Abstract:
Rice Yellow Mottle Virus (RYMV) is the most important pest constraint of rice in Tanzania and other sub Saharan Africa countries. Fertilizer management is recommended to minimize incidence and development of the disease in affected rice ecosystems. Field research was carried out in the 2014 cropping season at Sokoine University of Agriculture to determine the effect of nitrogen fertilizers on the development of RYMV and grain yield of rice. Split-split plot in a randomized complete block design (RCBD) with three replications was adopted. Three RYMV inoculated rice cultivars namely Mwangaza (R), Salama (MR) and Supa (S) were fertilized with four different types of nitrogen fertilizers (DAP, NPK, SA and Urea) each at two levels (100kgN/ha and 120kgN/ha). Urea was applied in split and single dose. Significant differences for area under disease progress curve (AUDPCs) (P<0.05) were detected among the varieties, nitrogen fertilizers and their interactions. The variety Supa had the highest mean AUDPC (100.6) followed by Salama (51.7) and Mwangaza (30.8). Single dose Urea application had highest disease levels (62.9 AUDPC) followed by NPK (60.1), DAP (59.8), SA (60.0) and split urea (59.9) (P<0.05). Nitrogen fertilizer at higher levels did not show significant effect on the development of RYMV (p≤0.05). The effect of nitrogen fertilizers on disease develop-ment depended on genotype. Yield was significantly affected by variety, type and amount of N fertilizer and their interactions (P<0.05). The variety Mwangaza had the highest grain yield (3.9ton/ha) followed by Salama (3.0ton/ha) and Supa (2.1ton/ha). Yield was highest with NPK (3.6ton/ha), DAP (3.5ton/ha), SA (3.5ton/ha) and split Urea (3.6ton/ha) and lowest was with Urea single dose (2.8ton/ha). Treatment with 120kgN/ha gave higher grain yield than 100kgN/ha. Urea decreased RYMV significantly but should always be applied in splits in order to fully utilize its potential for reducing RYMV and maximizing yield of rice.
