Abstract
2.3 Results
2.3.2 Ahrens trial
Soil test data
Analyses of soil samples taken after fertilizing confirmed that P and K increased with increasing applications (Tables 12a, 12b and 12c, and Tables 13a, 13b and 13c, respectively). Nitrogen, P and K applications did not make any unexpected changes to other soil nutrient levels (Miles, personal communication).
Table 12a. ANOVA table of soil phosphorus (mg kg"1) levels as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen Phosphorus Linear (P i 0.05) Potassium Nitrogen:
phosphorus Nitrogen:
potassium Phosphorus:
potassium Residual 24 Total 63
Degree of freedom
3 3
3 g
9
g
Mean square
g.igo 1966.1 go
60.330 18.110
51.60
20.970
F Value
0.350 74.120
2.270 0.680
1.950
0.790
Probability
0.792
< 0.001 " *
0.106 0.717
0.093
0.628
CV% = 37.7 - ^
NS = non-significant (P = > 0.05); * = significant (P *. 0.05); " = highly significant (P s0.01); " *
= very highly significant (P i 0.001)
115
Table 12b. Table of means of soil phosphorus levels (mg kg '1) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSDraos,
MAIN EFFECT - PHOSPHORUS
LSDr005,
MAIN EFFECT - POTASSIUM
LSD ra «„
Nitrogen (N) applied (kg ha 1) NO
10.35
N60 10.78
N120 10.5
N180 11.56 NS
Phosphorus (P) applied (kg ha 1)
P0 3.40
P30 5.96
P60 12.96
P120 20.87
2.66
Potassium (K) applied (kg ha1) K0
9.85
K50 9.86
K100 9.39
K150 12.09 2.66
All table figures refer to soil phosphorus levels (mg kg -1)
116
Table 12c. Table of means of soil phosphorus (mg kg '1) interactions as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTION
NO N60 N120 N180 L S Dm M,
NITROGEN : POTASSIUM INTERACTION
NO N60 N120 N180 LSDm n 5,
PHOSPHORUS : POTASSIUM INTERACTION
PO P30 P60 P120
LSDra0S1
Phosphorus (P) applied (kg ha 1)
PO 2.70 3.92 3.97 2.47
P30 5.82 5.4 5.20 5.92
P60 9.72 10.73 12.02 17.08
P120 22.25 16.98 21.10 19.80 NS
Potassium (K) applied (kg ha"1) KO
9.17 10.20 13.32 10.97
K50 9.77 8.82 11.52 11.32
K100 9.85 10.55
9.50 6.27
K150 11.70 7.45 7.95 16.7 NS
Potassium (K) applied (kg ha"1) KO
4.85 7.50 12.42 - 18.90
K50
=2.f7
4.75 12.22 21.70
K100 2.87 4.65 8.80 19.85
K150 2.57 5.45 16.1 19.67 NS
All table figures refer to soil phosphorus levels (mg kg-1)
117
Table 13a. ANOVA table of soil potassium (cmolckg "1) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen Phosphorus
Linear (P *. 0.05)
Potassium
Linear (P i 0.05)
Nitrogen : phosphorus Nitrogen : potassium Phosphorus:
potassium
Linear (P ;. 0.05)
Residual 24 Total 63
Degree of freedom
3 3
3
9
g
g
Mean square
0.012 0.046
0.035
0.009
0.010688
0.017875
F Value
2.42 g.21
6g.37
1.82
2.14
3.58
Probability
0.091
<0.001 ***
<0.001 ***
0.116
0.066
0.006 **
CV% =25.1
NS = non-significant (P = > 0.05); * = significant (P ± 0.05); ** = highly significant (P s0.01); *** = very highly significant (P < 0.001)
118
Table 13b. Table of means of soil potassium (cmolckg "1) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSD,0 M n
MAIN EFFECT - PHOSPHORUS
LSDm n m
MAIN EFFECT - POTASSIUM
LSDm n m
Nitrogen (N) applied (kg ha 1) NO
0.28
N60 - 0.24
N120 0.26
