Comparing Your Crop's Growth Stage to State Average - UNL CropWatch, June 17, 2011

Comparing Your Crop's Growth Stage to State Average - UNL CropWatch, June 17, 2011

June 17, 2011

The 2011 production season has already proved challenging for much of the United States. So far we have seen a crippling drought across the southern Great Plains and incessant rains across the northern Plains and eastern Corn Belt leading to significant planting delays and major floods in the Mississippi and Missouri river basins.

View current National Weather Service outlooks for July-August.

Heavy rains this spring resulted in 90% of the Ohio corn crop being planted three to four weeks behind normal. Significant acreage in the Dakotas qualified for prevented planting. Across the southern Great Plains, record dryness extending back to last fall has virtually eliminated much of the winter wheat crop. To add insult to injury, heat and dry conditions are beginning to expand northward into Arkansas, Tennessee, Missouri, and Kentucky.

Here in the western Corn Belt, persistently cool conditions have developed across the Dakotas and Montana, with above normal moisture common from Montana southeast through the eastern two-thirds of Iowa. In addition the Missouri River is flooding due to excessive spring rains and winter snow accumulations. Flooding is expected to continue into at least late August.

Estimating Crop Maturity for Your Field

Do you want to figure out when your particular corn variety might mature? You can use information on the CropWatch Weather Growing Degree Days page to do this.

Go to the Growing Degree Day table and select the location closest to you. You will notice that six emergence dates are given for corn, all spaced one week apart. Find the emergence date closest to the emergence date of the field you are analyzing. Then find the GDDs accumulated under the “Accum GDD” column.

  • Find your variety's total GDD units and subtract the accumulated GDD units listed in CropWatch
  • Divide the difference by 23
  • Add the resulting number to today’s date to get the estimated maturity date.

Let's look at an example: You have a 2200 GDD variety that emerged May 20 at Alliance. The chart shows that 313 units had accumulated as of June 15 and the difference was calculated to be 1887 GDDs (2200-313). Divide 1887 by 23 (the number of GDD units accumulating on an average day) and you get a value of 82. Your variety will reach maturity approximately 82 days after June 15. That's if we have normal temperatures for the remainder of the season.

Remember, if your variety’s maturity is listed in terms of number of days instead of GDD units, take the number of days and multiply by 23. Then proceed with calculating the estimate for your field.

Al Dutcher
Extension State Climatologist

For Nebraska, the average emergence date for the 2011 corn crop was May 20, according to the Nebraska Agricultural Statistics Service. This is about five days behind the five-year average.

For the past 30 days heat from the southern Plains and cold from the northern Plains have been battling it out over Nebraska. Generally, the southern third of the state has experienced above normal temperatures since May 20, while the northern third has fallen further behind normal with persistent below normal temperatures. See Table 1 for a complete list of the GDD accumulations for corn emerging on May 20.

Several columns in Table 1 provide insight as to where this crop stands and when it may mature if normal temperatures are realized from now to the end of the crop season. Under the GDD column, actual (act) accumulated GDD units and GDD units given normal (Norm) temperatures are listed. The “f +/-“ column calculates the percent of units ahead or behind normal when compared to the variety at full maturity. For this analysis all locations were assigned a 2569 GDD (110 day) variety .

The Cal/Day/Mature column lists the calendar day maturity that projects the day of the year the 2569 GDD variety will mature if normal temperatures are observed for the remainder of the growing season. Most producers in northern and western Nebraska typically grow varieties that can be 200-400 units less than the 2569 GDD units so be sure to consider the crop maturity you planted when reviewing this estimate.

It generally takes 23 GDD units to accumulate one day of crop growth. This is helpful in calculating where your crop stands in relation to the state average calculated by NASS. To determine how your crop relates to the state average, find the difference between actual GDD accumulations and normal GDD accumulations in Table 1 for the location nearest your farm. Divide the difference by 23.

For example, if the difference comes to -120, the crop is 5.2 days behind normal for the May 20 emergence date. Next, add the differential of this year’s crop compared to the five-year average. In this case it is five days. If you add together these two figures, you can estimate that your crop is about 10 days behind the five-year state average.

