Directory UMM :Data Elmu:jurnal:A:Agricultural Water Management:Vol46.Issue2.2000:
Agricultural Water Management 46 (2000) 111±119
Effect of de®cit irrigation on wheat and
opportunities of growing wheat on residual
soil moisture in southeast Zimbabwe
F.T. Mugabea,*, E.Z. Nyakatawab
a
Chiredzi Research Station, P.O. Box 97, Chiredzi, Zimbabwe
Department of Plant and Soil Science, Alabama A&M University,
P.O. Box 1208, Normal, AL 35762, USA
b
Accepted 31 January 2000
Abstract
Soil moisture from six sites in Romwe was measured at the end of the wet season (April) and at
the end of the dry season (October) and the available water calculated. Results from a variety by
irrigation trial run at Chiredzi Research Station for two seasons was used to assess the possibility of
growing wheat on residual soil moisture in Romwe. Six wheat genotypes (P1, P2, Pote, Deka, Nata
and Ruya) were grown under three irrigation regimes at Chiredzi Research Station during the 1996
and 1997 winter seasons. The irrigation regimes used were supplying irrigation water according to
the crop water requirements, supplying three quarters of the crop water requirements and half of the
crop water requirements at each irrigation day. Applying three quarters and half of the crop water
requirements resulted in a yield decrease of 12 and 20% in 1996 and 7 and 20% in 1997 season,
respectively. P2 gave the highest yields on average for the two seasons and was the least affected by
de®cit irrigation. However, Deka gave the least decrease in yield when the three-quarters and half
water requirements were supplied. Four of the sites in Romwe, where residual soil moisture was
measured, had more than half the water required to meet the crop water requirements of wheat.
# 2000 Elsevier Science B.V. All rights reserved.
Keywords: Wheat; De®cit irrigation; Yield stability; Residual soil moisture
1. Introduction
In Zimbabwe wheat is grown in winter (May±September) under irrigation, when the
temperatures are low and favorable for seed yield and quality. Only commercial farmers,
*
Corresponding author. Tel.: 263-037-369
E-mail address: mugabe@africaonline.co.zw (F.T. Mugabe).
0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 0 0 ) 0 0 0 8 4 - 6
112
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
with irrigation facilities, can grow winter wheat. However, some smallholder farmers,
especially in the wetter areas, grow wheat on residual soil moisture in wetlands (Adam
et al., 1997). Normally the water requirements of wheat grown on residual soil moisture is
not met resulting in low yields being attained.
There is very limited water loss from the soil surface during the cooler months
when wheat is grown. All the available residual soil moisture can be used by a crop
since dry soil conditions promote root elongation and branching (Sharma and Ghildyal,
1977). Wheat roots can abstract water from up to 2 m (Hurd, 1968; Prihar et al., 1977;
Arora and Prihar, 1983) and most of the residual soil water in the soil profile can be
utilized.
Wheat yields of the order of 2800 kg/ha have been reported by Mishra et al. (1995)
with 50 mm of precipitation grown on residual soil moisture in India. It has been
suggested that genotypes with lower yield potentials under test crop conditions but which
are much more stress resistant should be used where water deficits are anticipated. It is
quite possible that some released genotypes and promising wheat lines in the current
Zimbabwe breeding program can withstand drought.
Water has not been taken as a major limitation in the Zimbabwe breeding programme;
hence the drought tolerance of the released genotypes is not known. Farmers growing
wheat on limited soil moisture do not know which varieties to choose in order to realize
optimum yields. This study was conducted to compare the response of four released
genotypes and two promising genotypes to water deficits and to assess the possibility of
growing wheat on residual soil moisture.
2. Study sites and methods
2.1. Irrigation by variety trial at Chiredzi Research Station
The study was conducted at Chiredzi Research Station, (218S and 318E), at an altitude
of 429 m a.s.l. in the southeast Lowveld of Zimbabwe during the winters of 1996 and
1997. The region lies in natural region V of Zimbabwe that is semi-arid, with mean
annual rainfall of 500 mm with a seasonal range of 250±1000 mm. The natural regions
are a classification of the agricultural potential of the country, from natural region 1,
which represents the high altitude wet areas to natural region V which receives low and
erratic rainfall averaging 550 mm per annum (Vincent and Thomas, 1960). The soils at
Chiredzi Research Station are dark-reddish brown clays derived from basic gneiss and are
classified as the Triangle B2 series and typic rhodstuff in Zimbabwean and USDA
classification systems, respectively.
Four released wheat genotypes, Deka, Pote, Nata and Ruya and two promising varieties
S85331-3H-0H-3H-0H (P1) and S86073-5H-0H-3H-0-1H-0G (P2) were grown at three
regimes of drought stress in the 1996 and 1997 seasons. These were full, three-quarters
and half of normal irrigation requirements. The full treatment was irrigating the
genotypes at 50% allowable moisture depletion and applying water according to the crop
water requirements. All the irrigation treatments were based on the open pan irrigation
scheduling using the wheat standard crop factor progression of 0.3±1.0 (Cackett, 1972).
