William R. Jepsen
with Phil Nesse, Morrow and Gilliam Co. OSU Extension Agent

Objective

To determine if top dressing wheat with sulfur (ammonium sulfate) would increase yields.

Location: Heppner, Oregon
Annual precipitation: 12 inches
Soil: Morrow clay loam
Rotation: winter wheat - fallow

Treatments

50 lbs./acre ammonium sulfate (10.5 lbs. N, 12 lbs. S) topdress
100 lbs./acre ammonium sulfate (21 lbs. N, 24 lbs. S) topdress
200 lbs./acre ammonium sulfate (42 lbs. N, 48 lbs. S) topdress
untreated control - 40 lbs. N/acre as anhydrous ammonia in fallow

Comments

There is still mixed opinions in our lower rainfall area whether winter wheat will respond to sulfur treatments. A pooled, one-foot depth soil sample was taken from the test site and sent to two different labs. The labs reported 2.4 to 3.0 ppm sulfur - levels considered to be marginally adequate for this area. My experiment is a bit unusual in that three different ammonium sulfate rates were used as treatments versus adjacent control strips. Because of this design, only a plus or minus sulfur comparison can be made. Nothing can be said about rates per se. Ammonium sulfate treatments were applied to 40 ft. by 2284 ft. strips on frozen ground in January. Control strips were fertilized during the fallow the previous spring. The variety was Stephens, dusted in on October 20, 1994. Cheat grass pressure was tremendous in the spring. If the plots had not been established I would have reseeded the field to spring wheat. The plots were harvested in August using a weigh wagon. Protein levels and test weights were determined at Oregon State University.

Data

Treatment	Rep 1 (12 S)	Rep 2 (24 S)	Rep 3 (48 S)	Average
Yield (bu/a)
plus sulfur minus sulfur PLSD (5%)	23.3 23.5	23.6 37.8	22.5 36.2	23.1 32.5 NS
Test weight (lb/bu)
plus sulfur minus sulfur PLSD (5%)	59.8 59.8	58.8 59.4	58.1 59.7 NS	58.9 59.6
Protein percent
plus sulfur minus sulfur PLSD (5%)	8.07 8.50	8.83 8.57	9.48 8.86	8.79 8.64 NS

 

Conclusions

Variability in the plots made all yield differences insignificant. Proteins tended to increase and test weights decrease with the higher sulfur (and nitrogen) treatments. Much of the variability was due to cheatgrass. This could be visually seen. It was apparent that top dressing fed the cheat grass as evidenced by thicker stands in all top dress treatments. To illustrate the severity of the cheat infestation in this test area, my 1995 farm average yield was 49 bu/a while the highest plot yield was only 38 bu/a. This trial needs to be repeated on clean ground and the treatments need to be truly replicated.