Al Dutcher
Extension State Climatologist

 

Table 1. Growing degree day (GDD) accumulation for corn emerging May 20 through June 15, 2011.
 
GDD
f
Cal Day
Stage

GDD at Maturity

Location
Act
Norm
+/-
Mature
No.
Description
2569
Ainsworth
371
425
-0.02
270
3.2
6 leaves
2569
Alliance West
309
375
-0.03
295
2.7
4 leaves
2569
Arapahoe
352
414
-0.02
275
3.1
6 leaves
2569
Arthur
342
413
-0.03
276
3.0
4 leaves
2569
Barta
373
428
-0.02
269
3.2
6 leaves
2569
Beatrice
512
503
0.00
246
4.4
8 leaves
2569
Brule
398
414
-0.01
270
3.5
6 leaves
2569
Brunswick
387
456
-0.03
261
3.4
6 leaves
2569
Cedar Point
380
415
-0.01
272
3.3
6 leaves
2569
Central City
450
449
0.00
258
3.9
6 leaves
2569
Champion
396
417
-0.01
270
3.4
6 leaves
2569
Clay Center
469
444
0.01
258
4.0
8 leaves
2569
Cozad
392
426
-0.01
268
3.4
6 leaves
2569
Curtis
413
423
0.00
267
3.6
6 leaves
2569
Dickens
371
420
-0.02
271
3.2
6 leaves
2569
Elgin
402
448
-0.02
261
3.5
6 leaves
2569
Firth
514
503
0.00
246
4.4
8 leaves
2569
Gordon
299
393
-0.04
287
2.6
4 leaves
2569
Gothenburg
399
425
-0.01
267
3.5
6 leaves
2569
Grand Island
456
437
0.01
260
3.9
6 leaves
2569
Gudmundsen
319
417
-0.04
278
2.8
4 leaves
2569
Halsey
377
425
-0.02
269
3.3
6 leaves
2569
Higgins Ranch
379
427
-0.02
269
3.3
6 leaves
2569
Holdrege
443
429
0.01
263
3.8
6 leaves
2569
Indian Cave
592
503
0.03
243
5.1
10 leaves
2569
Kearney
451
432
0.01
262
3.9
6 leaves
2569
Lexington
412
427
-0.01
266
3.6
6 leaves
2569
Havelock
512
503
0.00
246
4.4
8 leaves
2569
McCook
449
424
0.01
264
3.9
6 leaves
2569
Mead
498
503
0.00
247
4.3
8 leaves
2569
Merna
393
428
-0.01
267
3.4
6 leaves
2569
Merritt
352
418
-0.03
273
3.1
6 leaves
2569
Minden
456
431
0.01
262
3.9
6 leaves
2569
Mitchell Farms
328
372
-0.02
294
2.9
4 leaves
2569
Monroe
468
465
0.00
254
4.0
8 leaves
2569
Nebraska City
553
503
0.02
245
4.7
8 leaves
2569
Newport
390
427
-0.01
268
3.4
6 leaves
2569
Concord
404
466
-0.02
258
3.5
6 leaves
2569
North Platte
387
421
-0.01
269
3.4
6 leaves
2569
Oakland
460
486
-0.01
251
4.0
6 leaves
2569
O'Neill
377
436
-0.02
266
3.3
6 leaves
2569
Ord
402
435
-0.01
265
3.5
6 leaves
2569
Red Cloud
493
444
0.02
256
4.2
8 leaves
2569
Scottsbluff
340
373
-0.01
292
3.0
4 leaves
2569
Shelton
452
434
0.01
261
3.9
6 leaves
2569
Sidney
323
396
-0.03
283
2.8
6 leaves
2569
Sparks
354
417
-0.02
274
3.1
6 leaves
2569
Smithfield
416
428
0.00
265
3.6
6 leaves
2569
West Point
446
485
-0.02
252
3.9
6 leaves
2569
York
485
457
0.01
254
4.2
8 leaves
2569