1.2--7.8 cm01 kg.-‘: organic carbon
0.23-0.X%: pH 5.8-6.5; exchangeable calcium + mapnesium 0.76 cmol
kg-‘; and sand 93.5%. The vegetation is woodcd Ciuinea rsavanna comprising
predominantly Comhretum sp.
FISH BY-PRO&JCT AS SOIL AMENDMENT
231
r
The fïsh (Sardinella orira) by-products were obtained from the fishing
villages of Joal and Mbour. The fish were fïrst smoked and then processed by
cleaning and removing the by-products which were made up of intestines, bonrs,
scales, fins and gills. The by-products were then placed into compost pits for 4--
6 weeks depending on location and farmer. Prior to planting, the contents of thc:
pits were removed, broadcast, and applied to the field, usually by incorporatitin.
Table 1 gives chemical content of the fïsh by-product at the time of field
application as determined hy standard analytical procedures
(IITA, 1977).
There were three field experiments from 1994 to 1996; two on the direct
effects of fish by-product on yields of millet and the third on the residual effects.
Fertilizer rates commonly recommended by ISRA (21 N, 4 P and 9 K kg
ha-’ as NPK + 46 N kg ha-’ as urea) were used (M. Ndiaye, persona1
communication, 1999).
Experiment I
The fïrst experiment was designed to test the effect of 0, 2, 4 or 6 Mg ha-’ fish
remains on the millet variety Souna 3 at Gandigal. Plot size was 4.5 by 9.0 rn
with six rows of millet spaced 0.9 m between rows and 0.9 m (thinned to three
plants per hill) within rows. Also, the effect of 0, 0.5, 1 .O, 1.5 or 2 Mg ha-’ fish
by-product on the groundnut variety 55437 at Ndianda was tested. Smaller
plots, 2.0 by 5.0 m, consisting of six groundnut rows were used; spacing was 0.4
m between rows and 0.2 within rows. Both millet and groundnut had a 90 day
growth cycle.
Seed bed preparation was done with a no-till method in conformity with
prevailing farmers’ practices in the Sahelian region of West Africa (Lai, 1987)‘.
Fish by-product was incorporated followed by seeding with a local disk planter;
the disk of thc planter was adjusted to deliver seeds at recommended plant
TABLE 1
Chemical analysis of processed fïsh by-product.
-
P H
C N P K Ca Mg Na
s,02 CI s
-
w a t e r KCI
IS)
Mcan
6.6
6 . 5
2 7 . 3
5.35
4.17
0.92
9 . 7 7
0.36
7.99 1 9 . 2
2 87
0.37
s.e
0.10
0.10
0.10
0.80
0.90
0.10
1 . 2 0
0.10
0.30
0.80
0.30
0.10
A I
Mn Fe
Zn
CU
(mg kg ‘)
Mean
tr
3 5
1493
8 4
30
SS?.
-
0.01
262
8 . 5
3 . 5
--
- - -- -_._ - .._.
332
MAMAIXKI NDIAYE AND O’lXF:RS
populations of 38,000 plants ha- ’ for millet and 125.000 plants ha-* for
groundnut. Two central rows wer’e harvested 1%r biomass and yield analysis.
Experimental design was a randomized complcl~: hlock with four replications.
Experiment II
The second study compared the effect of minera1 fcrtilizer and fish by-product
on millet and groundnut yields. Treatments for millet were (1) control;
(2) 21 kg N, 4 kg P, and 9 K kg h-’ (14-7-7 NPK fertilizer) followed by 46 kg
N ha-’ (urea) as top dressing; and (3) 4 Mg ha-’ fish by-product. Tbe NPK
fertilizer was broadcast at planting and the urca was split in equal proportions,
one half at 25 da,ys after planting and the rest -&30 davs
, later. The treatments for
groundnut were: (1) control; (2) 21 N, 4 P and 9 K kg ha-’ as NPK fertilizer
alone; or (3) 2 Mg ha-l fish by-product at planting. The design was a
randomized complete block with four replications. Planting arrangement and
other cultural practices were the same as Elxperiment 1.
