1. Effects of Moisture Stress Timing and Nitrogen Levels
on Growth and Yield of Upland Rice
ALIBU Simon1 and MAMADOU Fofana2
1National Crops Resources Research Institute (NaCRRI),
P. O Box 7084, Kampala, Uganda
2Africa Rice Centre (WARDA), 01 B.P. 2031, Cotonou, Benin

2. INTRODUCTION
Moisture stress and insufficient nitrogen are important factors that
simultaneously limit growth and yield of upland rice
These two factors have repeatedly been studied but little is known
about their interactive effects on growth and yield when the
timing of stress is varied.
The main purpose of this study was to examine the interactive
effects of nitrogen and water stress occurring at different growth
stages of upland rice on phenology, grain yield, yield components
and biomass production
Knowledge of this is important for planning interventions like
supplementary irrigation and fertilization in the context of Africa
where rainfall patterns are erratic and fertilizer unaffordable.

3. MATERIALS & METHODS
Experimental Layout: 2 Factor RCBD with 2 Replications
Replication 1 Replication 2
Factors: 3 Nitrogen levels and 5 stress treatments + Control
N Levels: 30 kg N ha-1, 60 kg N ha-1 and 90 kg N ha-1
60% applied as basal and 40% as topdress

4. STRESS TREATMENTS
Sowing
Maximum Tillering
10 DAH
Active Tillering
Early Vegetative
20 DAH
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Weeks Aft er Sowing
Control treatment (S-6) watered with 30 mm wk-1
Soil moisture stress initiated at 11 days, 32 days and 53 days after
sowing for S-1, S-2 and S-3 respectively

5. DATA COLLECTION
Plant height, tiller number, yield
& yield component measurements
Leaf area and dry
matter measurements
Tiller numbers plant height measured weekly from vegetative to
heading and at harvest.
On last day of stress, 3 hills harvested per plot to measure dry
matter accumulation. Dry weight taken after drying at 70o c for 72 h.
FreshWeight - Dry Weight
LRWC = X 100
Turgid- DryWeight

6. MONITORING SOIL MOISTURE
A Calibration curve was used
to transform moisture meter
readings to true soil moisture
values
Moisture Meter Callibration Curve
70
Moisture Meter Reading
Moisture Meter 60 y = 0.6091x + 21.607
type HH2 R2 = 0.9464
http://www.delta-
http://www.delta-t.co.uk 50
40
30
20
0 20 40 60 80
True Value
Due to large variation in single point
M.C readings within each box,
average of 10 readings taken/box

7. RESULTS AND DISCUSSION
Changes in volumetric water content
50 50 50
Early Veg. Stage Active Till. Stage Max. Till. Stage
45 45 45
40 40 40
35 35 35
Soil Water Content (%)
30 30 30
25 25 25
0 7 14 21 28 0 7 14 21 28 0 7 14 21 28
50 50
10 Days After Heading 20 Days After Heading
45 45
Volumetric soil water content
40 40
declined gradually from over
35 35
40% to less than 30% within
30 30
2 – 3 weeks
25 25
Changes in soil water status were
0 7 14 21 28 0 7 14 21 similar for all stress treatments
Duration of Stress (Days)
Control N-1 N-2 N-3

8. EARLY VEGETATIVE STAGE STRESS
100 89 87 88
80 77
Control Stressed 71 71 Moisture stress had a
LRWC %
60
small effect on LRWC
40
20
Nitrogen had negligible
0
S W S W S W
effect on LRWC
N-1 N-2 N-3
Stress effects mild
S: Stressed, W: Well watered
Stress effects (leaf rolling & tip drying) developed slowly and occurred
at lower soil moisture status than in older plants probably due to
limited water requirements of rice at this stage.
Dry matter production reduced by 44% because moisture stress
inhibited formation of new leaves. LAI reduced by 82%.
Plant height was not significantly affected by moisture stress and
Nitrogen

9. ACTIVE TILLERING STAGE STRESS
100 90 89 91
80
Moisture stress
LRWC %
62 considerably reduced
60 51 50
40 LRWC
20
0 Nitrogen had a minor
S W S W S W effect on LRWC
N-1 N-2 N-3
S: Stressed, W: Well watered Stress effects severe
Stress effects developed quickly due to a
Control Stressed large demand for transpiration water
140
Dry matter production was reduced by 37% 120
T i l l e rs m-2
because moisture stress prevented tillering. 100
LAI reduced by 50%. 80
60
Tillering was reduced by moisture stress at 40
higher N levels. 30 60 90
-1
Nitogen Level (Kg Ha )

