3.1 Selected Physicochemical Properties of the Study Site
The soil texture of the experimental area was appeared to be loamy sand (Table 3.1). Therefore, the soil texture of the study place is appropriate for groundnut production as the crop is grown mostly on light-textured soils ranging from coarse and fine sands to sandy clay loams. The total nitrogen content, available P and organic matter of the experimental site were 0.07%, 7.72 ppm and 0.09% respectively, which was very low to support the growth of plant. The pH value of the experimental site 7.25 was almost neutral according Tekalign (1991) within the ideal pH range value for groundnut production. Results of cation exchange capacity and electrical conductivity (2.7cmol (+)/kg/ha) and (0.045ms/cm) respectively were very low to groundnut cultivation (Landon, 1991) and it implied that the soil have low holding exchanging cations but free of salt problem. Results of potassium 238kg/ha was rated optimum for well growth of the crop (Landon, 1991). The level of available Zinc (Zn) in the experimental site was found to be 5.52 ppm which is very low to groundnut production.
Table 3.1: Some Physicochemical properties of the soil at the experimental field
Properties
|
Values
|
Remark
|
Soil physical properties
|
|
|
Sand (%)
|
88
|
|
Clay (%)
|
4
|
|
Silt (%)
|
8
|
|
Soil texture
|
|
Loamy sand
|
Soil chemical properties
|
|
|
pH (by 1:2.5 soil water ratio)
|
7.25
|
Almost neutral
|
Total nitrogen (%)
|
0.07
|
Very low
|
Organic carbon (%)
|
0.09
|
Very low
|
Available phosphorus (ppm)
|
7.72
|
Very low
|
Available Zn (ppm)
|
5.52
|
Very low
|
Cation exchange capacity (cmol(+)/kg/ha)
|
2.7
|
Very low
|
Electrical conductivity(ms/cm)
|
0.045
|
Very low
|
Mekelle soil laboratory (2017), As described by London (1991)
3.2 Effects on Phenological and Growth Traits of groundnut
The analysis of variance revealed a significant (P < 0.05) genotype and fertilizer main effects for days to 50% flowering. The Sedi variety appeared to flower earlier (35 days) followed by genotype ICGV91114 (36 days). While, the genotype coded as ICGV0308 flowered late (37 days) (Figure 3.1). Similar study by Sastry et al. (1985) stated that groundnut genotypes, which flower early during first and the second week of the flowering period produce better yield. The differences observed among the groundnut genotypes in relation to days to flowering can be attributed to the difference in growth characteristics among the genotypes. Verma et al. (2009) reported variable growth patterns in some groundnut genotypes, which could be due to differences in their genetic makeup. The main effect of combined phosphorus and foliar spray of zinc also showed significant effect on flowering. That combination may improve utilization of nutrients and water, which reflected on good growth and biological yield.
Figure 3.1: Effect of groundnut genotypes and PZn fertilizer on Phenology of groundnut
There was no interaction effect between genotype and fertilizer on between 50% maturity. The main effect of genotypes and fertilizer showed a significant difference for days to 50% maturity. The groundnut genotypes showed a significant difference for days to maturity where the Sedi matures relatively earlier than genotype ICGV91114 and ICGV00308 (Figure 3.1). Days to maturity showed a similar pattern with days to flowering with the application of combined fertilizer. The shortest maturity day was recorded from the highest rate.
Analysis of variance indicated that, nether the main effect nor the interaction effect were no significant difference on the leaf width.
Figure 3.2: Effect of genotypes and PZn fertilizers on leaf width and leaf length of groundnut
ANOVA table revealed that application of combined PZn fertilizer wes a significance effect (p<0.05) on leaf length. While the genotype main effect and interaction was no significant effects. The highest length was achieved at the maximum rate of P30Zn1.5 fertilizer (Figure 3.2). The average leaf length in the control plots was relatively lower than the treated plots. Increasing the joint application of phosphorus with foliar zinc up to P30Zn1.5 was increasing the leaf length on Sedi variety. In line with current study, Mirvat (2006) reported that increasing P fertilization up to 60 kg P2O5/fad with zinc concentration up to 1 g/L improves leaf length. These effects revealed that foliar nutrition of groundnut with zinc might increase the efficiency phosphorus utilization and enhancing vegetative growth.
3.3 Effects on Yield and Yield Components
The fertilizer main effect and interaction effects were statistically significant (P<0.01) for number of pods per plant. The highest number of pods per plant (35.4) was recorded from the interaction of genotype ICGV00308 with P30Zn1.5 at par with P20Zn1 (Table 3.2). This genotype (ICGV00308) depicted a relatively lower performance in average number of pods per plant (23.13) without fertilizer.