Experiment Ill
Experiment 3 was a millet (variety Souna3)-groundnut
(variety 55-437) rotation
conducted on 13 farmers’ fields at Lagnaer and Mbotile villages from 1995 to
1997. Tbere yere tbree treatments; (1) control; (2) 4 Mg ha-’ fish by-product;
or (3) 21 N, 4 P and 9 K kg ha-’ as NPK fertiljzer followed by 46 kg N ha-’
urea as top dressing. Half of the urea was a.pplied 25 days after planting and the
remaining 20 days later. Groundnut received 12 N, 12 P and 34 kg ha-’ as NPK
(8-18-27) and 2 Mg ha-’ fish by-product. Each farmers’ field was spiit in half
for planting millet or groundnut in each half of the fïeld. ‘IIe two crops and
fertilization treatments are presented sequr:ntially in Table 2. Within each split
treatments were superimposed with plot sires of 4.5 m by 9.0 m. The
experimental design was a randomized completc block with four replications.
TABLE 2
Ckops and fertilization treatment? schcme in Experiment 111
Yeÿr
Plot
Crop
tktilization treatments
-
_-II---.
199.5
1
Millet
Control, fertilizer. fïsh by-product
1995
2
Groundnut
~ontrol, fertilizer. fïsh by-product
1 9 9 6
1
Groundnut
VontroI, no fertilizr. no fïsh by-product
1 9 9 6
2
Millet
CJontwl. fertiliser, no fïsh by-product
1 9 9 7
1
Millet
(‘ontr,,l. krtilizer, no tïsh by-product
1 9 9 7
2,
Groundnut
(‘ontrul. no fertilizer, no fïsh hy-producr
FISH BY-PRODUCT AS SOIL AMENDMENT
333
Data was analysed hy standard ANOVA procedures
with mean separation
(p = 0.05) and second order regression, Y = a+bX+cX2 (where Y = yield and X
= fish by-product are in Mg ha-‘) to estimate optimum level of fish residue for
millet and groundnut yields. Fish by-product N-use efficiency (FNU) was
calculated as the ratio: (yield in Mg ha-’ N)/(Mg ha-’ N in fish by-product) * 100
SPSS (Norusic- 1997) and MSTAT-C software was used for the statistical
analysis.
RESULTS AND DISCUSSION
Nutrient contents of the fish by-product before field application are shown in
Table 1. According to the data, nutrient values for N = 5.35% and P = 4.17%
were relatively high, compared to the NPK fertilizer formula used in this study.
In the course of the study, it was noticed that rainfall was lower and more erratic
at Gandigal than Ndianda. Thus, under normal conditions, yields would be
expected to be higher at Ndianda than Gandigal.
Experiment
I
Manuring with processed fish by-product significantly (p < 0.05) increased
millet yield (Table 3). The lowest rate of 2 Mg ha-’ by-product increased yield
TABLE 3
Effect of tïsh by-product on yields of millet and groundnut
in Experiment 1.
trop
By-product rate
Yield
(Mg ha-‘)
(Mg ha-‘)
Millet
0
0.29
2
1 . 4 0
4
2.44
6
2.50
Standard error cs.e.)
0.15
Linear effect
0 . 0 5
Quadratic effect
0.10
Groundnut
0
0.23
0.5
0.57
1
0.81
1 .s
0.93
2
0 . 9 5
Standard errer ~s.e.)
0.056
Linear effect
p < 0.ooo1
Quadratic effect
p < 0.ooo1
~~-
- 7
----
---.---.-
..-----.
._
.__~
..__
.-..
.~
_
334
MAMADOU NDIAYE kND OTHERS
of millet by over 350% (frOm 0.292 kg ha-’ to 1, 392 Mg ha-‘) at Gandigal. The
highest yield of 2.50 Mg ha-’ wi’th 6 Mg fïsh by-product ha-’ did net differ frorn
that of 4 Mg ha-.‘. The second order regression. Y = 0.24 .t 0.78 -. 0.07X2
indicated that 4 Mg ha-’ fish hy-product
is ,the optimum rate. ‘T’he Equation
attributcd 98% of the variability of millet yield to fish by-product.
Similarly, fish by-product used as manure increased groundnut yield (Table
3). The lowesr rate of 0.5 Mg ha”* resulted in an increase of 1.50% (from 0.23
Mg ha ’ to 0.57 Mg ha-l) at Ndianda. Groundnut yield did not increase
significantly beyond the use of 1.0 Mg ha-’ manure. The yield data were hest
described by the second order regression function: Y = 0.23 + 0.80 - 0.22X’,
which also explained 99% of the variability of groundnut yield.
