Effects of Cultivar Mixtures, Fertilizer, and Plant Density on Grain Sorghum (Sorghum bicolor) / Striga hermonthica Relations

Increasing plant density of grain sorghum [Sorghum bicolor (L.) Moench.] from 57100 to 114300 plants/ha had no significant effect on grain yields, but significantly increased Striga hermonthica (Del.) ‘Benth’ # STRHE shoot yields by 49% in S. hermonthica infested soil of the Sudan. Addition of urea at 43, 86, and 172 kg N/ha increased grain yields by 14, 25, and 45%, respectively, above the control and S. hermonthica shoot yields were reduced by 14, 21, and 35%, respectively, below the control. Although average grain yields in 1981 were 77% less than in 1980, S. hermonthica shoot yields were significantly increased by about sixfold. Grain sorghum yields of pure stands were not consistent over both years. In 1980, the cultivar ‘Ariana’ outyielded ‘Tetron’, but in 1981 the reverse occurred. However, in both years, the 50:50 mixture of both cultivars gave intermediate grain yields. While pure stands of Tetron’ sustained the lowest infestations of S. hermonthica and ‘Ariana’ had the greatest, the mixture had intermediate infestations which were on average 31% less than those of ‘Ariana’. Thus, the results suggest that the cultivation of equiproportional mixtures of relatively resistant and susceptible grain sorghum varieties, coupled with the use of high rates of nitrogenous fertilizer and wider inter- and intra-row spacing, may be a better cultural practice under dense striga infestations.