10. Control Stressed MAXIMUM TILLERING STAGE STRESS
100 91 90
87
80
Moisture stress had a
large effect on LRWC
LRWC %
60 57
50 48
40
20 Increased N supply
0 decreased LRWC in the
S W S W S W stressed rice plants
N-1 N-2 N-3
S: Stressed, W: Well watered
Stress effects appeared almost immediately
after the onset of stress
A high degree of leaf senescence was
observed – signifying severity of the stress.
Dry matter and LAI were reduced by 49%
and 58% accordingly

11. GROWTH AFTER STRESS
Crop Growth Rate (CGR)
0.08 0.08
S1 S2 S3
Crop growth rate (gg-1 Day -1)
0.07 0.07 S1 S2 S3
0.06 0.06
0.05 0.05
0.04 0.04
0.03 0.03
0.02 0.02
0.01 0.01
0.00 0.00
30 60 90 30 60 90
Nitrogen level (kg ha-1) -1
Nitrogen Level (kg ha )
Post stress crop growth rate was highest in S-1 and lowest in S-3
Raising N level to 60 kg ha-1 increased the CGR in S-1. Beyond 60
kg ha-1, CGR declined.
N application reduced the CGR in S-2 and S-3 due to severity of soil
moisture stress during active vegetative growth.

12. Tillering Rate
0.14 0.14
S1 S-1
Tillering rate (tiller tiller day )
-1
0.12 0.12 S-2
S2 S-3
-1
0.10 0.10
S3
0.08 0.08
0.06 0.06
0.04 0.04
0.02 0.02
0.00 0.00
30 60 90 30 60 90
-1 -1
Nitrogen level (Kg ha ) Nitrogen Level (kg ha )
Tillering rate was highest in S-1 and lower in S-2 and S-3
respectively. A high correlation (r = 0.946) found between tillering
rate and CGR
Raising N level to 60 kg ha-1 increased the tillering rate in S-1. Over
60 kg ha-1, the tillering rate declined.
Low tillering rate in S-3 is because the maximum tiller number had
already been attained at the onset of stress

13. Recovery After Stress
Nitrogen application enhanced recovery in rice stressed at the early
vegetative stage (S-1)

14. TIME TO HEADING
S-3
S-2
S-1
Control
DAS 90 92 94 96 98 100 102 104 106 108 110 112 114 116 118 120 122 124 126
: 10 % Heading : 50 % Heading : 80 % Heading
Soil moisture stress in all the vegetative stages lengthened vegetative
growth and subsequently delayed heading.
Stress at early vegetative stage (S-1) delayed heading by 13 days.
Stress at active tillering (S-2) and maximum tillering delayed heading
by 16 and 19 days respectively.
Time to heading was little affected by nitrogen application

15. YIELD AND YIELD COMPONENTS
3000 N1 N2 N3 Filled Grain Ratio (%) 90
80
F ille d G ra in R a tio (% ))
2500
70
Y ie ld (k g /h a ))
2000 60
50
1500
40
1000 30
20
500
10
0 0
S0 S1 S2 S3 S4 S5
Stage of Stress
Moisture stress reduced grain yield averaged for N treatments
Stress during grain filling reduced grain yield by 50% due to poor
grain filling
Stress at active tillering stage and maximum tillering reduced yield
by 18% and 19% respectively

16. Yield components cont…
Mean grain weight was reduced by 10% and 7% in S-4 and S-5
Moisture stress at maximum tillering reduced grains per panicle only
slightly
Yield difference between rice stressed in the early vegetative stage
and control was negligible due extended recovery period after stress
Conclusion
N application caused greater growth reduction in rice stressed in the
active vegetative stage (S-2 & S-3), despite causing minor yield
increases.
N found to be effective in boosting vegetative recovery in rice stress in
early vegetative stage rather than later vegetative growth.
Rice found to be most sensitive to moisture stress after heading due to
poor grain filling. This underscores the importance of supplementary
irrigation during grain filling in drought prone environments