N180 0.24
NS
Phosphorus (P) applied (kg ha 1)
P0 0.30
P30 0.26
P60 0.24
P120
0.21
0.036
Potassium (K) applied (kg ha1) K0
0.13
K50 0.23
K100
0.28
K150
0.38
0.036
All table figures refer to soil potassium (cmolckg-1) levels
119
Table 13c. Table of means on soil potassium interactions levels (cmolckg '1) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTION
NO N60 N120 N180 LSDm n m
NITROGEN : POTASSIUM INTERACTION
NO N60 N120 N180 LSDm n m
PHOSPHORUS : POTASSIUM INTERACTION
PO P30 P60 P120 LSD-mM,
Phosphorus (P) applied (kg ha 1)
PO 0.30 0.25 0.33 0.31
P30 0.23 0.26 0.22 0.29
P60 0.27 0.25 0.24 0.17
P120 0.25 0.18 0.23 0.17 NS
Potassium (K) applied (kg ha"1) K0
0.13 0.10 0.15 0.12
K50 0.22 0.21 0.20 0.28
K100 0.29 0.31 0.33 0.22
K150 0.41 0.33 0.34 0.32 NS
Potassium (K) applied (kg ha"1) K0
0.13 0.10 0.15 0.12
K50 0.24 0.28 0.20 0.18
K100
^ 0.39 0.27 0.29 0.19
K150 0.43 0.35 0.28 0.34 NS
All table figures refer to soil potassium (cmolckg-1) levels
120
Leaf analyses
Leaf analyses confirmed that with increasing applications of N, P and K there was an increased uptake of these nutrients (Tables 14a, 14b and 14c, Tables 15a, 15b and 15c, and Tables 16a, 16b and 16c, respectively). Increasing applications of N, P and K did not show any unexpected changes in nutrient uptake (Miles, personal communication).
Table 14a. ANOVA table of leaf nitrogen (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen
Linear (P i 0.05)
Phosphorus Potassium Nitrogen : phosphorus Nitrogen:
potassium Phosphorus:
potassium Residual 24 Total 63
Degree of freedom
3
3 3 9
9
9
Mean square
2.734
0.053 0.045 0.067
0.038
0.014
F Value
73.770
1.430 1.230 1.810
1.030
0.390
Probability
<0.001*"
0.258 0.322 0.119
0.445
0.930
—
CV% =6.5
NS = non-significant (P = > 0.05); * = significant (P ^ 0.05); ** = highly significant (P s0.01); *** = very highly significant (P <, 0.001)
121
Table 14b. Table of means of leaf nitrogen (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSDm o s,
MAIN EFFECT - PHOSPHORUS
LSD,no(n
MAIN EFFECT - POTASSIUM
LSDmnB,
Nitrogen (N) applied (kg ha 1) NO
2.37
N60 3.00
N120 3.17
N180 3.30
0.041
Phosphorus (P) applied (kg ha 1)
P0
3.03
P30
2.89
P60
2.95
P120
2.97
NS
Potassium (K) applied (kg ha"1) K0
2.89
K50
3.01
K100
2.99
K150
2.95
NS
All table figures refer to leaf nitrogen (%) levels
122
Table 14c. Table of means of leaf nitrogen interactions (%) as affected by nitrogen, phosphorus and potassium applications at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTIONS
NO N60 N120 N180 LSD m M,
NITROGEN : POTASSIUM INTERACTIONS
NO N60 N120 N180 LSDm n m
PHOSPHORUS : POTASSIUM INTERACTIONS
PO P30 P60 P120 LSDm M,
Phosphorus (P) applied (kg ha 1) PO
2.66 3.01 3.13 3.32
P30 2.34 2.97 3.03 3.22
P60 2.17 2.99 3.33 3.30
P120 2.30 3.02 3.18 3.37 NS
Potassium (K) applied (kg ha1) K0
2.32 2.97 3.09 3.16
K50 2.49 2.97 3.19 3.38
K100 2.40 2.94 3.16 3.47
K150 2.26 3.10 3.24 3.20 NS
Potassium (K) applied (kg ha1) K0
2.95 2.85 2.87 2.76
K50 3.06 2.94 3.05 2.98
K100 -i 3.04
2.91 3.04 2.96
K150 3.06 2.85 2.84 3.05 NS
