259 T. Oweis et al. European Journal of Agronomy 11 1999 255–266
Table 2 Amount of irrigation water, application dates, and emergence dates for durum wheat sown at different times in the full supplemental
irrigation SI treatment Season
Sowing date a
Emergence date Irrigation amount mm
b and date Total
19921993 10 November 1992
9 December 1992 133 24; 146 154; 118 234;151 215
548 10 December 1992
16 January 1993 95 14; 100 234; 100 45; 146 215
441 16 January 1993
20 February 1993 62 64; 84 234; 130 225
276 19931994
5 November 1993 22 November 1993
113 64; 85 214; 125 165 323
5 December 1993 20 December 1993
106 74; 84 214; 164 155 354
12 January 1994 28 January 1994
80 54; 89 224; 150 165 319
19941995 8 November 1994
23 November 1994 50 93; 65 273; 145 144; 94 65
354 10 December 1994
30 December 1994 63 273; 97 154; 94 65
254 15 January 1995
6 February 1995 42 293; 122 154; 104 55
268 19951996
5 November 1995 17 November 1995
100 55; 80 145 180
12 December 1995 3 January 1996
100 65; 100 145 200
28 January 1996 17 February 1996
100 75; 120 145; 100 265 320
a The dates represent early, normal, and late sowing times. b Gross amount of SI water mm applied to the full SI treatment; the other irrigation rates were 23 and 13 of the amount applied
to full SI application dates in parentheses.
treatments automatically received fixed propor-
3. Results
tions 13 and 23 of that amount. The root zone depth was estimated before each irrigation based
3.1. Grain and straw yields on the depletion pattern of the soil profile. The
amounts of irrigation water and application dates All major factors, except variety, had significant
effects on grain and straw yields. Overall rain-fed are given in Table 2.
During the
growing season,
measurements grain yield varied with the year 2.1–3.6 t ha
−1, with no consistent relationship with seasonal rain-
included: date of emergence Table 2, plant and head numbers per m
2, and green leaf area and fall. Although there were differences between vari-
eties, three of them Cham 1, Cham 3, and Omrabi biomass at stem elongation, heading and anthesis.
However, only grain and straw yields, grain protein, 5 were similar, giving slightly higher yields than
Lahn. However, the overall effects of SI and N and vitreousness are reported here. The yield and
harvest index were sampled in 7.9 and 0.3 m 2,
were dominant. With increasing water availability, from rain-fed to 13, 23, and full SI levels, the
respectively. Grain protein was calculated by multiplying the
N values from the Kjeldahl grain yields were 2.6, 3.8, 4.6 and 4.8 t ha
−1, respectively, whereas the straw yields were 4.9, 5.9,
digestion by 5.7 AACC, 1983, whereas virtuous- ness was visually assessed based on the presence of
6.7, and 7.2 t ha −1, respectively. Nitrogen also had
a consistent positive effect on yield. With the 0, opaque blotches or ‘yellow berry’ in the grain.
Analysis of variance was used to assess statistical 50, 100, and 150 kg ha
−1 rates, the yields were 2.8, 3.9, 4.4, and 4.6 t ha
−1, respectively, with corre- significance
using BLOCK
STRUCTURE, TREATMENT STRUCTURE and ANOVA com-
sponding straw values of 4.3, 5.9, 6.9, and 7. 5 t ha
−1. mands set in GENSTAT 5 program. Production
functions and
their corresponding
predicted The overall interaction between rainfall and
irrigation water level with season, variety and response surfaces were developed using variety, rate
of N, rate of SI, and date of sowing, and their sowing date are shown in Table 3 for grain and
straw yield. Despite differences in rainfall, the interactions, which were seen to account for the
high variability. Further, the model was kept simple response to SI was similar for the first 2 years;
however, its effect decreased in subsequent years, by ignoring interactions due to three factors or more.
