Directory UMM :Data Elmu:jurnal:A:Agricultural Water Management:Vol46. Issue1.Nov2000:
Agricultural Water Management 46 (2000) 15±27
De®cit irrigation and nitrogen effects on
maize in a Sahelian environment
II. Shoot growth, nitrogen uptake and
water extraction
R.K. Pandey1, J.W. Maranville*,2, M.M. Chetima
Institut National De Recherche Agronomique Du Niger (INRAN) B.P. 429, Niamey, Niger
Accepted 14 December 1999
Abstract
Maize growth in arid and semiarid regions is often limited by variation in the amount and
frequency of irrigation or rainfall. Sub-optimal supply of nitrogen (N) may further curtail growth
and development of the crop. Simultaneous optimization of these two inputs provides optimum
conditions for crop growth and productivity. A maize (Zea mays L.) crop was subjected to different
periods of de®cit irrigation and rates of N in the ®eld on a medium-deep Tropudalf clay loam soil.
Water de®cit effects on shoot growth, N uptake and water extraction with varying level of N supply
were analyzed to determine their inter-relationships. Water de®cit was created by withholding irrigation
at different stages of crop development. Increasing moisture stress resulted in progressively less leaf
area, crop growth rate (CGR), plant height, shoot dry matter and harvest index. Mean increase in above
ground biomass was 7.7 and 8.7 kg per mm of water used in the 1996/1997 and 1997/1998 seasons,
respectively. De®cit irrigation stress indices (DISI) for above ground biomass when the crop was
subjected to a 2 week stress was 11.0 and 20.1 compared to 4 week stress values of 3.2 and 16.5 in the
1996/1997 and 1997/1998, respectively, indicating greater stress the ®rst season during vegetative
growth. When de®cit irrigation was increased to 8 weeks, DISI values were 34.1 and 39.8 for the
respective seasons. Biomass production response to N in both years was quadratic; however, N response
differed with irrigation level in both seasons. Highest biomass yield with no irrigation de®cit was
obtained at 120 kg N in 1996/1997 and at 160 kg N haÿ1 in 1997. Nitrogen uptake was more dependent
on applied N than water supply although N uptake decreased with greater water and N de®cits. Water
extraction was highest at the 120 and 160 kg N haÿ1 rates with soil water de®cit.
*
Corresponding author. Present address: Department of Agronomy, 102 KCR Lab, University of Nebraska,
Lincoln, NE 68583-0817 USA. Tel.: 1-402-472-3057; fax: 1-402-472-3654.
E-mail address: [email protected] (J.W. Maranville).
1
Agronomist, Program Leader and technician, PNRA/INRAN, PB 429, Niamey.
2
Professor, University of Nebraska, Lincoln, NE.
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 7 4 - 3
16
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
This study showed that a maize crop differs in its ability to maintain LAI, CGR and above ground
dry matter production at different levels of water de®cit and N supply. The adaptive strategy of
maize plants under vegetative water stress appears to be extended rooting depth and water
extraction from the deeper soil pro®le, and simultaneous reduction in leaf area to decrease
transpiration. Optimizing the inputs of water and N at the farm level would maximize biomass
production and harvest index. This information can be useful to guide crop management strategy to
enhance maize production in the irrigated perimeter of a Sahelian environment. # 2000 Elsevier
Science B.V. All rights reserved.
Keywords: De®cit irrigation; Crop growth rate; Leaf area index; Water extraction pattern; Shoot and root growth
1. Introduction
There has been an increasing interest in scheduling deficit irrigation in order to
conserve water and maintain crop productivity in the Sahel of West Africa. In these areas,
total biomass production is often as important to farmers as grain since animals are a
significant part of their livelihood. We reported on the effect of seasonal water deficit and
nitrogen (N) rate on grain yield and yield components (Pandey et al., 2000). This research
suggested that irrigation deficit during the vegetative stages of maize (Zea mays L.)
growth was possible without sacrificing significant grain yield. This irrigation response
was dependent on the N application rate. Research has shown the importance of water
and N interactions in optimizing maize productivity (Eck, 1984; Eghball and Maranville,
1993a). Most studies suggest that water shortage during vegetative growth reduces leaf
area (Boyer, 1970; Acevedo et al., 1971; NeSmith and Ritchie, 1992; McCullough et al.,
1994), internode elongation (Novoa and Loomis, 1981), and leaf and stem weight
(Denmead and Shaw, 1960; Eck, 1984). In a field study conducted under semi arid
environment of Texas, water deficits imposed 41 days after planting reduced leaf, stalk
and ear yields of maize, while those imposed 55 days after planting reduced only stalk
and ear yields. Water deficit during grain filling did not affect leaf and stalk yields (Eck,
1984). Management of water shortage through frequency and quantity of irrigaiton water
during vegetative growth and/or reproductive growth merits attention in high evaporative
environments to minimize curtailment of crop growth and yield and achieve higher water
use efficiency (Eck, 1985; Chapman and Barreto, 1997).
Nitrogen requirement by maize compared with other nutrients is large in Sahelian soils
for optimum vegetative and reproductive growth. Many physiological processes
associated with maize growth are enhanced by N supply (Eck, 1984). Nitrogen has
dramatic effects on maize growth, development and grain yield on soils that are limiting
in N supply. Numerous studies have shown the effects of reduced N supply on leaf area
index (LAI), plant height, shoot weight and plant N uptake (Eck, 1984; Pandey et al.,
1984; Muchow, 1988; McCullough et al., 1994). In most maize producing areas,
increasing rate of N supply results in greater LAI and leaf N (McCullough et al., 1994).
Variation in N supply affects crop growth, development and potential kernel set and grain
yield (Greenwood, 1976; Pandey et al., 2000). Leaf area index, leaf area duration, crop
photosynthetic rate, radiation interception and radiation use efficiency are increased by N
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
17
supply (Muchow, 1988). Reduced N supply decreases crop growth (Cox et al., 1993);
however, N response is modified by water supply under field condition (Greenwood,
1976; Pandey et al., 2000). Variable water supply either due to shortage of water or failure
of the irrigation system to supply water during vegetative and/or reproductive growth
stages in many irrigated areas of sub-Saharan Africa, particularly in the Sahel, is common
and often results in deficit irrigation.
Information on frequency and quantity of irrigation water and effect of deficit irrigation on
shoot and root growth of maize and the subsequent water and N extraction patterns have not
been well elucidated under the stressful Sahelian environment, more so with differential rates
of N supply. Further, information on crop growth responses and morphological/physiological
yield determinants are needed to analyze crop productivity that relate to crop water
production function and economic returns. The objectives of this study were to (i) determine
the effects of timing and duration of deficit irrigation on maize shoot growth and water
extraction, (ii) evaluate water deficit and N rate effects on N uptake, and (iii) analyze
relationships between grain yield, plant growth and deficit irrigation and N supply.
