El Nino - Southern Oscillation influences on soybean yields in eastern Paraguay

Soybean (Glycine max. L. Merrill) production in Paraguay has increased dramatically during the last decade and the country is now the fourth largest soybean exporter it) the world, producing about 3% of the world's soybean production. This paper explored associations between soybean yield in eastern Paraguay and the El Nino Southern Oscillation (ENSO) phases. Historical soybean yield data front official government Sources were detrended to remove the effects of technological advances, and yield residuals were computed. In addition, differences in mean precipitation among ENSO phases were investigated under the context of crop development phases. The C soybean model Was used to simulate soybean development for two locations representing the most important soybean producing areas in Paraguay. Influences of ENSO phases on mean precipitation during planting and blooming, blooming and seed podding, and from Young pods to physiological maturity were explored through tests of differences in the central tendency. Relative yield residuals during El Nino years were Positive Six Out of seven events and varied from -9.4 to +24.2% for the 1991/1992 and 2002/2003 cropping seasons, respectively. During La Nina years, calculated residuals were negative For three Out Of four events and varied from -37.9 to +1.5% for the 2005/2006 and 1988/1989 cropping season, respectively. Analysis of precipitation records showed significantly lower precipitation levels between planting and blooming during La Nina years than during El Nino years. Differences in mean precipitation during blooming and beginning of seed formation were found to be not significant. Mean precipitation between seed podding and crop maturity was found to be significantly lower during La Nina years than during El Nino years in one of the locations studied. Copyright (C) 2007 Royal Meteorological Society.