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
113
The land on which the study was carried out was ploughed and a basal fertilizer of
700 kg/ha compound X (20:10:5) was disced into the soil before planting. Sowing was
done in the first week of May, that is the recommended sowing time for wheat in the
Lowveld. The seeds were sown in rows 25 cm apart in 3.5 m3.5 m plots at a seed rate of
100 kg/ha. The experiment was designed as a 63 factorial in a split plot design with four
replications. The irrigation level was the main plot factor whereas genotype was the subplot factor.
The site was irrigated to field capacity soon after planting and 21.8 mm emergence
irrigation was applied about 7 days later. Thereafter, the irrigation treatments were
imposed. Weed control was hand hoeing. Regular scouting for insect and disease was
done throughout the duration of the study. Measurements taken included days to 50%
flowering, days to maturity, stand counts at harvest, plant heights at harvest, number of
ears/m2, number of spiklets/ear, 1000 seed weight and grain yield. The data were
subjected to the ANOVA procedure using MSTA-C statistical package.
The yield stability of the wheat genotypes was assessed, using Eq. (1), where Ys is
the yield stability of a given genotype when deficit irrigation is applied, Yg1 is the genotype yield grown without water stress and Yg2 is the genotype yield grown under water
stress.
Ys
100 Yg1 ÿ Yg2
Yg1
(1)
2.2. Assessment of residual soil moisture at Romwe
Romwe, in Chivi, lies in natural region IV. The average annual rainfall at Chendebvu
dam, a rainfall station located 12 km to the north of the catchment, over the last 40 years
(1952±1992) is 581 mm (Butterworth et al., 1995) with a standard deviation of 263 mm.
The soils are light grey colored, sandy soils formed from granitic gneiss. These are
kaolinitic, fersialitic soils (III 5P) according to the Zimbabwean soil classification system
(Thompson and Purves, 1978). In many locations, a thick clay layer underlines light
textured horizons.
One access tube (external diameter 45 mm) was installed to 120 cm in the center of
each of seven sites chosen. A neutron probe (Wallingford MK III) was used to measure
soil moisture. Counts were taken over 16 s at 10 cm intervals at the end of the wet season
(5 April 1994) and at the end of dry season (8 September 1994). Soil samples were sent to
Center of Nuclear Studies (Cadarache, France) for calibration of the neutron probe
(Mugabe, 1998). Particle size on each horizon for the seven sites was measured at the
Institute of Soils and Chemistry, Harare. Horizon delineation was based on color and
observable textural and structural differences. In this study, percent sand refers to the
combination of coarse, medium and fine sand. The pressure chamber method was used to
determine the gravimetric moisture content at ÿ1500 kPa following the technique
described by Black (1965). Saturated paste for each of the samples was prepared and
replicated twice in rings that were placed in ceramic plate. The samples were left to
equilibrate until there was no significant amount of water increase in the burettes
collecting the outflow. After equilibrium the samples were transferred into weighed
114
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 1
Irrigation dates and amounts for the wheat trial and rainfall received during the winters of 1996 and 1997
1996
1997
Amount of water applied (mm)
Full
16/5
23/5
14/6
11/7
8/8
27/8
Total
Rain
Comment
Three quarters
Half
10/5
22/5
17/6
10/7
8/8
18/8
50
22
50
50
50
50
50
22
38
38
38
38
50
22
25
25
25
25
272
60
11
224
172
1996
1997
Planting
Emergence
Treatment
Treatment
Treatment
Treatment
aluminum foil. The weight of the wet soil plus aluminum foil was determined and the
sample was dried at 1058C hours before reweighing.
3. Results and discussion
3.1. Irrigation levels
Table 1 shows the amounts of irrigation water applied for each treatment in 1996 and
1997. For each treatment similar amounts of irrigation water were applied in both years.
Irrigating three quarters and half of the crop water requirements at each irrigation day
resulted in water deficits of 16 and 31% in the 1996 season and 20 and 38% in the 1997
season, respectively. More rainfall was received in 1996 (60 mm) than 1997 (11 mm). In
1996 the mean monthly temperatures for June, July and August were lower than that of
1997 (Table 2).
At all the irrigation levels, the 1996 crop took longer to mature, had more ears/m2, and
was taller because of cooler conditions (Cackett and Wall, 1971; Mashiringwani and
Schwepppenhauser, 1991) (Table 2) compared to 1997. On average, yields were heavier
in 1996 than in 1997.
Table 3 shows that supplying less water than the crop water requirements has no effect
on days to 50% flowering, number of ears/m2, plant height and 1000 seed weight.
