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Department of Agronomy

Kansas State University

1712 Claflin Rd.

2004 Throckmorton PSC

Manhatan, KS 66506

785-532-6101

agronomy@ksu.edu

Extension Agronomy

Growing degree update for grain sorghum

With the cooler than average temperatures, questions have come up regarding growing degree units and how far behind the accumulation might be.  The accumulated GDUs for the KSRE Research fields are reported daily on the K-State Weather Data Library web page at  http://www.ksre.ksu.edu/wdl/Text%20files/text/GDU.TXT

Below is a table that shows the current accumulated GDU for Sorghum, how far behind that is, the average freeze date, and how many GDUs on average accumulate from the 15th through the average freeze date:

GROWING DEGREE ACCUMULATION from April 1 -  August 15, 2013

 

Division

Location

Current

Sorghum

GDU

Average

Sorghum

GDU

Departure

Approx

No. Days

Average

Freeze Date

Average number of GDU’s remaining from Aug. 15 through first freeze

Northwest

Colby

3909

4126

-217

-11

2-Oct

1679

Southwest

Garden City

4192

4361

-169

-8

13-Oct

2232

Central

Hays

4279

4460

-181

-9

10-Oct

1957

South Central

Hutchinson

4232

4813

-581

-29

17-Oct

2225

Northeast

Manhattan

4328

4591

-263

-13

15-Oct

2032

East Central

Ottawa

4231

4831

-600

-30

17-Oct

2231

Southeast

Parsons

4498

4834

-336

-17

23-Oct

2380

Northeast

Rossville

4173

4591

-418

-21

11-Oct

1942

South Central

St. John

4321

4848

-527

-26

22-Oct

2279

North Central

Scandia

4051

4535

-484

-24

16-Oct

2034

Northeast

Silver Lake

4207

4637

-430

-22

11-Oct

1941

West Central

Tribune

4058

4117

-59

-3

7-Oct

1717

 

**Sorghum GDU: (Maximum temperature + Minimum temperature)/2-35, when minimum temperature is greater than 32 oF

 

Most sorghum hybrids need about 1,900 GDU’s from half bloom to physiological maturity, using the 35 degree minimum temperature (or 1,500 if a 42 degree minimum temperature is used in the calculation).  Comparing that to the last column in the chart above, that means there is still time for the sorghum to reach physiological maturity in most areas if the sorghum is now, or soon will be, at half bloom – assuming average weather and average dates of the first freeze.

Mary Knapp, State Climatologist
mknapp@ksu.edu          

Kraig Roozeboom, Cropping Systems and Crop Production Agronomist
kraig@ksu.edu