260 T. Oweis et al. European Journal of Agronomy 11 1999 255–266
Table 3 Mean durum wheat grain and straw yields under rain-fed and varying levels of supplemental irrigation in relation to season, variety
and sowing date a
Variable Rain-fed
13 23
Full SI Mean
Grain Straw
Grain Straw
Grain Straw
Grain Straw
Grain Straw
t ha −1
Season 19921993
2.24 3.50
4.24 5.61
5.23 6.93
5.94 8.17
4.41 6.05
19931994 3.63
6.75 4.49
6.74 5.46
7.60 5.29
7.89 4.71
7.12 19941995
2.15 4.02
3.47 5.36
4.06 6.29
4.40 6.86
3.52 5.63
19951996 2.59
5.76 3.17
5.95 3.37
5.95 3.48
5.94 3.15
5.90 Variety
Cham 1 2.65
4.91 3.91
6.11 4.51
6.67 4.91
7.26 4.00
6.24 Lahn
2.37 4.65
3.66 6.10
4.19 6.76
4.45 7.21
3.67 6.18
Cham 3 2.69
5.13 3.80
5.88 4.53
6.93 5.00
7.55 4.01
6.37 Omrabi 5
2.91 4.85
4.00 5.58
4.60 6.40
4.75 6.84
4.07 5.92
Sowing date November
2.72 5.32
4.26 6.96
4.76 7.61
4.98 7.86
4.18 6.94
December 2.75
4.98 3.69
5.56 4.34
6.30 4.65
6.86 3.85
5.93 January
2.49 4.35
3.57 5.23
4.27 6.17
4.71 6.92
3.76 5.67
a All interactions with irrigation are significant P≤0.001, except for variety. Standard error of means for grain: water×year= 0.52; water
×variety=0.071; water×sowing date=0.08.
possibly due to heat stress during the grain-filling response to N was maximum at 100 kg ha
−1, whereas at the two higher SI levels 23 and Full
period. Reflecting a significant interaction between water levels and sowing time, the responses to
SI , responses continued up to 150 kg N ha −1. In
contrast to seasonal and water effects on N irrigation were highest with early sowing, with
little difference between the later sowing dates. response, there was no effect of variety. Thus, the
four varieties responded in the same way to added However, the pattern of response to SI levels was
generally similar for the four varieties. As the N. A delay in sowing date from November to
December and
January consistently
reduced responses for straw yields paralleled these of grain
yield, only the latter data are subsequently responses to N.
The significant parameters and significant inter- presented.
The interactions involving applied N and the actions affecting the yield components of durum
wheat were used in a regression model to develop other management inputs are presented in Table 4.
Again, a strong seasonal effect was evident. The the production functions of grain, total dry matter,
and straw yields. The resulting general production data illustrate that the responses to N are related
to yields of the unfertilized control and the factors function and regression coefficients for all the
varieties and yield components are presented in that influence growth. On average, the addition
of 50 kg N ha
−1 increased
grain yield
by Table 5. The interaction of variety with precipita-
tion and with N was significant and accounted for 1.1 t ha
−1 compared to the control 2.8 vs. 3.9. The responses were positive but relatively lower
a high percentage of variation to be included in the model. Examples of the resulted response
for each additional 50 kg N, i.e. +0.5 t ha−1 for
100 kg N ha −1
and +0.2 t ha−1
for the
surfaces that could be developed are depicted in Fig. 1 for the Cham 3 variety. These surfaces can
100 kg N ha −1 and 150 kg N levels. The responses
to N were strongly modified by irrigation water provide the required information on production
potential under any combination of factors levels. For rain-fed conditions, the response was
limited to 50 kg N ha −1. With limited SI 13, the
involved.
