Research Assesses Nitrogen Use in Winter Wheat

Research Assesses Nitrogen Use in Winter Wheat

March 7, 2008

In Western Nebraska

UNL research on nitrogen in winter wheat in west central and western Nebraska is leading to new insights into nitrogen use and the significance of soil testing and accounting for all nitrogen resources. Research was conducted under dryland and irrigated conditions for normal production practices.

Value of Soil Testing

Soil testing is still the best method for determining the soil's fertility status and the need for additional fertilizer nutrients. Most current soil tests have been developed from hundreds of locations across Nebraska over many years and reflect the best "probabilities" for yield increases at different soil test levels. They are not perfect, however.

Fertilizer management means managing four factors: fertilizer rate, method of placement, fertilizer source, and timing of application. Adequate soil fertility B not too high or too low B should be the goal of producers.

 

Dryland Nitrogen Rates

Fertilizer N recommendations (NebGuide 1460, Fertilizing Winter Wheat I: Nitrogen, Potassium, and Micronutrients) provide optimum N rates (lbs N/acre) for winter wheat (with a maximum rate of 100 lb N/ac for dryland and 150 lb N/ac for irrigated) calculated from the following equation:

((N PRICE / WHEAT PRICE) + 0.014558 * NO3-N - 0.235) / -0.00138

Where, 

 

— N Price is the price of nitrogen fertilizer in dollars per pound
— Wheat price is the price of wheat in dollars per bushel
— NO3-N is the average ppm nitrate-N in the top three feet of soil.
Table 1 shows an example for two N fertilizer costs and two wheat prices. Both wheat and fertilizer prices are much higher than they have been for several years and this provides an incentive to take a serious look at N management this spring. Fertilizer prices have remained strong through the winter and early spring due to an expected increased demand for corn acreage. Currently projections are that N will cost from $0.42 to $0.45 per pound of N for ammonia to $0.57 to $0.60 per pound of N for urea and N solutions. Spring application usually means paying the higher N price for liquid or dry.




Table 1. N fertilizer recommendations for winter wheat at current wheat and fertilizer prices.
Residual Nitrate
Wheat (price per bushel)
Average ppm nitrate-N ina 3 foot depth
-----$7.00-----
-----$8.00-----
Nitrogen (price per pound)
$0.45
$0.60
$0.45
$0.60
Nitrogen Rate (lbs per acre)
2
100
90
110
95
4
80
65
90
75
6
60
45
65
55
8
40
25
45
30
10
20
0
25
10

Recommendations in Table 1 are assumed adequate for yields of 70 bu/ac or less. UNL soil fertility staff are developing a web-based Excel calculator for N recommendations. A test version is at http://soilfertility.unl.edu. The NebGuide can also be used to calculate N recommendations.

Irrigated Wheat

For irrigated wheat, guidelines suggest adding 20 pounds of N to the recommended rate (Table 1). A better approximation may be to add 1.5 pounds of N per bushel above the 70 bu/ac yield level if you have consistently produced over 85 bu/ac. Remember, simply adding more N will not "enhance" yield potential. Many other production factors (seeding rate, variety, planting date, row spacing, irrigation timing, weed, disease and insect management) are controlling factors for consistently high yields.

What's the best way to manage the higher nitrogen applications required for irrigated wheat? Are split N applications preferable to applying all of the N preplant? A current research project in western Nebraska (Panhandle and southwest Nebraska, funded by the Nebraska Wheat Board) is looking at N rate and timing on irrigated white wheat. We expect similar N responses on irrigated hard red winter wheat. State average yields of irrigated wheat during the last decade have ranged from 55 to 70 bu/ac, however, yields of 90 to 110+ bu/ac are possible in the high plains under irrigation (Nebraska irrigated wheat trials 2005-07 http://varietytest.unl.edu/winterwheat.html).

There is limited information about N management for irrigated wheat in Nebraska (red or white). To enhance yields and manage protein, research is being conducted to learn more about N rates and application timing, thanks to funding from the Nebraska Wheat Board.

The objectives of the project are:

  1. to determine optimum N rates and timing to achieve specific yield and protein content goals for irrigated white wheat based on soil nitrate-N and organic matter levels; and
  2. to determine N rate and timing effects on selected crop parameters (test weight, harvest index, moisture, baking quality).

The N rates are 0, 60, 100 and 140 lbs of N per acre. The three timing regimes are:

  1. all preplant;
  2. one-fourth at preplant, one-half at jointing, then one-fourth at boot; and
  3. one-third at preplant and two-thirds at jointing.

The 2006 plots were at the High Plains Ag Lab at Sidney, at Scottsbluff (PHREC) and near Alliance. The Scottsbluff site included three irrigation levels (low (4 inches), limited (8 inches) and full (12 inches). Soil test information is shown in Table 2. Antelope white winter wheat was planted at all 2006 locations except Alliance where Lakin was included. Planting dates were September 23, 2005 for Alliance and Sidney and September 26, 2005 for Scottsbluff. All these dates are about 7 to 10 days later than optimum for maximum yield potential. Wheat followed dry beans at two locations (Alliance and Scottsbluff), so yields are representative of predominant cropping systems where irrigated wheat will be planted in the Panhandle.

The 2007 plots were at the same three Panhandle locations plus three sites in west central Nebraska were added: one at the West Central REC at North Platte and two sites between Imperial and Brandon. The variety Antelope was planted October 3, 2006 at Alliance, September 27, 2006 at Sidney and September 14, 2006 at Scottsbluff. Agripro NuDakota was used for the west central sites and planted at North Platte October 16, 2006, at Hajek September 29, 2006 and at Krajewski October 31, 2006. Several of these dates are later than optimum for maximum yield potential, but wheat followed dry beans at thre locations (Alliance, Hajek, Krajewski), so yields should be representative of cropping systems where irrigated wheat is planted after dry beans in western Nebraska.

