Pre planting soil property of the study sites
Table 1: soil sample result before planting
Sites
|
pH
|
EC
|
OC %
|
TN %
|
Avai.P ppm
|
Particle size distribution
|
|
|
|
|
|
|
Sand%
|
Silt%
|
Clay%
|
Textural class
|
Woleh
|
7.6
|
0.13
|
0.43
|
0.04
|
15.45
|
32.66
|
33.65
|
33.69
|
Clay loam
|
Kechin Abeba
|
7.3
|
0.12
|
0.55
|
0.02
|
18.04
|
30
|
30
|
40
|
Clay loam
|
EC stands for electrical conductivity, OC stands for organic carbon, TN stands for total nitrogen, Avai.P stands for available phosphorous ppm stands for parts per million
Soil laboratory analysis
At Woleh, soil pH, EC and total nitrogen were numerically higher than at Kechin Abeba, but organic carbon and available phosphorus were lower at Woleh. The sites had a textural class of
clay loam. The soil pH value of the surface soil at Woleh and Kechin Abeba was 7.3 and 7.6 respectively. According to Landon, (1991) soil pH rating is classified as neutral and slightly alkaline. Similarly, the electrical conductivity of the study sites soil was free from salt (Landon 1991). The organic carbon and total nitrogen content were rated at low categories. According to Olson (1951), the available phosphorous was high on both sites. This might be the area had a long history on agriculture without replacing the complete removal of cover crop and burning crop residue as fuel are the main cause for nutrient loses.
A significant interaction (N*P) was observed for plant height and marketable yield in both years but total tuber yield was interacted in the year 2015 at Lalibela Kechin Abeba irrigation command area (Table 2 and 3). But the main effect of nitrogen was significantly affected all the parameters and the main effect of phosphorous was affect the only marketable and total yield of potato in 2017. In the year 2015, the main effect of phosphorous was affected marketable, total yield and plant height. Whereas at Woleh irrigation command area except for plant height significant interaction was observed on the other stated parameter (Table 4). The main effect of nitrogen and phosphorous fertilization was significantly influenced the plant height, marketable yield, unmarketable yield and total yield of potato but, phosphorous was not affecting the plant height.
Table 2: ANOVA for the effect of N and P fertilizers on the plant height (cm), marketable yield, unmarketable yield and total yield (t ha-1) of potato 2017 at Kechin Abeba
Source of variation
|
DF
|
Mean square values
|
Plant Height(cm)
|
Marketable yield
|
Unmarketable yield
|
Total yield
|
N
|
3
|
638.44*
|
418.95*
|
5.60*
|
451.10*
|
P
|
3
|
5.56ns
|
67.91*
|
0.27ns
|
65.04*
|
N*P
|
9
|
45.77*
|
69.57*
|
0.82ns
|
71.06
|
Error
|
32
|
15.56
|
4.50
|
1.20
|
4.72
|
Table 3: ANOVA for the effect of N and P fertilizers on the plant height (cm), marketable yield, unmarketable yield and total yield (t ha-1) of potato 2015
Source of variation
|
DF
|
Mean square values
|
Plant Height
|
Marketable yield
|
Unmarketable yield
|
Total yield
|
N
|
3
|
518.94*
|
101.55*
|
4.14*
|
138.09*
|
P
|
3
|
92.15*
|
11.94*
|
1.11ns
|
12.04*
|
N*P
|
9
|
44.91*
|
12.75*
|
0.89ns
|
12.57*
|
Error
|
32
|
19.38
|
2.50
|
0.57
|
3.81
|
Table 4: Combined ANOVA for the effect of N and P fertilizers on the plant height (cm), marketable yield, unmarketable yield and total yield (t ha-1) of potato at Woleh
Source of variation
|
DF
|
Mean square values
|
Plant Height
|
Marketable yield
|
Unmarketable yield
|
Total yield
|
N
|
3
|
193.65*
|
159.35*
|
5.79*
|
233.68*
|
P
|
3
|
35.86ns
|
17.02*
|
2.76*
|
30.54*
|
N*P
|
9
|
51.45ns
|
221.53*
|
1.33*
|
9.44*
|
Error
|
57
|
34.54
|
3.32
|
0.35
|
3.44
|
Plant height
Both the main and interaction effect of nitrogen and phosphorus fertilizer application affect marketable yield and total yield significantly in the 2015 and 2017 at Kechin Abeba whereas the plant height and unmarketable yield were significantly affected by nitrogen application (Table 2 &3). The highest plant height 72.58 cm was recorded from the application of 138 N kg ha-1 in the 2017 irrigation season whereas the highest plant height 54.85 and 51.90 cm was a record from by application of 92 N and 69 P2O5 kg ha-1 in the year of 2015. In all parameters, the 2017 cropping season exceeded the 2015 production year. This is probably due to variation in irrigation water availability in the year between 2015 and 2017 (Table 5). That means water is essential for the germination of seeds, growth of plant roots, and nutrition, photosynthesis, transpiration, to maintain the turgidity of cell walls and multiplication of soil organisms. There was a shortage of irrigation water in the 2015 irrigation season in the command area. The increasing rate of nitrogen and phosphorus fertilizer in the irrigation season of 2015 increases plant height by 14.81 and 4.97cm whereas, in the irrigation season of 2017 application of nitrogen alone at a rate of 138 kg ha-1 increases plant height by 16.14 over the control treatment. The current study in line with Zelalem et al., (2009) who reported that nitrogen and phosphorus at a rate of 207 and 60 kg ha-1 increases plant height by 24 cm and 10.5cm respectively. Similarly, Israel et al., (2012), Alemayehu et al., (2015) and Fayera, (2017) and have found that increasing the application of nitrogen and phosphorus significantly increased plant height.
