As a rule, high wheat yields are usually associated with low protein concentrations due to a dilution effect. Given the excellent protein premiums and the high nitrogen prices, the strategy to strive for is trying to attain maximum yields and high grain protein levels without having to use excessive levels of nitrogen. The objectives of this study were to examine the effects of late-season nitrogen foliar applications on grain protein and grain yield in spring wheat.
Studies were initiated in 1994 in the Indian Head area on two soil types, an Indian Head Heavy clay soil and an Oxbow loam soil. Four rates of nitrogen (0, 50, 75 and 100 lbs N/acre) were side-banded at seeding time. Liquid nitrogen (28-0-0) was applied just prior to heading (GS45) or after flowering (GS69) using a rate equivalent to 15 lbs N /ac (4.2 gal of liquid N /ac diluted with 5.8 gal of water /ac). The liquid nitrogen was applied during the day using a regular ground sprayer and some leaf scorching was observed. The plots on the Oxbow loam were hailed out in 1995.
Applying nitrogen at GS45 or GS69 had no effects on grain yield except when no fertilizer was applied at seeding (Table 1). On the other hand, late applications of nitrogen increased grain protein. In 1994, only the application at GS45 increased grain protein while in 1995, the increase was observed at both application times. In 1995, we had significant precipitation during the grain filling period. From a practical standpoint, in order to minimize risk, it would be preferable to apply the nitrogen at GS45 because of the greater opportunity to receive precipitation and the ease of identifying the growth stage. Also we had positive results in both years at GS45 while only in one year at GS69.
The other important consideration is the relative economic performance of this management strategy.
Table 2 shows gross and net returns for different initial rates of fertilizer and different foliar application times for the two soil types. Gross returns are determined by yield and price for the particular protein level. Net returns are gross returns minus the fertilizer cost for that treatment.
Generally, foliar nitrogen application at GS45 showed the best
net returns on both soil types which initially had low to average
fertilizer applied. Application at GS69 and on treatments with
higher initial application of nitrogen produced more variable
results.
When would it be practical to make use of such a strategy?
Firstly, the size of the protein premiums will warrant the use
of such a technique and secondly the price differential between
liquid nitrogen and other forms of nitrogen that can be
side-banded at seeding time (e.g., urea or anhydrous ammonia)
also has to be taken into account as well as the cost associated
with the foliar application. On the crop side of things, a good
estimate of the yield potential just before GS45 would have to be
made and the decision would also have to take into consideration
the amount of nitrogen applied prior or at seeding and some
estimate of the nitrogen supplying power of the soil. The soil's
ability to supply nitrogen would be influenced by factors such as
crop rotation and previous use of nitrogen fertilizers.
Table 1. The effects of foliar applied N on grain yield and
grain protein concentration at different rates of nitrogen in
spring wheat in 1994 and 1995 at two locations.
|
Heavy Clay Soil - 1994
|
Heavy Clay Soil - 1995
|
Oxbow Loam - 1994
|
|||||||
|
Grain Yield (bus/ac)
|
|||||||||
|
Nitrogen Rate lbs/ac
|
Check
|
GS45
|
GS69
|
Check
|
GS45
|
GS69
|
Check
|
GS45
|
GS69
|
|
0
|
21
|
32
|
22
|
25
|
29
|
28
|
28
|
34
|
28
|
|
50
|
37
|
38
|
38
|
42
|
42
|
43
|
45
|
45
|
43
|
|
75
|
39
|
41
|
39
|
42
|
43
|
45
|
48
|
42
|
44
|
|
100
|
41
|
40
|
40
|
46
|
42
|
44
|
50
|
47
|
45
|
|
Mean
|
34
|
38
|
35
|
39
|
39
|
40
|
43
|
42
|
40
|
|
Grain Protein (%)
|
|||||||||
|
0
|
12.5
|
12.8
|
13.1
|
11.7
|
13.0
|
13.0
|
12.0
|
12.3
|
12.3
|
|
50
|
12.7
|
13.2
|
12.7
|
12.7
|
13.8
|
14.0
|
12.1
|
13.1
|
12.1
|
|
75
|
13.1
|
14.1
|
13.6
|
13.7
|
15.0
|
15.4
|
12.8
|
13.6
|
13.2
|
|
100
|
13.8
|
14.7
|
14.2
|
15.1
|
16.0
|
16.2
|
13.7
|
15.0
|
13.8
|
|
Mean
|
13.0
|
13.7
|
13.4
|
13.3
|
14.4
|
14.6
|
12.7
|
13.5
|
12.9
|
Table 2. The effects of foliar applied N on grain yield and grain protein concentration at different rates of nitrogen in spring wheat in 1994 and 1995 at two locations.
|
Heavy Clay Soil - 1994
|
Heavy Clay Soil - 1995
|
Oxbow Loam - 1994
|
|||||||
|
Gross Returns - $
|
|||||||||
|
Nitrogen Rate lbs/ac
|
Check
|
GS45
|
GS69
|
Check
|
GS45
|
GS69
|
Check
|
GS45
|
GS69
|
|
0
|
64.05
|
97.60
|
71.50
|
105.00
|
128.76
|
124.32
|
85.40
|
103.70
|
85.40
|
|
50
|
112.85
|
123.50
|
115.90
|
183.12
|
193.20
|
205.11
|
137.25
|
146.25
|
131.15
|
|
75
|
126.75
|
155.39
|
134.55
|
193.20
|
228.33
|
238.95
|
146.40
|
144.90
|
143.00
|
|
100
|
141.45
|
165.20
|
151.60
|
244.26
|
223.02
|
233.64
|
172.50
|
194.11
|
155.25
|
|
Mean
|
111.28
|
135.42
|
118.39
|
181.40
|
193.33
|
200.51
|
135.39
|
147.24
|
128.70
|
|
Net Returns - $
|
|||||||||
|
0
|
64.05
|
93.85
|
67.75
|
105.00
|
123.15
|
118.71
|
85.40
|
99.95
|
81.65
|
|
50
|
100.35
|
107.25
|
99.65
|
164.42
|
168.89
|
180.80
|
124.75
|
130.00
|
114.90
|
|
75
|
108.00
|
132.89
|
112.55
|
165.15
|
194.67
|
205.29
|
127.65
|
122.40
|
120.50
|
|
100
|
116.45
|
136.45
|
122.85
|
209.56
|
180.01
|
190.63
|
147.50
|
165.36
|
126.50
|
|
Mean
|
97.21
|
117.61
|
100.70
|
161.03
|
166.68
|
173.86
|
121.33
|
129.43
|
110.89
|
| Assumptions: | 1995 Grain Prices | 1994 Grain Prices |
| #1CWRS | 4.20 $/bu | 3.05 $/bu |
| 12%protein | 4.27 | |
| 12.5% | 4.36 | |
| 13.0 | 4.44 | 3.25 |
| 13.5 | 4.60 | 3.45 |
| 14.0 | 4.77 | 3.79 |
| 14.5 | 5.04 | 4.13 |
| 15.0 | 5.31 |
Note: There are NO protein
premiums more than 15%
1994 N Price - 25¢/lb
1995 N Prices - Courtesy of Bell Agro Ltd., Indian Head
Liquid N - 28-0-0 - 37.4¢/lb
Dry N - 46-0-0 - 37.4¢/lb
Application cost of Liquid N is not included
Final prices for grain grades will affect total income.