Illinois
Fertilizer Conference Proceedings
January 24-26, 2005
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L.E. Paul, E.A. Adee, and S.A. Ebelhar1
Work with nitrogen wheat fertilization has been limited in recent years. This may be the result of decreasing total wheat acreage in the state. The number of acres of wheat varies annually as a result of the previous year's yields and fall weather in the various areas of the state. With the recent high yield levels in the various areas of the state, there has been renewed interest in wheat production.
With the concern for nitrogen showing up in undesired areas and the increasing cost of nitrogen fertilizer, more fine tuning of the nitrogen rate recommendations for wheat is needed. The nitrogen recommendations listed in the Illinois Agronomy Handbook (Hoeft and Peck 2002) have increased by 20 pounds of nitrogen per acre in the past 20 years. These recommendations are still listed as a range of rates depending on soil organic matter. Additional work is also needed to fine tune the fall-spring timing and the best rate for both application times to establish nitrogen rate levels as determined by projected yields similar to what is presently recommended as is done with corn.
The studies were established as planned in the fall of the 2004. The areas were established as split–plot designs with fall n rates 0, 20, and 40 pounds per acre as the main plots and the spring n rates of 0, 25, 50, 75, 100, 125, and 150 pounds per acre split in the main plots. These studies are established on four University of Illinois Crop Science Research and Education Centers and one Southern Illinois University Research Center: DeKalb — Flanagan sil; Monmouth — Sable sicl; Brownstown — Cisne sil; Dixon Springs - Grantsburg sil; and SIU Belleville — Iva/Weir sil.
The studies reported in this summary are the nitrogen studies that were established on wheat at each of the Centers, The treatments were different at the different centers so the results will be listed separately and discussed separately. The three southern Illinois sites had the same treatments. Nitrogen rates of 0, 25, 50, 75, 100, 125 and 150 pounds of nitrogen applied in the spring with no fall nitrogen. The Monmouth site had 2 separate studies. The first is a study with 0, 20, or 40 pounds of nitrogen in the fall followed by 0, 20, 40, 60 or 80 pounds of nitrogen applied in the spring. The other study was 40 pounds of nitrogen applied in the fall and 0, 20, 40, or 80 pounds of nitrogen applied at Feekes' growth stage 3 and/or 5. The DeKalb site had 40 pounds of nitrogen applied in the fall followed by 0, 25, 50, 75, 100, 125 or 150 pounds of nitrogen applied in the spring.
The response to nitrogen at Dixon Springs and Bellville in 2004 was a linear response. Yields increased with increasing nitrogen rates to the levels of 125 pounds or 150 pounds of nitrogen. The Brownstown response was a quadratic response as the yields decreased after 100 pounds of nitrogen. (Figures 1 & 2). The optimal nitrogen rate at Brownstown was 55.6 pounds of nitrogen per acre using the regression model and 47 pounds of nitrogen using the quadratic plateau model.
At Monmouth over the three year period of 2002-2004 showed linear response to nitrogen when part of the nitrogen was applied in the fall. If all of the nitrogen was applied in the spring, there was a quadratic response with the yields falling off as nitrogen exceeded 60 pounds per acre. In 2003-2004, nitrogen was applied at two different growth stages of the wheat. The later nitrogen application timing (GS5) seemed to be better than the earlier timing(GS3), but this difference is not significant.
The response to total nitrogen at DeKalb in 2004 was quadratic. With the fall application of 40 pounds of nitrogen, levels of spring application above 50 pounds per acre of nitrogen produced decreasing yields and showed a definite quadratic response.
Based on a limited number of years and locations of these studies, the results seem to indicate that the nitrogen recommendations in the Illinois Agronomy Handbook that are based on the organic matter of the soil and the location in the state appear to do a fairly good job of optimizing the nitrogen rate. Also the application of some of the nitrogen in the fall seems to be beneficial to yields, at least in the northern part of the state.
Figure 3. N response to fall and spring nitrogen rates – Monmouth 2002–2004
Figure 4. N response by timing of spring nitrogen – Monmouth 2003–2004
Figure 5.N response to spring nitrogen – DeKalb 2004
1 L.E. Paul and S.A. Ebelhar are agronomists and E.A. Adee is a principal research specialist, Dept. of Crop Sciences, University of Illinois, Urbana, IL.
Hoeft, R.G. and T.R. Peck. 2002. Soil testing and fertility. In Illinois Agronomy Handbook, 23rd Edition. College of Agricultural, Consumer, and Environmental Sciences, Dept. Of Crop Sciences, UI Extension, University of Illinois.
