Influence of White Clover Traits on Biomass and Yield in Winter Wheat- or Winter Oilseed Rape-Clover Intercrops

The potential to use differences in traits of white clover (Trifolium repens L.) varieties to improve mature yield of winter wheat or winter oilseed rape (Brassica napus L.) sown in white clover living mulch was studied in two field experiments conducted in Southern Sweden. The clover varieties Sonja, S184 and AberCrest, differing in leaf size and winter hardiness, were undersown in spring barley. Three consecutive crops of winter wheat or one crop of winter rape sown at two densities followed the barley. In the first year, the mature yields of wheat and high density rape equalled yields without white clover when AberCrest was used, while Sonja reduced the wheat yield by one third and the rape yield to nothing. S184 was intermediate. White clover increased yields by 14–19% in the second wheat crop, but had no effect in the weed infested third wheat crop. The average amount of white clover at flowering of wheat was always largest with Sonja, which increased its biomass earlier in spring than AberCrest. It was concluded that white clover traits are important when developing the intercropping system for large mature yields, especially when herbicides are avoided.