Table 2
Monthly maximum, minimum and mean temperatures (8C) from May to August 1996 and 1997 at Chiredzi
Research Station
Year
1996
1997
May
June
July
August
Max
Min
Mean
Max
Min
Mean
Max
Min
Mean
Max
Min
Mean
26.4
26.2
12.9
12.3
19.7
19.3
26.6
28.7
9.7
11.9
17.2
20.3
23.3
24.0
7.3
12.1
15.3
18.1
26.6
29.0
10.7
10.2
18.7
19.6
Days to 50%
flowering
Days to
maturity
1996
1997
1996
1997
1996
Irrigation level
Full
Three quarter
Half
75.0a
74.8a
73.9a
±b
±
±
114.3a
112.1ab
109.7b
112.0a
110.5a
108.5b
Genotype
P1
P2
Pote
Deka
Nata
Ruya
Mean
LSD
CV%
Interaction
65.8d
74.1bc
73.0c
79.8a
79.5a
75.3b
74.4
1.531
1.44
NS
±
±
±
±
105.2c
109.0b
106.3bc
116.8a
117.0a
117.9a
112.0
3.18
1.99
NS
108.0c
110.0ab
109.5bc
111.6a
111.3ab
111.4a
110.3
1.875
1.19
NS
a
b
Number of
ears/m2
Numbers with the same letter are not signi®cantly different.
Missing data.
Plant Height
(cm)
1000 seed
weight
Grain yield
(kg/ha)
1997
1996
1997
1996
1997
1996
1997
375a
367a
358a
350a
345a
318a
95.9a
95.0a
93.8a
87.5a
86.8a
84.9a
37.1a
35.0a
34.9a
41.9a
40.7a
39.7a
5537a
4862b
4431b
5290a
4894a
4223b
363ab
324b
386ab
353b
416a
358ab
367
62.2
11.9
NS
344a
325ab
362a
296b
355a
344a
338
47.3
9.8
NS
91.2b
89.7b
95.4ab
101.2a
92.6b
99.4a
94.9
5.812
4.30
NS
79.3c
84.2b
88.4a
91.7a
84.8b
89.8a
86.4
3.557
2.89
NS
41.6a
35.3b
34.5b
36.5b
30.7c
35.6b
35.7
3.703
7.29
NS
43.8a
40.8a
42.3a
41.9a
32.8b
42.0a
40.8
6.141
10.58
NS
4622bc
5513a
4538c
5101abc
5144ab
4743bc
4944
585.6
8.32
S
3895b
5150a
4875a
5060a
5020a
4834a
4806
575.6
8.41
S
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 3
Effect of de®cit irrigation on wheat yields and yield attributes of six genotypes during the 1996 and 1997 winter seasonsa
115
116
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Irrigating half of the irrigation water requirements resulted in significantly fewer days to
maturity compared to irrigation according to the crop's water requirements and supplying
three-quarters of irrigation in 1997. Ehdaie (1995) also reported that water stressed wheat
matures earlier than that which is not stressed. In 1996, applying less water gave
significantly lower yields compared to irrigating according to the crop water
requirements. There was a 21 and 20% decline in yield when three quarters and half
irrigation water were applied, respectively. In 1997, there were no significant yield
differences between full irrigation and three-quarter water application. Applying half the
irrigation water resulted in significantly lower yields than applying all the crop water
requirements and applying three quarters irrigation water.
3.2. Wheat genotypes
There were significant differences in days to 50% flowering. Days to maturity, number
of ears/m2, plant height, 1000 seed weight and grain yield among the six genotypes
(Table 3). The promising, genotype P2, gave the highest yields in both seasons though it
was not significantly different from most of the genotypes (Deka and Nata in 1996 and all
except P1 in 1997).
In 1996 P2 performed better than all the genotypes at all the three irrigation regimes
(Table 4) while in 1997 it out performed all the genotypes at full irrigation only. Of the
released genotypes, Deka produced the highest yields in 1997 season at half irrigation and
was second at three quarters irrigation in 1996. On average Deka yielded highest at both
three-quarters and half irrigation in the two seasons. Yield stability of genotypes can be
calculated by comparing yields of crop grown under deficit irrigation and that obtained at
Table 4
Mean yields (kg/ha) of six genotypes of wheat for 1996 and 1997 at three levels of irrigation
Irrigation level
Genotype
1996
1997
Full
P1
P2
Pote
Deka
Nata
Ruya
4938
5983
5498
5432
5834
5541
4483
6011
5382
5232
5681
4951
Three quarters
P1
P2
Pote
Deka
Nata
Ruya
5153
5631
3754
5342
4989
4305
4026
5118
5236
4999
5002
4987
Half
P1
P2
Pote
Deka
Nata
Ruya
3776
4926
4364
4528
4609
4385
3176
4322
4008
4950
4377
4565
117
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 5
Percent yield deviation from two de®cit irrigations for six genotypes during the 1996 and 1997 seasons
Irrigation level
Three quarters
Genotype
1996
P1
P2
Pote
Deka
Nata
Ruya
a
a
ÿ4
6
32
2
14
22
Half
1997
Average
1996
1997
Average
10
15
3
4
11
ÿ1a
3
10
17
3
13
10
24
18
21
17
21
20
29
28
26
6
22
8
26
23
23
11
21
14
Indicates an increase in yield resulting from de®cit irrigation.
