Factors affecting rice yield and fertilizer response in rainfed lowlands of northeast Thailand

Rice-based (Oryza sativa L.) rainfed lowlands are the major cropping system in northeast Thailand. Earlier research on nutrient management of rainfed lowland rice produced conflicting results with respect to inherent soil fertility, fertilizer response, and the importance of organic fertilizers. most probably because of highly variable soil quality and water resources. The objectives of this paper were to advance the understanding of soil fertility and fertilizer response in northeast Thailand and thereby provide a basic framework for improved nutrient management of rainfed lowland rice. For this purpose, we analyzed an existing database on fertilizer trials conducted between 1995 and 1997 at eight different sites in northeast Thailand, which were previously described by Wade et al. [Wade, L.J., Amarante, S.T., Olea, A., Hampichitvitaya. D., Naklang, K., Wihardjaka, A., Sengar, S.S., Mazid, M.A., Singh, G., McLaren, C.G., 1999a. Nutrient requirements in rainfed lowland rice. Field Crops Res., 64, 91-107]. Average annual rainfall across sites and seasons was 1300 rum, but half of all rainfed trials (12 of 23) experienced substantial water stress during the growing season. Average grain yield in N-omission plots was low (1.6 t ha(-1)), even when compared with that of rainfed lowlands in neighboring Lao PDR. Nitrogen was clearly the most limiting element, whereas PK treatments increased yields significantly in only 6 out of 78 observations. Average agronomic efficiency of applied N was good ( 16 kg grain kg 1 N). but highly variable among sites. Two groups of soils (i.e., sites) were separated because of their distinct differences in reaction to inorganic and organic fertilizer. Better nutrient availability improved crop performance at all field water stress levels occurring at the trial sites. However, yield reductions caused by water stress seemed to interact with the level of nutrient supply, that is, absolute yield differences between different fertilizer treatments decreased with increasing water stress. We concluded that efficient fertilizer use in rainfed rice of northeast Thailand can be achieved, but that existing uniform recommendations do not provide farmers with much useful advice. Therefore, we proposed a set of basic guidelines for improved nutrient management, which, after further efforts of all stakeholders involved, could contribute to increased system productivity. (c) 2006 Elsevier B.V. All rights reserved.