Table 3.2: The interaction effect of genotypes and PZn fertilizer on pod number/plant
Genotypes(G)
|
Combined fertilizers(F)
|
|
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Mean
|
ICGV00308
|
23.13
|
31.27
|
33.20
|
35.40
|
30.75
|
ICGV91114
|
28.07
|
30.27
|
31.00
|
30.73
|
30
|
Standard check (Sedi)
|
28.13
|
29.40
|
30.50
|
32.73
|
30.19
|
Mean
|
26.4
|
30.3
|
31.6
|
33
|
|
LSD(0.05) GxF
|
2.153
|
|
|
|
|
CV (%) GxF
|
4.2
|
|
|
|
|
|
|
|
|
|
|
|
Where P=kg/ha Zn=g/L, LSD (0.05) =Least Significant Difference at 5% level; CV= Coefficient of variation.
A statistically significant main and interaction effects were showed on pod yield (P<0.01). The highest pod yield was attended from the higher rate of fertilizer with sedi variety. Whereas the lowest pod yield was recorded from ICGV00308 genotype without fertilizer (control) (Table 3.3).
Table 3.3: Interaction effect of genotypes and PZn on pod yield kg/ha of groundnut
Genotypes(G)
|
Combined fertilizers(F)
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Mean
|
ICGV00308
|
2904
|
3072
|
3198
|
3302
|
3119
|
ICGV91114
|
3059
|
3028
|
3180
|
3135
|
3101
|
Standard check(sedi)
|
3341
|
3302
|
3475
|
3567
|
3421
|
Mean
|
3101
|
3134
|
3284
|
3335
|
LSD (0.05) GxF
|
237.3
|
|
|
|
|
CV (%) GxF
|
3.5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Where P=kg/ha Zn=g/L, LSD (0.05) =Least Significant Difference at 5% level; CV= Coefficient of variation.
Analysis of variance showed that, there were a significant main and interaction effects on number of seeds per pod. The result exhibited that, the highest number of seeds per pod was obtained from Sedi variety with P30Zn1.5 fertilizer (Table 3.4). While the lowest number of seeds per pod was recorded from the genotype ICGV00308 with P20Zn1 fertilizer. This is may be due to the genetic makeup of the genotype and/or effect of the combined fertilizer.
Table 3.4: The interaction effect of genotypes and PZn fertilizer on number of seeds/pod
|
Genotypes(G)
|
Combined fertilizers (F)
|
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Mean
|
|
ICGV00308
|
2
|
1.80
|
1.67
|
1.73
|
1.8
|
|
ICGV91114
|
1.87
|
1.93
|
1.87
|
2.07
|
1.94
|
|
Standard check(Sedi)
|
2.33
|
2.67
|
2.67
|
2.87
|
2.64
|
|
Mean
|
2.06
|
2.13
|
2.07
|
2.22
|
LSD(0.05) GxF
|
0.23
|
|
|
|
|
CV (%) GxF
|
6.3
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Where P=kg/ha Zn=g/L, LSD (0.05) =Least Significant Difference at 5% level; CV= Coefficient of variation.
There were a significant interaction and main effect of groundnut and fertilizer on seed yield of groundnut (p < 0.01). The highest seed yield (2,529 kg/ha) and (2,516 kg/ha) was obtained from variety Sedi with P30Zn1.5 and P20Zn1 combined fertilizer rate, respectively (Table 3.5).
Table 3.5: Seed yield (kg/ha) as affected by interaction of genotypes and PZn fertilizers
|
Genotypes(G)
|
Combined fertilizers(F)
|
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Mean
|
|
ICGV00308
|
1908
|
2205
|
2326
|
2378
|
2204
|
|
ICGV91114
|
2204
|
2201
|
2221
|
2296
|
2230
|
|
Standard check(sedi)
|
2351
|
2384
|
2516
|
2529
|
2445
|
|
Mean
|
2154
|
2263
|
2354
|
2401
|
LSD(0.05) GxF
|
170.8
|
|
|
|
|
CV (%) GxF
|
4.4
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Where P=kg/ha Zn=g/L, LSD (0.05) =Least Significant Difference at 5% level; CV= Coefficient of variation.
While the lowest seed yield (1908 kg/ha) was recorded from ICGV00308 genotype without fertilizer. The highest recorded seed yield increment over this treatment was 33%. Under this treatment significant increase in seed yield may be due to associated improvement in leaf length, leaf width, pod number/plant, pod yield/ha and number of seeds /pod as reported by Jeetarwal, (2013). The seed yield has a highly significant and positive correlation with those yield attributes that further support their direct and indirect effect on seed yield in consistency with the report of Bethlehem (2011).
Application of combined fertilizers on sedi variety was increase productivity of groundnut per unite area from the current farmers yield of Tanqua-Abergelle (1200 kg/ha) which is very low compare to the yield obtained from the current research finding 2,529 kg/ha that proved more than double yield advantage than the farmers practice in the woreda. Thus, result also exhibited promising increment than the average yield (700 kg/ha) of the region Tigray and 1,330 kg/ha of the national productivity (CSA, 2016).