All table figures refer to leaf nitrogen (%) levels
123
Table 15a. ANOVA table of leaf phosphorus (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen Phosphorus
Linear (P i 0.05)
Potassium Nitrogen : phosphorus
Linear (P *. 0.05)
Nitrogen : potassium Phosphorus:
potassium Residual 24 Total 63
Degree of freedom
3 3
3 9
9
9
Mean square
0.002 0.014
0.001 0.002
0.000
0.001
F Value
2.910 17.310
1.740 2.520
0.420
0.890
Probability
0.055
<0.001***
0.185 0.034*
0.912
0.552
CV% =12.8
NS = non-significant (P = > 0.05); * = significant (P < 0.05); ** = highly significant (P .0.01); *** = very highly significant (P <. 0.001)
124
Table 15b. Table of means of leaf phosphorus (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSD m ns,
MAIN EFFECT - PHOSPHORUS
LSD,o o m
MAIN EFFECT - POTASSIUM
L S Dm n m
Nitrogen (N) applied (kg ha 1) NO
0.21
N60 0.23
N120 0.24
N180 0.24 NS
Phosphorus (P) applied (kg h a1) P0
0.19
P30 0.22
P60 0.24
P120 0.27 0.02
Potassium (K) applied (kg ha1) K0
0.24
K50 0.23
K100 0.22
K150 0.23 NS
All table figures refer to leaf phosphorus (%) levels
125
Table 15c. Table of means of leaf phosphorus interactions (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTIONS
NO N60 N120 N180 LSDmnm
NITROGEN : POTASSIUM INTERACTIONS
NO N60 N120 N180 LSD,n(m
PHOSPHORUS : POTASSIUM INTERACTIONS
PO P30 P60 P120 LSDm n m
Phosphorus (P) applied (kg ha 1)
PO 0.18 0.21 0.23 0.16
P30 0.21 0.23 0.21 0.22
P60 0.21 0.24 0.24 0.28
P120 0.25 0.25 0.28 0.28 NS
Potassium (K) applied (kg ha1) K0
0.22 0.26 0.25 0.25
K50 0.21 0.24 0.24 0.23
K100 0.21 0.22 0.24 0.22
K150 0.21 0.22 0.23 0.24 NS
Potassium (K) applied (kg ha1) K0
0.20 0.25 0.25 0.28
K50 0.21 0.2 0.23 0.28
K100
*. 0.16 0.21 0.23 0.26
K150 0.16 0.22 0.25 0.25 NS
All table figures refer to leaf phosphorus (%) levels
126
Table 16a. ANOVA table of leaf potassium (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen
Linear (P =. 0.05)
Phosphorus]
Linear (P i. 0.05)
Potassium
Linear (P s. 0.05)
Nitrogen : phosphorus Nitrogen : potassium Phosphorus:
potassium Residual 24 Total 63
Degree of freedom
3
3
3
9
9
9
Mean square
0.217
0.632
4.989
0.150
0.073
0.083
F Value
3.120
9.070
71.600
2.150
-1.050
1.200
Probability
0.045*
< 0.001 ***
< 0.001 ***
0.065
0.434
0.342
CV% =18.4
NS = non-significant (P = > 0.05); * = significant (P u 0.05); ** = highly significant (P i,0.01); *** = very highly significant (P •_ 0.001)
127
Table 16b. Table of means of leaf potassium (%) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSDmr»,
MAIN EFFECT - PHOSPHORUS
LSD(005,
MAIN EFFECT - POTASSIUM
LSDmnm
Nitrogen (N) applied (kg ha 1) NO
1.61
N60 1.41
N120 1.35
N180 1.37 NS
Phosphorus (P) applied (kg ha 1)
PO 1.71
P30 1.44
P60 1.30
P120 1.29 0.19
Potassium (K) applied (kg ha'1) K0
0.68
K25 1.36
K50 1.80
K150 1.90 0.19
All table figures refer to leaf potassium (%)
128
Table 16c. Table of means of leaf potassium (%) interactions as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTIONS
NO N60 N120 N180 LSD m M,
NITROGEN : POTASSIUM INTERACTIONS
