Phosphogypsum effkiencg to correct soi1 P ...
Phosphogypsum effkiencg to correct soi1 P
deficiency and/or soi1 acidity
M. SENE, M. DUCK ami A. BABWE
ISRA, Sénég;;rl
Paper prepared for the fïrst annual ‘Uorkshop of IbterCRSP
West Afiica gynup
Kaolack, January 1 1 - 14 January 1999
INTRODUCTION
Tbe locally industrial produced phosphoric acid for chemical fertility processing fiom naturai
rock phosphate deposits leads to huge amount of phosphogypsum pïled up near by the
factories. This materials for which chemical characteristics are given (see annex ) is now being
used on a large scale (nationwide) for the national programm aiming at boosting the
agricultural production. The newly processed P-source amendment material bags distributed to
farmers consists of the mix of of 50 % rock phosphate (RP) and 50 % phosphogypsum. But,
there is no previous study that prove the efficency of PG to correct soi1 P deficiency for trop
uses, or to reduçe eventually soil acidity given the large Ca content.
The objective is to study the efficiency of PG as compared with rock phosphate and lime.
MATERlALS AND METHODS
Site selection
This long term experiment started in 1997 is installed. in the NIORO ISBA agronomie research
station in a ferrigjneous leached soil. For the purpose ofthis study, a highly chemically
degraded soil site @H < 5.5 and available P < 30 ppm) was selectecd. This had been enabled
by the soil fertilty assessment undertaken throughout the research station three years ago
(Agetip, 1995). The 20 m by 20 m grid sampling used allowed a spatial variability analysis of
tbe various plots within the station.
Cropping system
Tbe Nioro area is a still reliable zone, as far as the rainfall is concemed. Peanut (variety 73-33)
as a cash trop and corn (variety Synthetic C) which is very sensitive ÉO soi1 fertility are the
chosen crops. The corn/peanut rotation used has started in 11997 with the com. The potential
yield is 4 t/ha for com, and 2,5 t/ha for peanut.
-_-----
c-
-----wrru.
l’reatments
Treatments under comparison cons& of combined use of phosphogypsum and. rock phosphate
as indicated (Table 1) ; the lime treatment acting as a reference for soi1 acidity control.
Table 1: Treatments under comparison
Treatments
Specifïcations
--“.Y
1.
I Check : No P added, only N and K
I
2 .
0 % P fiom rock phosphate (RP) + 0 %P fi-om
t-
phosphogypsum (PG) + 30 kg/ha P204 f?om triple
superphosphate (TSP)
3 .
O%Pf?omFW+100%PfiomPG
..--
4
25%PfiomRP+75%PfiomPG
- - -
5 .
50%Pf?omRP+50%Pfi-omPG
- ==l
0.
I 75 % P f?om RP + 25 % P fiom PG
I
I
7 .
100%PÇomRP+O%Pf?omPG
---1
PT-Ca f?om lime (CaO)
----l
Rate of application is d.i@erent for the two P sources : 1.00 % P fi-om RP corresponds with an
application rate of 400 kg/ha of RP, and 100 % P fiom PG defines an application rate of 700
kg/ha of PG. For treatment 8, 100 % Ca fiom Ca0 refus to a lime application of 400 kg/ha.
Frorn the chemical analysis data ofthese fertilizers, the P and/or Ca quantity added on each
plot cari be determined. These rates will be applied once every 4 years after 2 complete
rotation.
Experimental design
It is a randomized complete block design with 8 treatments and 4 repetitions.The size for each
of the 32 plots is 84 m2 (15 x 5.6). The number of row; to be sown each year depend on the
trop : 7 for com sown at a spacing of 80 cm, and 11 far peanut sown at a spacing of 50 cm.
tu--
.
L
---
Measurements
a) on soils
Afier the initial soi1 physical and chemical characterization mentionned above, soi1 samples are
taken once a year aRer harverst to monitor soil pH P and Ca contents within the profile. For
the first sampling performed in december 1997 alter the corn harvest, 108 samples have been
collected according the following scheme :
?
For treatment 1, 3 and 7, ail the plot s are sampled at 4 depths (0- 10, 1 O-20, 20-40, and
40-60 cm The treatments have been chosen to allow a analysis of Ca movement in the
profile ;
?
For the treatment,, all the plots have been sampled at only 3 depths (O-10, 1 O-20, 20-40 cm)
The soi1 analyses r-un on those samples are : particle size analysis, pH (water and KCl), carbon,
nitrogen (total N and nitrates), bases elements, CEC, Ahtnimq sulfin.
Part of the results of these analyses now available is presented in this report.
b) on plant
This sampling were not done in 1997 for corn.
Peanut plant samples are taken fiom each of the 32 plots at flowering/pegging stage for foliar
diagnosis. For each plot, four rephcate samples were analyzed for N, P, K Ca, and Mg.
