Study of the impact of different indices associated with El Niño southern oscillation on soybean yield in Rio Grande do Sul

The main factor associated with decreaes in soybean yield in Rio Grande do Sul is the irregular distribution of precipitation and the El Nino Southern Oscillation (ENSO) is the major responsible for the precipitation variability. The aim of this work was to analyze the relationship between climatic indicators associated with ENSO and soybean yield in the State. Series of soybean yield from 87 municipalities were evaluated between 1984 and 2013. These series were ordered in three groups of similar behavior (high, medium and low yield). The mean profiles of these groups were correlated with indices for Sea Surface Temperature anomalies in the Nino 3.4 region, the Southern Oscillation Index (SOI) and the Multivariate ENSO Index (MEI) with differents lags. SOI and MEI showed higher correlations with yield in periods of higher water requirement of the crop. El Nino episodes have been associated with increased yield and in situations of neutrality and La Nina, the influence of the phenomenon is less evident. In addition, the absence of a significant correlation in the time of preparation of the crop and in the beginning of the plantation evidences the necessity of including new indices in the discussions of agricultural planning in the State.