Responses of upland nerica rice to nitrogen and phosphorus in forest agroecosystems
New Rice for Africa (NERICA) cultivars are widely adopted interspecific crosses between Oryza sativa and O. glaberrima but their responses to fertilizer was not known. In 2004 and 2005, four released NERICAs (NERICA 1, 2, 3, 6) under two levels of phosphorus (0 and 2.6 g m–2) and four of nitrogen (0, 3, 6, and 12 g m–2) were evaluated on an acid Typic Haplustult at Ikenne (6°54' N, 3°42' E) in the Nigerian forest agroecosystem. In 2004, averaged over N levels, NERICA 3 attained physiological maturity most quickly (92 days after seeding [DAS]) at 2.6 g P m–2. But under drought stress (2005), although NERICA 3 was the first to initiate panicles (49 DAS) and to reach midflowering (73 DAS), maturity was delayed until 100 to 101 DAS with or without P. Also, in 2005, NERICA 6 took a much longer time to mature (110–111 DAS) than the other cultivars. Therefore, NERICAs 3 and 6 were the least suitable cultivars for low-input, drought-prone environments. At low N of 3 g m–2 and zero P, paddy yield was highest in NERICA 1. With application of 12 g N m–2, NERICA 1 also yielded 20 to 41% more than the others, implying that it had a potential for tolerance to low N and was the most N-responsive among the cultivars evaluated under limited P. Moderate levels of N (6 g m–2) and P (2.6 g m–2) are recommended for NERICAs in smallholder low-input production systems.