Field operations
When applying the phosphocalcic amendment, plowing was used to mix the fertilizer in the top
20 soi1 layer. The timing of the difXerent operations performed in 1997 for cor-n and in 1998 for
peanut is presented (Table 2).
*--
--
--.
Table 2 : Field operations during the 1998 cropping season
-
I
l-RP, PG or Lime application 1 07/02
----i-r--
-----1
oxen drivenplowmg
07/03-04
-j_
l
1 sowing
1 07/10
) 06/21
I
tib-“““‘”
07102
08,05
--
p7127
----j
Pre-emergence weeding
----+&Y------------;
-
I
1 * urea pplication
os/05
---piï-
-----y
I
t
t-2nd urea application
08125
---r--- 1
2"dweeding
08125
Bedding
09/01
I
Harvest
1 10/31
N and K are applied on each plot at the following rates
a) 12 kg/ha of N at sowing, 22 kg/ha Nat the f%-st and at the second urea applicationfor cor-n ;
12 kg/ha of N at sowing for peanut
b ) 30 kg/ha of K at sowing for both peanut and corn.
Rainfall conditions
Rainfall patterns are diEerent for the 2 years (1997 and 1998) in figure 1
In fact, we have experienced one early rainy season in 1997 as opposed to a late rainy season
in 1998. The total annual ramfall is about the same for the 2 cropping seasons (580 mm).
However, While the rainy season started early june 1997, the Crst important rain was recorded
late July 1998. Although characterized by a rather shokl rainy season, the 1998 cropping
season has a much better ratiall distribution. A long drought period occurred early during the
1998 croppmg season, causing a severe plant water stress, while in 1998 there were no major
water stress problem, except at the trop maturity phase.
--
--
.“-..,-
,-II-
Fig. Nioro Fig. : Cumulative Rainfall by Dxade - 1997 and 1998
1 4 0
120
r----j
lc998
100
8 0
6 0
4 0
2 0
0
June
JW
August
Sept Oct
Months
RESULT AND DISCUSSION
As mentioned above, the selected site is part of the most degraded bloc of Nioro Station. The
comparison ofthe effects of P and/or Ca amendments o, com in 1997 and on peanut in 1998
has given production results shown (table 3).
For the fïrst year of the experiment corresponding with cor-n production, the ANOVA
indicated no significant treatment effect. Au important variability has been observed among
treatment. Com grain yields obtained are low compared to the variety yield potential which is
around 4 tons/ha. Two severe drought periods have occurred during the cropping season, early
in the vegetative phase and late at the maturity phase, which party explain the low obtained this
year in the Peauut Basin.
Peanut (1998)
In I QW. no significant effect is observed except for pod yields. Highest pod yields arc obtz,iIled
?i;ith trcatment where lime is applied and bv the treatrrents where phosphogysum is added: 7 :e
kcst among these being the consisting in 50 % PG + 50 % RP mix. This indicates the relati\\,-:
importance of Ca in pod production. The positive action of Ca to the degraded soi1 could arise
c*-oi?-r lo aspects. First of ail, there is the improvement of pod filling, and secondly the soi1 pl.1
increane and/or aluminum toxicity decrease could occur. This cari be confirmed hy the soi1
profile Ca enrichment resulting tiom the different P o;* Ca source amendments. This hypothesis
k supported by the fact that the plant analysis done kllowing the chlorosis observed at mid-
sc:ason does not reveal any significant treatment difference.
!fft:r a second year study, the tria1 starts the show the possible effects that cari result from thr
P and/or Ca source of soi1 amendments. The pursue of the experiment for 2 to 4 more years
should give a better idea on the real agronomie value oi‘phosphogypsum as an amendment
material.
-.
--“=-.m.