full irrigation (without water stress). Table 5 shows the percent deviation in yield of the
six wheat genotypes under deficit irrigation during the 1996 and 1997 seasons. Deka gave
the least deviation at both three-quarters and half irrigation regimes and this implies that
Deka is not as much affected by deficit irrigation compared to the other genotypes. This
might not mean that it would give the highest yields under deficit irrigation. For example
P2 (though it has an average deviation of 23%) yielded highest at three-quarters and half
irrigation in 1996. In the same year Deka gave second and third highest yields,
respectively, but had a smaller average deviation of 11%.
3.3. Possibility of growing wheat on residual soil moisture
Table 6 shows that there is lot of variation in the texture of the sites chosen, though
they are all sandy at the surface except F5. The soils used for this analysis are sandy at the
surface and clayey below 70 cm. In wet years the soils will be water logged in the
summer season and very moist at the end of the wet season. Available moisture to 110 cm
was more than 77 mm at the end of the rainy season in April for all the sites. The
difference in soil moisture between 5 April and 8 September is water loss through soil
evaporation, weed uptake or some limited drainage.
This water could be used to grow a winter crop like wheat or beans and the expected
yield levels will depend on the ability of the crop grown to withstand drought. The sites
had different total soil moistures and water remaining at permanent wilting point.
This depended on the individual site's texture. Four of the seven sites (F4, F7, F8 and
F9) selected had soil moisture above half of the wheat crop water requirements.
The water available to the wheat grown on residual soil moisture can be more than the
figures given in Table 6, for water can be withdrawn from depths of up to 2 m when
wheat is grown under water stress conditions (Sharma and Ghildyal, 1977).
The results from the irrigation trial carried out at Chiredzi Research Station (Table 3)
shows that wheat yields of more than 4000 kg/ha can be expected when wheat is grown
on deficit irrigation of at least 170 mm. Mishra et al. (1995) recorded wheat yields of the
order of 2800 kg/ha when they grew wheat on residual soil moisture with 50 mm of rain
only. Work carried out by Chaudhary and Bhatnagar (1980) shows that frequent
irrigations must be provided throughout the growing season to ensure maximum yield of
118
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 6
Clay, silt and sand contents of the sites, and available soil water at the end of the rainy season (April) and at the
end of the dry season (September)
Site
Depth
Clay (%)
Silt (%)
Sand (%)
Total available soil water
in 110 cm profile (mm)
5 September
1994
8 November
1994
F4
0±13
13±44
44±79
79
11
24
53
34
11
11
13
10
78
65
33
55
240
178
F5
0±26
26±46
46
20
14
15
10
18
14
70
68
71
77
36
F6
0±9
9±16
16±85
85
4
4
8
3
7
7
9
6
89
89
83
91
106
54
F7
0±13
13±81
81
6
7
25
9
8
5
85
85
70
194
109
F8
0±26
26±78
78
4
8
38
3
9
7
93
85
55
212
127
F9
0±15
15±100
100
9
12
29
10
10
8
81
78
63
220
98
F10
0±19
19±74
74
9
7
33
13
9
5
78
84
62
147
101
wheat. This would mean that the expected yields from wheat grown on residual soil
moisture would be lower than those obtained from wheat grown on deficit irrigation
where frequent irrigation is supplied. Table 7 shows that winter rains are expected in most
of the years at Romwe and this would increase the water available to the crop.
Table 7
Romwe winter rainfall (mm) in 1994, 1995, 1996 and 1997
Months
1994
1995
1996
1997
May
June
July
August
2
0
13
14
64
1.5
5
8
38
13
35
13
1.5
1
29
0
Total
29
78
99
31
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
119
Deka recorded the least reduction at the two water levels even though it did not record
the highest yields when optimum water was added. This suggests possible benefits of
growing Deka on residual soil moisture, because of the yield stability at water levels
below wheat crop water requirements.
Acknowledgements
The authors would like to thank Dr. M.D.S. Nzima and P. Nyamudeza for their critical
review on this paper, Dr. N. Mashirinwani for providing us with wheat genotypes,
Messers D. Maringa, D. Muzenda and Mhlanga, for their roles in trial management and
data collection.
References
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Punjab, India. Field Crops Res. 6, 41±50.
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catchment study: effect of land management on groundwater recharge, and implications for small-scale
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(Triticum, aestivum L) in Rhodesia. Rhodesia J. Agric. Res. 9, 107±120.
