ISSUE 2 May 11, 2006
FERTILIZER STRATEGIES REVISITED
Due to the high Nitrogen (N) costs, growers are looking for ways to reduce rates. From our ND yield response data, generally reductions of 10-15% are justified in the current crop price/N cost situation. Beyond that, growers must rely on an assessment of the "yield goal" concept that factors into the NDSU N rate recommendations. In the past, growers have often made the yield goal some sort of Christmas wish, based on what they wished the field would achieve and not on what they probably will yield. Using a yield based on a historical yield average (perhaps the last seven years throwing out the highest and lowest years) would be a better factor to consider in the yield equation. For example, if the historic yield average for a field was 45 bu/a of wheat, it would be a rare event for the field to yield much over 50 bu/a. If it did, it would be because climate was incredibly favorable. The same conditions that would result in increased release of N from the soil. For example, a couple years ago when fields fertilized for 50 bushels reached 80-90 bushels in some areas.
Other strategies for further reducing N rates are not well founded. Some growers believe that moving towards banded N applications will allow them to reduce N rates. These rate reductions are not substantiated by research trials. Although Phosphorus (P) is more efficiently used by crops in a near-seed band, N efficiency is not. Side-dress can be helpful in sandy soils where the risk of loss from early rains is great. However, in medium or heavier soils, there appears to be no agronomic advantage to side-dress, although there are several practical and possibly economic reasons beyond crop yield that would compel a grower to use this method. Banding P has been shown most efficient when the fertilizer band is near or with the seed, depending on the salt/N tolerance of the crop seed. Between-row banding of P may be a little more efficient than broadcast, but it has no early starter benefit. In early-seeded crops, the P starter effect is very important.
Several states are throwing out the yield-based N recommendation formulas of the past. In ND, we do not have the recent N response database in any crop except for dry edible beans. During the next several years, there will be an effort to fortify our research base to determine whether such a change is justified.
Dr. Dave Franzen
NDSU Extension Soil Specialist
Fargo, ND. 701-231-8884