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

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.

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

STRESS TREATMENTS

Early Vegetative

Active Tillering

Maximum Tillering

10 DAH

Sowing

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Weeks After Sowing

Early Vegetative

20 DAH

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

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.

Weight Dry - Turgid

WeightDry -Weight Fresh LRWC = X 100

Moisture Meter Callibration Curve

y = 0.6091x + 21.607

R2 = 0.9464

50

60

70

Moisture M

eter Reading

MONITORING SOIL MOISTURE

A Calibration curve was used

to transform moisture meter

readings to true soil moisture

values

Moisture Meter

type HH2http://www.deltahttp://www.delta--t.co.ukt.co.uk

20

30

40

50

0 20 40 60 80

True Value

Moisture M

eter Reading

Due to large variation in single point

M.C readings within each box,

average of 10 readings taken/box

http://www.deltahttp://www.delta--t.co.ukt.co.uk

RESULTS AND DISCUSSION

Soil W

ater Content (%

)

Max. Till. Stage

25

30

35

40

45

50

0 7 14 21 28

Active Till. Stage

25

30

35

40

45

50

0 7 14 21 28

Early Veg. Stage

25

30

35

40

45

50

0 7 14 21 28

Changes in volumetric water content

Control N-1 N-2 N-3

Soil W

ater Content (%

)

0 7 14 21 280 7 14 21 280 7 14 21 28

20 Days After Heading

25

30

35

40

45

50

0 7 14 21

10 Days After Heading

25

30

35

40

45

50

0 7 14 21 28

Duration of Stress (Days)

� Volumetric soil water content

declined gradually from over

40% to less than 30% within

2 – 3 weeks

� Changes in soil water status were

similar for all stress treatments

� Moisture stress had a

small effect on LRWC

� Nitrogen had negligible

effect on LRWC

� Stress effects mildN-1 N-2 N-3

EARLY VEGETATIVE STAGE STRESS

87

71

8977

71

88

0

20

40

60

80

100

S W S W S W

LRWC %

StressedControl

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

89

51

90

6250

91

0

20

40

60

80

100

S W S W S W

LRWC %

ACTIVE TILLERING STAGE STRESS

� Moisture stress

considerably reduced

LRWC

� Nitrogen had a minor

effect on LRWC

� Stress effects severe

N-1 N-2 N-3

S: Stressed, W: Well watered

40

60

80

100

120

140

30 60 90

Nitogen Level (Kg Ha-1)

Tille

rs m

-2

StressedControl

� Stress effects severe

� Dry matter production was reduced by 37%

because moisture stress prevented tillering.

LAI reduced by 50%.

� Tillering was reduced by moisture stress at

higher N levels.

� Stress effects developed quickly due to a

large demand for transpiration water

S: Stressed, W: Well watered

Control Stressed

91

50

87

5748

90

0

20

40

60

80

100

S W S W S W

LRWC %

N-1 N-2 N-3

� Moisture stress had a

large effect on LRWC

� Increased N supply

decreased LRWC in the

stressed rice plants

MAXIMUM TILLERING STAGE STRESS

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

GROWTH AFTER STRESS

Crop Growth Rate (CGR)

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

S1 S2 S3

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Crop growth rate (gg-1 Day

-1) S1 S2 S3

0.00

30 60 90

Nitrogen Level (kg ha-1)

0.00

30 60 90

Nitrogen level (kg ha-1)

Crop growth rate (gg

� 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.

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

30 60 90

Tillering rate (tiller tiller -1day-1) S1

S2

S3

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

30 60 90

S-1S-2S-3

Tillering Rate

30 60 90

Nitrogen level (Kg ha-1)

30 60 90Nitrogen Level (kg ha

-1)

� 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

Recovery After Stress

Nitrogen application enhanced recovery in rice stressed at the early

vegetative stage (S-1)

TIME TO HEADING

: 10 % Heading : 80 % Heading: 50 % Heading

Control

S-3

S-1

S-2

90 92 94 96 98 100 102 104 106 108 110 112 114 116 118 120 122 124 126DAS

: 10 % Heading : 80 % Heading: 50 % 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

500

1000

1500

2000

2500

3000

Yie

ld (kg/h

a))

10

20

30

40

50

60

70

80

90

Fille

d G

rain

Ratio (%

))

N1 N2 N3 Filled Grain Ratio (%)

YIELD AND YIELD COMPONENTS

0

S0 S1 S2 S3 S4 S5

Stage of Stress

0

10

� 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

� 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

Yield components cont…

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