Sesame (sesamum indicum l.)response to nitrogen and phosphorus fertilizers as influenced by mycorrhizal infection

Response of sesame to varying rates of nitrogen (0, 100, 200 and 300 kg ha"), phosphorous (0, 50, 100 and 200 kg ha') and farmyard manure (0, 3, 6 and 9 Tonnes ha') was studied in a series of experiments conducted at University of Nairobi's Kibwezi dryland field station and at Siaya Farmers Training Centre (F. T. C.) during the short rains of November 1993 to February 1994 and the long rains of April 1994 to July 1994. In a glasshouse at University of Nairobi's Kabete field station, the influence of soil-borne mycorrhizal infection on sesame response to Nand P was examined in pot experiments. Varying levels of N (0, 0.02, 0.04, 0.07 and 0.14 g/I) and P (0, 0.13, 0.25, 0.51 and 1.01 g/I) in Hoagland solution were applied to sesame plants grown in different media namely unsterilised field soil, acid washed sand and steam sterilised field soil. The field soils were obtained from plough layer at Siaya F.T.C. The white seeded unimproved sesame landrace cultivated in Western Kenya was used in all experiments. The results showed that Nand P fertilizers and similarly farmyard manure applied in the field, did not significantly affect the yield of sesame. Nitrogen and phosphorous application to the potted plants did not significantly affect growth and biomass in the unsterilised field soil but did significantly enhance growth in the sterilised field soil and acid washed sand. Roots of plants grown in the unsterilised field soil were highly infected with mycorrhizal fungi but roots from the sterilised field soil and acid washed sand were barely infected by mycorrhizal fungi, when assessed at eight weeks after emergence. It was concl uded that the local white seeded land race was not responsive to nitrogen and phosphorous application nor to farmyard manure under field conditions due to mycorrhizal infection.