NO N60 N120 N180 LSD( n n s,
PHOSPHORUS : POTASSIUM INTERACTIONS
PO P30 P60 P120 LSDm n m
Phosphorus (P) applied (kg ha ') PO
1.74 1.54 1.67 1.90
P30 1.41 1.56 1.41 1.40
P60 1.78 1.31 1.07 1.04
P120 1.49 1.25 1.26 1.14 NS
Potassium (K) applied (kg ha1) K0
0.94 0.49 0.66 0.62
K50 1.58 1.37 1.09 1.38
K100 1.80 1.93 1.84 1.66
K150 2.10 1.88 1.83 1.81 NS
Potassium (K) applied (kg ha1) K0
0.69 0.65 0.71 0.66
K50 1.65 :
1.47 1.19 1.12
K100
•«. 2.16 1.78 1.64 - 1.64
K150 2.36 1.89 1.66 1.71 NS
All table figures refer to leaf potassium (%) levels
129
Final percentage leaf blighting (146 DAP)
Increased leaf blighting occurred with increased applications of N, P and K
(Tables 17a, 17b and 17c) (Fig. 5a, 5b and 5c). However, P was found to have little (P
< 0.05) effect on final percentage leaf blighting.
Table 17a. ANOVA table of final percentage leaf blighting (146 DAP) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen
Linear (P *. 0.05)
Phosphorus
Linear (P *. 0.05)
Potassium
Linear (P •, 0.05)
Nitrogen : phosphorus Nitrogen : potassium Phosphorus:
potassium Residual 24 Total 63
Degree of freedom
3
3
3
9
9
9
Mean square
103.792
34.375
54.740
9.292
15.642
7.740
I
F Value
11.280
3.740
5.950
1.010
1.700
0.840
Probability
<0.001 ***
0.025 *
0.004 **
0.460
0.144
0.587
CV% =20.9
NS = non-significant (P = > 0.05); * = significant (P < 0.05); ** = highly significant (P s0.01); *** = very highly significant (P <. 0.001)
130
Table 17b. Table of means of final percentage leaf blighting (146 DAP) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSDmns,
MAIN EFFECT - PHOSPHORUS
LSDr 0 Kn
MAIN EFFECT - POTASSIUM
LSD,005)
Nitrogen (N) applied (kg ha 1) NO
3.31
N60 6.94
N120 7.00
N180 9.50 2.21
Phosphorus (P) applied (kg ha 1)
PO 4.56
P30 6.87
P60 7.56
P120 7.75 2.21
Potassium (K) applied (kg ha"1) KO
4.12
K50 6.91
K100 7.19 2.21
K150 8.53
All table figures refer to final % leaf blighting
131
Table 17c. Table of means of final percentage leaf blighting (146 DAP) interactions as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTION
NO N60 N120 N180 LSD,n o s,
NITROGEN : POTASSIUM INTERACTION
NO N60 N120 N180 LSD,0O51
PHOSPHORUS : POTASSIUM INTERACTION
PO P30 P60 P120 L S Dm 0 M
Phosphorus (P) applied (kg ha 1)
PO 1.37 6.25 3.00 7.62
P30 3.75 5.75 7.12 10.88
P60 4.00 9.38 7.50 9.38
P120 4.12 6.37 10.38 10.13 NS
Potassium (K) applied (kg ha'1) K0
3.37 5.25 3.75 4.12
K50 4.12 7.00 6.50 10.00
K100 2.50 8.63 7.50 10.13
K150 3.25 6.87 10.25 13.75 NS
Potassium (K) applied (kg ha"1) K0
4.50 2.75 5.00 4.25
K50 3.00 8.88 7.50 8.25
-i K100 4.62 7.37 7.75 9.00
K150 6.12 8.50 10.00
9.50 NS
All table figures refer to final percentage leaf blighting
132
(a)
(b)
(c)
Fig. 5. Effect of nitrogen, phosphorus and potassium (kg ha'1) on final percentage leaf blighting on non-fungicide treated maize at Ahrens (1995/96) (a. nitrogen and phosphorus; b. nitrogen and potassium; c. phosphorus and potassium)
133
Grain yield
Increases in N, P and K resulted in increased maize grain yields (Tables 18a, 18b and 18c) (Fig. 6a, 6b and 6c).