In general, FNU decreases with increasing rai.es of N. Fish by-product N-use
effïciency was lO%, and the by-product rate was optimum between 2 and 4 Mg
ha-’ in the millet; FNU in the groundnut system was 4.5% and the rate was
optimum between 0.5 and 1.0 Mg ha-*. Groundnut trop meets part of its N
requirement through atmospheric N fixation and therefore it is less dependent on
N from an external source.
Experiment II
Experiment II assessed the potential value of fish by-product as a fertilizer
amendment (Table 4). Millet grain tid residue yields with the application of 4
Mg ha-’ fish hy-product signilbcantly out-performed the use of the recom-
mended dose of minera1 fertilizer for two consecutive
years. Total N applied as
minerai fertilizer in the recommended dose was 67 kg ha-’ giving N efficiencies
of 11% and 4% respectively in 1995 and 1996 at Ndianda. The same minerai
lèrtilizcr had a N effïciency of 5% at Gandigal in 1996. Generally, N from
TABLE 4
I;ffects of fïsh by-product and inorganic fertilizer on millet (Souna 3) yields at
Ndianda and Gandigai in 1995-1996 in Experiment Il.
-
-
-
Yield (Mg ha-‘)
_--.-_
---_-
Nduanda
Gandigal
- _
199s
1996
1 9 9 5
1996
-
-
-
-
- - - -
l reattnent~
Grain
Stover
Grain
Grain
Stover
Grain
-~-
- - -
-
-
Control
0 . 2 3
1.06
0.5 1
1.52
3.31
0 . 9 3
Fertiliser
I .44
?,.41
0.91
2 . 2 3
4 . 3 3
1 .w
Fish by-product
2 . 2 3
6 . 1 5
1.48
2 . 3 1
5 . 3 8
1.89
Standard errer
0.12
0 . 1 9
0 . 9 2
0 . 0 7
0.14
0.06
-
-
-
-
FISH BY-PRODUCT AS SOIL AMENDMENT
335
inorganic sources is more readily available to crops than N from organic sources
such as green manure and compost (Palm & Sanchez, 1990).
Mean yields of groundnut from fish by-product treakd plots and plots
fertilized with NPK were comparable (Table 5). Yields from the two abovc
treatments were significantly
(p < 0.05) better than the control. Fertilizer N use
efficiencies were 4% in 1995 and 6% in 1996. Yieids of millet and groundntrt
did not differ (p > 0.05) between sites.
Experiment III
Direct and residual effects of fish by-product on millet and groundnut yields are
presented in Table 6. Years, fertilization and years by fertilization interaction
were significantly different (p < 0.0001). Yields of both crops in the control
plots decreased slightly with years of cultivation due to decline in native soi1
fertility. Millet yields fertilized with fkh by-product were much higher in 1995
and 1996 than yields in the fertilizer treated and control plots, even though millet
was fertilized with inorganic fertilizer every year. This suggests that fish by-
product may have an added effect on millet yield that goes beyond its nutrient
contribution, because the inorganic fertilizer treatment is high enough to
maximize yields. Perhaps, increased trop biomass after harvest in addition to the
remaining fish by-product improved the soi1 structure to enhance root activity.
Organîc additions provide the important substrates for microbial activity that
stimulates physical enmeshment of soi1 particles and the organic compounds that
bind particles together (Tate, 1987). Although the amount of C added by organic
amendments is low relative to the total organic matter, recent additions cari
signifïcantly
affect aggregation and aggregate stability. As an example, Martin
(1942) showed that various compost amendments increased water stable
aggregates from 26 to 49% over the control even after 200 days on soi1 that was
82% Sand. Subsequent studies havt: found that organic inputs cari affect
TABLE 5
Effects of f%h hy-product and inorganic fertilizer on groundnut yields at
Ndianda and Gandigal in 1995-1996 in Experirnent II.
Yield (Mg ha ‘)
Ndlanda (1995)
Gandigal ( 1996)
-
_-
Treatments
stover
P o d s
Grain
sto\\c1
Pods
Grain
Control
1.62
1.11
0.69
1 . 1 0
0 . 8 8
0.46
Fertilizer
2 . 8 8
1.50
0.90
2.4.T
1.15
0.88
Fish by-product
2 . 9 5
1.22
0.94
227
1 . 1 0
0.75
Standard error
0.10
0 . 0 6
0.04
0.0x
0 . 0 2
0.03
336
MAMAWU NDIAYE AND 0TtIERS
TABLE 6
Effe(:t of direct and residual affects of fish Ihy-pruducts and inorganic
fcnihzer on yields of millet and groundnut in Experimem 111.