In Woleh the main effect of nitrogen fertilization was significantly influenced the plant height of potato but, their interaction exhibited a non-significant effect on the stated parameter (table 4). The highest plant height (49.82cm) was obtained from applied fertilizer rates of 138 N kg ha-1 at Woleh while the lowest plant height (43.15) was obtained from the control treatment (Table 5). The application of phosphorous fertilizer didn’t show a significant effect on the plant height at Woleh during the study (Table 5). This might be the fact that nitrogen plays a most important role in various physiological processes. The current study inlined with Sanjana et al., (2014) who reported that increasing the rate of nitrogen up to 375 kg ha-1 increases the plant height of potato. A study conducted in eastern Ethiopia to ascertain the effect of nitrogen and planting density on yield and yield components of potato shows that increasing the rate of nitrogen from 0 to 165 kg ha-1 increases the plant height of potato.
Table 5: Effect of Nitrogen and phosphorus on plant height (cm) at Kechin Abeba and Woleh sites
N level kg ha-1
|
Plant height (at Kechin Abeba)
|
|
Plant height (at Woleh)
|
2015
|
2017
|
|
2015
|
2017
|
Combined
|
0
|
40.05
|
55.86
|
|
46.63
|
39.66
|
43.15
|
46
|
46.67
|
61.94
|
|
48.89
|
41.95
|
45.42
|
92
|
54.85
|
68.14
|
|
51.13
|
43.65
|
47.39
|
138
|
52.35
|
72.58
|
|
53.13
|
46.50
|
49.82
|
LSD (0.05)
|
3.24*
|
3.28*
|
|
3.18*
|
5.69*
|
3.39*
|
P2O5 level kg ha-1
|
|
|
|
|
|
|
0
|
46.93
|
65.34
|
|
49.28
|
42.07
|
45.67
|
23
|
49.45
|
63.75
|
|
50.36
|
40.44
|
45.40
|
46
|
45.65
|
64.66
|
|
50.64
|
45.59
|
48.11
|
69
|
51.90
|
64.81
|
|
49.50
|
43.66
|
46.58
|
LSD(0.05)
|
3.24*
|
3.28ns
|
|
ns
|
ns
|
ns
|
CV
|
9.08
|
6.10
|
|
7.43
|
15.95
|
12.65
|
Marketable yield
Both the main and interaction effect of nitrogen and phosphorus fertilizer application were affect the marketable yield significantly at Kechin Abeba and Woleh. The increasing rate of nitrogen and phosphorus significantly increases the marketable yield of potato in both sites. In Kechin Abeba marketable yield was increased with the increasing rate of nitrogen and phosphorus. The highest marketable yield (45.55 t ha-1) was recorded from 138 kg ha-1 nitrogen is combined with phosphorus at a rate of 23 kg ha-1 in 2017 and 19.57 t ha-1 was recorded from 138 nitrogen is combined with phosphorus at a rate of 23 kg ha-1 in 2015 (Table 6) whereas the lowest marketable yield (17.71 t ha-1) and (8.1 t ha-1) was recorded from treatment (0, 69 NP) in 2017 and 2015 respectively. The marketable yield of potato gained in the year of 2017 irrigation season was exceeded the irrigation season of 2015. This is probably due to irrigation water availability in the year between 2015 and 2017. There was irrigation water scarcity in the year of 2015. In case of Woleh the highest marketable yield (17. 12 t ha-1) was recorded from 138 kg ha-1 nitrogen in combined with phosphorus at a rate of 46 kg ha-1 whereas the lowest marketable yield (8.16 t ha-1) was recorded from the control treatment (0, 0 NP kg ha-1) (Table 7). There was tuber yield reduction in Woleh and Kechin Abeba in 2015 by half as compared to tuber yield gained in 2017 Kechin Abeba. This was attributed to the fact that water is the most important limiting factor for potato production and it’s possible to increase production levels by well-scheduled irrigation programs throughout the growing season (Liu et al., 2006). Similarly, (Demile, 2012) observed that 4.09 t ha-1 (64%) and 39% tuber yield reduction were recorded from the application of 25%, and 50% (deficit) of the total crop water requirement at all stages, respectively. However, the marketable yield was increased by 24.95 t ha-1 and 8.96 t ha-1 over control treatment at Kechin Abeba and Woleh respectively. This might be the fact that nitrogen is part of the chlorophyll molecule, which gives plants their green color and is involved in creating food for the plant through photosynthesis and phosphorus is involved in the metabolic processes responsible for transferring energy from one point to another in the plant. It's also critical in root development and flowering. The current study is in agreement with previous study Zelalem et al., (2009), Israel et al., (2012), Gebremariam, (2014), and Alemayehu et al.,(2015), who reported that increasing rate of nitrogen increases marketable tuber yield significantly. Similarly, Desalegn et al., (2016) observed an increment of potato marketable yield with increasing of NP fertilizer in southern Ethiopia.
