Quantifying Drought Tolerance in Root Crops- The FAO AquaCrop Model’s Perspective on Jamaican Sweet potatoes,

Ipomoea batatas

Collaborators:

Dale Rankine, Jane Cohen, Michael Taylor, Andre Coy and Tannecia Stephenson

September 14, 2016

JaREEACH Climate Smart Agriculture Symposium

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Contents

1. Introduction Sweet Potato- An Important Root CropThe Challenges with Modelling Crop Yields

2. Methodology

3. Results

4. Conclusions

5. Next Steps

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Sweet potato, Ipomoea batatas (L.), is a 5-month root crop, a dicotyledonous herbaceous trailing vine and the only economically important member of the family Convolvulaceae.

The crop is the 6th most important globally and is propagated from cuttings sown in the Caribbean during the period September to December.

This period is coincident with the late rainfall season in Jamaica. The crop rainfall requirement is 750-1250 mm; of this, about 500 mm should occur during the first third of the crop life

Sweet potato is drought tolerant but…

Crop most sensitive to dry conditions at the tuber initiation stage (about 40-50 days after planting) but requires less water as it nears maturity (CARDI 2010; Stathers et al. 2013).

Central to pursuit of reducing imports of, and reliance on externally grown wheat and cereals

1. Introduction- Sweet Potato An Important Root Crop

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1. Introduction- Challenges with Modelling Crop Yields

Annual drought index (SPI-12) versus mean annual Sweet potato yields (detrended) for Jamaica 1961-2009) Source: FAOSTAT; Climate Studies Group, Mona

1961196419681972197619801984198719911995199920032007

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SPI-12 Detrended Yield

SPI-1

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Yiel

d (t

/ha)

Annual drought index (SPI-12) versus mean annual Sweet potato yields for Jamaica (1961-2009)

Source: FAOSTAT; Climate Studies Group, Mona

1961196519691973197719811985198919931997200120052009

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SPI-12 Yield

SPI

Yiel

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/ha)

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Wavelet analysis (Cazelles et al. (2007), of area harvested data (1961-2009) suggests strongest periodic signal at 2-6 years (1985-2010) The high value of the power curve also indicates that this is a statistically significant cyclical pattern.Source: Climate Studies Group Mona (CSGM)

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1. Introduction- Challenges with Modelling Crop Yields

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2. Methodology: Research Design Summarised

AquaCrop Model Explained

•Biomass=WP x ΣTr [Biomass]•ET=E +Tr•WP normalised for ET and CO2 • Y=B x HI [Yield]

•Robust, Accurate yet simple

Devon

Ebony Park

Passley GardensBodles** *

* On site weather station

Randomised Complete Blocks (RCBs)

Parameters:•Rainfall•Temperature•Relative Humidity•Solar Radiation•Wind•ETo

Canopy cover, Biomass (above & Below)

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2. Methodology- An Analogue Approach for Climate Change Data

The method: Attempts to produce data representative of extremes climate such as could occur under climate change in the absence of long-terms records

• Uses data from an existing station (NMIA) for a specified period (1996-2013)• Ranks growing season (Sept 1- Dec 31) temperature and rainfall into quartiles• Selects a baseline (the median for both temperature and rainfall) using an ensemble average

of three years (2000, 2001, 2012)• Two alternative future climates were chosen from the extremes of the ranked data (relative to

baseline): Warm and Dry (2006); and Cool and Wet (2010).• Simulations were done for Rainfed and Irrigated cultivation• The irrigation schedule was generated in AquaCrop and based on a maximum allowable

depletion of readily available water (RAW) of 50% and an irrigation depth of 15 mm.

