VARYING WINTER-WHEAT SEEDING RATES AMONG LANDSCAPE POSITIONS

Recent research in the Palouse region of eastern Washington has sugges ted that traditional seeding rates may not be adequate to maximize win ter wheat (Triticum aestivum L.) yield on all landscape positions. Low spike densities due to reduced light intensities, longer snow cover, and cool temperatures result in lower than expected yields on north-ba ckslope (N-backslope) landscape positions. The objective of this exper iment was to determine if higher seeding rates could increase spike de nsity and yield. Three seeding rates, 1.0X standard grower rate (1.0X) , 1.5X standard rate (1.5X), and 2.0X standard rate (2.0X), were teste d on toeslope, south-backslope (S-backslope), shoulder, and N-backslop es at two locations, Farmington and Pullman, WA, in 1992 and 1993. The 1.5X and 2.0X treatments were established with an additional seeding operation perpendicular to the 1.0X drill passes. Increasing seeding r ates resulted in greater spike density on all landscape positions. Spi ke density of wheat seeded at the 2.0X rate was from 11% greater on th e S-backslope to 24% greater on the N-backslope in comparison with the 1.0X rate. Yield, however, only increased on the N-backslope with whe at seeded at the 2.0X rate yielding 10.3% more than wheat seeded at th e 1.0X rate. On the three other landscape positions, a reduction in ke rnel number per spike resulted in no yield increase. Based on expected costs, the 2.0X seeding rate would increase net return on the N-backs lope by $2.35/acre given $3.55/bu wheat. Research is needed to determi ne if similar yield increases could be achieved without making a perpe ndicular drill pass to double the seeding rate, which would increase n et returns by $13.23/acre.