261 T. Oweis et al. European Journal of Agronomy 11 1999 255–266
Table 4 Table 5
Estimates of regression coefficient for durum wheat production Mean effects of fertilizer nitrogen on durum wheat grain yield
in relation to season, water levels, variety and sowing date a
functions a
Variable N kg ha
− 1
Variable Grain
Straw Total dry
matter 50
100 150
Mean t ha
−1 Intercept Cham1
−0.995 −1.825
−1.63 Intercept Lahn
−0.720 −1.796
−2.00 Season
Intercept Cham3 −0.980
−1.594 −1.45
19921993 3.84
4.45 4.64
4.73 4.42
Intercept Omrabi5 0.818
−2.354 −2.20
19931994 3.53
4.59 5.07
5.38 4.64
PR Cham 1 0.01123
0.01992 0.02863
19941995 2.41
3.50 4.02
4.15 3.52
PR Lahn 0.00910
0.01992 0.02863
19951996 1.58
3.07 3.83
4.14 3.16
PR Cham3 0.01115
0.01992 0.02863
Water PR Omrabi5
0.00566 0.01992
0.02863 Rain-fed
2.21 2.77
2.89 2.76
2.64 N Cham 1
−0.00553 −0.01051
−0.0234 13 SI
2.77 3.90
4.32 4.36
3.84 N Lahn
−0.00553 −0.01113
−0.0241 23
3.10 4.31
4.96 5.44
4.45 N Cham 3
−0.00553 −0.01112
−0.0235 Full SI
3.28 4.63
5.37 5.83
4.78 N Omrabi 5
−0.00553 −0.00765
−0.0194 Variety
SI 0.03003
0.03359 0.05715
Cham1 2.90
4.02 4.44
4.62 4.00
D −0.2571
−0.2702 −0.5494
Lahn 2.65
3.58 4.15
4.28 3.67
PR ×SI
−0.00007 −0.00009
−0.00015 Cham3
3.89 3.97
4.49 4.69
4.01 PR
×N 0.000066
0.00011 0.00017
Omrabi 5 2.91
4.04 4.50
4.80 4.06
PR ×D
0.00078 0.00076
0.00158 Sowing date
SI ×N
0.000083 0.00009
0.0002 November
2.88 4.74
4.98 4.12
4.18 N
×D −0.000067
−0.00013 0.0000
December 2.72
4.28 4.61
3.82 3.86
SI 2
−0.00001 0.00000
0.0000 January
2.92 4.14
4.21 3.77
3.76 N
2 −0.00007
−0.00009 −0.00012
D 2
0.00372 0.00408
0.00804 a All interactions with N are significant P≤0.001, except
for N ×variety. Standard error of means N×water=0.051;
a PR=total annual precipitation mm; SI=supplemental N
×variety=0.048; N×sowing date=0.065. irrigation amount mm; N
=applied nitrogen kg ha−1 and D
=delay in sowing after 1 November days. Variance accounted for: grain 81.4
, dry matter 82.2 , and straw 80.1
Y =a
+a 1
PR +a
2 SI
+a 3
N +a
4 D
+a 5
PR ×SI +a
6 PR
×
3.2. Grain and straw protein
N +a
7 PR
×D+a 8
SI ×N +a
9 N
×D+a 10
SI 2
+a 11
N 2
+ a
12 D
2 , where Y is yield in t ha
−1; a0 is the intercept; a1 to
The influence of all production and manage-
a 12
are the regression coefficients of the independent variables
ment factors on quality was just as pronounced as
and the significant interactions involved.
for yield. While grain protein levels varied with the season, some overall trends were evident. With
increasing N levels, grain protein concentration As N has a dominant effect on cereal protein
levels, the interaction of N and the other factors rose from 9.6
with no added N to 11.7 with
150 kg N ha −1. Similarly, delayed sowing, on
are presented Table 6. The decrease in grain protein caused by irrigation was modified by the
average, increased protein from 9.9 to 11.3 ,
whereas the addition of irrigation water decreased N application rate. However, the N required for
maximum yield did not compensate for the reduc- protein from 11.7
under rain-fed conditions to 10
with 23 and full SI. The four varieties were tion due to irrigation compared to rain-fed condi-
tions, i.e. and 13.6 vs. 10.8 grain protein at the
generally similar in terms of protein content, rang- ing from 10.4 to 10.7
. The protein content in highest N level. Straw under fertilized rain-fed
conditions contained almost twice the protein straw followed similar trends as in grain. For
example, irrigation reduced straw protein from 2.8 content compared to irrigated conditions with the
same applied N level. While the interaction to 1.8
, whereas 150 kg N ha −1 increased values
from 1.7 to 2.6 , a substantial enhancement in
between N and varieties was significant, differences between varieties were minor; at the higher N
terms of feeding quality.
262 T. Oweis et al. European Journal of Agronomy 11 1999 255–266
sowing date were accentuated by added N. Late sowing, relative to early sowing, increased the
grain protein from 10.9 to 12.8 and straw protein
from 2.4 to 2.9 at the highest N level.
3.3. Grain vitreousness The variety and the other management factors
Table 7 significantly affected vitreousness. The overall mean percentage values were 67 Cham 1,
72 Lahn, 63 Cham 3, and 52 Omrabi 5. Rain- fed values were 79
, decreasing to 62 13 SI
and 57 23 SI , with no further decrease.
Nitrogen consistently increased vitreousness or reduced ‘yellow berry’ from 44 to 83
; the delay in sowing also increased vitreousness from 50 to
78 . Given the magnitude of these influences, it
was not surprising that the interaction of N and the other factors were also significant.
