Response of traditional and improved upland rice cultivars to N and P fertilizer in northern Laos

Upland rice is typically grown under slash-and-burn systems in the mountainous regions of northern Laos by resource-poor farmers for subsistence. Upland rice cultivars are all traditional and no fertilizer inputs are used. In these systems, grain yields average only 1.7 t/ha. A multi-site experiment was conducted in Luang Prabang province to examine cultivar and fertilizer effects on grain yield. Three traditional and three improved cultivars were grown under four fertilizer treatments: no added fertilizer, nitrogen only (N; 90 kg N/ha), phosphate only (P; 50 kg P/ha), and N and P (NP) at three locations. No severe water stress developed at any location.The two improved cultivars, IR55423-01 and B6144-MR-6-0-0 out-yielded traditional cultivars in all locations and fertilizer treatments. They had higher total dry matter and harvest index, lower plant height and more panicles than traditional cultivars. N fertilizer application increased grain yields of the two improved cultivars from 3.1 to 4.0 t/ha while increasing those of traditional cultivars from 1.6 to 1.9 t/ha. Applying only P gave no effect on grain yield, and applying P with N increased grain yield only by 0.5 t/ha over N application alone on average over all cultivars at all locations. However, there was cultivar and location difference in the yield response to P applied with N. Further studies are required on the genotype-by-environment interaction in the effect of P applied with N under upland conditions. These results indicate that upland rice cultivars with high HI, which have been selected under favorable conditions, can perform well under low fertility conditions but also respond well to applied N fertilizer.