2. Materials and methods
A field experiment was conducted for 2 years (1996±1997 and 1997±1998) at INRAN
(Institut National de Recherche Agrononmique du Niger) research station near Konni
(lat. 118N, long. 128E) on a Tropudalph clay loam soil (fine kaolintic thermic kanolic
tropudalph). The site description, crop culture, and weather conditions were previously
described (Pandey et al., 2000). Water deficits were imposed as previously described
(Pandey et al., 2000). Irrigation was withheld at various crop growth stages (Ritchie and
Hanway, 1982) at five N levels.
2.1. Plant sampling and data collection
Plant samples from 1 m row length (five plants) were harvested for above ground
biomass at the tasseling (VT) crop growth stage and at physiological maturity. At grain
maturity, plant height was recorded. Crop growth rate (CGR) was computed by sampling
from between VT and physiological maturity. To monitor the greenness of the crop in
response to N status, chlorophyll meter readings were collected each season using the
Minolta SPAD 502 meter at the silking stage and converted to chlorophyll content
(Markwell et al., 1995). Measurements were taken midway between the margin and the
mid-rib of the ear-leaf from 10 representative plants from the center two rows from each
plot (Chapman and Barreto, 1997). At 2 days past VT, data on LAI using the leaf canopy
analyzer Li-Cor 2000 from the center rows of each treatment were collected in 1997/1998
according to Welles and Norman (1991). Soil moisture extraction patterns were
monitored to a depth of 1.5 m using a neutron probe from three irrigation regimes at the
R1 stage as previously described (Pandey et al., 2000).
At harvest, number of ears were recorded from each plot. Above ground vegetative
biomass and ear yield were recorded after 4 days of air drying. Grain yield was
determined from shelled ears and adjusted to 14% after a small sample of stover and grain
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R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
were taken and dried at 608C for 48 h. Total biomass included grain and stover. Harvest
index was calculated by dividing grain per plot by total biomass after adjusting for
moisture content. Grain and stover N was determined on composite samples from all
replications from every treatment combination using the Kjeldahl procedure. Deficit
irrigation stress index (DISI) was calculated as yield for unstressed treatment minus
stressed treatment divided by unstressed treatment times 100 (Pandey et al., 1984). A N
stress index (NSI) was calculated in a similar manner (Greenwood, 1976).
2.2. Statistical analysis
All plant data collected were statistically analyzed as a split plot factorial with four
replications except water use where three treatments and three replications were used.
Analysis of variance (ANOVA) was made to determine crop parameter response to
irrigation and N rates. Means among treatments were compared using least significant
difference at P0.05 probability. Regression analysis was performed on the relationship
between measured crop parameters and water applied and N rates. Best fit regression
equations were calculated.
3. Results and discussion
3.1. Aboveground biomass
Aboveground biomass production was different each season and presented separately
in Table 1. There was less differential in biomass production between zero N and
160 kg haÿ1 in 1996/1997 than in 1997/1998. The greater rates of N in 1997/1998
resulted in markedly more biomass production than those rates in 1996/1997 and
markedly less biomass at the low N rates for the second season. Response to applied N
was quadratic each year. There was little difference, however, between the two seasons
for response to deficit irrigation which was linear each year.
Deficit irrigation adversely affected total biomass yield at all N levels. The greatest
reduction was observed at the 160 kg N haÿ1 of 10.7 and 14.8 kg per mm of deficit
irrigation over the control in the respective seasons. The quadratic response to N peaked
at 120 kg haÿ1 in 1996/1997 and at 160 kg haÿ1 in 1997/1998. Total biomass response
was also reflected in the plant height (data not shown).
Irrigation deficit during any reproductive stage of maize resulted in marked loss of
biomass production compared to deficits only during vegetative growth (Table 1). The
DISI was approximately 3±10 times greater when water was withheld during
reproductive stage (I-5) than at the vegetative stage (I-2). Even withholding water once
during the reproductive phase (I-3) plus vegetative stages resulted in a considerable
increase in DISI from that of I-2. The NSI was twice as great in the 1997/1998 season as
the 1996/1997 season at the lower N rates (Table 1). This was mostly due to the higher
yields in the 1997/1998 season with high N rates making the yield response to N steeper
than in 1996/1997, although still quadratic. Grain yield and grain yield components were
found to react in a similar manner in these experiments (Pandey et al., 1999).
19
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 1
Aboveground biomass yield of maize at physiological maturaity as affected by irrigation (I) and nitrogen (N)
de®cits imposed at different growth stages at Konni, Niger in the 1996/1997 and 1997/1998 growing seasons.
De®cit irrigation stress indices (DISI) and N stress indices (NSI) are shown for individual irrigation and N
treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
1996/1997
I-1
I-2
I-3
I-4
I-5
Mean
NSI
6791
6187
5938
5762
5402
6016
26.2
8886
6953
6927
6377
6100
7049
13.5
9410
8119
7069
6661
5972
7446
8.7
9800
9446
8476
6748
6297
8153
0.0
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
5008
4557
4040
3827
3222
4131
55.1
6706
6231
5991
5218
4397
5709
38.0
8471
8378
8240
6111
5952
7430
19.3
10810
10553
8743
6399
6130
8527
7.4
160
Mean
DISI
9473
8756
7038
6044
5461
7454
8.6
8872
7892
7090
6318
5846
0.0
11.0
20.1
28.8
34.1
11723
11632
8640
8024
6026
9209
0.0
8544
8270
7131
5916
5145
0.0
3.2
16.5
30.8
39.8
a
a
b
LSD(0.05) I591; N402; IN694; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
LSD(0.05) I673; N341; IN763; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
3.2. Harvest index, crop growth rate (CGR) and leaf area index (LAI)
Harvest index (Table 2) was reduced by both water and N deficits each year as was
CGR (Table 3). The greatest reduction for each of these calculated parameters was in the
1997/1998 season. Although total biomass yield was reduced by the deficits imposed,
grain production was obviously more affected than stover production, and reflects these
stress affects on partitioning efficiency of the crop. The influence of water deficit on these
parameters was linear while N deficit effects were quadratic. Maize response to N
application for CGR was modified by water stress, with the least response occurring on
the most severely stressed irrigation regime (I-5).
The DISI and NSI values were generally less for harvest index compared to CGR
which were comparable to the LAI response in 1997/1998 measured at tasseling (Table 4).
Maximum LAI values were found at higher N rates under full irrigation as would be
expected. The very low LAI values of plants under stress may be underestimates of the
procedure since water stress causes leaf wilting (Hicks and Lascano, 1995). Leaf area
index values generally range from 2±6 in maize during grain fill (Tollenaar, 1986).
Nonetheless, intercepted radiation determines, in part, the CGR. Williams et al. (1965)
achieved growth rates of 32.5 g mÿ2 dayÿ1 in hydroponically grown corn which
compares to a maximum of 22.3 g mÿ2 dayÿ1 in the current experiment in 1997/1998.