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2.Methodology-Analogue

Scenario(year)

Total Seasonal (Sept 1-Dec 31) Rainfall (mm)

Crop Season Mean Temperature (°C)

Comparison relative to Baseline

Baseline (Mean of

2000, 2001, & 2012) 453.8 ± 46.2 28.4 ± 0.1

Warm and Dry (2006)

116.9 29.1

Rainfall: -74%

Temperature:

+0.7°C

Cool and Wet (2010)

800.8 27.3

Rainfall : +77% Temperature:

-1.0°C

(a) Rainfall and (b) Temperature for NMIA(1996-2013)

Baseline and alternative climates

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a

b

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Varietal differences:

•Colour (Flesh and skin)

•Texture

• Foliage

Source: CARDI 2010

2. Methodology: Five Varieties of Sweet potato

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3. Results: Drought Tolerance in Devon, Manchester

Ideal growing conditions favours higher yields (both treatments) relative to other zones

• Temperature, (warm days, cool nights) ,

• Rainfall (above 1200 mm),

• Elevation (high),

• Soil: well drained Chudliegh Soil

Rainfed vs Irrigated Yields (t/ha) 2013

Variety Rainfed Irrigated

Ganja 12.07 ± 5.36 22.48 ± 0.14

Uplifta 15.84 ± 4.57 8.39 ± 0.14

Yellow Belly 21.26 ± 4.57 5.0 ± 0.14

Varietal Mean 16.70 ± 2.80 11.96 ± 0.08

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3. Results: Drought Tolerance in Ebony Park and Portland

Passely Gardens, Portland- 2011/2012

Irrigated Yield (t ha-1)

Rain-fed Yields (t ha-1)

Variety 2012 2012

Ganja 9.14 ± 1.47 4.50 ± 0.22Uplifta 4.33 ± 1.14 6.28 ± 3.22Yellow Belly 8.53 ± 1.14 2.26 ± 0.87

Fire on Land 8.92 ± 1.14 5.92 ± 1.49Clarendon 6.47 ± 1.14 3.35 ± 0.76

Varietal Mean 7.48 ± 0.55 4.60 ± 0.95

Ebony Park, Clarendon-2013 Yields (t/ha-1)

Variety Irrigated (t/ha) Rain-fed ( t ha-1)

Ganja 31.49 ± 0.08 9.70 ± 0.08

Uplifta 10.33 ± 0.12 5.73 ± 0.09

Yellow Belly 18.31 ± 0.09 5.04 ± 0.09

Varietal Mean 21.11 ± 0.06 6.74 ± 0.05•Waterlogging, high rainfall inhibits growth in Portland

•Low rainfall thwarts growth in at Ebony, in rain-fed production; high benefits from irrigation

•Highest overall yield recorded in irrigated Ganja at Ebony Park

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3. Results: Overall Assessment of Drought Tolerance

Irrigation

Rainfall

High Medium Low

High

Ganja/Fire on Land

Ganja / Fire on Land

Clarendon /Ganja

Medium Ganja Uplifta Ganja

Low GanjaYellow

Belly/ Ganja Ganja

•The Ganja Variety appears the most drought tolerant and ‘adaptable’ variety

•Uplifta variety does well under medium (750-1250 mm) water availability

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3. Results: AquaCrop a Model to widely Test Drought Tolerance

0 14 28 42 56 70 84 98 112126140020406080

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Devon, Manchester: Rain-fed (2013)

Simulated Measured

DAPCano

py C

over

(%

)

0 14 28 42 56 70 84 98 1121261400

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Simulated Measured

DAP

Biom

ass

(t/h

a)

0 7 142128354249566370778491980

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Ebony Park, Clarendon-Irrg. (2013)

Simulated Measured

DAP

Cano

py C

over

(%)

0 7 142128354249566370778491980

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Simulated Measured

DAP

Biom

ass

(t/h

a)

• Parameterization of Sweet potato in AquaCrop- Original contribution

• Excellent agreement between simulated and measured canopy cover (CC)

• Model exhibits good skill in the simulation of biomass at both locations and for the two treatments

• When CC is well simulated, so also is Biomass. All based on dry weights

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3. Results: Validation of AquaCrop- Model Performance Summarised

•Deviation = {(Simulated- Measured)/Measured} *100 •Biomass estimation within 30% of ‘actual’ values for 4 of 6 simulations (further refined)• Yields: Deviation for 3 out of 6 treatments < 40 % (highest for rain-fed)

