Dynamics of soil volumetric moisture contents
Changes in the volumetric soil water content of the irrigation regime treatments during the first year experimental periods shown in Figure 2. Although the experiment conducted during the dry season, there was a rainfall (31mm at Ribb and 42 mm at Koga) during middle stage of the crop both years, leading to increase soil moisture content of the entire treatments. Even though both 14 and 21-day irrigation interval received the same rainfall, irrigation depths of 21-day interval is below FC due to less irrigation volume as compared to 14-day irrigation interval.
Effect of irrigation regime on grain yield, yield component and water use efficiency
Most parameters showed no significant difference for the interaction of irrigation interval and irrigation depth at (P<0.05).
Grain yield
Effect of variable irrigation regime on yield is presented in table 4a, irrigation depth alone significant (P<0.05) in Koga. The maximum (7.3 t ha-1) grain yield was scored at 100 %ETc. this implies application of optimum irrigation regime increased the grain yield over the deficit and excess irrigation regime. This is in close agrement with Ekubay TG, (2020) who report the maximum grain yield (7.3 t ha-1) achieved in 100% ETc in northern Ethiopia.
At Ribb, irrigation interval showed significant difference and the maximum (10.97 t ha-1) grain yield was scored at 21 day irrigation interval and the minimum (9.97 t ha-1) at 14 day irrigation interval as described in Table 4b. Maximum yield response to 21-day irrigation interval might be high water holding capacity of the soil and manageable volumetric soil moisture content during the experimental season as shown in Figure 1a. Besides 75 % ETc gives maximum yield (10.88 t ha-1) as compared to full irrigation. This might be the occurrence of rainfall during middle stage of the crop, lead to increase soil moisture content of the deficit treatments. The finding is in close agreement to (Demelash K and Ranamukhaarachchi SL,2004), Ekubay TG,( 2020), Libing S et al, (2019),who report irrigating sufficient water during the reproductive period of maize increase the grain yield.
The grain yield production at Koga irrigation scheme is low as compared to Ribb. This might be due to poor soil fertility and acidification at Koga and good nutrient content at Ribb as described in Table 1. Maize is sensitive to soil acidity and its suitable pH ranges from 5.8 to 7, while at Koga, it was about 4.6 that are below the critical level. Besides, the soil organic matter and available phosphorus was very low based on (Clements and McGowen, 1994) category'.
Green cob number
Application of optimum irrigation regime increased the green cob number over the deficit and excess irrigation regime plot as shown in Table 4 a&b. Irrigation interval showed significant difference (P<0.05) in Koga ,the maximum 50148 and the minimum 44481green cob number (approximately 1 cob per plant) was scored at 21 and 14 day irrigation interval respectively. The finding is in close agrement with Tesfaye et al. (2018); BH-545 gives one cob number per plant in Koga irrigation scheme. Despite the non-significance response of irrigation regime to cob number in Ribb, the maximum 47527-cob number scored at 21 - day irrigation interval. The finding is in close agrement with Tesfaye et al. (2018); BH-545 gives one cob number per plant in Koga irrigation scheme.
Cob length and cob diameter
The maximum 14 cm cob length and 3.9 cm cob diameter scored at 21- day irrigation interval in Koga. Similarly, the maximum 17.5 cm cob length and 4.96 cm cob diameter scored at 21- day irrigation interval in Ribb. The result is in close agreement to (Tesfaye et al. 2018) who reported the mean average cob length 15.9 cm and cob diameter 5.1 cm.
Water use efficiency
Interaction effect between irrigation interval and depth showed a non-significant (P < 0.05) in both locations. Increasing the water depth from 50 to 150 % ETc resulted in a decrease of water productivity from 2.7 to 1.1 kg m-3 in Ribb and 1.4 to 0.6 kg m-3 in Koga. By reducing frequency of irrigation from 14 to 21 days water productivity increased from 1.6 to 1.9 kg m-3 in Ribb and 1.2 to 1.4 kg m-3 in Koga. Compared with optimum irrigation regime, the deficit irrigation treatments saved significant depth of water with a minimum yield loss. This is in line with the finding of Ekubay TG, (2020), Libing S et al, (2019) and Enyew et al,(2020) who reported that when irrigation water becomes a limiting factor, yield losses due to reduced soil moisture could be compensated for by water use efficiency.
Table 4; combined mean of yield and yield component a) inKoga and b) in Ribb irrigation scheme
a)
|
|
Gy
|
Gcn
|
CL
|
CD
|
WUE
|
D
|
1
|
6.2
|
44630
|
13.6
|
3.9
|
1.4
|
|
2
|
5.6
|
47315
|
14
|
3.8
|
0.9
|
|
3
|
7.3
|
49537
|
13.7
|
3.9
|
0.9
|
|
4
|
6.9
|
48148
|
13.3
|
3.9
|
0.7
|
|
5
|
7.1
|
46944
|
14
|
3.9
|
0.6
|
F
|
1
|
6.6
|
44481.5
|
13.5
|
3.9
|
1.2
|
|
2
|
6.6
|
50148
|
14
|
3.9
|
1.4
|
Lsd(5%)
|
D
|
0.01
|
0.44
|
0.14
|
0.12
|
0.001
|
|
F
|
0.86
|
0.001
|
0.008
|
0.66
|
0.13
|
|
F*D
|
0.91
|
0.58
|
0.047
|
0.35
|
0.95
|
CV
|
|
19.6
|
13.5
|
5.7
|
3.6
|
19.1
|
b)
|
|
Gy
|
Gcn
|
CL
|
CD
|
WUE
|
D
|
1
|
10.49
|
44912
|
16.9
|
4.92
|
2.7
|
|
2
|
10.88
|
45328
|
17.58
|
4.8
|
2.1
|
|
3
|
10.34
|
47448
|
17.1
|
4.9
|
1.6
|
|
4
|
10.57
|
45787
|
16.6
|
4.95
|
1.3
|
|
5
|
10.1
|
47447
|
17.5
|
4.96
|
1.1
|
F
|
1
|
9.97
|
44858
|
16.8
|
4.9
|
1.6
|
|
2
|
10.97
|
47527
|
17.5
|
4.92
|
1.9
|
Lsd (5%)
|
D
|
0.87
|
0.8
|
0.09
|
0.018
|
0.001
|
|
F
|
0.04
|
0.12
|
0.004
|
0.57
|
0.0001
|
|
F*D
|
0.3
|
0.19
|
0.04
|
0.11
|
0.2
|
CV
|
|
18.1
|
14.4
|
5.3
|
2.7
|
19.8
|
Note- F- irrigation water frequency(day), D- Irrigation depth(mm), Gcn-Green cob number (no/ha), Gy-Grain yield(t ha-1), CL- Cob length (cm) CD- Cob diameter (cm), and WUE- water use efficiency (kg m-3),