Characterizing nitrogen response of upland rice in an acid upland soil
2001
Magbanua, R.D. (International Rice Research Inst., DAPO Box 7777, Metro Manila (Philippines)) George, T.
Unlike traditional upland rice, improved upland rice cultivars are high yielding but they require more nutrients, especially N. However, not much information characterizing the N response of upland rice is available. To describe the response of improved upland rice genotypes to applied N, experiments were conducted in two consecutive wet seasons in an acid upland in Siniloan, Laguna, Philippines. Treatments were four genotypes and five fertilizer levels in 1999 and five genotypes and four N levels in 2000. Cultivars UPLRi 5 and IR55423-01 were common to both years. Designated N fertilizers were split into weekly application and were applied starting 2 weeks after emergence up to 2-3 weeks after flowering. Yields were generally high in 2000: average grain yields varied among cultivars from 1.3 to 1.6 t/ha in 1999 and 1.4 to 3.4 t/ha in 2000. Response to N was observed in the higher yielding 2000 season, but cultivars differed in the nature of their response to N, namely, 1) low-yielding, non responsive, 2) high-yielding, non responsive, and 3) high-yielding, responsive. Both UPLRi5 and IR55423-01 yielded high in 2000: yield with no applied N were 3.2 t/ha and 2.8 t/ha, respectively. Only IR55423-01 responded to applied N, yielding 4.0 t/ha. Results indicate that the differential behavior of cultivars between and within years needs to be further investigated to develop appropriate N management strategies
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