The positive effect of N on percentage vitreous- ness varied with irrigation levels Table 7. Under
rain-fed conditions, N raised values as high as 92 from 57
under unfertilized conditions, whereas with irrigation, the maximum effect was 75
. Under any level of N, vitreousness varied for the
varieties, with differences being most pronounced under unfertilized conditions; in all cases, Omrabi
5 had the lowest values. The interaction with sowing date and N was similarly variable; the
differences were large 33–58
under unfertilized conditions, but diminished as the N application
rate increased. 3.4. Thousand-kernel weight
Though of lesser importance than either protein or vitreousness, the 1000-kernel weight TKW
was also influenced by variety and the main factors,
a
b
c Fig. 1. Response surfaces of durum wheat Cham 3 grain yield
but the effects were less consistent and much
in relation to rainfall, supplemental irrigation, nitrogen and
smaller Table 8. Overall, Cham 1 had the lowest
sowing date: a 100 kg N ha −1, 350 mm rainfall and varying
TKW at 43 and Lahn the highest at 52. There
irrigation and sowing date; b early sowing, 350 mm rainfall
were large differences between rain-fed 41 and
and varying irrigation and nitrogen rates; c early sowing, no
irrigated conditions 47–49, with essentially no
irrigation and varying rainfall and nitrogen rates.
difference between irrigation levels. In marked contrast to other parameters, N had no effect on
the mean TKW. However, the interactions between rates, Omrabi 5 tended to have a lower grain and
straw protein than the other three varieties. For N and the other factors were significant. Added N
tended to decrease the TKW values of rain-fed all varieties, the increases in protein with delayed
263 T. Oweis et al. European Journal of Agronomy 11 1999 255–266
Table 6 Nitrogen effects on grain and straw protein in durum wheat by irrigation level, variety and planting datea
Variable Nitrogen kg ha
−1 50
100 150
Mean Grain
Straw Grain
Straw Grain
Straw Grain
Straw Grain
Straw Season
19921993 10.6
2.0 11.6
2.3 12.8
2.6 13.6
3.2 12.1
2.5 19931994
9.6 1.5
9.7 1.6
10.2 1.8
11.0 2.1
10.1 1.8
19941995 9.0
1.5 9.5
1.8 10.4
2.2 11.1
2.8 10.0
2.1 19951996
9.3 1.8
9.0 1.6
9.8 1.9
11.2 2.3
9.3 1.9
Water Rain-fed
9.8 2.0
10.9 2.4
12.2 3.0
13.6 3.8
11.7 2.8
13 SI 9.3
1.6 9.7
1.7 10.4
2.0 11.6
2.5 10.3
1.9 23
0.5 1.6
9.6 1.6
10.1 1.8
10.9 2.2
10.0 1.8
Full SI 9.8
1.7 9.5
1.6 10.1
1.8 10.8
2.1 10.1
1.8 Variety
Cham1 9.7
1.7 10.1
1.9 11.0
2.2 12.1
2.6 10.7
2.1 Lahn
9.6 1.8
10.1 1.9
10.8 2.3
11.8 2.9
10.5 2.2
Cham3 9.6
1.7 9.8
1.8 10.7
2.2 11.7
2.9 10.5
2.2 Omrabi 5
9.6 1.6
9.8 1.7
10.6 1.9
11.4 2.2
10.4 1.9
Sowing date November
9.3 1.6
9.5 1.7
10.1 2.0
10.9 2.4
10.0 1.9
December 9.5
1.7 9.7
1.8 10.5
2.1 11.5
2.5 10.3
2.0 January
10.1 1.8
10.6 2.0
‘11.7 2.3
12.8 2.9
11.3 2.3
a All interactions are significant P≤0.001. Standard error of means, grain: N×water=0.089; N×variety=0.097; N×sowing date
=0.086. Standard error of means, straw: N×water=0.051; N×variety=0.052; N×sowing date=0.049.
wheat, but slightly increased the TKW with irri- within 3–15
of that achieved by full SI. Such yield increases clearly show the potential for water
gated conditions. However, the differences between varieties were fairly consistent with N application
savings with proper conjunctive use of irrigation and rainfall in rain-fed agricultural systems. The
rates, with Lahn being highest in all cases. Added N had no effect on TKW with varying sowing
strategy of applying restricted amounts of water based on the amount and distribution of rainfall
dates. in addition to the incremental effect of water on
crop yield is the essence of the SI concept. The mean rainfall WUE was about 1.1 kg grain
4. Discussion
