Extension Ag Update
July/August 2007
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Predicting Wheat Straw Yields in Northern Illinois

Jim Morrison, Extension Educator, Crop Systems, Rockford Extension Center, University of Illinois Extension, 815-397-7714, morrison@uiuc.edu

A study was conducted in 2004 and 2005 at the Northern Illinois Agronomy Research Center, Shabbona to document straw yields from commonly grown soft red winter wheat varieties and to determine if straw yield from winter wheat in northern Illinois can be predicted.

We measured straw yield of six soft red winter wheat varieties (Cardinal, Growmark FS 634, Kaskaskia, Madison, Pioneer 25R47, and Roane) grown at the Center as part of the University of Illinois wheat grain variety trial. 

The previous crop was soybean.  The seeding rate was 36 seeds per square foot in 7.5-inch rows.  Approximately 40 pounds of nitrogen per acre were applied in the fall and 35 pounds per acre in the spring.  Averaged across both years, the seeding and harvest (grain and straw) dates were September 23 and July 11, respectively.  A four-inch stubble remained after grain harvest.  Straw was hand harvested and weighed immediately after grain harvest.

Results are shown in the following tables and figure.   

Table 1. Straw and grain data from 2004 and 2005.


Variety

Grain, bpa
(13.5% moisture)

Straw, t/a
(100% DM)

Lb. Straw per Lb. Grain

Plant Height (inches)

Pioneer 25R47

95.8

2.47

0.87

33.7

Cardinal

76.0

2.71

1.20

39.8

Growmark FS634

84.2

2.72

1.08

38.5

Kaskaskia

87.5

3.15

1.21

40.9

Madison

70.1

2.34

1.12

37.2

Roane

80.5

2.28

0.95

32.5

Average

82.4

2.61

1.07

37.1

LSD, 10%

6.4

0.31

0.13

1.5

Table 2. Correlations of variables.


Variables

Correlation (r value)

Plant height and grain yield

-0.226

Grain yield and straw yield

0.302

Straw yield and straw:grain

0.659

Plant height and straw yield

0.822

Plant height and straw:grain

0.934

Figure 1. Straw yield as a function of grain yield and plant height.

Figure 1. Straw yield as a function of grain yield and plant height.

In summary, significant differences existed between varieties in grain and straw yield, and plant height.  A negative correlation (r = -0.23) existed between plant height and grain yield.  A positive correlation (r = +0.30) was found between grain yield and straw yieldA high, positive correlation (r = +0.82) existed between plant height and straw yield.  Straw yield was described by the equation of -2.223 + 0.09*height (inches) + 0.018*grain yield (bushels per acre); r2 = 0.928.
 
The best way to predict straw yields, at least for high-yielding soft red winter wheat in northern Illinois, was a combination of grain yield and plant height.  Collaborators in the study were:  Dr. Emerson Nafziger, Extension specialist, and Lyle Paul, agronomist at the Northern Illinois Agronomy Research Center.