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affected by placement of nitrogen and phosphorus. Ind. J. Ecol. 4, 23±31.
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Sharma, R.B., Ghildyal, B.P., 1977. Soil water-root relations in wheat: water extraction rate of wheat roots that
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Effect of de®cit irrigation on wheat and
opportunities of growing wheat on residual
soil moisture in southeast Zimbabwe
F.T. Mugabea,*, E.Z. Nyakatawab
a
Chiredzi Research Station, P.O. Box 97, Chiredzi, Zimbabwe
Department of Plant and Soil Science, Alabama A&M University,
P.O. Box 1208, Normal, AL 35762, USA
b
Accepted 31 January 2000
Abstract
Soil moisture from six sites in Romwe was measured at the end of the wet season (April) and at
the end of the dry season (October) and the available water calculated. Results from a variety by
irrigation trial run at Chiredzi Research Station for two seasons was used to assess the possibility of
growing wheat on residual soil moisture in Romwe. Six wheat genotypes (P1, P2, Pote, Deka, Nata
and Ruya) were grown under three irrigation regimes at Chiredzi Research Station during the 1996
and 1997 winter seasons. The irrigation regimes used were supplying irrigation water according to
the crop water requirements, supplying three quarters of the crop water requirements and half of the
crop water requirements at each irrigation day. Applying three quarters and half of the crop water
requirements resulted in a yield decrease of 12 and 20% in 1996 and 7 and 20% in 1997 season,
respectively. P2 gave the highest yields on average for the two seasons and was the least affected by
de®cit irrigation. However, Deka gave the least decrease in yield when the three-quarters and half
water requirements were supplied. Four of the sites in Romwe, where residual soil moisture was
measured, had more than half the water required to meet the crop water requirements of wheat.
# 2000 Elsevier Science B.V. All rights reserved.
Keywords: Wheat; De®cit irrigation; Yield stability; Residual soil moisture
1. Introduction
In Zimbabwe wheat is grown in winter (May±September) under irrigation, when the
temperatures are low and favorable for seed yield and quality. Only commercial farmers,
*
Corresponding author. Tel.: 263-037-369
E-mail address: mugabe@africaonline.co.zw (F.T. Mugabe).
0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 0 0 ) 0 0 0 8 4 - 6
112
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
with irrigation facilities, can grow winter wheat. However, some smallholder farmers,
especially in the wetter areas, grow wheat on residual soil moisture in wetlands (Adam
et al., 1997). Normally the water requirements of wheat grown on residual soil moisture is
not met resulting in low yields being attained.
There is very limited water loss from the soil surface during the cooler months
when wheat is grown. All the available residual soil moisture can be used by a crop
since dry soil conditions promote root elongation and branching (Sharma and Ghildyal,
1977). Wheat roots can abstract water from up to 2 m (Hurd, 1968; Prihar et al., 1977;
Arora and Prihar, 1983) and most of the residual soil water in the soil profile can be
utilized.
Wheat yields of the order of 2800 kg/ha have been reported by Mishra et al. (1995)
with 50 mm of precipitation grown on residual soil moisture in India. It has been
suggested that genotypes with lower yield potentials under test crop conditions but which
are much more stress resistant should be used where water deficits are anticipated. It is
quite possible that some released genotypes and promising wheat lines in the current
Zimbabwe breeding program can withstand drought.
Water has not been taken as a major limitation in the Zimbabwe breeding programme;
hence the drought tolerance of the released genotypes is not known. Farmers growing
wheat on limited soil moisture do not know which varieties to choose in order to realize
optimum yields. This study was conducted to compare the response of four released
genotypes and two promising genotypes to water deficits and to assess the possibility of
growing wheat on residual soil moisture.
2. Study sites and methods
2.1. Irrigation by variety trial at Chiredzi Research Station
The study was conducted at Chiredzi Research Station, (218S and 318E), at an altitude
of 429 m a.s.l. in the southeast Lowveld of Zimbabwe during the winters of 1996 and
1997. The region lies in natural region V of Zimbabwe that is semi-arid, with mean
annual rainfall of 500 mm with a seasonal range of 250±1000 mm. The natural regions
are a classification of the agricultural potential of the country, from natural region 1,
which represents the high altitude wet areas to natural region V which receives low and
erratic rainfall averaging 550 mm per annum (Vincent and Thomas, 1960). The soils at
Chiredzi Research Station are dark-reddish brown clays derived from basic gneiss and are
classified as the Triangle B2 series and typic rhodstuff in Zimbabwean and USDA
classification systems, respectively.