Results showed that main effect of fertilizer rates and interaction effects were statistically significant (P<0.005) effect on shelling percentage. The highest shelling percentage (73.33) was recorded form genotype ICGV91114 with P30Zn1.5 fertilizer. The lowest shelling percentage was record form genotype ICGV00308 (65.68%) percentage without fertilizer (Figure 3.3) and It has a positive correlation with seed yield (r=0.62) and this was may be due to the application of more fertilizer to the soil and foliar, which enhances these parameters.
Figure 3.3: The interaction effect of genotypes and PZn fertilizer on shelling percentage of groundnut
Hundred seed weight was significantly (p <0.05) influenced by the genotype main effect. However, the fertilizer main effect and the interaction component were not significant. The genotype coded as ICGV91114 had relatively higher mean seed weight (47.23 g) than the other genotypes in the finding (Figure 3.4). This result is may be due to the genetic differences between the genotypes that is consistent with the idea of Mulatu (2014) who stated that the seed weight characters is more influenced by genetic factors than environment. In other hand, hundred seed weight (45.12g) of the genotype had found in the rage of 35-70 g is under the rage, which fulfills the international market quality of seed grade (Acland, 1971).
Figure 3.4: Main effect of genotypes and PZn on hundred seed weight of groundnut
3.4 Effects on Seed Nutrition Content
The main effect fertilizer level and the interaction effects were statistically highly significant (P < 0.01) for crude protein content. The maximum protein content (37.79%) was recorded from sedi variety at the rate of P30Zn1.5 fertilizer. Nevertheless, the lowest protein content was also recorded from the same variety (Sedi) in the lowest rate of fertilizer (Table 3. 6).
Table 3.6: The interaction effect of genotypes and PZn fertilizers on protein content (%)
Genotypes(G)
|
Combined fertilizers(F)
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Mean
|
ICGV00308
|
36.78
|
37.25
|
37.46
|
37.46
|
37.24
|
ICGV91114
|
37.13
|
37.10
|
36.65
|
37.03
|
36.98
|
Standard check(Sedi)
|
36.69
|
35.90
|
37.36
|
37.79
|
36.94
|
Mean
|
36.87
|
36.75
|
37.16
|
37.43
|
LSD (0.05) GxF
|
0.6938
|
|
|
|
|
CV (%) GxF
|
1.1
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Where P=kg/ha Zn=g/L, LSD (0.05) =Least Significant Difference at 5% level; CV= Coefficient of variation.
The analysis variance showed fat content was exhibited a significant main effect and the interaction effects. The highest percentage of fat content (43.95%) was extracted from ICGV00308 under the highest level of fertilizer (P30Zn1.5) (Table 3.7). While, the lowest fat content was gained from Sedi at untreated condition (P0Zn0). The significant interaction effects of genotype and fertilizer on crude protein and fat (%) were found in the range of 36.69 - 37.79 and 41.44 - 43.95% by the application of P30Zn1.5 fertilizer on Sedi and ICGV00308, respectively. As the rate of fertilizer increases, the percentage of crude protein and fat content tend to increase linearly. Okello et al. (2010) who found 20-50% and 40-50% protein and fat content on groundnut due to fertilizer application, respectively reported similar finding. The current result was in line with Majumdar et al. (2001) also reported that, the percentage of protein increase as a result of an application of phosphorus up to 70 kg P2O5/ha. Gobarah et al. (2006) also noted that P application significantly increased protein (25.82%) contents on groundnut over control.
Table 3.7: The interaction of genotypes and PZn fertilizer on fat content (%) of groundnut
Genotypes
|
Combined fertilizers
|
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Mean
|
ICGV00308
|
43.67
|
43.76
|
43.91
|
43.95
|
43.81
|
ICGV91114
|
42.03
|
41.45
|
41.71
|
43
|
42.04
|
Standard check(sedi)
|
41.78
|
41.93
|
43.63
|
42.9
|
42.56
|
Mean
|
42.49
|
41.71
|
43.08
|
43.28
|
LSD(0.05) GxF
|
0.712
|
|
|
|
|
CV (%) GxF
|
1
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Where P=kg/ha Zn=g/L, LSD (0.05) =Least Significant Difference at 5% level; CV= Coefficient of variation.
3.5 Associations among the Groundnut Parameters
A bivariate correlation analysis between the measured traits had positive and negative associations (Table 3.8). Seed yield had a strong and positive correlation with pod yield (r=0.936), leaf length (0.927), pod number/plant (r=0.683), shelling percentage (r=0.616) and number seeds/pod (r=0.576). Nevertheless, days to 50% flowering and days to 50% maturity were negatively correlated with seed yield, (r=-0.833) and (r=-0.91), respectively.