Table 6: Effect of nitrogen and phosphorus on tuber marketable yield of potato t ha-1 at Kechin Abeba 2015 and 2017
|
2015
|
2017
|
|
P2O5 kg ha-1
|
P2O5 kg ha-1
|
N kgha-1
|
0
|
23
|
46
|
69
|
0
|
23
|
46
|
69
|
0
|
11.26
|
11.66
|
11.87
|
8.10
|
20.60
|
21.89
|
23.66
|
17.71
|
46
|
16.76
|
17.91
|
17.56
|
12.96
|
23.82
|
28.53
|
28.93
|
27.24
|
92
|
15.01
|
15.68
|
19.23
|
14.29
|
26.54
|
19.67
|
29.23
|
33.52
|
138
|
14.95
|
19.57
|
17.02
|
16.77
|
14.95
|
45.55
|
37.70
|
29.35
|
LSD(0.05)
|
2.63*
|
3.53**
|
CV
|
10.52
|
7.58
|
Table 7: Combined analysis of potato marketable yield t ha-1 at Woleh
|
P2O5 kg ha-1
|
N kg ha-1
|
0
|
23
|
46
|
69
|
0
|
8.16
|
11.00
|
10.77
|
11.76
|
46
|
13.66
|
13.49
|
14.28
|
13.61
|
92
|
12.04
|
15.23
|
14.58
|
14.15
|
138
|
15.99
|
16.99
|
17.12
|
16.76
|
LSD(0.05)
|
3.15*
|
CV
|
14.55
|
Unmarketable and total yield of potato
Both the main and interaction effect of nitrogen and phosphorus fertilizer application were affected the unmarketable and total yield of potato significantly at Woleh but, at Kechin Abeba only the application of nitrogen was affected significantly the unmarketable and total yield of potato (Table 2, 3, and 5). The highest unmarketable yield (2.88 & 4.06 t ha-1) was recorded at a rate of 92 kg ha-1 N in the year 2015 and 2017 respectively at Kechin Abeba (Table 8). Phosphorus fertilizer application did not significantly affect the total yield of potato in the year of 2017 but, in the year of 2015, the highest yield was recorded at an application rate of 23 kg ha-1 P2O5. The highest total yield (25.39 and 38.82 t ha-1) was recorded at a rate of 138 kg ha-1 N. In the case of Woleh the highest total yield (19.39 t ha-1 & 16.84 t ha-1) was obtained from the application of 138 kg ha-1 N and 46 kg ha-1 P2O5 and the lowest (11.80 & 14.21 t ha-1) were obtained from the unfertilized treatment. Similarly highest unmarketable yield was obtained from the application of N 138 and P2O5 46 kg ha-1 (Table 8).