Four released wheat genotypes, Deka, Pote, Nata and Ruya and two promising varieties
S85331-3H-0H-3H-0H (P1) and S86073-5H-0H-3H-0-1H-0G (P2) were grown at three
regimes of drought stress in the 1996 and 1997 seasons. These were full, three-quarters
and half of normal irrigation requirements. The full treatment was irrigating the
genotypes at 50% allowable moisture depletion and applying water according to the crop
water requirements. All the irrigation treatments were based on the open pan irrigation
scheduling using the wheat standard crop factor progression of 0.3±1.0 (Cackett, 1972).
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
113
The land on which the study was carried out was ploughed and a basal fertilizer of
700 kg/ha compound X (20:10:5) was disced into the soil before planting. Sowing was
done in the first week of May, that is the recommended sowing time for wheat in the
Lowveld. The seeds were sown in rows 25 cm apart in 3.5 m3.5 m plots at a seed rate of
100 kg/ha. The experiment was designed as a 63 factorial in a split plot design with four
replications. The irrigation level was the main plot factor whereas genotype was the subplot factor.
The site was irrigated to field capacity soon after planting and 21.8 mm emergence
irrigation was applied about 7 days later. Thereafter, the irrigation treatments were
imposed. Weed control was hand hoeing. Regular scouting for insect and disease was
done throughout the duration of the study. Measurements taken included days to 50%
flowering, days to maturity, stand counts at harvest, plant heights at harvest, number of
ears/m2, number of spiklets/ear, 1000 seed weight and grain yield. The data were
subjected to the ANOVA procedure using MSTA-C statistical package.
The yield stability of the wheat genotypes was assessed, using Eq. (1), where Ys is
the yield stability of a given genotype when deficit irrigation is applied, Yg1 is the genotype yield grown without water stress and Yg2 is the genotype yield grown under water
stress.
Ys
100 Yg1 ÿ Yg2
Yg1
(1)
2.2. Assessment of residual soil moisture at Romwe
Romwe, in Chivi, lies in natural region IV. The average annual rainfall at Chendebvu
dam, a rainfall station located 12 km to the north of the catchment, over the last 40 years
(1952±1992) is 581 mm (Butterworth et al., 1995) with a standard deviation of 263 mm.
The soils are light grey colored, sandy soils formed from granitic gneiss. These are
kaolinitic, fersialitic soils (III 5P) according to the Zimbabwean soil classification system
(Thompson and Purves, 1978). In many locations, a thick clay layer underlines light
textured horizons.
One access tube (external diameter 45 mm) was installed to 120 cm in the center of
each of seven sites chosen. A neutron probe (Wallingford MK III) was used to measure
soil moisture. Counts were taken over 16 s at 10 cm intervals at the end of the wet season
(5 April 1994) and at the end of dry season (8 September 1994). Soil samples were sent to
Center of Nuclear Studies (Cadarache, France) for calibration of the neutron probe
(Mugabe, 1998). Particle size on each horizon for the seven sites was measured at the
Institute of Soils and Chemistry, Harare. Horizon delineation was based on color and
observable textural and structural differences. In this study, percent sand refers to the
combination of coarse, medium and fine sand. The pressure chamber method was used to
determine the gravimetric moisture content at ÿ1500 kPa following the technique
described by Black (1965). Saturated paste for each of the samples was prepared and
replicated twice in rings that were placed in ceramic plate. The samples were left to
equilibrate until there was no significant amount of water increase in the burettes
collecting the outflow. After equilibrium the samples were transferred into weighed
114
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 1
Irrigation dates and amounts for the wheat trial and rainfall received during the winters of 1996 and 1997
1996
1997
Amount of water applied (mm)
Full
16/5
23/5
14/6
11/7
8/8
27/8
Total
Rain
Comment
Three quarters
Half
10/5
22/5
17/6
10/7
8/8
18/8
50
22
50
50
50
50
50
22
38
38
38
38
50
22
25
25
25
25
272
60
11
224
172
1996
1997
Planting
Emergence
Treatment
Treatment
Treatment
Treatment
aluminum foil. The weight of the wet soil plus aluminum foil was determined and the
sample was dried at 1058C hours before reweighing.
3. Results and discussion
3.1. Irrigation levels
Table 1 shows the amounts of irrigation water applied for each treatment in 1996 and
1997. For each treatment similar amounts of irrigation water were applied in both years.
Irrigating three quarters and half of the crop water requirements at each irrigation day
resulted in water deficits of 16 and 31% in the 1996 season and 20 and 38% in the 1997
season, respectively. More rainfall was received in 1996 (60 mm) than 1997 (11 mm). In
1996 the mean monthly temperatures for June, July and August were lower than that of
1997 (Table 2).
At all the irrigation levels, the 1996 crop took longer to mature, had more ears/m2, and
was taller because of cooler conditions (Cackett and Wall, 1971; Mashiringwani and
Schwepppenhauser, 1991) (Table 2) compared to 1997. On average, yields were heavier
in 1996 than in 1997.
Table 3 shows that supplying less water than the crop water requirements has no effect
on days to 50% flowering, number of ears/m2, plant height and 1000 seed weight.