Table 2. Soil test information for 2006 and 2007 sites.
Location  

pH

 

OM

 

Olsen P

ppm NO3-N lbs NO3-N
       
0-8 inches
8-24 inches
24-48 inches
in 4 feet
Alliance 2006
7.0
2.1%
29
20.4
10.1
4.6
130
Sidney 2006
7.8
2.2%
48
17.2
15.3
18.5
240
Scottsbluff 2006
8.2
1.2%
12
0.6
1.8
5.3
50
Alliance 2007
7.3
1.8%
25
12.1
7.2
4.9
120
Sidney 2007
8.0
2.0%
79
10.9
19.0
36.1
370
Scottsbluff 2007
7.6
1.4%
17
12.6
9.4
16.1
190
Hajek 2007
6.3
1.8%
15
15.1
4.3
5.0
110
Krajewski 2007
7.1
1.9%
6
13.7
25.9
8.4
224
North Platte 2007
7.3
2.4%
14
6.2
3.8
2.5
55
*50 lb phosphate added to plot area due to low soil P.

Residual nitrate at Alliance and Sidney in 2006 were much higher than desired, but Scottsbluff was low enough for a good N response. Residual nitrate levels in 2007 were high at four of the six locations, but site selection was limited.The 2006 data showed a slight N response at Alliance and Scottsbluff at the 12-inch irrigation level (Table 3). Yield levels were very good at Alliance and Scottsbluff but were lower than expected at Sidney, due to the site, later planting date, poor emergence and stand.


Table 3. 2006 irrigated white wheat grain yields.
  Alliance Alliance PREC- 4 inches PREC 8 inches PREC 12 inches Sidney
Variety Antelope Lakin Antelope Antelope Antelope Antelope
N Rate and Timing
------------------------bu/acre ------------------------
0 Preplant* 83 85 77 88 90 66
30 Preplant -- -- 81 -- -- --
60 Preplant 91 90 82 83 87 72
100   Preplant 90 90 85 88 97 69
140  Preplant 76 75 -- 80 100 66
        
30 3p-2j-3b -- -- 83 -- -- --
60 3 p-2j-3b 82 93 85 94 99 66
100 3 p-2j-3b 82 89 85 83 100 67
140 3 p-2j-3b 78 90 -- 77 98 65
        
30 ap-bb -- -- 84 -- -- --
60 ap-bb 81 92 85 90 99  68
100 ap-bb 83 80 87 90 96 66
140 ap-bb 69 85 -- 95 95 67

*Preplant = all N applied broadcast preplant;
3p-2j-3b = N application with one-fourth preplant, one half at jointing and the remaining one-fourth at boot stage;
ap - bb = one-third preplant and two-thirds at jointing.

The 2007 data showed a slight N response at Alliance and Scottsbluff at the 12-inch irrigation level (Table 4). Yield levels were very good at Alliance and Scottsbluff but were again low at Sidney, due to the site and poor stand. There were significant N responses at the WCREC and Hajek sites but the late planting, poor stands and high nitrate-N contributed to no N response at Krajewski.

Summary

The results from these two years of research reinforces the importance of measuring residual N. Yield levels were high at some locations, but usually if the total fertilizer N plus residual soil nitrate-N in 4 feet of soil was 200 pounds N, yields were maximized. Further analysis of this data is underway.

Too much N can cause problems in wheat. Note that when all the N was applied preplant, yields tended to be reduced at the higher N rates. As N rates increased, regardless of application method, yields often decreased. This again supports the idea that testing for residual nitrate is as important in irrigated wheat production as dryland.

This work is continuing and five locations were planted for 2008 — four in the Panhandle and one in west central Nebraska.

Acknowledgements

Thanks to Jim Petersen, research technologist at WCREC for finding locations and cooperators and conducting the research at the west central sites. Paul Burgener provided economic info for the proceedings and information that will be in the PowerPoint presentation.

Gary Hergert
Extension Soils Specialist
Panhandle REC
Jim Petersen
Research Technologist
West Central REC
Paul Burgener
Extension Agricultural Economist
Panhandle REC


 




Table 4a. 2007 irrigated white wheat grain yields, western Nebraska trials.
 
 
PHREC (irrigation levels)
Alliance
HPAL
 
 
4 inches
8 inches
12 inches
 
 
Treatment   N Rate
bu/ac
All Preplant

0

62

80

89

102

65

 

30

58

----

----

----

----

 

60

49

78

96

106

68

 

100

50

74

90

111

63

 

140

----

77

92

113

65

1/4P-1/2J-1/4B

30

54

----

----

----
63
 

60

62

82

93

106

64

 

100

59

78

99

113

63

 

140

----

71

99

115

---

1/3P-2/3J

30

57

----

----

----

----

 

60

59

79

96

109

62

 

100

53

77

98

109

62

 

140

----

77

96

150

68

Table 4b. 2007 irrigated white wheat grain yields, west central Nebraska trials.
       

Krajewski*

Hajek

North Platte

      N Rate
bu/ac
    All Preplant

0

54

64

57

     

40

49

71

67

     

100

50

82

65

     

160

48

89

82

    /14P-1/2J-1/4 B

40

55

74

75

     

100

54

87

79

     

160

51

89

71

    1/3P-2/3J
40

52

78

71

     

100

80

87

73

     

160

47

92

75

    * N rates were 0, 40, 80 and 120 lb N/acre.