Effect of Seed Size and Density on Winter Wheat Performance

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Procedure
Foundation seed grown at the Colby Experiment Station was used for the research in this report.Three varieties of winter wheat were used.Tests at Colby ineluded Newton and Eagle in 1980, 1981, 1982and 1983, plus Vona in 1982and 1983.All three varieties were tested at Hays in 1982.
• Seeds were divided into the following seedlot fractions: Coritrol-unselected seedlot Small-smallest seed, hand-screened Large-largest seed,.hand-screened Light-lightest density, gravity table Heavy-heaviest density seed, gravity table Each of the four separated variants represented less than 10% of the total seedJot.Screen size varied due to seed size of each variety.Seed produced in 1979 was used for the test years 1980 and 1981, and 1981-produced seed was used for the test years 1982 and 1983.The year refers to year of grain harvest.
All fields were planted in four-row plots, 10 feet long with 14" row spacing at Colby and 12" spacing at Hays.Seeding rate was constant at 850 seeds per plot, or approximately 45 lbs./acre for the control seedlots.All planting was done with a hoe-drill at normal seeding time.Each seed lot was seeded at two depths, normal and deeper to simulate more unfavorable planting conditions.Deep-seeded plots had approximately one inch more soil coverage than normally seeded plots.llesults Field emergence counts tended to favor the normal depth of planting; however, the differences generally were not significant.Greater emergence differences were observed with the small and light seed and smaller differences with the larger and heavier seed.
Yields were influenced by depth of planting and the seedlots used (Figure 1).The greatest effect on yield was a reduction of 9 bu./acre with small seed in deep-seeded plots.Large seed provided the highest yields at the normal depth of planting and heavy seed provided highest-yields at the deep planting.
Figure 2 shows the relationship of yield and seed weight for the three varieties studied.Vona yields were most influenced by seed size (as measured by seed weight, g/1000 seeds), and Eagle the least influenced.Vona also had the smallest seed of the varieties studied.Test weights and gm/1000 seeds f all seedlots of the three varieties are shown in Table Table 2 shows overall averages for yield, test weight and seed size of the five seedlots.Yield appears to be affected more by grams/ 1000 seeds than by test weight.This relationship is supported by correlation values obtained from each of the years of this study (Table 3).Grams/1000 seeds had a closer relatiGQship with yield in 4 of the 5 location years studied than did test weight.
. .Seed size has an influence on the microamp reading due to quantity of mass in the seed (Table 1) .When the effect of seed size was removed , microamp readings were strongly associated with yield (Table 3).In this study, percent seed protein did not appear to be.as important as the amount of protein per seed, again indicating importance of seed size.

Conclusions
Winter wheat yields are influenced by the quality ~~~.~ .• . .'. ~nd characteristics of the seed planted.Seed size ~)grams/1000 seeds) appears to be the most important single characteristic but test weight and protein per seed are also important.Yield differences of 10-15% were measured, with the lowest yields resulting from deep seeding depths.Small and/ or light seed always yielded less than the control, heavy or 1arge seed.An electronic seed analyzer appears to be capable of predicting relative performance of seedlots.Attention in selecting seed can help assure maximum yield of wheat.High-quality seed can be selected at present with little or no increase in seed costs.

Figure 1 .
Figure 1.Influence of seed/ots and planting depth on yield of winter wheat.

Table 1 .
Seed characteristics of three varieties of winter wheat.

Table 2 .
Overall averages • for yield, test weight and thou• sand seed weight.
'Averages for all varieties, years, seeding depths, and locations of tests .
The instrument works by measuring electrical conductivity (in microamps) of seed leachate.Higher readings indicate less seed membrane integrity and increased ionic leakage from the seed, which results in reduced germination and vigor.Lower readings are associated with high germination and vigor.