Table 2
Monthly maximum, minimum and mean temperatures (8C) from May to August 1996 and 1997 at Chiredzi
Research Station
Year
1996
1997
May
June
July
August
Max
Min
Mean
Max
Min
Mean
Max
Min
Mean
Max
Min
Mean
26.4
26.2
12.9
12.3
19.7
19.3
26.6
28.7
9.7
11.9
17.2
20.3
23.3
24.0
7.3
12.1
15.3
18.1
26.6
29.0
10.7
10.2
18.7
19.6
Days to 50%
flowering
Days to
maturity
1996
1997
1996
1997
1996
Irrigation level
Full
Three quarter
Half
75.0a
74.8a
73.9a
±b
±
±
114.3a
112.1ab
109.7b
112.0a
110.5a
108.5b
Genotype
P1
P2
Pote
Deka
Nata
Ruya
Mean
LSD
CV%
Interaction
65.8d
74.1bc
73.0c
79.8a
79.5a
75.3b
74.4
1.531
1.44
NS
±
±
±
±
105.2c
109.0b
106.3bc
116.8a
117.0a
117.9a
112.0
3.18
1.99
NS
108.0c
110.0ab
109.5bc
111.6a
111.3ab
111.4a
110.3
1.875
1.19
NS
a
b
Number of
ears/m2
Numbers with the same letter are not signi®cantly different.
Missing data.
Plant Height
(cm)
1000 seed
weight
Grain yield
(kg/ha)
1997
1996
1997
1996
1997
1996
1997
375a
367a
358a
350a
345a
318a
95.9a
95.0a
93.8a
87.5a
86.8a
84.9a
37.1a
35.0a
34.9a
41.9a
40.7a
39.7a
5537a
4862b
4431b
5290a
4894a
4223b
363ab
324b
386ab
353b
416a
358ab
367
62.2
11.9
NS
344a
325ab
362a
296b
355a
344a
338
47.3
9.8
NS
91.2b
89.7b
95.4ab
101.2a
92.6b
99.4a
94.9
5.812
4.30
NS
79.3c
84.2b
88.4a
91.7a
84.8b
89.8a
86.4
3.557
2.89
NS
41.6a
35.3b
34.5b
36.5b
30.7c
35.6b
35.7
3.703
7.29
NS
43.8a
40.8a
42.3a
41.9a
32.8b
42.0a
40.8
6.141
10.58
NS
4622bc
5513a
4538c
5101abc
5144ab
4743bc
4944
585.6
8.32
S
3895b
5150a
4875a
5060a
5020a
4834a
4806
575.6
8.41
S
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 3
Effect of de®cit irrigation on wheat yields and yield attributes of six genotypes during the 1996 and 1997 winter seasonsa
115
116
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Irrigating half of the irrigation water requirements resulted in significantly fewer days to
maturity compared to irrigation according to the crop's water requirements and supplying
three-quarters of irrigation in 1997. Ehdaie (1995) also reported that water stressed wheat
matures earlier than that which is not stressed. In 1996, applying less water gave
significantly lower yields compared to irrigating according to the crop water
requirements. There was a 21 and 20% decline in yield when three quarters and half
irrigation water were applied, respectively. In 1997, there were no significant yield
differences between full irrigation and three-quarter water application. Applying half the
irrigation water resulted in significantly lower yields than applying all the crop water
requirements and applying three quarters irrigation water.
3.2. Wheat genotypes
There were significant differences in days to 50% flowering. Days to maturity, number
of ears/m2, plant height, 1000 seed weight and grain yield among the six genotypes
(Table 3). The promising, genotype P2, gave the highest yields in both seasons though it
was not significantly different from most of the genotypes (Deka and Nata in 1996 and all
except P1 in 1997).
In 1996 P2 performed better than all the genotypes at all the three irrigation regimes
(Table 4) while in 1997 it out performed all the genotypes at full irrigation only. Of the
released genotypes, Deka produced the highest yields in 1997 season at half irrigation and
was second at three quarters irrigation in 1996. On average Deka yielded highest at both
three-quarters and half irrigation in the two seasons. Yield stability of genotypes can be
calculated by comparing yields of crop grown under deficit irrigation and that obtained at
Table 4
Mean yields (kg/ha) of six genotypes of wheat for 1996 and 1997 at three levels of irrigation
Irrigation level
Genotype
1996
1997
Full
P1
P2
Pote
Deka
Nata
Ruya
4938
5983
5498
5432
5834
5541
4483
6011
5382
5232
5681
4951
Three quarters
P1
P2
Pote
Deka
Nata
Ruya
5153
5631
3754
5342
4989
4305
4026
5118
5236
4999
5002
4987
Half
P1
P2
Pote
Deka
Nata
Ruya
3776
4926
4364
4528
4609
4385
3176
4322
4008
4950
4377
4565
117
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 5
Percent yield deviation from two de®cit irrigations for six genotypes during the 1996 and 1997 seasons
Irrigation level
Three quarters
Genotype
1996
P1
P2
Pote
Deka
Nata
Ruya
a
a
ÿ4
6
32
2
14
22
Half
1997
Average
1996
1997
Average
10
15
3
4
11
ÿ1a
3
10
17
3
13
10
24
18
21
17
21
20
29
28
26
6
22
8
26
23
23
11
21
14
Indicates an increase in yield resulting from de®cit irrigation.
