Temporal variability of ENSO effects on corn yield at the central region of Argentina
The yield of corn is strongly affected by climatic conditions during the growing season. In the central region of Argentina, this crop is mainly managed under rainfed conditions. Hence, in most years, it is subjected to drought at some period during the growing season. El Niño Southern Oscillation (ENSO) is known to influence rainfall in this region, mainly during the warm semester, hence affecting summer crops yields. This study assessed the relationship between ENSO [analysed through the June–July–August Oceanic Niño Index (JJA-ONI)] and corn yields in the provinces of Buenos Aires, Entre Ríos and Santa Fe, which is the main corn-growing area in Argentina. This was performed for two contrasting periods regarding technology applied in the agricultural sector: 1972–1991 and 1992–2012. Remarkable increases in corn yield between periods were found for the entire region. Except for the province of Entre Ríos, we found statistically significant differences between periods in the trends of corn yield by performing the Chow test. Significant correlations (P < 0.01) between the JJA-ONI and corn yield were found in many counties of Buenos Aires, Entre Ríos and Santa Fe provinces. The correlation was higher in the second period for most counties. We consider that two hypotheses could explain this correlation increase: (1) in previous decades the best growing seasons (from a climatic point of view) were not fully exploited because of a low use of inputs and technology; and (2) the correlation between the ONI and rainfall could have increased in the last decades. We confirmed the latter hypothesis with rainfall data from conventional meteorological stations of 11 locations of the region under analysis. The JJA-ONI assessed in this research is available before farmers make their most relevant corn management decisions (fertilizer dose, sowing date, density, etc.), thus making this index highly valuable.