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

The purpose of this study was to characterize the varietal responses of rice (Oryza sativa L.) to N fertilization 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 flooded water regime. Among the semi-dwarf cultivars, the earlier maturing ‘IR8x2019; produced a maximum yield of 11.7 ton/ha at 480 kg N/ha and the later maturing ‘IR5’ 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 maximum 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 40 kg N/ha. Yield responses to N were primarily a function of effective tillering capacity and not of panicle size. Increases in dry matter production from panicle initiation to harvest were highly correlated with grain yields. A 0.85% N content in the above-ground parts at harvest was 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 averaged 30%, which is considerable lower than in constantly 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.

Key Words: Plant type • Growth duration • N uptake • N fertilizer efficiency • Internal N requirement

² Associate Professor of Soil Science and Coleader National Rice Program, North Carolina State University, Raleigh, N. C. 27607; and Soil Specialists, National Rice Program, Centro Regional de Investigaciones Agropecuarias del Norte, Ministerio de Agricultura Zona Agraria II, Lambayeque, Peru.

Received for publication June 28, 1972.