full irrigation (without water stress). Table 5 shows the percent deviation in yield of the
six wheat genotypes under deficit irrigation during the 1996 and 1997 seasons. Deka gave
the least deviation at both three-quarters and half irrigation regimes and this implies that
Deka is not as much affected by deficit irrigation compared to the other genotypes. This
might not mean that it would give the highest yields under deficit irrigation. For example
P2 (though it has an average deviation of 23%) yielded highest at three-quarters and half
irrigation in 1996. In the same year Deka gave second and third highest yields,
respectively, but had a smaller average deviation of 11%.
3.3. Possibility of growing wheat on residual soil moisture
Table 6 shows that there is lot of variation in the texture of the sites chosen, though
they are all sandy at the surface except F5. The soils used for this analysis are sandy at the
surface and clayey below 70 cm. In wet years the soils will be water logged in the
summer season and very moist at the end of the wet season. Available moisture to 110 cm
was more than 77 mm at the end of the rainy season in April for all the sites. The
difference in soil moisture between 5 April and 8 September is water loss through soil
evaporation, weed uptake or some limited drainage.
This water could be used to grow a winter crop like wheat or beans and the expected
yield levels will depend on the ability of the crop grown to withstand drought. The sites
had different total soil moistures and water remaining at permanent wilting point.
This depended on the individual site's texture. Four of the seven sites (F4, F7, F8 and
F9) selected had soil moisture above half of the wheat crop water requirements.
The water available to the wheat grown on residual soil moisture can be more than the
figures given in Table 6, for water can be withdrawn from depths of up to 2 m when
wheat is grown under water stress conditions (Sharma and Ghildyal, 1977).
The results from the irrigation trial carried out at Chiredzi Research Station (Table 3)
shows that wheat yields of more than 4000 kg/ha can be expected when wheat is grown
on deficit irrigation of at least 170 mm. Mishra et al. (1995) recorded wheat yields of the
order of 2800 kg/ha when they grew wheat on residual soil moisture with 50 mm of rain
only. Work carried out by Chaudhary and Bhatnagar (1980) shows that frequent
irrigations must be provided throughout the growing season to ensure maximum yield of
118
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
Table 6
Clay, silt and sand contents of the sites, and available soil water at the end of the rainy season (April) and at the
end of the dry season (September)
Site
Depth
Clay (%)
Silt (%)
Sand (%)
Total available soil water
in 110 cm profile (mm)
5 September
1994
8 November
1994
F4
0±13
13±44
44±79
79
11
24
53
34
11
11
13
10
78
65
33
55
240
178
F5
0±26
26±46
46
20
14
15
10
18
14
70
68
71
77
36
F6
0±9
9±16
16±85
85
4
4
8
3
7
7
9
6
89
89
83
91
106
54
F7
0±13
13±81
81
6
7
25
9
8
5
85
85
70
194
109
F8
0±26
26±78
78
4
8
38
3
9
7
93
85
55
212
127
F9
0±15
15±100
100
9
12
29
10
10
8
81
78
63
220
98
F10
0±19
19±74
74
9
7
33
13
9
5
78
84
62
147
101
wheat. This would mean that the expected yields from wheat grown on residual soil
moisture would be lower than those obtained from wheat grown on deficit irrigation
where frequent irrigation is supplied. Table 7 shows that winter rains are expected in most
of the years at Romwe and this would increase the water available to the crop.
Table 7
Romwe winter rainfall (mm) in 1994, 1995, 1996 and 1997
Months
1994
1995
1996
1997
May
June
July
August
2
0
13
14
64
1.5
5
8
38
13
35
13
1.5
1
29
0
Total
29
78
99
31
F.T. Mugabe, E.Z. Nyakatawa / Agricultural Water Management 46 (2000) 111±119
119
Deka recorded the least reduction at the two water levels even though it did not record
the highest yields when optimum water was added. This suggests possible benefits of
growing Deka on residual soil moisture, because of the yield stability at water levels
below wheat crop water requirements.
Acknowledgements
The authors would like to thank Dr. M.D.S. Nzima and P. Nyamudeza for their critical
review on this paper, Dr. N. Mashirinwani for providing us with wheat genotypes,
Messers D. Maringa, D. Muzenda and Mhlanga, for their roles in trial management and
data collection.
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