Seeding Rate for Dryland Wheat

Four winter wheat varieties (PlainsGold Byrd, Limagrain T158, Syngenta TAM 111, and WestBred Winterhawk) were planted at five seeding rates (30, 45, 60, 75, and 90 lb/a) in the fall of 2014, 2015, and 2016 at Colby, Garden City, and Tribune, KS. The objective of the study is to identify appropriate seeding rates for dryland winter wheat in western Kansas. Averaged across varieties, a seeding rate of 60 lb/a seemed to be adequate at all locations in 2015. However, with higher yields in 2016, a higher seeding rate (75 lb/a) was beneficial. Although yields were less in 2017 than 2016, a seeding rate of 75 lb/a generally produced the highest yields. The wheat variety T158 was the highest yielding (or in the highest group) at all locations in 2015. Other varieties may have been affected by differential response to stripe rust and winter injury resulting in lower yields. In 2016, the highest yielding variety varied by location. TAM 114 was in the highest yielding variety at each location in 2017. Variety selection and growing season appears to have more effect on wheat yields than seeding rate.


Introduction
The purpose of this project is to determine appropriate seeding rates for dryland winter wheat in western Kansas.In recent years, there appears to be an increase in seeding rate without corresponding increase in grain yields.A preliminary study conducted in 2014 found no yield benefit from increasing seeding rates from 30 to 75 lb seed/a for 4 wheat varieties at Tribune, while a similar study at Garden City suffered severe hail damage causing yields to be less than 10 bu/a.The objective is to evaluate seeding rates on grain yield of several popular wheat varieties representing a range of genetic backgrounds and tillering ability under dryland conditions at three sites in western Kansas.

Experimental Procedures
Four winter wheat varieties (Byrd, T158, TAM111, and Winterhawk) were planted at five seeding rates (30, 45, 60, 75, and 90 lb/a) in the fall of 2014 to 2016 at Colby, Garden City, and Tribune, KS.The date of seeding was October 20, 2014, October 14, 2015, and October 10, 2016 at Colby;October 9, 2014, October 9, 2015, and October 14, 2016 at Garden City;and September 26, 2014, October 13, 2015, and October 5, 2016at Tribune. Seed size in 2015 was 15,839, 15,479, 17,627, and 12,921 seed/lb for Byrd, T158, TAM 111, and Winterhawk, respectively.All plots were planted on no-till fallow land.Harvest was done on July 4, 2015, July 10, 2016, and July 1, 2017at Colby, June 29, 2015, June 22, 2016, and July 6, 2017at Garden City, and June 30, 2015, July 4, 2016, and June 28, 2017 at Tribune.Growing season precipitation (October through June) for 2015 wheat was 14.03 in.at Colby, 12.18 in. at Garden City, and12.83 in. at Tribune. For 2016, growing season precipitation was 12.36 in. at Colby, 11.31 in. at Garden City, and14.32 in. at Tribune. For 2017, growing season precipitation was 16.05 in. at Colby, 11.14 in. at Garden City, and14.89 in. at Tribune. Starter fertilizer was applied (5.5-26-0 (nitrogen, N;phosphorus, P;and potassium, K)) at Garden City and (6-20-0) at Tribune each year.The wheat was topdressed with 90 lb N/a at Colby, 30 lb N/a at Garden City, and 60 lb N/a at Tribune in 2015.In 2016, wheat was fertilized pre-plant with 90 lb N/a at Colby, and topdressed with 100 lb N/a at Garden City, and 80 lb N/a at Tribune.In 2017, wheat was fertilized pre-plant with 60 lb N/a at Colby, and topdressed with 80 lb N/a at Garden City, and 80 lb N/a at Tribune.Herbicides were applied in the spring for weed control: Ally Extra (0. Grain yields were determined by harvesting with a plot combine with moisture corrected to 13%.