-
-
L
Yield (Mg ha-‘)
- ---~-
YGU
Treatmcnt
Millet
Groundnut
199.5 (direct effectf
Control
0.6 I
0.46
Fertilizer
0.90
0.79
Fish by-product
1.13
0.17
1996 (fïrst year effect)
Control
0.59
0.43
Fertiliser
0.80
0.66
Fish by-producl
1.77
0.7 1
1997 (second year effect)
Control
0.57
0.38
Fertiliser
0.83
0.43
Fish by-product
0.82
0.57
Level of significance
Year (Y,,
p < o.ooo1
p < o.ooo1
Treatment (T)
p < o.ooo1
p < o.c@01
YxT
p < 0.0001
p < O.c@OI
aggregation within a growing season (Gilmour et al., 1948; Griffiths & Jones,
196.5; Oades, 1984). More recent studies have shown that recently deposited
organic matter (l-4 years, Buyanovsky st ai., 1994; < 6 years, Puget et al.,
1995) is important in macroaggregate stabilization. Recent organic matter
additions cari also increase a light fraction organic matter, also known as
particulate organic matter which is undecomposed
plant and microbial debris
(Cambardella & Elliot, 1992) which cari also provide structure to soils.
Millet yields in 1997 were about half the harvest of 1996, and this may
suggest that positive effect of fish by-product on yield lasts only one year and
has to be renewed thereafter. But, even in 1997, the yiclds were comparable with
inorganic fertilized millet and better than the control.
Groundnut yields in 1995 were higher in the fïsh by-product and inorganic
fertilized plots. Groundnut yields with fertilizer and manure were about equal.
In I996, fish by-product out yielded inorganic fertilizer by 7% and the control
by 62%. Groundnut yield dropped by 20% from 1996 to 1997 with fish by-
product but it still remained superior to inorganic fertilizer and the control.
Yields in the third year (i.e. second year effect) were 0.43 Mg ha-’ for inorganic
fertiiizer as opposed to 0.57 Mg ha-’ with fish by-product, a difference of 34%
with respect to inorganic fertilizer.
Figure 1 presents information on adaptability and stability of millet yields as
affected by fish hy-product, inorganic fertilizer and the control across a11 13
farms in the three experiments. The treatments responded positively and
signifïcantly (p < 0.01) across farms. Clearly, fish by-product produced hrgher
FISH BY-PRODUCT AS SOIL AMENDMENT
331
3000
2500
f - 2 0 0 0
f
g 1500
w
z
h 1000
500
0
200
700
1200
1700
2200
Site mean yield (kg ha-‘)
FIGURE 1. Stability analysis of millet yields as affected by fish by-producr and inorganic
krtilizer treatments.
yields than the inorganic fertilizer and the control treatments, but the yields were
more variable across farms as indicated by large standard error (s.e. = 0.31).
Although inorganic fertîlizer wa$ not as high-yielding as fïsh by-product, yields
were more responsive to fertilizer as shown in Figure 1 with the steepest positive
slope of the three treatments (p < 0.0001) and stable from farm-to-farm
(s.e. = 0.16).
The conclusion from this study is that fish by-product has potential to increase
trop yields but its effect on yields is more variable across farms reflecting the
numerous ways farmers process their lish by-products. There was indirect
evidence that the increase in yield due to fish by-products was not ,solely due to
the nutrient addition because even with adequate applications of inorganic
fertiiizer, the fish by-product caused an additional yield response. The by-
products are currently causing an environmental problem in the communily
because of the bad odour and are free of cost. Storing them in compost pits is
a means to improve the environment and soi1 fertility. By-product is available in
s>Jfficient quantities now to be agronomically important (Ndiaye et al., 1994)
and likely to increase in availability as the population grows and demand for fish
consumption
increases. Mixing the fish by-product with trop residues Will result
in improved compost that could fertilize a greater number of farms or to fertilize
specialized high value crops.
.“.. -
338
MAMA»O~: F~DIAYE AND ,D THfRs
ACKNOWLEDGMENTS
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