20
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 2
Harvest index of maize as affected by irrigation (I) and nitrogen (N) de®cits imposed at different growth stages
at Konni, Niger in the 1996/1997 and 1997/1998 growing seasons. De®cit irrigation stress indices (DISI) and N
stress indices (NSI) as shown for individual irrigation and N treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
160
Mean
DISI
1996/1997
I-1
I-2
I-3
I-4
I-5
Mean
NSI
35.1
34.2
33.4
32.8
30.8
33.3
15.3
37.0
36.5
35.8
33.4
31.0
34.7
11.7
39.0
38.6
38.8
37.5
32.5
37.3
5.1
41.0
41.1
39.5
38.5
34.1
38.8
1.3
41.0
41.8
39.1
38.6
36.0
39.3
0.0
38.6
38.4
37.3
36.2
32.9
0.0
0.0
3.3
6.2
14.8
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
24.1
26.8
20.3
20.1
19.9
22.2
43.1
39.5
33.7
29.2
32.4
28.2
32.6
16.4
41.1
38.8
31.6
38.0
29.8
35.9
7.9
43.7
38.2
40.2
36.1
36.9
39.0
0.0
44.5
38.4
42.0
35.5
34.0
38.9
0.0
38.6
35.2
32.7
32.4
29.8
0.0
8.8
15.3
16.1
22.8
a
a
b
LSD(0.05) I2.1; N2.1; INns; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
LSD(0.05) I2.8; N2.8; INns; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
It is interesting that the lowest value of CGR in that season (I-5; zero N) was 19.5% of the
maximum CGR value achieved at the I-1, 160 kg haÿ1 treatment (Table 3) corresponded
to the difference in LAI (23%) for the same two treatment comparisons (Table 4).
Patterns of CGR and LAI response to irrigation and N deficits also corresponded to
biomass production in these experiments.
3.3. SPAD chlorophyll content and nitrogen uptake
Leaf chlorophyll content was not altered by irrigation deficit (Table 5) but decreased
significantly and linearly with decreased N supply both seasons. Wolfe et al. (1988)
showed that chlorophyll concentration (leaf greenness) in maize was positively correlated
to leaf N concentration. This would indicate that leaf N content decreased with lower N
treatments and leaves became progressively yellow with greater N deficits. Blackmer and
Schepers (1995) found that the SPAD 502 m was able to distinguish between fertilizer N
treatments for maize which resulted in differential yields. Chapman and Barreto (1997)
found that SPAD meter readings were positively correlated with both leaf N
concentration and specific leaf N in tropical maize and suggested that SPAD meters
provide an inexpensive method to estimate these parameters. In the current experiment,
leaf chlorophyll corresponded to biomass yield across N treatments, but was not related to
yield with irrigation treatment. The estimate of leaf chlorophyll may provide producers
21
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 3
Crop growth rate of maize between tasseling and physiological maturity as affected by irrigation (I) and nitrogen
(N) de®cits imposed at different growth stages at Konni, Niger in the 1996/1997 and 1997/1998 growing
seasons. De®cit irrigation stress indices (DISI) and N stress indices (NSI) as shown for individual irrigation and
N treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
160
Mean
DISI
1996/1997
I-1
I-2
I-3
I-4
I-5
Mean
NSI
12.74
11.32
10.53
10.09
9.75
10.89
28.1
15.09
12.67
11.05
10.92
10.33
12.01
20.7
15.89
13.03
12.35
11.80
10.71
12.76
15.8
18.38
17.26
15.47
13.26
11.36
15.15
0.0
17.98
15.95
14.62
12.30
9.94
14.16
6.5
16.01
14.05
12.80
11.67
10.42
0.0
12.2
20.0
27.1
34.9
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
9.06
7.07
6.69
6.02
4.35
6.64
60.0
12.44
11.05
9.37
9.26
6.72
9.76
41.2
14.92
15.21
13.43
12.92
8.62
13.02
21.5
17.71
17.32
16.91
13.65
9.80
15.08
9.1
22.27
20.36
16.80
13.91
9.62
16.59
0.0
15.28
14.20
12.64
11.15
7.82
0.0
7.1
17.3
27.0
48.8
a
a
b
LSD(0.05) I3.41; N2.80; INns; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
LSD(0.05) I320; N2.90; IN5.45; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
with a management tool to detect a need for N in the sorghum crop. Generally, farmers
would not have the resources or expertise to effectively use a SPAD meter, but an
extension agent or research specialist may find these more useful to recommend N
application rates to meet certain yield goals.
Table 4
Leaf area index of maize as affected by irrigation (I) and nitrogen (N) de®cits imposed at the tasseling growth
stage at Konni, Niger in the 1997/1998 growing season. De®cit irrigation stress indices (DISI) and N stress
indices (NSI) as shown for individual irrigation and N treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
160
Mean
DISI
1.10
1.07
0.98
0.89
0.78
0.96
63.9
1.53
1.43
1.30
1.22
1.00
1.30
51.1
2.52
2.10
1.75
1.47
1.37
1.84
30.8
3.24
2.76
2.20
2.32
1.82
2.47
7.1
3.39
2.81
2.60
2.39
2.10
2.66
0.0
2.36
2.03
1.77
1.66
1.41
0.0
14.0
25.0
29.7
40.3
a
1997/1998
I-1
I-2
I-3
I-4
I-5
Mean
NSI
a
LSD(0.05) I0.47; N0.45; INns; I linear(0.05) is signi®cant; N linear(0.05) is signi®cant.
22
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 5
Chlorophyll content of maize leaves as affected by irrigation (I) and nitrogen (N) de®cits imposed at different
growth stages at Konni, Niger in the 1996/1997 and 1997/1998 growing season. Nitrogen stress indices (NSI) are
shown for individual irrigation and N treatments
Irrigation
regime
N applied (kg haÿ1)
0
(mmol mÿ2)
40
(mmol mÿ2)
80
(mmol mÿ2)
120
(mmol mÿ2)
160
(mmol mÿ2)
Mean
(mmol mÿ2)
1996/1997a
I-1
I-2
I-3
I-4
I-5
Mean
NSI
237
187
225
250
317
243
61.0
349
456
304
315
498
384
38.4
368
605
376
376
530
426
31.6
587
652
493
493
539
553
11.2
625
695
601
648
548
623
0.0
433
519
400
416
486
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
114
171
168
259
278
198
67.8
304
303
274
331
301
303
50.7
441
373
411
468
477
434
29.3
506
613
593
648
617
585
4.7
587
603
605
627
650
614
0.0
390
412
410
467
465
a
b
LSD(0.05) Ins; N41.0; INns; N linear(0.05) is signi®cant.
LSD(0.05) Ins; N44.6; INns; N linear(0.05) is signi®cant.
