RESPONSE OF NERICA AND SATIVA RICE LINES TO NITROGEN AND PHOSPHORUS RATES BY NUMBER OF TILLERS AND SHOOT BIOMASS YIELD

An experiment was conducted at the Savanna Agricultural Research Institute on a Euteric Gleisol on latitude 9-25-41” N longitude O-58’ 42”W in the Guinea Savanna Zone of West Africa, Ghana. The objective was to establish the responses of the lowland “New Rice for Africa” (NERICA) and Sativa varieties for recommendation of optimum N and P rates. Six lowland NERICAs, three Oryza sativa

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and one Oryza glaberima were used. Number of tillers/m² quadrant and shoot dry biomass /15cm² was used to evaluate the P/N response of crop performance. For the dry biomass weight, destructive sampling was done at the 50% flowering stage. The Phosphorus and Nitrogen fertilizers rates were 0, 13, 26 kg P/ha and 0, 30, 60, 120 kg N/ha respectively. Potassium was applied at a uniform rate of 30 kg K₂O/ha to all plots before planting. The average days of 50% flowering and 80 % maturity of all varieties used, counting from seedling emergence, were 73 to 82 days and 104 to 113 days respectively. There were significant differences on the effect of P and N-levels on shoot –biomass/15 cm² quadrant (p< 0.05) but number of tillers/ m² quadrant were not (p > 0.05). The interaction of P/N fertilizer levels by variety was highly significant (p < 0.001). Increasing N levels increased biomass and tillers more markedly than increasing P-levels. It was noted that P may have been fixed because available Bray 1 P was not appreciably higher in the 26 kg P/ha plots than 0 kg P/ha. It could have been due to the oxidation of Iron (II) to Iron (III) resulting in insoluble Iron (III) Phosphate complexes or by formation of complex insoluble Aluminium (III) phosphates. Varieties such as V1, V2, V3, V8 and V9 were responsive to lower P and N inputs such as P0/N0 or P0/N30 and also to moderate inputs such as P13/N30, P26/N30 or P13/N60. Varieties such as, V4, V5 and V6 are not responsive to lower inputs but were very responsive to the higher inputs outlined above. Phosphorus and Nitrogen main plots pool for two years at high input rate, (P26/N60 and P26/N120), has no significant advantage over the lower (P0/N0 or P0/N30, P13/N0, P13/N30) and moderate combinations, (P13/N60, P13/120) as regards biomass yields (p .> 0.05).