Undersowing wheat with annual legumes: Effects on wheat yields and legume seed yields in the south-eastern wheat belt of Western Australia

Ten annual Trifolium and Medicago cultivars were sown at low (1-6 lb an acre) and high (3-18 lb an acre) seeding rates with wheat crops in five trials in the south-eastern wheatbelt of Western Australia. Wheat and legume seed yields from these mixed stands were compared with stands of the same rates of wheat and legume sown alone. Sowing the legumes with the crop reduced wheat yields by from 7.4 bushels an acre (25 per cent) in one trial to 1.5 bushels an acre (5 per cent) in another. The evidence did not suggest which factors caused the different response. Legume seed production under the crop was severely reduced in all trials. In 30 of the 44 comparisons made it was reduced by more than 50 per cent, and in 13 cases by more than 75 per cent. In 9 cases the amount of seed set under the crop was less than 30 lb an acre. In most cases trebling the amount of legume seed sown under the crop greatly increased legume seed yield but caused only a small (less than one bushel per acre) further decrease in wheat yield.