Plot direction and spacing effects on interplot interference in spring wheat cultivar trials

Interplot interference can distort treatment estimates when genotypes diffe r for height. Two field arrangements were examined to determine if interplo t interference could be reduced. One arrangement compared north-south vs. e ast-west row direction at Saskatoon in 1995 and 1996. The other experiment investigated the effects of separating plots with a row of spring-planted w inter wheat (Triticum aestivum L.) at Regina and Swift Current in 1995 and 1996. Interplot interference was evaluated with two spring wheat cultivars differing for height, Oslo (short) and Glenlea (tall). Interplot interferen ce caused a 12% yield reduction in Oslo in the north-south rows, which was significantly greater than the 7% yield reduction in the cast-west rows. Th e 7% yield reduction when spring-planted winter wheat separated the plots w as significantly less than the 18% yield reduction when plots were adjacent . This study was conducted at fairly high latitudes and the conclusions sho uld be restricted to higher latitudes. We conclude that spring wheat field trials with plots differing for height may have less Interplot interference if rows are oriented east-west and separated with winter wheat.