Rice Responses to Nitrogen Under High Solar Radiation and Intermittent Flooding in Peru1

The purpose of this study was to characterize the va. rietal responses of rice (Oryza sativa L.) to N fertiliza. tion in a tropical desert climate where extremely high N application rates are needed to attain maximum yields, Eight rice cultivars of contrasting plant type and growth duration were tested at applied N levels of 0 to 480 kg N/ha in a field experiment with an intermittently flood. ed water regime. Among the semi-dwarf cultivars, the earlier maturing 1R8' produced a maximum yield of 11.7 ton/ha at 480 kg N/ha and the later maturing '1iR5' produced a maximum yield of 9.9 ton/ha at 400 kg N/ha. Among the tall-statured cultivars of the traditional plant type, the earlier maturing 'CEL 895' produced a maxi. mum yield of 10.6 ton/ha at 320 kg N/ha and the later maturing 'Minabir 2' attained its highest yield of 7.9 ton/ ha at 400 kg N/ha. Yield responses to N were primarily a function of effective tillering capacity and not of piA cle size. Increases in dry matter- production from panicle initiation to harvest were highly correlated with grain lelds. A 0.85% N content in the above.ground parts at arvest wa- associated with maximum yields as well as a total N uptake of approximately 180 kg N/ha, suggesting the existence of an internal N requirement for rice in this environment. The apparent recovery of added N aver. aged 30%, which is considerable lower titan in constant. ly flooded environments. The results indicate that: i) the shorter the growth duration of a cultivar within a specific plant type, the higher the yields and N response; ii) the extremely high N rates required are due to high levels of N uptake and low fertilizer recovery intermittent flooding.