Table 3.8: Correlation coefficients between the groundnut parameters as affected by genotypes and PZn combined fertilizers
Parameters
|
DF (%)
|
LW (cm)
|
LL (cm)
|
DM (%)
|
PN/P
|
PY (kg/ha )
|
NS/P
|
S (%)
|
SY (kg/ha)
|
HSW (g)
|
CP (%)
|
F (%)
|
DF (%)
|
1
|
|
|
|
|
|
|
|
|
|
|
|
LW(cm)
|
-0.339
|
1
|
|
|
|
|
|
|
|
|
|
|
LL(cm)
|
-0.737**
|
0.474
|
1
|
|
|
|
|
|
|
|
|
|
DM (%)
|
0.942**
|
-0.286
|
-0.824**
|
1
|
|
|
|
|
|
|
|
|
PN/P
|
-0.377
|
0.235
|
0.801**
|
-0.529
|
1
|
|
|
|
|
|
|
|
PY (kg/ha)
|
-0.874**
|
0.175
|
0.821**
|
-0.938**
|
0.513
|
1
|
|
|
|
|
|
|
NS/P
|
-0.788**
|
0.114
|
0.408
|
-0.732**
|
-0.101
|
0.722**
|
1
|
|
|
|
|
|
S (%)
|
-0.33
|
0.58*
|
0.674*
|
-0.373
|
0.679*
|
0.305
|
-0.001
|
1
|
|
|
|
|
SY (kg/ha)
|
-0.833**
|
0.371
|
0.927**
|
-0.91**
|
0.683*
|
0.936**
|
0.576*
|
0.616*
|
1
|
|
|
|
HSW(g)
|
0.013
|
0.235
|
0.004
|
0.158
|
0.161
|
-0.269
|
-0.34
|
-0.47*
|
-0.239
|
1
|
|
|
CP (%)
|
-0.024
|
0.296
|
0.445
|
-0.243
|
0.509
|
0.260
|
-0.126
|
0.216
|
0.342
|
-0.031
|
1
|
|
F (%)
|
0.112
|
0.033
|
0.186
|
-0.033
|
0.252
|
0.056
|
-0.186
|
-0.067
|
0.049
|
-0.094
|
0.542
|
1
|
Where; *and ** significant at P<0.05 and P<0.01, respectively and numbers with no*are non-significant. DF (%) = Days to 50% flowering, LW (cm)=Leaf width, LL(cm)= Leaf length, DM (%)=Days to 50% maturity, PN/P=pod Number/plant, PY (kg/ha)= Pod yield, NS/P =Number of seeds/pod, S%=shelling%, SY(kg/ha)=Seed yield, HSW (g)=100seed (g) weight (g),CP= Crude protein (%), F (%)=Fat (%)
3.6 Partial Budget Analysis
Partial budget analysis of the interaction effect showed that highest marginal rate of return (380.58%) was obtained from the ICGV00308 genotype at the application of P10Zn0.5 (Table 3.9). This rate of fertilizer application was economically above the minimum acceptable marginal rate of return (100%) (CIMMYT, 1988).This implies that for one birr invested in groundnut production, the producer can get 3.8 ETB.
Table 3.9: Partial budget analysis for groundnut genotypes and fertilizer treatments
ICGV00308
|
Fertilizers
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Net Returns (ETB/ha)
|
42930
|
48222
|
50017
|
50259.5
|
Total input cost (ETB/ha)
|
0
|
1390.5
|
2318
|
3245.5
|
Domination rank
|
|
ND
|
ND
|
ND
|
Marginal benefit (ETB/ha)
|
0
|
5292
|
1795
|
242.5
|
Marginal cost (Birr/ha)
|
0
|
1390.5
|
927.5
|
927.5
|
MRR (%)
|
-
|
380.583
|
193.531
|
26.1456
|
ICGV91114
|
Fertilizers
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Net Returns (ETB/ha)
|
49590
|
48132
|
47654.5
|
48414.5
|
Total input cost (ETB/ha)
|
0
|
1390.5
|
2318
|
3245.5
|
Domination rank
|
|
D
|
D
|
D
|
Sedi
|
Fertilizers
|
P0Zn0
|
P10Zn0.5
|
P20Zn1
|
P30Zn1.5
|
Net Returns (Birr/ha
|
52897.5
|
52249.5
|
54292
|
53657
|
Total input cost (ETB/ha)
|
0
|
1390.5
|
2318
|
3245.5
|
Domination rank
|
|
D
|
ND
|
D
|
Marginal benefit (ETB/ha)
|
0
|
|
1394.5
|
|
Marginal cost (ETB/ha)
|
0
|
|
2318
|
|
MRR (%)
|
|
|
60.16
|
|
Where: D=dominated treatment; ND=non dominated; P=kg/ha; Zn=g/L