Use of chlorophyll meter sufficiency indices for nitrogen management of irrigated rice in Asia

Low N fertilizer recovery efficiency (RE) remains a problem in rice (Oryza sativa L,) production in Asia. The chlorophyll meter has been shown to iden tify when rice is in need of a N top-dressing, that if applied would result in greater agronomic efficiency (AE) of N fertilizer than commonly practic ed, pre-set timing schemes, Critical chlorophyll meter readings have been u sed to match N top-dressing with plant demand for the cultivar IR72, but fi xed critical readings may not apply to multiple cultivars and locations. Ou r objective was to test the approach of using sufficiency indices, calculat ed from chlorophyll meter readings relative to well-fertilized reference pl ots, with several rice cultivars in the Philippines and in India by compari ng with local fixed N timing recommendations. Chlorophyll meter readings we re significantly affected by N management practice, cultivar, and time of a pplication at both locations. Similar rice yields were produced with chloro phyll meter sufficiency indices compared with the fixed N timing treatment with 30 kg less N ha(-1) in the wet season in all cultivars at both locatio ns. Compared with fixed-timing, 45 kg less N ha(-1) was used with the chlor ophyll meter in the Philippines dry season without a yield reduction in thr ee of four cultivars. In conclusion, chlorophyll meter sufficiency indices identified when several rice cultivars at two locations needed a N top-dres sing, which resulted in greater AE of N fertilizer than local, pre-set spli ts.