1--
Total Elements
PG
50% PG + 50%
Taiba RP
R P
Ca0 %
32,3
40,6
49,4
Mg0 %
0,Ol
0,04
0,116
K20 %
< 0,5
< 0,5
0,02
Na20 %
0,07
0,08
0,09
Fe203 %
0,15
0,49
1 ,!i9
Al203 %
0,27
0,77
0,98
P205 %
0,99
19,12
37,2
s %
14,64
6,79
.A
Mn PPm
2,3
108
404
0.1 wm
335
27,7
72
Zn PPm
< 1,o
290
522
Pb wm
593
593
5,‘4
Cr PPm
24,2
96,7
198
Ni ppm
24
29,8
86,4
cd wm
15,8
51,6
70,8
Solubles elements
Echantillons
Ca0 %
10,48
10,9
Mgo %
0,Ol
0,03
K~O %
0,44
0,32
Na2o %
0,07
0,07
P205 %
0,39
0,47
S
%
4,86
4,81
Ph eau %
4,67
3,91
deficiency and/or soi1 acidity
M. SENE, M. DUCK ami A. BABWE
ISRA, Sénég;;rl
Paper prepared for the fïrst annual ‘Uorkshop of IbterCRSP
West Afiica gynup
Kaolack, January 1 1 - 14 January 1999
INTRODUCTION
Tbe locally industrial produced phosphoric acid for chemical fertility processing fiom naturai
rock phosphate deposits leads to huge amount of phosphogypsum pïled up near by the
factories. This materials for which chemical characteristics are given (see annex ) is now being
used on a large scale (nationwide) for the national programm aiming at boosting the
agricultural production. The newly processed P-source amendment material bags distributed to
farmers consists of the mix of of 50 % rock phosphate (RP) and 50 % phosphogypsum. But,
there is no previous study that prove the efficency of PG to correct soi1 P deficiency for trop
uses, or to reduçe eventually soil acidity given the large Ca content.
The objective is to study the efficiency of PG as compared with rock phosphate and lime.
MATERlALS AND METHODS
Site selection
This long term experiment started in 1997 is installed. in the NIORO ISBA agronomie research
station in a ferrigjneous leached soil. For the purpose ofthis study, a highly chemically
degraded soil site @H < 5.5 and available P < 30 ppm) was selectecd. This had been enabled
by the soil fertilty assessment undertaken throughout the research station three years ago
(Agetip, 1995). The 20 m by 20 m grid sampling used allowed a spatial variability analysis of
tbe various plots within the station.
Cropping system
Tbe Nioro area is a still reliable zone, as far as the rainfall is concemed. Peanut (variety 73-33)
as a cash trop and corn (variety Synthetic C) which is very sensitive ÉO soi1 fertility are the
chosen crops. The corn/peanut rotation used has started in 11997 with the com. The potential
yield is 4 t/ha for com, and 2,5 t/ha for peanut.
-_-----
c-
-----wrru.
l’reatments
Treatments under comparison cons& of combined use of phosphogypsum and. rock phosphate
as indicated (Table 1) ; the lime treatment acting as a reference for soi1 acidity control.
Table 1: Treatments under comparison
Treatments
Specifïcations
--“.Y
1.
I Check : No P added, only N and K
I
2 .
0 % P fiom rock phosphate (RP) + 0 %P fi-om
t-
phosphogypsum (PG) + 30 kg/ha P204 f?om triple
superphosphate (TSP)
3 .
O%Pf?omFW+100%PfiomPG
..--
4
25%PfiomRP+75%PfiomPG
- - -
5 .
50%Pf?omRP+50%Pfi-omPG
- ==l
0.
I 75 % P f?om RP + 25 % P fiom PG
I
I
7 .
100%PÇomRP+O%Pf?omPG
---1
PT-Ca f?om lime (CaO)
----l
Rate of application is d.i@erent for the two P sources : 1.00 % P fi-om RP corresponds with an
application rate of 400 kg/ha of RP, and 100 % P fiom PG defines an application rate of 700
kg/ha of PG. For treatment 8, 100 % Ca fiom Ca0 refus to a lime application of 400 kg/ha.
Frorn the chemical analysis data ofthese fertilizers, the P and/or Ca quantity added on each
plot cari be determined. These rates will be applied once every 4 years after 2 complete
rotation.
Experimental design
It is a randomized complete block design with 8 treatments and 4 repetitions.The size for each
of the 32 plots is 84 m2 (15 x 5.6). The number of row; to be sown each year depend on the
trop : 7 for com sown at a spacing of 80 cm, and 11 far peanut sown at a spacing of 50 cm.
tu--
.
L
---
Measurements
a) on soils
Afier the initial soi1 physical and chemical characterization mentionned above, soi1 samples are
taken once a year aRer harverst to monitor soil pH P and Ca contents within the profile. For
the first sampling performed in december 1997 alter the corn harvest, 108 samples have been
collected according the following scheme :
?
For treatment 1, 3 and 7, ail the plot s are sampled at 4 depths (0- 10, 1 O-20, 20-40, and
40-60 cm The treatments have been chosen to allow a analysis of Ca movement in the
profile ;
?
For the treatment,, all the plots have been sampled at only 3 depths (O-10, 1 O-20, 20-40 cm)
The soi1 analyses r-un on those samples are : particle size analysis, pH (water and KCl), carbon,
nitrogen (total N and nitrates), bases elements, CEC, Ahtnimq sulfin.
Part of the results of these analyses now available is presented in this report.
b) on plant
This sampling were not done in 1997 for corn.
Peanut plant samples are taken fiom each of the 32 plots at flowering/pegging stage for foliar
diagnosis. For each plot, four rephcate samples were analyzed for N, P, K Ca, and Mg.