Results and Discussion
Growing season precipitation was below normal for Garden City all years, but normal to above normal for Tribune and Colby.In addition, precipitation was infrequent and variable across the growing seasons.In 2015, precipitation was high in May (6.38 in. in Garden City,6.16 in. at Tribune,and 6.42 in.at Colby) making up for a dry winter and early spring.For 2016, rainfall was above normal for Tribune, slightly below normal for Garden City, and below normal at Colby.April was wet with 5.16 in.at Tribune, 4.59 in.at Garden City, and 5.64 in.at Colby.In 2017, precipitation was above average at Tribune for April (4.67 in.) and May (5.00 in.), however, wheat streak mosaic virus reduced grain yield.At Garden City conditions were very dry in the fall of 2016 (0.3 in.between October and January), and the majority of the precipitation (6.58 in.) occurred in March and April.At Colby, conditions were extremely dry at seeding time followed by above normal precipitation in the late spring.A blizzard event on April 30 to May 1, 2017 resulted in the wheat being completely laid flat at the boot stage at Tribune and Colby with 14-20 inches of snow on top.
In 2015, averaged across seeding rates at Tribune, T158 and Winterhawk produced the greatest yields with TAM 111 producing the lowest yields (Table 1).At Colby and Garden City in 2015, T158 produced significantly higher yields than all other varieties.Stripe rust was prevalent in the 2015 growing season.Resistance ratings from the Kansas State University Department of Plant Pathology (publication MF991, Wheat Variety Disease and Insect Ratings 2016, E.D. Dewolf, R. Lollato, and R.J. Whitworth.),with a scale of 1 being resistant to 10 being susceptible, were 8, 2, 8, and 6 for Byrd, T158, TAM111, and Winterhawk, respectively.Stripe rust infestation and associated yield reductions at Colby (and other locations) were consistent with these ratings.At all sites averaged across varieties in 2015, there was a positive yield response to increased seeding rates with greatest response when increasing from 30-60 lb/a with minimal response above 60 lb/a.Wheat yields were very good at all locations in 2016 (Table 2).The response to variety and seeding rate varied greatly across locations.Averaged across seeding rates, Byrd produced the greatest yields at Tribune while it produced the lowest yields at Garden City.Winterhawk and T158 were the lowest yielding at Tribune while they were the highest yielding at Garden City and Colby.There was a significant positive yield response to increased seeding rate at Tribune and Colby but no significant response to seeding rate at Garden City.
Wheat yields were increased by increased seeding rates at all locations in 2017 (Table 3).Wheat yields were the lowest at Tribune (significant wheat streak mosaic virus damage) and greatest at Colby.TAM 114 was in the highest yielding group at all locations.The ranking of the other varieties depended upon location.The dry fall conditions in 2016 at Garden City likely reduced tiller development, resulting in reduced wheat yields at seeding rates less than 60 lb/a.Relative differences in growth stage among varieties at the time of the late spring blizzard may have affected their yield potential, however this was very difficult to assess.
Averaged across years (2015-2017), T158 was the highest yielding variety at Garden City and Colby (Table 4).Byrd was the highest yielding variety at Tribune, but the lowest yielding at the other two locations.At all locations, grain yields were increased by increased seeding rate.When averaged across all locations and years, yields were increased 8 bu/a by increasing seeding rate from 30 to 60 lb/a and an additional 3 bu/a when seeding rate was increased to 90 lb/a.There was not a significant variety × seeding rate interaction as all varieties responded positively to increased seeding rate.These results support a previous Kansas State University recommendation that the economic optimum seeding rate for rainfed winter wheat production in western Kansas is 60 lb/a, while the highest yield can be obtained with a 75 lb/a seeding rate.

Table 1 .
Dryland wheat response to variety and seeding rate at three locations in 2015

Table 1 .
Dryland wheat response to variety and seeding rate at three locations in 2015

Table 2 .
Dryland wheat response to variety and seeding rate at three locations in 2016

Table 2 .
Dryland wheat response to variety and seeding rate at three locations in 2016

Table 3 .
Dryland wheat response to variety and seeding rate at three locations in 2017

Table 4 .
Dryland wheat response to variety and seeding rate at three locations from Means within a column with the same letter are not statistically different at P = 0.05.ANOVA = analysis of variance.LSD = least significant difference.