  Final (Total) Biomass (t/ha) Tuber Yield (t/ha)

Year Treatment Measured Simulated Deviation Measured Simulated DeviationDevon

2012Irrigated 14.5 ± 6.3 10.3 -29.2 11.2 ± 5.7 5.2 -53.1

Rain-fed 28.4 ± 18.5 7.7 -72.7 20.8 ± 14.9 3.9 -81.1

2013 Irrigated 16.9 ± 5.7 13.5 -20.1 6.3 ± 4.9 6.7 7.5

Rain-fed 17.8 ± 2.4 13.5 -24.2 6.7 ± 2.0 6.7 0.24

Ebony Park

2013 Irrigated 27.8 ± 2.8 11.2 -51.8 11.0 ± 5.8 6.7 -39.5Rain-fed 14.6 ± 4.2 10.6 -8.6 2.6 ± 1.4 7.2 158.6

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3. Results: Testing Drought Tolerance under Climate Change

2006-P

resen

t

RCP 2

.6 2030

B2-20

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A2-203

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RCP 4

.5 2030

RCP 6

.0 203

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RCP 8

.5 2030

RCP 2

.6 205

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B2-205

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A2-205

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RCP 4

.5 205

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RCP 6

.0 2050

RCP 8

.5 20

50-6-149

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Yield Changes (%) Warm and Dry Climate

Rainfed Irrigated

Scenario/RCP

Perc

enta

ge (%

) Cha

nge

2010

-Prese

nt

RCP 2

.6 203

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B2-203

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A2-203

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RCP 4

.5 2030

RCP 6

.0 20

30

RCP 8

.5 20

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RCP 2

.6 2050

B2-205

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A2-205

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RCP 4

.5 205

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RCP 6

.0 2050

RCP 8

.5 2050

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Yield (t/ha) changes (%)-Cool & Wet Climate

Rainfed Irrigated

Scenario/RCP

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enta

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nge

• Warmer and drier conditions resulted in earlier maturity, declines in biomass and yield while cooler and wetter conditions favoured production, but suggested longer maturity period.

• Elevated CO2 (under A2, B2 SRES and RCP 2.6, 4.5, 6.0 and 8.5), had a net benefit for both yield in both the

warm and dry; and cool and wet climates.

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4. Conclusions

Agroecology: sweet potato production is affected by agroecology but the crop is versatile and adaptations and could be pursued as one to reduce reliance on imported wheats and ceareals.

Drought Tolerance: deep roots and extensive trailing vines are among the properties that make sweet potato tolerant to drought, but yields are considerably reduced by dry conditions (especially up to 42 DAP)

Parameterization: of root and tuber crops in AquaCrop is challenging (perhaps more so than for other types of crops). Experience allows for much wider application

Model Performance: Fairly accurate prediction of sweet potato crop growth under both rain-fed and irrigated conditions. Canopy cover was reasonably well simulated by the model but some divergence was noted for biomass

and yield. The overall simulation of biomass was good with deviations of less than 30% for four out of six

simulations and season-long performance of the model was commendable

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• Warm and dry (cool and wet) conditions were found to be least (most) favourable to future production of sweet potato, but overwatering was also found to be counterproductive.

• The results suggest that elevated CO2 benefits future production with yield increases ranging to a high of over 20%.

• The benefits however seem to taper off as 2050 is approached.

• Reduced stomatal conductance seem to contribute to a reduction in transpiration and coupled with the increased biomass and yield gave significantly higher (maximum of 89%) water use efficiency.

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4. Conclusions

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5. Next Steps

Further refinements of model parameters to increase accuracy of predictions;

Testing in other environments: soil, climates, other scenarios of water limitation;

Downscaling of climate model outputs using weather generator to provide multiple scenarios of future climates;

Expansion to other important crops;

Training and capacity building;

Routine incorporation of crop modelling into operations of agriculture sector.

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THANK YOU