Field operations
When applying the phosphocalcic amendment, plowing was used to mix the fertilizer in the top
20 soi1 layer. The timing of the difXerent operations performed in 1997 for cor-n and in 1998 for
peanut is presented (Table 2).
*--
--
--.
Table 2 : Field operations during the 1998 cropping season
-
I
l-RP, PG or Lime application 1 07/02
----i-r--
-----1
oxen drivenplowmg
07/03-04
-j_
l
1 sowing
1 07/10
) 06/21
I
tib-“““‘”
07102
08,05
--
p7127
----j
Pre-emergence weeding
----+&Y------------;
-
I
1 * urea pplication
os/05
---piï-
-----y
I
t
t-2nd urea application
08125
---r--- 1
2"dweeding
08125
Bedding
09/01
I
Harvest
1 10/31
N and K are applied on each plot at the following rates
a) 12 kg/ha of N at sowing, 22 kg/ha Nat the f%-st and at the second urea applicationfor cor-n ;
12 kg/ha of N at sowing for peanut
b ) 30 kg/ha of K at sowing for both peanut and corn.
Rainfall conditions
Rainfall patterns are diEerent for the 2 years (1997 and 1998) in figure 1
In fact, we have experienced one early rainy season in 1997 as opposed to a late rainy season
in 1998. The total annual ramfall is about the same for the 2 cropping seasons (580 mm).
However, While the rainy season started early june 1997, the Crst important rain was recorded
late July 1998. Although characterized by a rather shokl rainy season, the 1998 cropping
season has a much better ratiall distribution. A long drought period occurred early during the
1998 croppmg season, causing a severe plant water stress, while in 1998 there were no major
water stress problem, except at the trop maturity phase.
--
--
.“-..,-
,-II-
Fig. Nioro Fig. : Cumulative Rainfall by Dxade - 1997 and 1998
1 4 0
120
r----j
lc998
100
8 0
6 0
4 0
2 0
0
June
JW
August
Sept Oct
Months
RESULT AND DISCUSSION
As mentioned above, the selected site is part of the most degraded bloc of Nioro Station. The
comparison ofthe effects of P and/or Ca amendments o, com in 1997 and on peanut in 1998
has given production results shown (table 3).
For the fïrst year of the experiment corresponding with cor-n production, the ANOVA
indicated no significant treatment effect. Au important variability has been observed among
treatment. Com grain yields obtained are low compared to the variety yield potential which is
around 4 tons/ha. Two severe drought periods have occurred during the cropping season, early
in the vegetative phase and late at the maturity phase, which party explain the low obtained this
year in the Peauut Basin.
Peanut (1998)
In I QW. no significant effect is observed except for pod yields. Highest pod yields arc obtz,iIled
?i;ith trcatment where lime is applied and bv the treatrrents where phosphogysum is added: 7 :e
kcst among these being the consisting in 50 % PG + 50 % RP mix. This indicates the relati\\,-:
importance of Ca in pod production. The positive action of Ca to the degraded soi1 could arise
c*-oi?-r lo aspects. First of ail, there is the improvement of pod filling, and secondly the soi1 pl.1
increane and/or aluminum toxicity decrease could occur. This cari be confirmed hy the soi1
profile Ca enrichment resulting tiom the different P o;* Ca source amendments. This hypothesis
k supported by the fact that the plant analysis done kllowing the chlorosis observed at mid-
sc:ason does not reveal any significant treatment difference.
!fft:r a second year study, the tria1 starts the show the possible effects that cari result from thr
P and/or Ca source of soi1 amendments. The pursue of the experiment for 2 to 4 more years
should give a better idea on the real agronomie value oi‘phosphogypsum as an amendment
material.
-.
--“=-.m.
1--
Total Elements
PG
50% PG + 50%
Taiba RP
R P
Ca0 %
32,3
40,6
49,4
Mg0 %
0,Ol
0,04
0,116
K20 %
< 0,5
< 0,5
0,02
Na20 %
0,07
0,08
0,09
Fe203 %
0,15
0,49
1 ,!i9
Al203 %
0,27
0,77
0,98
P205 %
0,99
19,12
37,2
s %
14,64
6,79
.A
Mn PPm
2,3
108
404
0.1 wm
335
27,7
72
Zn PPm
< 1,o
290
522
Pb wm
593
593
5,‘4
Cr PPm
24,2
96,7
198
Ni ppm
24
29,8
86,4
cd wm
15,8
51,6
70,8
Solubles elements
Echantillons
Ca0 %
10,48
10,9
Mgo %
0,Ol
0,03
K~O %
0,44
0,32
Na2o %
0,07
0,07
P205 %
0,39
0,47
S
%
4,86
4,81
Ph eau %
4,67
3,91