Water Productivity: Considering more carefully the farm-level perspective

Dennis Wichelns December 8, 2014

1

Water Productivity: Outline

1. Definitions 2. Brief History 3. Current Use

4. Inherent Limitations Conceptual Framework Empirical Examples

5. A Better Way Forward

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Water Productivity: Definitions

WPAW = Crop Output__ Water Applied

WPET = Crop Output_________ Water Evapotranspired

“Maximizing the crop-per-drop”

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Water Productivity: Brief History

1. Introduced in mid-1990s

2. Applications expanded and increased in the 2000s

3. Very frequent use today

4

Articles in Scopus, per year

Year

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60

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160

1996 1998 2000 2002 2004 2006 2008 2010 2012

Search: ‘water productivity’ and agriculture or irrigation

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Current Uses

2. Comparing observations, over time and across locations

3. Evaluating opportunities for increasing yields and improving livelihoods

1. Identifying optimal strategies

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Water Productivity: Limitations

WPAW = Crop Output__ Water Applied

WPET = Crop Output_________ Water Evapotranspired

We work in both AW and ET space

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Conceptual Framework

In this example, WP = 1.25 kg / m3

Water productivity is the slope of a ray from the origin through a given point on a production function Applied Water

Crop Yield

Y = Y(AW)

7,500 kg/ha

6,000 m3 / ha

A

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Conceptual Framework

Typical for supplemental irrigation

Yield = Y(AW) Positive vertical axis intercept

Applied Water

Crop Yield

Y = Y(AW)

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Conceptual Framework

Typical for fully irrigated production

Yield = Y(AW) Negative vertical axis intercept

Applied Water

Crop Yield

Y = Y(AW)

C B

A

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Conceptual Framework

Water productivity diminishes with ET

Yield = Y(ET) Positive vertical axis intercept

Evapotranspiration

Crop Yield

Y = Y(ET)

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Conceptual Framework

Water productivity increases with ET

Yield = Y(ET) Negative vertical axis intercept

Evapotranspiration

Crop Yield

Y = Y(ET)

A

B

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Comparing Observations

Water productivity: insufficient indicator

Suppose we observe points A,B,C. Which point is best? Is water productivity helpful? Applied Water

Crop Yield

Y = Y(AW)

B

A C

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Evaluating Opportunities

Point B likely is preferred to point A

Improving technology... Shifting the functions outward

Applied Water

Crop Yield

Y = Y(AW)

B

A

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Evaluating Opportunities

Point B likely is preferred to point A

Evapotranspiration

Crop Yield

Y = Y(ET)

B

A

Improving technology... Shifting the functions outward

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0

1

2

3

4

5

6

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0 100 200 300 400 500 600 700

Durum Wheat Production

Yield = Y(AW)

Yield (t / ha)

Supplemental irrigation (mm)

Empirical Examples

Zhang and Oweis, 1999 Supplemental irrigation of durum wheat in Syria

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Solution Values, per Objective

Applied Crop Water Net Maximizing Water Yield Productivity Revenue Objective (mm) (t / ha) (kg / m3) ($ / ha) Water productivity 270 5.40 2.00 866 Net revenue 454 6.58 1.45 1,048 Crop yield 510 6.65 1.30 1,032 Source: Zhang and Oweis, 1999. Note: This example pertains to durum wheat

production at Tel Hadya in Syria.

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Solution Values, per Objective

Source: Zhang et al., 1999. Note: This example pertains to winter wheat

production on the North China Plain.

Applied Crop Water Net Maximizing Water Yield Productivity Revenue Objective (mm) (t / ha) (kg / m3) ($ / ha) Water productivity 0 3.07 n.a. 491 Net revenue 195 5.13 2.63 737 Crop yield 230 5.17 2.25 729

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Rainfed Crops in India

Source: Chander et al., 2012 Notes: Gumla is in Jharkand. Jabhua is in Madhya Pradesh. Farmer pack is N,P,K. Plus adds zinc, boron, gypsum.

Comparing Years Water Crop Yield Productivity Year Location Crop Farm Plus Farm Plus Rainfall (kg / ha) (kg/ha/mm) (mm)

2009. Gumla Maize 5,500 7,000 5.89 7.49 934 2010. Gumla Maize 2,530 3,950 6.87 10.70 368

2009. Jabhua Soybean 1,530 1,750 2.72 3.11 563 2010. Jabhua Soybean 1,460 1,660 3.82 4.35 382

2009. Gumla Paddy 3,325 4,615 3.56 4.94 934 2010. Gumla Paddy 3,560 4,910 9.67 13.30 368

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Rainfed Crops in India

Source: Chander et al., 2012 Notes: Gumla and Sareikela are in Jharkhand. Jhabua and Mandla are in Madhya Pradesh. Farmer pack is N,P,K. Plus adds zinc, boron, gypsum.

Comparing Locations Water Crop Yield Productivity Year Location Crop Farm Plus Farm Plus Rainfall (kg / ha) (kg/ha/mm) (mm)

2009. Gumla Paddy 3,325 4,615 3.56 4.94 934 2009. Jhabua Paddy 2,800 3,550 4.97 6.31 562

2010. Gumla Paddy 3,560 4,910 9.67 13.30 368 2010. Mandla Paddy 2,070 2,910 3.34 4.69 620

2010. Gumla Maize 2,530 3,950 6.87 10.70 368 2010. Sareikela Maize 2,070 2,990 5.73 8.28 361

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Rainfed Crops in India

Source: Chander et al., 2012 Notes: Gumla and Sareikela are in Jharkhand. Jhabua and Mandla are in Madhya Pradesh. Farmer pack is N,P,K. Plus adds zinc, boron, gypsum. Gr.nut is Groundnut, Bl.gram is Blackgram.

Comparing Years and Locations Water Crop Yield Productivity Year Location Crop Farm Plus Farm Plus Rainfall (kg / ha) (kg/ha/mm) (mm)

2009. Gumla Gr.nut 1,465 1,950 1.57 2.09 934 2010. Mandla Gr.nut 1,090 1,710 1.76 2.76 620

2009. Jabhua Bl.gram 550 695 0.98 1.23 562 2010. Mandla Bl.gram 570 630 0.92 1.02 620

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Summing Up

1. Water productivity is not a helpful optimization criterion

2. Nor is it a helpful descriptor of better or worse production outcomes

3. Water productivity is not a helpful guide regarding initiatives to increase farm output or enhance livelihoods

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Yet, recall the increasing popularity ...

This trend likely will continue

0

20

40

60

80

100

120

140

160

1996 1998 2000 2002 2004 2006 2008 2010 2012

Search: ‘water productivity’ and agriculture or irrigation

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A Better Way Forward

1. Experiment station and field studies

3. Studies of risk, uncertainty, stochastics

4. Seek progress in shifting crop-water production functions outward

2. Farm household panel studies

Much of humanity awaits our success 24