Table 8: Effect of nitrogen and phosphorus on unmarketable and total yield (t ha-1) of potato at Woleh
|
Kechin Abeba
|
Woleh
|
N level kg ha-1
|
Unmarketable yield
|
Total yield
|
Unmarketable yield
|
Total yield
|
2015
|
2017
|
2015
|
2017
|
2015
|
2017
|
Combined
|
2015
|
2017
|
Combined
|
0
|
1.45
|
2.87
|
12.18
|
23.88
|
1.32
|
1.65
|
1.48
|
12.76
|
10.84
|
11.80
|
46
|
2.14
|
2.47
|
18.44
|
30.29
|
2.41
|
1.96
|
2.18
|
18.83
|
12.45
|
15.64
|
92
|
2.88
|
4.06
|
20.94
|
31.68
|
2.34
|
1.89
|
2.11
|
18.04
|
14.66
|
16.35
|
138
|
2.31
|
3.36
|
25.39
|
38.82
|
3.19
|
2.17
|
2.68
|
20.60
|
18.18
|
19.39
|
LSD (0.05)
|
0.58*
|
0.91*
|
1.01*
|
1.80*
|
0.41*
|
0.39*
|
0.34*
|
1.11*
|
1.41*
|
1.07*
|
P2O5 level kg/ha
|
|
|
|
|
|
|
|
|
|
|
0
|
2.37
|
3.14
|
16.87
|
34.53
|
19.45
|
1.71
|
1.83
|
15.52
|
12.90
|
14.21
|
23
|
2.40
|
3.23
|
18.61
|
30.85
|
20.83
|
1.91
|
2.00
|
18.99
|
13.51
|
16.25
|
46
|
1.75
|
3.38
|
17.23
|
29.31
|
33.88
|
1.83
|
2.61
|
18.69
|
15.00
|
16.84
|
69
|
2.26
|
3.02
|
16.24
|
29.98
|
18.38
|
2.22
|
2.03
|
17.03
|
14.71
|
15.87
|
LSD(0.05)
|
0.58*
|
Ns
|
1.01*
|
2.54*
|
4.13*
|
0.39*
|
0.34*
|
1.11*
|
1.41*
|
1.07*
|
CV
|
34.51
|
34.35
|
11.33
|
6.96
|
20.82
|
24.87
|
28.08
|
7.41
|
12.10
|
11.75
|
Partial budget analysis
The application of nitrogen at a rate of 138 kg ha-1 with 23 kg ha-1 phosphorus had the highest marketable yield (15.29 t ha-1) and net benefit (164597 Ethiopian Birr) in Woleh irrigation command area (Table 9). The MRR (1606.90 %) was gained from the treatment of 138 N and 23 P2O5 kg ha-1, this implies that for each Birr that invested in the new technology, the producer can receive to recover the one Birr invested plus an additional return of 16.06 Ethiopian birr.
Table 9: partial budget analysis at Woleh
N
|
P2O5
|
Unadjusted yield(t ha-1)
|
Adjusted(t ha-1)
|
Gross benefit (Ethiopian Birr)
|
Costs that varies
(Ethiopian Birr)
|
Net benefit (Ethiopian Birr)
|
MRR%
|
0
|
0
|
9.86
|
8.874
|
97614
|
0
|
97614
|
|
0
|
23
|
11
|
9.9
|
108900
|
580
|
108320
|
1845.86
|
46
|
0
|
11.66
|
10.49
|
115434
|
1008
|
114426
|
1426.64
|
0
|
46
|
10.77
|
9.69
|
106623
|
1160
|
105463
|
D
|
46
|
23
|
13.49
|
12.14
|
133551
|
1588
|
131963
|
3023.62
|
0
|
69
|
11.76
|
10.58
|
116424
|
1740
|
114684
|
D
|
92
|
0
|
12.04
|
10.83
|
119196
|
2016
|
117180
|
D
|
46
|
46
|
14.28
|
12.85
|
141372
|
2168
|
139204
|
1248.45
|
92
|
23
|
15.23
|
13.70
|
150777
|
2596
|
148181
|
2097.43
|
46
|
69
|
13.61
|
12.24
|
134739
|
2748
|
131991
|
D
|
138
|
0
|
15.99
|
14.39
|
158301
|
3024
|
155277
|
1657.94
|
92
|
46
|
14.58
|
13.12
|
144342
|
3176
|
141166
|
D
|
138
|
23
|
16.99
|
15.29
|
168201
|
3604
|
164597
|
1606.90
|
92
|
69
|
14.15
|
12.73
|
140085
|
3756
|
136329
|
D
|
138
|
46
|
17.12
|
15.40
|
169 488
|
4184
|
165304
|
121.90
|
138
|
69
|
16.76
|
15.08
|
165924
|
4764
|
161160
|
D
|
D stands for dominated treatment
Conclusion and recommendation
The current investigation showed that both nitrogen and phosphorus rates had a high significant effect
on the tuber yield of potato. This study confirmed that nitrogen and phosphorus rates and their interaction have a sound and promising impact on marketable and total tuber yield of potato. However, the cost benefits analysis indicated that the application of 138 kg N ha-1 and 23 kg ha-1 P2O5 had a yield advantage of 86.64% or 7.13 t ha-1 over the control treatment at Woleh irrigation command area. Similarly, at Kechin Abeba application of 138 kg ha-1 nitrogen fertilizer and 23 t ha-1 phosphorus fertilizers resulted in the highest yield (45.55 t ha-1) of potato tuber which exceeds by 121.11% or 24.95 t ha-1 from the control. Hence the application of nitrogen 138 and 23 P2O5 kg ha-1 is the optimum rate for potato at Woleh and Kechin Abeba irrigation command areas. Therefore, the application of 138 kg N and 23 kg P ha-1 is the appropriate rate for optimum productivity of Potato for Woleh and Kechin Abeba under irrigation and the same agro-ecologies.