Lowland rice improvement in northern and northeast Thailand 2. Cultivar differences

Seven rice experiments were conducted each with 4-6 cultivars to determine if cultivars differed in response to fertiliser and irrigation application in lowland conditions in Thailand. Severe drought did not develop in any of the experiments, but irrigation and fertiliser application increased the yield in most experiments. There were significant cultivar differences in each experiment and cultivar ranking was consistent across experiments. Thus W57514-PMI-5-B-1-2 out-yielded traditional cultivars KDML105 and NSG19 in most environments, except in very unfavourable conditions where mean yield was below 1000 kg ha(-1). Quick maturing cultivars yielded least because they produced less total dry matter than later maturing cultivars in most environments. Recently developed cultivars had higher harvest index compared to traditional cultivars. In some experiments there were significant cultivar-by-fertiliser or cultivar-by-irrigation interactions. In one experiment, IR20 was more sensitive to soil water deficit than other cultivars whereas response to fertiliser was greatest in IR57514-PMI-5-B-1-2. Overall, however, experimental conditions were favourable and under these conditions these interactions were small. It is, therefore, concluded that cultivars selected under high fertiliser and irrigated conditions are likely to perform better in all but most unfavourable growing conditions. (C) 1998 Elsevier Science B.V. All rights reserved.