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Simulating Cropping Systems in the Guinea Savanna Zone of Northern Ghana
with DSSAT-CENTURY
J. B. Naab1, Jawoo Koo2, J.W. Jones2, and K. J. Boote2,
1Savanna Agricultural Research Institute (SARI)
Tamale, Ghana, 2Univ. of Florida,
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Introduction
• To be useful to community decision makers, models must be capable of quantifying crop performance in the communities where they are to be used.
• Necessary to adapt the model to soils, climate and cropping systems of interest and to evaluate predictions from the model relative to local data
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Objective
• Present progress in the adaptation of DSSAT-CENTURY to the cropping systems in two locations in Northern Ghana and its ability to simulate growth, yield and soil carbon sequestration.
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Peanut experiments in 1997 & 1998
• Cultivars: Chinese (90 d) & F-mix (120 d)• Sowing dates: 3 or 4 sowing dates• Complete growth analyses• Detailed soil water measurements • Used PNUTGRO model to simulate soil water
balance & potential growth
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JULIAN DAY
TO
TA
L B
IOM
AS
S,
kg
/ha
a) Chinese, 1998 season
b) F-Mix, 1998 season
0
2000
4000
6000
8000
150 200 250 300 350
D1, DEF (Sim.)
D3, DEF (Sim.)
D1 (Sim.)
D3 (Sim.)
D1 (Obs.)
D3 (Obs.)
0
1000
2000
3000
4000
5000
6000
150 200 250 300 350
a) Chinese, 1997 season
b) F-Mix, 1997 season
J. Naab – Ghana,
Two peanut cult.
Simulated with no disease effect
Simulated with input defoliation and leafspot injury
Crop had no fungicide applied
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0
500
1000
1500
2000
2500
3000
3500
4000
150 200 250 300 350
D1, DEF (Sim.)
D3, DEF (Sim.)D1 (Sim.)
D3 (Sim.)D1 (Obs.)
D3 (Obs.)
0
500
1000
1500
2000
2500
3000
3500
150 200 250 300 350
JULIAN DAY
PO
D W
EIG
HT
, k
g/h
a
a) Chinese, 1997 season
b) F-Mix, 1997 season
J. Naab – Ghana,
Two peanut cult.
Simulated with no disease effect
Simulated with input defoliation and leafspot injury
Crop had no fungicide applied
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Peanut Experiments:1999-2001
• Simulation analyses suggested yield losses of 50 to 70% from disease effects.
• Leaf spot disease is common on peanut in Ghana, where fungicides are not used.
• Can peanut produce simulated yield levels with fungicide? Can the model predict this?
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Materials and methods
• Same cultivars as in 1997 & 1998
• 3 sowing dates
• With (+) and without (-) fungicide applied
• Fungicide: Folicur and Abound
• Detailed growth analysis
• Used CROPGRO-peanut model to simulate growth under disease epidemics
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Measurements
• Phenology data (flowering, 1st pod and 1st seed )
• Time-series growth analysis of leaf, stem, pod and seed mass
• Defoliation and disease scores
• Yield and yield components (pod and seed yields, HI, threshing %, 100-seed weight)
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150 175 200 225 250 275 3000
2000
4000
6000
8000
10000
150 175 200 225 250 275 3000
2000
4000
6000
8000
10000
Day of year
Chinese
Tot
al d
ry w
eigh
t (k
g ha
-1)
Day of the year
F-mix
Nyankpala: 1999 Fungicide
No Fungicide
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175 200 225 250 275 3000
1000
2000
3000
4000
5000
175 200 225 250 275 3000
1000
2000
3000
4000
5000
Day of year
Chinese
Pod
dry
wei
ght
(kg
ha-1
)
Day of the year
F-mix
Nyankpala: 1999 Fungicide
No Fungicide
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Maize Rotation Experiments (1996-1998)
• Location: Nyankpala & Wa• 3 cropping systems: continuous maize,
maize-peanut, & peanut-maize• Nitrogen levels: 0, 30, 60, 4 t/ha manure• Yearly experiment files and annual
measurement files setup• Four sequence files for rotating crops
were also setup for maize plots
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Yearly maize experiment and measurement files File Field Treatment Fertilizer for Maize GHNY9601.MZX, GHNY9601.MZA A-1 1 None A-2 2 30kg N A-3 3 60kg N GHNY9701.MZX, GHNY9701.MZA A-1 1 None A-2 2 30kg N A-3 3 4ton cow manure GHNY9801.MZX, GHNY9801.MZA A-1 1 None A-2 2 30kg N A-3 3 4ton cow manure
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Yield variability in response to N fertilization
