A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF CROP SCIENCE OF SOKOINE UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA.Performances of three sorghum (Sorghum bicolor L. Moench) genotypes (Wahi, Hakika and Pato) and inorganic soil amendments were studied under naturally Striga asiatica [L.] Kuntze infestation for one cropping season (2015/16) in two locations, using a split plot design laid out in a randomized complete block design with four replications. A susceptible sorghum (Pato cultivar) was used as a bioassay to evaluate the effectiveness of reduced rates of N under Striga infestation. At Hombolo, 40 Kg N/ha had significantly (P< 0.05) lower emerged Striga shoots count/m2 than all other rates of N, except at 11 WAP. Yields with 30 Kg N/ha (0.64t/ha) was significantly (P< 0.05) lower than yields from all other rates of nitrogen (1.08 - 1.52t/ha). At Ngamu, fertilization played no significantly (P< 0.05) role in Striga emergence and attachment. Yields with 10 Kg N/ha (4.89t/ha) was significantly (P< 0.05) lower than yields from all other rates of nitrogen (5.2 – 6.0t/ha). Across locations, variety Hakika had significantly (P< 0.05) fewer emerged Striga shoots count/m2 compared with varieties Wahi and Pato. At Hombolo, Yields on Hakika variety (0.96t/ha) was significantly (P< 0.05) lower than the yield in all other varieties (1.21 - 1.28t/ha). At Ngamu, variety Pato gave more yields (7.21t/ha than other varieties (2.81 – 5.95t/ha). This study showed that the most effective rates of nitrogen; 40 and 60 Kg N/ha (Hombolo) and 50 Kg N/ha (Ngamu) should be promoted in semi-arid areas of Tanzania where Striga poses a serious threat. Results also showed that varieties Hakika and Wahi proved their resistance/ tolerance to Stiga asiatica compared to variety Pato.