Nitrogen uptake (Fig. 1) decreased as irrigation deficits were imposed, and total uptake
was dependent on amount of applied N. Uptake was linear (P0.05) over irrigation
regimes both seasons and the response slopes were similar each season. The decrease in
response to irrigation deficit was greater at the zero N treatment than the 120 or 160 kg
N haÿ1 treatments. The decrease in plant N corresponded to similar decreases in leaf
chlorophyll and biomass production when N deficits were imposed. However, the
decreased N uptake due to irrigation deficit corresponded to only biomass production
with irrigation treatment. Zweifel et al. (1987) found that N utilization efficiency of
sorghum was most influenced by N level and not altered due to irrigation regime.
3.4. Water extraction pattern
Water extraction from 1.5 m of soil profile differed more with irrigation regime than
with N level (Fig. 2). However, the total amount of water extracted was greater at 160 kg
N haÿ1 than at zero kg N haÿ1 suggesting that more N may have been conducive to
greater root development. However, Champigny and Talouizte (1981) found that under N
deprivation, translocation of photoassimilates from shoot to root increased as roots
became a stronger sink compared to other sinks. Conversely, Eghball et al. (1993b) found
that N stress resulted in less root branching in maize which would imply an impaired
ability to take up nutrients. Mackay and Barber (1986) also found that N supply affected
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
23
Fig. 1. Nitrogen uptake in maize at ®ve different N rates over ®ve irrigation regimes in the 1996/1997 and 1997/
1998 growing seasons at Konni, Niger.
maize root morphology, but the effect was genotype dependent. The highest water
extraction occurred at the fully irrigated 160 kg N haÿ1 treatment. When water was
withheld during both vegetative and reproductive stages of growth (I-5), markedly less
extraction occurred to 1.5 m in comparison to the fully irrigated regime (I-1). Extraction
24
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Fig. 2. Water extraction of maize from 1 Sm of soil pro®le measured at the R1 growth stage in the 1996/1997
and 1997/1998 seasons at Konni, Niger. Soil moisture was measured from the depleted soil (~) and after
irrigation (&) at 0 and 160 kg N haÿ1 and at three irrigation de®cit regimes. Horizontal bars represent the
standard deviation.
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
25
of water at the 80 kg N haÿ1 rate was between the zero and 160 kg N haÿ1 rates (data not
shown) indicating a linear response to treatment.
Water extraction patterns within the soil profile are generally indicative of root activity.
Eghball and Maranville (1993a) showed that greater root depth and water extraction from
the lower profile was associated with greater corn yield and varied with cultivar. They
found that severe water or N stress appeared to damage root systems while moderate
stresses enhanced them. It would appear in the current experiment that severe stresses
were detrimental to root system development in the deeper profile which was most likely
one factor in reducing yield.
Since more N resulted in more water extracted, the crop would require a higher amount
of irrigation water to meet the demand of more biomass since evapotranspiration (ET) is
directly correlated to biomass production (Stewart, 1989). Currently, the cost of irrigation
water to farmers in this region is constant regardless of irrigation frequency. Should
policies change so that producers are required to pay per unit of water used, then each
producer must balance cost inputs against returns due to irrigation. Our research has
shown that yields can be maximized by choosing the proper stage of growth to irrigate.
When water supplies are limited, it is much more efficient to use less irrigation on more
land than to fully irrigate less land.
4. Conclusions
Maize is commonly grown in humid and subhumid tropics, but in Sahelian countries, it
is grown either in high rainfall zones or with supplementary irrigation in low rainfall
zones. Water limitation is a major constraint to maize production. High evaporative
demand and warm temperatures expose the crop to water stress if irrigation is not
adequately provided. Efficient production of maize where soils are extremely poor in N
and where rainfall is highly variable, requires simultaneous attention to these two most
important production inputs. Results of our study clearly demonstrate that these two
inputs must be judiciously optimized to maximize productivity. Biomass yields were
linearly related to water application each season. Water use efficiency was increased
slightly with deficit irrigation. Applied N enhanced biomass yields and WUE both years,
but to the greatest magnitude in the 1997/1998 season. Deficit irrigation during early
vegetative growth modestly reduced LAI, plant height, CGR, N uptake and total biomass
production. Deficit irrigation during late vegetative and reproductive growth stages
severely reduced these growth parameters.
Nitrogen deficits reduced leaf chlorophyll content, thus, leaf N concentration. Nitrogen
uptake was increased linearly as irrigation increased, but total uptake was more
influenced by the amount of applied N. Total water extracted from a 1.5 m profile
depended on both soil moisture and soil N supply, but more on the latter. It was
speculated that root production was stimulated in the deeper soil profile when greater
amounts of water and N were supplied. Very little extraction occurred when DISI and NSI
values were high.
This study demonstrated that maize production is determined by optimizing both water
supply and N application. Reducing irrigation during vegetative growth had less impact
26
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
on biomass production and N uptake than when irrigation deficits occur during
reproductive stages. These reductions are a direct result of diminished LAI, CGR and root
activity. The adaptive strategy of maize under moderate vegetative stress appears to relate
to an extension of rooting depth and extraction of water deeper in the profile while
simultaneously reducing LAI to decrease transpiration. Severe stresses may be
detrimental to root development. Producers need to carefully weigh input costs against
market income when considering the economic maximum they choose for irrigation and
N use in Sahelian production areas.
References
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to changes in water stress. Plant Physiol. 48, 631±636.
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maize during vegetative growth. Agron. J. 89, 557±562.
Cox, W.J., Kalonge, S., Cherney, D.J.R., Reid, W.S., 1993. Growth, yield and quality of forage maize under
different nitrogen management practices. Agron. J. 85, 34 1±347.
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Eck, H.V., 1985. Effects of water de®cits on yield, yield components, and water use ef®ciency of irrigated corn.
Agron. J. 78, 1035±1040.
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development and dry matter accumulation of an old and new maize hybrid. Can. J. Plant Sci. 74, 471±477.
Muchow, R.C., 1988. Effect of nitrogen supply on the comparative productivity of maize and sorghum in semiarid tropical environment I. Leaf growth and leaf nitrogen. Field Crops Res. 18, 1±16.
NeSmith, D.S., Ritchie, J.T., 1992. Short- and long-term response of corn to a preanthesis soil water de®cit.
Agron. J. 84, 107±113.
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Pandey, R.K., Herrera, W.A.T., Pendelton, J.W., 1984. Drought response of grain legume under irrigation
gradient. Yield and yield components. Agron. J. 76, 549±553.
Pandey, R.K., Maranville, J.W., Admou, A., 2000. De®cit irrigation and nitrogen effects on maize in a Sahelian
envrionment. I. Grain yield and yield components. Agric. Water Manage. 46, 1±13.
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Ritchie, S.W., Hanway, J.J., 1982. How a corn plant develops. Spec. Rep. 48. Rev. Iowa State Univ. Coop. Ext.