Table 18a. ANOVA table of grain yield (t ha '1) as affected by nilrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
Rep N.P.K stratum Nitrogen
Linear (P i 0.05)
Phosphorus
Linear (P *. 0.05)
Potassium
Linear (P .. 0.05)
Nitrogen : phosphorus Nitrogen : potassium Phosphorus:
potassium Residual 24 Total 63
Degree of freedom
3
3
3
9
9
9
Mean square
5.257
1.322
1.201
5.377
1.261
1.985
F Value
5.570
14.02Q
12.740
0.57C
1.340
2.100
Probability
0.005 **
<0.001 ***
<0.001 ***
0.808
0.270
0.071
C V % = 2 6 . 2
NS = non-sig~nificant (P = > 0.05);* = significant (P < 0.05;]; ** = highly significant (P :;0.01); *** = very highly significant (P <. 0.001)
134
Table 18b. Table of means of grain yields (t ha "1) as affected by nitrogen, phosphorus and potassium fertilizer applications at Ahrens (1995/96)
MAIN EFFECT - NITROGEN
LSD(00S,
MAIN EFFECT - PHOSPHORUS
LSDm n 5,
MAIN EFFECT - POTASSIUM
-
LSDronsi
Nitrogen (N) applied (kg ha 1) NO
2.93
N60 3.61
N120 4.11
N180 4.24 0.71
Phosphorus (P) applied (kg h a1) P0
2.43
P30 3.75
P60 4.36
P120 4.53
0.71
Potassium (K) applied (kg ha1) K0
2.42
K50 4.13
K100 4.14
K150 4.37
0.71
All figure tables refer to maize grain yields (t ha"1)
135
Table 18c. Table of means of grain yield (t ha '1) interactions as affected by nitrogen, phosphorus and potassium interactions at Ahrens (1995/96)
NITROGEN : PHOSPHORUS INTERACTIONS
NO N60 N120 N180 LSD m n m
NITROGEN : POTASSIUM INTERACTIONS
NO N60 N120 N180 LSDm 0 R,
PHOSPHORUS : POTASSIUM INTERACTIONS
PO P30 P60 P120 L S Dm m,
Phosphorus (P) applied (kg ha ')
PO 1.58 2.66 2.92 2.68
P30 2.53 3.80 4.07 4.24
P60 4.02 4.16 4.38 4.49
P120 3.64 3.88 5.05 5.32 NS
Potassium (K) applied (kg ha1) KO
2.76 1.88 2.40 2.64
K50 2.97 3.86 4.89 4.57
K100 3.21 40.60
4.52 4.50
K150 2.80 4.71 4.61 5.02 NS
Potassium (K) applied (kg ha1) KO
2.44 1.54 3.02 2.69
K50 2.06 4.77 4.70 4.76
K100 2.64 4.40 4.32 4.92
K150 2.66 3.94 5.02 5.52 NS
All figure tables refer to maize grain yields (t ha"1)
136
(a)
(b)
w
Fig. 6. Effect of nitrogen, phosphorus and potassium (kg ha'1) on grain yield (tonnes ha'1) of non-fungicide treated maize at Ahrens (1995/96) (a. nitrogen and phosphorus;
b. nitrogen and potassium; c. phosphorus and potassium)
137