Researchers in Minnesota, N. Dakota and Saskatchewan have recently
evaluated the use of foliar applied N (usually as 28% UAN) to
increase or enhance protein of hard red spring wheat. Late
applications may increase protein content but generally are too late
to increase yield. Preplant or seeding time N must be applied at
rates to optimize yield when late N is to be applied for protein.
Results and opinions of this practice are not consistent.
Following are some of these differences.
1. Movement of foliar N into the plant |
European and US work with urea indicates that
60% of total N is recovered in the plant, and at least 80% of
urea-N recovered in plants is translocated to grain. |
U of Manitoba work used 15N – labeled fertilizer
and found less than 1% was taken up through leaves. Most uptake
occurred after N washed to the soil and was taken up by roots.
Others feel foliar N may increase plant nutrition and stimulate
roots to extract more N (up to 1/3 of total plant N uptake may
occur after heading. |
2. Time of foliar N application |
US studies -7-10 days after flowering (anthesis) |
Saskatchewan studies found superior protein
enhancement at boot vs post-heading. |
3. Application methods |
To maximize foliar uptake a fine spray for
complete leaf coverage. |
To optimize root uptake, and minimize leaf burn,
apply 28% in strips or bands to minimize leaf contact, or
broadcast 34-0-0 |
4. Leaf burning |
NDSU report yields loss is consistent only after
40% of leaf is damaged. Burn tends to occur along leaf margins
and does not coalese like leaf disease, allowing continued leaf
functions. Leaf burn can be minimized through management. |
Leaf burn can be severe. Protein enhancement
occurs as a result of yield suppression from leaf burning.
Disease control studies indicate 50% of final yield depends on
health and function of flag leaf. |
5. Varietal responses |
Minnesota and NDSU find similar protein increase
for high yield – low protein varieties and low yield – high
protein varieties. |
Alberta studies found reduced baking quality
(loaf volume) when protein was increased from 12% to over 16%
using foliar urea in combination with heavy soil applications of
34-0-0 |
Level of Protein Enhancement
Following are protein enhancement levels achieved in various
studies and the break-even protein premiums required to cover N cost
(35˘/lb) and application and risk (application at $5/acre, and risk
to provide a 2:1 return on N cost and applications). In all cases
sufficient N was applied at seeding to optimize yield.
Study |
Foliar N rate (lb/ac) |
Yield bu/ac |
Protein enhancement |
Break-even premium (˘/pt/bu) to cover |
Cost of N |
Cost of N, application, risk |
NDSU – Carrington |
30 lbs
30 lbs
15 lbs
15 lbs |
28 dry
50 irrigated
28 dry
50 irrigated |
+1.1
+1.8
+0.2
+0.5 |
34
12
94
21 |
101
23
366
82 |
U of Minnesota – Crookston |
30 lbs
60 lbs
90 lbs |
54
54
54 |
+0.4
+1.0
+2.0 |
49
39
29 |
144
96
68 |
AAFC – Indian Head |
15 lbs
15 lbs |
42 Boot
38 Heading |
+0.9
+0.6 |
14
23 |
54
90 |
U of M Winnipeg |
30-16 lbs |
45 |
+1.0 |
23-47 |
46-94 |
*additional N required at seeding to raise protein one percentage
point. It is apparent that protein enhancement is not consistent.
Profitability with this practice improves when:
- Yields are high
- Protein enhancement is great
- N costs are low
- Protein premiums are high
Historic
Protein premiums for # 1 CWRS in ˘/bu (additional premiums for
each protein level) |
Protein |
96/97* |
95/96 |
94/95 |
93/94 |
15% |
13 |
16 |
|
|
14.5% |
13 |
14 |
39 |
93 |
14% |
11 |
14 |
28 |
|
13.5% |
11 |
11 |
16 |
82 |
13% |
6 |
12 |
25 |
|
12.5% |
5 |
10 |
|
|
12% |
6 |
15 |
|
|
*estimated |
|
|
|
|
At recent premium levels, only those studies with very high
yields and high protein enhancement would cover the cost of N.
If growers are interested in this practice:
- Encourage them to try strips in fields – if farmers do gain
experience with this, it may be very profitable to implement in
years when projected protein premiums are high (eg. 1993/94)
- Warn them of the possible consequences – leaf burn, possible
yield loss, cost of N and application, etc. The level of protein
enhancement may not be sufficient to move up to the next premium
level.
- Offer suggestions on ways to minimize leaf burning. (Dilute
28% N half and half with water and apply later in the day since
damage is greater with high temperatures, low humidity and high
sunlight intensity.
|