Serv., Ames, IA.
Stewart, B.A., 1989. Conjunctive use of rainfall and irrigation in semi-arid regions. In: Proc. Intl. Workship. Soil,
Crop and Water Management Systems for Rainfed Agriculture in the Sudano-Sahelian Zone. Niamey, Niger.
ICRISAT, Patancheru, AP 502 324, India, pp. 107±116.
Tollenaar, M., 1986. Effect of assimilate partitioning during the grain ®lling period of maize on dry matter
accumulation. In: Crenshaw, J. et al. (Eds.), Phloem Transport. Allan R. Liss, New York, pp. 551±556.
Welles, J.M., Norman, J.M., 1991. Instrument for indirect measurement of canopy architecture. Agron. J. 83, 8
18±825.
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Productivity in relation to interception of solar radiation. Crop Sci. 5, 211±215.
Zweifel, T.R., Maranville, J.W., Ross, W.M., Clark, R.B., 1987. Nitrogen fertility and irrigation in¯uence on
grain sorghum nitrogen ef®ciency. Agron. J. 79, 4 19±422.
Wolfe, D.W., Henderson, D.W., Hsiao, T.C., Alvino, A., 1988. Interactive water and nitrogen effects on
senescence of maize II. Photosynthetic decline and longevity of individual leaves. Agron. J. 80, 865±870.
De®cit irrigation and nitrogen effects on
maize in a Sahelian environment
II. Shoot growth, nitrogen uptake and
water extraction
R.K. Pandey1, J.W. Maranville*,2, M.M. Chetima
Institut National De Recherche Agronomique Du Niger (INRAN) B.P. 429, Niamey, Niger
Accepted 14 December 1999
Abstract
Maize growth in arid and semiarid regions is often limited by variation in the amount and
frequency of irrigation or rainfall. Sub-optimal supply of nitrogen (N) may further curtail growth
and development of the crop. Simultaneous optimization of these two inputs provides optimum
conditions for crop growth and productivity. A maize (Zea mays L.) crop was subjected to different
periods of de®cit irrigation and rates of N in the ®eld on a medium-deep Tropudalf clay loam soil.
Water de®cit effects on shoot growth, N uptake and water extraction with varying level of N supply
were analyzed to determine their inter-relationships. Water de®cit was created by withholding irrigation
at different stages of crop development. Increasing moisture stress resulted in progressively less leaf
area, crop growth rate (CGR), plant height, shoot dry matter and harvest index. Mean increase in above
ground biomass was 7.7 and 8.7 kg per mm of water used in the 1996/1997 and 1997/1998 seasons,
respectively. De®cit irrigation stress indices (DISI) for above ground biomass when the crop was
subjected to a 2 week stress was 11.0 and 20.1 compared to 4 week stress values of 3.2 and 16.5 in the
1996/1997 and 1997/1998, respectively, indicating greater stress the ®rst season during vegetative
growth. When de®cit irrigation was increased to 8 weeks, DISI values were 34.1 and 39.8 for the
respective seasons. Biomass production response to N in both years was quadratic; however, N response
differed with irrigation level in both seasons. Highest biomass yield with no irrigation de®cit was
obtained at 120 kg N in 1996/1997 and at 160 kg N haÿ1 in 1997. Nitrogen uptake was more dependent
on applied N than water supply although N uptake decreased with greater water and N de®cits. Water
extraction was highest at the 120 and 160 kg N haÿ1 rates with soil water de®cit.
*
Corresponding author. Present address: Department of Agronomy, 102 KCR Lab, University of Nebraska,
Lincoln, NE 68583-0817 USA. Tel.: 1-402-472-3057; fax: 1-402-472-3654.
E-mail address: [email protected] (J.W. Maranville).
1
Agronomist, Program Leader and technician, PNRA/INRAN, PB 429, Niamey.
2
Professor, University of Nebraska, Lincoln, NE.
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 7 4 - 3
16
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
This study showed that a maize crop differs in its ability to maintain LAI, CGR and above ground
dry matter production at different levels of water de®cit and N supply. The adaptive strategy of
maize plants under vegetative water stress appears to be extended rooting depth and water
extraction from the deeper soil pro®le, and simultaneous reduction in leaf area to decrease
transpiration. Optimizing the inputs of water and N at the farm level would maximize biomass
production and harvest index. This information can be useful to guide crop management strategy to
enhance maize production in the irrigated perimeter of a Sahelian environment. # 2000 Elsevier
Science B.V. All rights reserved.
Keywords: De®cit irrigation; Crop growth rate; Leaf area index; Water extraction pattern; Shoot and root growth
1. Introduction
There has been an increasing interest in scheduling deficit irrigation in order to
conserve water and maintain crop productivity in the Sahel of West Africa. In these areas,
total biomass production is often as important to farmers as grain since animals are a
significant part of their livelihood. We reported on the effect of seasonal water deficit and
nitrogen (N) rate on grain yield and yield components (Pandey et al., 2000). This research
suggested that irrigation deficit during the vegetative stages of maize (Zea mays L.)
growth was possible without sacrificing significant grain yield. This irrigation response
was dependent on the N application rate. Research has shown the importance of water
and N interactions in optimizing maize productivity (Eck, 1984; Eghball and Maranville,
1993a). Most studies suggest that water shortage during vegetative growth reduces leaf
area (Boyer, 1970; Acevedo et al., 1971; NeSmith and Ritchie, 1992; McCullough et al.,
1994), internode elongation (Novoa and Loomis, 1981), and leaf and stem weight
(Denmead and Shaw, 1960; Eck, 1984). In a field study conducted under semi arid
environment of Texas, water deficits imposed 41 days after planting reduced leaf, stalk
and ear yields of maize, while those imposed 55 days after planting reduced only stalk
and ear yields. Water deficit during grain filling did not affect leaf and stalk yields (Eck,
1984). Management of water shortage through frequency and quantity of irrigaiton water
during vegetative growth and/or reproductive growth merits attention in high evaporative
environments to minimize curtailment of crop growth and yield and achieve higher water
use efficiency (Eck, 1985; Chapman and Barreto, 1997).
Nitrogen requirement by maize compared with other nutrients is large in Sahelian soils
for optimum vegetative and reproductive growth. Many physiological processes
associated with maize growth are enhanced by N supply (Eck, 1984). Nitrogen has
dramatic effects on maize growth, development and grain yield on soils that are limiting
in N supply. Numerous studies have shown the effects of reduced N supply on leaf area
index (LAI), plant height, shoot weight and plant N uptake (Eck, 1984; Pandey et al.,
1984; Muchow, 1988; McCullough et al., 1994). In most maize producing areas,
increasing rate of N supply results in greater LAI and leaf N (McCullough et al., 1994).
