Agronomic responses of upland rice lines to two NPK application timings in a coconut-based dryland agroforestry system

Introduction Expanding rice cultivation into dryland coconut agroforestry systems may contribute to more efficient use of existing agricultural land in Indonesia. However, agronomic responses of upland rice genotypes to fertilizer application timing under these conditions remain insufficiently characterized. This study evaluated the agronomic responses of ten advanced Gamagora rice lines and the check variety Inpago 12 to two NPK application timings. Methods A site- and season-specific field study was conducted in an open area within a mature coconut plantation landscape in North Halmahera, Indonesia. A low-input compound NPK fertilizer rate (100 kg ha -1 of NPK 15:15:15) was applied once at either 14 or 35 days after sowing (DAS). Agronomic traits and grain components were evaluated under both application timings, whereas harvest-plot grain yield was assessed only under the 14 DAS treatment. Results Genotypes exhibited distinct responses to the two fertilizer application timings for traits measured under both treatments, including differences in grain number and grain-filling characteristics among several Gamagora lines. Under the 14 DAS treatment, grain productivity differed among genotypes, with Gamagora 7 (1.41 t ha -1 ) and Gamagora 9 (1.40 t ha -1 ) among the better-performing lines under the evaluated site and season. Discussion The results identify genotype-specific agronomic responses to the two tested NPK application timings but do not establish an optimum fertilizer schedule or support a yield-based fertilizer-timing recommendation. Further multi-season and multi-location studies, including complete yield measurements under all fertilizer treatments and appropriate control treatments, are required before broader agronomic recommendations can be made.