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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 — labelled 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 believe 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 versus 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.|
|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 coalesce 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|
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:
|Historic Protein premiums for # 1 CWRS in ¢/bu (additional premiums for each protein level)|
|*based on payments made as of July 31, 2006|
For more information, contact your local MAFRI GO Representative.