Variation in N supply affects crop growth, development and potential kernel set and grain
yield (Greenwood, 1976; Pandey et al., 2000). Leaf area index, leaf area duration, crop
photosynthetic rate, radiation interception and radiation use efficiency are increased by N
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
17
supply (Muchow, 1988). Reduced N supply decreases crop growth (Cox et al., 1993);
however, N response is modified by water supply under field condition (Greenwood,
1976; Pandey et al., 2000). Variable water supply either due to shortage of water or failure
of the irrigation system to supply water during vegetative and/or reproductive growth
stages in many irrigated areas of sub-Saharan Africa, particularly in the Sahel, is common
and often results in deficit irrigation.
Information on frequency and quantity of irrigation water and effect of deficit irrigation on
shoot and root growth of maize and the subsequent water and N extraction patterns have not
been well elucidated under the stressful Sahelian environment, more so with differential rates
of N supply. Further, information on crop growth responses and morphological/physiological
yield determinants are needed to analyze crop productivity that relate to crop water
production function and economic returns. The objectives of this study were to (i) determine
the effects of timing and duration of deficit irrigation on maize shoot growth and water
extraction, (ii) evaluate water deficit and N rate effects on N uptake, and (iii) analyze
relationships between grain yield, plant growth and deficit irrigation and N supply.
2. Materials and methods
A field experiment was conducted for 2 years (1996±1997 and 1997±1998) at INRAN
(Institut National de Recherche Agrononmique du Niger) research station near Konni
(lat. 118N, long. 128E) on a Tropudalph clay loam soil (fine kaolintic thermic kanolic
tropudalph). The site description, crop culture, and weather conditions were previously
described (Pandey et al., 2000). Water deficits were imposed as previously described
(Pandey et al., 2000). Irrigation was withheld at various crop growth stages (Ritchie and
Hanway, 1982) at five N levels.
2.1. Plant sampling and data collection
Plant samples from 1 m row length (five plants) were harvested for above ground
biomass at the tasseling (VT) crop growth stage and at physiological maturity. At grain
maturity, plant height was recorded. Crop growth rate (CGR) was computed by sampling
from between VT and physiological maturity. To monitor the greenness of the crop in
response to N status, chlorophyll meter readings were collected each season using the
Minolta SPAD 502 meter at the silking stage and converted to chlorophyll content
(Markwell et al., 1995). Measurements were taken midway between the margin and the
mid-rib of the ear-leaf from 10 representative plants from the center two rows from each
plot (Chapman and Barreto, 1997). At 2 days past VT, data on LAI using the leaf canopy
analyzer Li-Cor 2000 from the center rows of each treatment were collected in 1997/1998
according to Welles and Norman (1991). Soil moisture extraction patterns were
monitored to a depth of 1.5 m using a neutron probe from three irrigation regimes at the
R1 stage as previously described (Pandey et al., 2000).
At harvest, number of ears were recorded from each plot. Above ground vegetative
biomass and ear yield were recorded after 4 days of air drying. Grain yield was
determined from shelled ears and adjusted to 14% after a small sample of stover and grain
18
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
were taken and dried at 608C for 48 h. Total biomass included grain and stover. Harvest
index was calculated by dividing grain per plot by total biomass after adjusting for
moisture content. Grain and stover N was determined on composite samples from all
replications from every treatment combination using the Kjeldahl procedure. Deficit
irrigation stress index (DISI) was calculated as yield for unstressed treatment minus
stressed treatment divided by unstressed treatment times 100 (Pandey et al., 1984). A N
stress index (NSI) was calculated in a similar manner (Greenwood, 1976).
2.2. Statistical analysis
All plant data collected were statistically analyzed as a split plot factorial with four
replications except water use where three treatments and three replications were used.
Analysis of variance (ANOVA) was made to determine crop parameter response to
irrigation and N rates. Means among treatments were compared using least significant
difference at P0.05 probability. Regression analysis was performed on the relationship
between measured crop parameters and water applied and N rates. Best fit regression
equations were calculated.
3. Results and discussion
3.1. Aboveground biomass
Aboveground biomass production was different each season and presented separately
in Table 1. There was less differential in biomass production between zero N and
160 kg haÿ1 in 1996/1997 than in 1997/1998. The greater rates of N in 1997/1998
resulted in markedly more biomass production than those rates in 1996/1997 and
markedly less biomass at the low N rates for the second season. Response to applied N
was quadratic each year. There was little difference, however, between the two seasons
for response to deficit irrigation which was linear each year.
Deficit irrigation adversely affected total biomass yield at all N levels. The greatest
reduction was observed at the 160 kg N haÿ1 of 10.7 and 14.8 kg per mm of deficit
irrigation over the control in the respective seasons. The quadratic response to N peaked
at 120 kg haÿ1 in 1996/1997 and at 160 kg haÿ1 in 1997/1998. Total biomass response
was also reflected in the plant height (data not shown).
Irrigation deficit during any reproductive stage of maize resulted in marked loss of
biomass production compared to deficits only during vegetative growth (Table 1). The
DISI was approximately 3±10 times greater when water was withheld during
reproductive stage (I-5) than at the vegetative stage (I-2). Even withholding water once
during the reproductive phase (I-3) plus vegetative stages resulted in a considerable
increase in DISI from that of I-2. The NSI was twice as great in the 1997/1998 season as
the 1996/1997 season at the lower N rates (Table 1). This was mostly due to the higher
yields in the 1997/1998 season with high N rates making the yield response to N steeper
than in 1996/1997, although still quadratic. Grain yield and grain yield components were
found to react in a similar manner in these experiments (Pandey et al., 1999).
19
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 1
Aboveground biomass yield of maize at physiological maturaity as affected by irrigation (I) and nitrogen (N)
de®cits imposed at different growth stages at Konni, Niger in the 1996/1997 and 1997/1998 growing seasons.
De®cit irrigation stress indices (DISI) and N stress indices (NSI) are shown for individual irrigation and N
treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
1996/1997
I-1
I-2
I-3
I-4
I-5
Mean
NSI
6791
6187
5938
5762
5402
6016
26.2
8886
6953
6927
6377
6100
7049
13.5
9410
8119
7069
6661
5972
7446
8.7
9800
9446
8476
6748
6297
8153
0.0
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
5008
4557
4040
3827
3222
4131
55.1
6706
6231
5991
5218
4397
5709
38.0
8471
8378
8240
6111
5952
7430
19.3
10810
10553
8743
6399
6130
8527
7.4
160
Mean
DISI
9473
8756
7038
6044
5461
7454
8.6
8872
7892
7090
6318
5846
0.0
11.0
20.1
28.8
34.1
11723
11632
8640
8024
6026
9209
0.0
8544
8270
7131
5916
5145
0.0
3.2
16.5
30.8
39.8
a
a
b
LSD(0.05) I591; N402; IN694; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
LSD(0.05) I673; N341; IN763; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
3.2. Harvest index, crop growth rate (CGR) and leaf area index (LAI)
Harvest index (Table 2) was reduced by both water and N deficits each year as was
CGR (Table 3). The greatest reduction for each of these calculated parameters was in the
1997/1998 season. Although total biomass yield was reduced by the deficits imposed,
grain production was obviously more affected than stover production, and reflects these
stress affects on partitioning efficiency of the crop. The influence of water deficit on these
parameters was linear while N deficit effects were quadratic. Maize response to N
application for CGR was modified by water stress, with the least response occurring on
the most severely stressed irrigation regime (I-5).