MaizeWa, Ghana in 1997-1999
0.0
0.5
1.0
1.5
2.0
0kg N 4ton Manure 30kg N 60kg N
Fertilizer
Obs
. Yie
ld (t
on/h
a)
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Yield variability in response to total
cumulative rainfall during the crop season
MaizeWa, Ghana in 1997-1999
0.5
1.0
1.5
2.0
300 400 500 600 700 800
Cumulative Rainfall (mm)
Obs
. Yie
ld (t
on/h
a)
0kg N4ton MN30kg N60kg N
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Legume yield variability with total cumulative rainfall
LegumeWa, Ghana in 1997-1999
0.0
0.5
1.0
1.5
2.0
400 500 600 700 800
Cumulative Rainfall (mm)
Obs
. Yie
ld (t
on/h
a)
SoybeanPeanut
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Relationship between simulated nitrogen
stress factor and rainfall amount
MaizeWa, Ghana in 1997-1999
0.0
0.1
0.2
0.3
0.4
200 400 600 800 1000
Total rainfall during growth season (mm)
Sim
. N s
tress
fact
or
Beginning of grain f illingEnd of grain f illingMaturity
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Simulated nitrogen leaching as a function of rainfall
MaizeWa, Ghana in 1997-1999Fertilizer: 30kg N
6
8
10
12
400 500 600 700 800
Total rainfall during growth season (mm)
N le
ache
d (k
g[N]
/ha)
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Simulation of 2003 On-farm Maize Rotations
• Location: Nakor village, Wa
• Three farmers collaborated
• Four cropping systems studied: continuous -maize + low N (30kg/ha)
-continuous maize + high N (80 kg/ha)
-maize-peanut + 40 kg/ha N
-peanut-maize + 40 kg/ha N to maize
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Measurements
• Initial soil carbon content
• Soil texture
• Biomass at final harvest
• Grain yield at final harvest
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Calibration
• Changed genetic coefficients of maize based on observed biomass and grain yield.
• Photosynthetic factor for each field set=0.85
• SLNF for each field was set = 1.0
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Calibration continues..
• Initial SOM pool fractions calibrated as follows:• (i) On-farm experiments were simulated for 50
years using the reported SOM fractions for Mali cropping system condition (SOM1:SOM2:SOM3 = 0.02:0.41:0.57, Walen et al., 2002);
• (ii)Yearly carbon initially decreased, then stabilized after about 50 years;
• (iii) The SOM pool fractions were then obtained when soil carbon stabilized (SOM1:SOM2:SOM3 = 0.01:0.14:0.85).
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Simulated and observed maize biomass in
Nakor village, Wa, Ghana
MaizeOn-farm experimentsNakor village, Ghana
3
4
5
6
20 30 40 50 60 70 80 90
kg[N fertilizer]/ha
ton[
biom
ass]
/ha
SimulatedObserved
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Correlation between simulated maize biomass and top 20cm soil carbon content
in three farmers' field
Carbon vs. Biomass
3
4
5
6
7
0.3 0.4 0.5 0.6 0.7
% Carbon in top 20cm soil
biom
ass
(ton/
ha)
WounbunoDramaniBoakye
30 kg N
80 kg N 40 kg N
30 kg N
80 kg N
40 kg N
30 kg N
80 kg N40 kg N
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Total carbon sequestration in farmers fields
Total Carbon Sequestration12 plots (1800 m2) in Nakor, Wa, Ghana
5.6
5.8
6.0
2003 2008 2013 2018 2023
ton[
C]/re
gion
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Conclusions
• Model able to predict peanut growth and yield under varying sowing dates, varieties, and leafspot disease epidermics after calibration
• It was reasonably accurate in simulating maize yield variability under different nitrogen regimes
• Simulated yield highly correlated with soil C; fertilizer use efficiency was lower for low soil C situations
• Simulation, after calibration, suggest that there is potential for soil C sequestration in maize cropping systems with fertilizer and manure.
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Simulated maize biomass in Boakye's farm
BiomassBoakye's farm
0
2
4
6
8
0 20 40 60 80 100 120
DAP
biom
ass
(ton/
ha)
30 kg N40 kg N80 kg N
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Simulated maize biomass in Dramani's farm
BiomassDramani's farm
0
2
4
6
8
0 20 40 60 80 100 120
DAP
bioma
ss (t
on/ha
)
30 kg N40 kg N80 kg N
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Simulated maize biomass in Wounbuno's
farm
BiomassWounbuno's farm
0
2
4
6
8
0 20 40 60 80 100 120
DAP
bioma
ss (t
on/ha
)
30 kg N40 kg N80 kg N