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Screening Deficit Irrigation Strategies Using Crop Growth Simulation R. Louis Baumhardt and Scott A. Staggenborg USDA- ARS Conservation and Production Res. Lab. Bushland , TX Kansas State University Plant Science Center, Manhattan, KS. Depth to Water. Depth to Water.

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slide1

Screening Deficit Irrigation Strategies Using Crop Growth Simulation

R. Louis Baumhardt and Scott A. Staggenborg

USDA-ARS Conservation and Production Res. Lab. Bushland, TX

Kansas State University Plant Science Center, Manhattan, KS

slide2

Depth to Water

Depth to Water

Irrigation Well No. 2 - Bushland, TX

Irrigation Well No. 2 - Bushland, TX

0

0

-50

-50

1957-77

1957-77

-100

-100

65 ft Decline

65 ft Decline

-150

-150

1977-98

1977-98

21 ft Decline

Depth Below Ground - ft

-200

21 ft Decline

Depth Below Ground - ft

-200

-250

-250

Red Bed

Red Bed

-300

-300

(aquifer bottom)

(aquifer bottom)

-350

-350

1955

1965

1975

1985

1995

2005

1955

1965

1975

1985

1995

2005

Year

Year

  • Well capacity has declined with the decreasing water table.
  • The choice is between deficit irrigation or concentrating water to adequately irrigate a portion.
slide3

Irrigation-strategy Question:

  • Will uniformly spreading water resources to deficit irrigate a large area produce more or less crop yield than if that same water resource was concentrated to irrigate a smaller area and averaged with the complementary dryland area?

Uniformly Irrigate

Variably Irrigate

slide4

APPROACH

  • Use crop growth simulators (SORKAM and GOSSYM) and recorded weather at Bushland from 1958-1999 to calculate sorghum grain and cotton lint yields for several deficit irrigation combinations.
  • Determine crop growth and yield response to deficit irrigation levels for various planting practices or cultivar maturity.
slide5

IRRIGATION PARAMETERS

  • Irrigation – 7 d application interval and 4 capacity levels:
    • No – Irrigation = Rain only
    • Irrigation + Rain = 2.5 mm d-1 (2 gpm/ac)
    • Irrigation + Rain = 3.75 mm d-1 (3 gpm/ac)
    • Irrigation + Rain = 5.0 mm d-1 (4 gpm/ac)
slide6

OTHER FACTORS

  • Sorghum:
    • Cultivar Maturity = Early (15-leaf), Medium (17-leaf), Late (19-leaf)
    • PlantingDate = 15 May, 5 June, 25 June
  • Cotton:
    • Irrigation Duration = 4 and 8 weeks
model validation
MODEL VALIDATION

7000

SIMULATED = 390 + 0.95*MEASURED

r2 = 0.70

6000

RMSE = 903.5 kg ha -1

5000

4000

Simulated Grain Yield, kg ha-1

3000

2000

1:1

1000

0

0

1000

2000

3000

4000

5000

6000

7000

Measured Grain Yield, kg ha-1

slide9

1:1

Dryland

5.0 mmd-1

2:1

3.75 mmd-1

Dryland

UNIFORM

2.5 mmd-1

slide10

1:1

Dryland

5.0 mmd-1

2:1

3.75 mmd-1

Dryland

UNIFORM

2.5 mmd-1

slide11

SUMMARY

  • Simulated grain yield increased with increasing irrigation, but simulations also reflect generally better WUE at 3.75 mm d-1 than at 5.0 mm d-1 irrigation levels.
  • The weighted average grain yield for variable irrigation strategies with a dryland component increased net grain yield from 13% to >20% over uniformly irrigated sorghum.
slide12

CONCLUSION

  • For declining water resources, converting uniform deficit irrigation (water spreading) of a determinate crop like grain sorghum to variable irrigation that concentrates water on smaller areas with a complementary dryland area will increase overall sorghum grain yield.
slide14

4

-

Week irrigation

8

-

Week irrigation

Weighted

Percent

Weighted

Percent

Irrigation

Irrigation

Averag

e

of Base

Average

of Base

Strategy

Capacity

Yield

Yield

Yield

Yield

Yield

Yield

____

____

____

____

mm/d

%

%

kg/ha

kg/ha

UNIFORM

2.5

390

390

87

450

450

100

2:1

3.75

530

425

94

615

480

106

Dryland

220

220

1:1

5.0

660

440

98

7

20

470

104

Dryland

220

220

1:1

Dryland

5.0mm/d

2:1

3.75mm/d

Dryland

UNIFORM

2.5 mm/d

SIMULATED COTTON YIELD vs IRRIGATION STRATEGIES

slide15

CONCLUSION

  • Cotton yield levels are maintained or increased by converting from uniform deficit irrigation (water spreading) to variable irrigation on part of a field (concentrating water) with a complementary dryland area.
slide16

}

YEAR = 3

YEAR = 1

}

2.5”

2.0”

WHEAT

1.5”

O

S

A

N

D

1.0”

J

J

J

F

M

FALLOW

0.5”

A

M

0.0” Rain

A

M

F

M

J

J

SORGHUM

D

J

N

A

O

S

}

FALLOW

O

S

A

N

YEAR = 2

J

D

J

J

F

M

A

M

Wheat-Sorghum-Fallow Rotation

  • Two crops in three years,
  • Storage of precipitation as soil water,
  • Stable grain crop yields
35 11 n 102 5 w elevation 1170 m growing season 181 d
35 11’ N, 102 5’ WElevation = 1170 mGrowing season = 181 d

2500

Pan-Evaporation

2000

Precipitation

1500

WATER DEPTH, mm

1000

500

0

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

MONTH

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