The DISI and NSI values were generally less for harvest index compared to CGR
which were comparable to the LAI response in 1997/1998 measured at tasseling (Table 4).
Maximum LAI values were found at higher N rates under full irrigation as would be
expected. The very low LAI values of plants under stress may be underestimates of the
procedure since water stress causes leaf wilting (Hicks and Lascano, 1995). Leaf area
index values generally range from 2±6 in maize during grain fill (Tollenaar, 1986).
Nonetheless, intercepted radiation determines, in part, the CGR. Williams et al. (1965)
achieved growth rates of 32.5 g mÿ2 dayÿ1 in hydroponically grown corn which
compares to a maximum of 22.3 g mÿ2 dayÿ1 in the current experiment in 1997/1998.
20
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 2
Harvest index of maize as affected by irrigation (I) and nitrogen (N) de®cits imposed at different growth stages
at Konni, Niger in the 1996/1997 and 1997/1998 growing seasons. De®cit irrigation stress indices (DISI) and N
stress indices (NSI) as shown for individual irrigation and N treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
160
Mean
DISI
1996/1997
I-1
I-2
I-3
I-4
I-5
Mean
NSI
35.1
34.2
33.4
32.8
30.8
33.3
15.3
37.0
36.5
35.8
33.4
31.0
34.7
11.7
39.0
38.6
38.8
37.5
32.5
37.3
5.1
41.0
41.1
39.5
38.5
34.1
38.8
1.3
41.0
41.8
39.1
38.6
36.0
39.3
0.0
38.6
38.4
37.3
36.2
32.9
0.0
0.0
3.3
6.2
14.8
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
24.1
26.8
20.3
20.1
19.9
22.2
43.1
39.5
33.7
29.2
32.4
28.2
32.6
16.4
41.1
38.8
31.6
38.0
29.8
35.9
7.9
43.7
38.2
40.2
36.1
36.9
39.0
0.0
44.5
38.4
42.0
35.5
34.0
38.9
0.0
38.6
35.2
32.7
32.4
29.8
0.0
8.8
15.3
16.1
22.8
a
a
b
LSD(0.05) I2.1; N2.1; INns; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
LSD(0.05) I2.8; N2.8; INns; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
It is interesting that the lowest value of CGR in that season (I-5; zero N) was 19.5% of the
maximum CGR value achieved at the I-1, 160 kg haÿ1 treatment (Table 3) corresponded
to the difference in LAI (23%) for the same two treatment comparisons (Table 4).
Patterns of CGR and LAI response to irrigation and N deficits also corresponded to
biomass production in these experiments.
3.3. SPAD chlorophyll content and nitrogen uptake
Leaf chlorophyll content was not altered by irrigation deficit (Table 5) but decreased
significantly and linearly with decreased N supply both seasons. Wolfe et al. (1988)
showed that chlorophyll concentration (leaf greenness) in maize was positively correlated
to leaf N concentration. This would indicate that leaf N content decreased with lower N
treatments and leaves became progressively yellow with greater N deficits. Blackmer and
Schepers (1995) found that the SPAD 502 m was able to distinguish between fertilizer N
treatments for maize which resulted in differential yields. Chapman and Barreto (1997)
found that SPAD meter readings were positively correlated with both leaf N
concentration and specific leaf N in tropical maize and suggested that SPAD meters
provide an inexpensive method to estimate these parameters. In the current experiment,
leaf chlorophyll corresponded to biomass yield across N treatments, but was not related to
yield with irrigation treatment. The estimate of leaf chlorophyll may provide producers
21
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 3
Crop growth rate of maize between tasseling and physiological maturity as affected by irrigation (I) and nitrogen
(N) de®cits imposed at different growth stages at Konni, Niger in the 1996/1997 and 1997/1998 growing
seasons. De®cit irrigation stress indices (DISI) and N stress indices (NSI) as shown for individual irrigation and
N treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
160
Mean
DISI
1996/1997
I-1
I-2
I-3
I-4
I-5
Mean
NSI
12.74
11.32
10.53
10.09
9.75
10.89
28.1
15.09
12.67
11.05
10.92
10.33
12.01
20.7
15.89
13.03
12.35
11.80
10.71
12.76
15.8
18.38
17.26
15.47
13.26
11.36
15.15
0.0
17.98
15.95
14.62
12.30
9.94
14.16
6.5
16.01
14.05
12.80
11.67
10.42
0.0
12.2
20.0
27.1
34.9
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
9.06
7.07
6.69
6.02
4.35
6.64
60.0
12.44
11.05
9.37
9.26
6.72
9.76
41.2
14.92
15.21
13.43
12.92
8.62
13.02
21.5
17.71
17.32
16.91
13.65
9.80
15.08
9.1
22.27
20.36
16.80
13.91
9.62
16.59
0.0
15.28
14.20
12.64
11.15
7.82
0.0
7.1
17.3
27.0
48.8
a
a
b
LSD(0.05) I3.41; N2.80; INns; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
LSD(0.05) I320; N2.90; IN5.45; I linear(0.05) is signi®cant; N quadratic(0.05) is signi®cant.
with a management tool to detect a need for N in the sorghum crop. Generally, farmers
would not have the resources or expertise to effectively use a SPAD meter, but an
extension agent or research specialist may find these more useful to recommend N
application rates to meet certain yield goals.
Table 4
Leaf area index of maize as affected by irrigation (I) and nitrogen (N) de®cits imposed at the tasseling growth
stage at Konni, Niger in the 1997/1998 growing season. De®cit irrigation stress indices (DISI) and N stress
indices (NSI) as shown for individual irrigation and N treatments
Irrigation regime
N applied (kg haÿ1)
0
40
80
120
160
Mean
DISI
1.10
1.07
0.98
0.89
0.78
0.96
63.9
1.53
1.43
1.30
1.22
1.00
1.30
51.1
2.52
2.10
1.75
1.47
1.37
1.84
30.8
3.24
2.76
2.20
2.32
1.82
2.47
7.1
3.39
2.81
2.60
2.39
2.10
2.66
0.0
2.36
2.03
1.77
1.66
1.41
0.0
14.0
25.0
29.7
40.3
a
1997/1998
I-1
I-2
I-3
I-4
I-5
Mean
NSI
a
LSD(0.05) I0.47; N0.45; INns; I linear(0.05) is signi®cant; N linear(0.05) is signi®cant.
