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.

玉米产量深受生长季节气候条件的影响。在阿根廷中部地区，该作物主要在雨养条件下进行管理。因此，在大多数年份，生长季节的某个时期会受到干旱的影响。已知厄尔尼诺南方涛动（ENSO）会影响该地区的降雨量，尤其是在暖季，从而影响夏季作物的产量。本研究评估了ENSO（通过六月、七月、八月海洋尼诺指数（JJA-ONI）分析）与阿根廷布宜诺斯艾利斯、恩特雷里奥斯和圣菲省的玉米产量之间的关系，这些省份是阿根廷主要的玉米种植区。这项研究分别针对农业部门应用技术的两个对比时期进行了：1972年至1991年和1992年至2012年。在整个地区发现了玉米产量在这两个时期之间显著增加。除恩特雷里奥斯省外，通过进行Chow检验，我们发现玉米产量的趋势在这两个时期之间存在统计学上的显著差异。在布宜诺斯艾利斯、恩特雷里奥斯和圣菲省的许多县，JJA-ONI与玉米产量之间存在显著的相关性（P < 0.01）。在大多数县，第二时期的相关性更高。我们认为有两个假设可以解释这种相关性增加：一是由于对投入和技术的低使用率，在过去的几十年中，最佳的生长期（从气候角度来看）并未得到充分利用；二是ONI与降雨量之间的相关性可能在过去的几十年中有所增加。我们通过分析该地区11个地点的传统气象站的降雨数据证实了后一个假设。本研究评估的JJA-ONI在农民做出最相关的玉米管理决策（如施肥量、播种日期、密度等）之前即可获得，因此，该指数具有极高的价值。