22
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Table 5
Chlorophyll content of maize leaves as affected by irrigation (I) and nitrogen (N) de®cits imposed at different
growth stages at Konni, Niger in the 1996/1997 and 1997/1998 growing season. Nitrogen stress indices (NSI) are
shown for individual irrigation and N treatments
Irrigation
regime
N applied (kg haÿ1)
0
(mmol mÿ2)
40
(mmol mÿ2)
80
(mmol mÿ2)
120
(mmol mÿ2)
160
(mmol mÿ2)
Mean
(mmol mÿ2)
1996/1997a
I-1
I-2
I-3
I-4
I-5
Mean
NSI
237
187
225
250
317
243
61.0
349
456
304
315
498
384
38.4
368
605
376
376
530
426
31.6
587
652
493
493
539
553
11.2
625
695
601
648
548
623
0.0
433
519
400
416
486
1997/1998b
I-1
I-2
I-3
I-4
I-5
Mean
NSI
114
171
168
259
278
198
67.8
304
303
274
331
301
303
50.7
441
373
411
468
477
434
29.3
506
613
593
648
617
585
4.7
587
603
605
627
650
614
0.0
390
412
410
467
465
a
b
LSD(0.05) Ins; N41.0; INns; N linear(0.05) is signi®cant.
LSD(0.05) Ins; N44.6; INns; N linear(0.05) is signi®cant.
Nitrogen uptake (Fig. 1) decreased as irrigation deficits were imposed, and total uptake
was dependent on amount of applied N. Uptake was linear (P0.05) over irrigation
regimes both seasons and the response slopes were similar each season. The decrease in
response to irrigation deficit was greater at the zero N treatment than the 120 or 160 kg
N haÿ1 treatments. The decrease in plant N corresponded to similar decreases in leaf
chlorophyll and biomass production when N deficits were imposed. However, the
decreased N uptake due to irrigation deficit corresponded to only biomass production
with irrigation treatment. Zweifel et al. (1987) found that N utilization efficiency of
sorghum was most influenced by N level and not altered due to irrigation regime.
3.4. Water extraction pattern
Water extraction from 1.5 m of soil profile differed more with irrigation regime than
with N level (Fig. 2). However, the total amount of water extracted was greater at 160 kg
N haÿ1 than at zero kg N haÿ1 suggesting that more N may have been conducive to
greater root development. However, Champigny and Talouizte (1981) found that under N
deprivation, translocation of photoassimilates from shoot to root increased as roots
became a stronger sink compared to other sinks. Conversely, Eghball et al. (1993b) found
that N stress resulted in less root branching in maize which would imply an impaired
ability to take up nutrients. Mackay and Barber (1986) also found that N supply affected
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
23
Fig. 1. Nitrogen uptake in maize at ®ve different N rates over ®ve irrigation regimes in the 1996/1997 and 1997/
1998 growing seasons at Konni, Niger.
maize root morphology, but the effect was genotype dependent. The highest water
extraction occurred at the fully irrigated 160 kg N haÿ1 treatment. When water was
withheld during both vegetative and reproductive stages of growth (I-5), markedly less
extraction occurred to 1.5 m in comparison to the fully irrigated regime (I-1). Extraction
24
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
Fig. 2. Water extraction of maize from 1 Sm of soil pro®le measured at the R1 growth stage in the 1996/1997
and 1997/1998 seasons at Konni, Niger. Soil moisture was measured from the depleted soil (~) and after
irrigation (&) at 0 and 160 kg N haÿ1 and at three irrigation de®cit regimes. Horizontal bars represent the
standard deviation.
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
25
of water at the 80 kg N haÿ1 rate was between the zero and 160 kg N haÿ1 rates (data not
shown) indicating a linear response to treatment.
Water extraction patterns within the soil profile are generally indicative of root activity.
Eghball and Maranville (1993a) showed that greater root depth and water extraction from
the lower profile was associated with greater corn yield and varied with cultivar. They
found that severe water or N stress appeared to damage root systems while moderate
stresses enhanced them. It would appear in the current experiment that severe stresses
were detrimental to root system development in the deeper profile which was most likely
one factor in reducing yield.
Since more N resulted in more water extracted, the crop would require a higher amount
of irrigation water to meet the demand of more biomass since evapotranspiration (ET) is
directly correlated to biomass production (Stewart, 1989). Currently, the cost of irrigation
water to farmers in this region is constant regardless of irrigation frequency. Should
policies change so that producers are required to pay per unit of water used, then each
producer must balance cost inputs against returns due to irrigation. Our research has
shown that yields can be maximized by choosing the proper stage of growth to irrigate.
When water supplies are limited, it is much more efficient to use less irrigation on more
land than to fully irrigate less land.
4. Conclusions
Maize is commonly grown in humid and subhumid tropics, but in Sahelian countries, it
is grown either in high rainfall zones or with supplementary irrigation in low rainfall
zones. Water limitation is a major constraint to maize production. High evaporative
demand and warm temperatures expose the crop to water stress if irrigation is not
adequately provided. Efficient production of maize where soils are extremely poor in N
and where rainfall is highly variable, requires simultaneous attention to these two most
important production inputs. Results of our study clearly demonstrate that these two
inputs must be judiciously optimized to maximize productivity. Biomass yields were
linearly related to water application each season. Water use efficiency was increased
slightly with deficit irrigation. Applied N enhanced biomass yields and WUE both years,
but to the greatest magnitude in the 1997/1998 season. Deficit irrigation during early
vegetative growth modestly reduced LAI, plant height, CGR, N uptake and total biomass
production. Deficit irrigation during late vegetative and reproductive growth stages
severely reduced these growth parameters.
Nitrogen deficits reduced leaf chlorophyll content, thus, leaf N concentration. Nitrogen
uptake was increased linearly as irrigation increased, but total uptake was more
influenced by the amount of applied N. Total water extracted from a 1.5 m profile
depended on both soil moisture and soil N supply, but more on the latter. It was
speculated that root production was stimulated in the deeper soil profile when greater
amounts of water and N were supplied. Very little extraction occurred when DISI and NSI
values were high.
This study demonstrated that maize production is determined by optimizing both water
supply and N application. Reducing irrigation during vegetative growth had less impact
26
R.K. Pandey et al. / Agricultural Water Management 46 (2000) 15±27
on biomass production and N uptake than when irrigation deficits occur during
reproductive stages. These reductions are a direct result of diminished LAI, CGR and root
activity. The adaptive strategy of maize under moderate vegetative stress appears to relate
to an extension of rooting depth and extraction of water deeper in the profile while
simultaneously reducing LAI to decrease transpiration. Severe stresses may be
detrimental to root development. Producers need to carefully weigh input costs against
market income when considering the economic maximum they choose for irrigation and
N use in Sahelian production areas.
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