South America Calling

Good weather continues for most of South America in the early portion of their very long growing season; but there are some areas that aren't doing as well as others. Assessing crop health in South America is a tricky endeavor without walking through the fields. But we can try to accomplish it using satellite data. The Normalized Difference Vegetation Index (NDVI) is one way to do so. It calculates the difference in how much visible and infrared light is reflected by vegetation and compares it to the average for this time of year. The more visible light reflected, the lower the crop health as plant material is absorbing less of it to grow.

Patches of low NDVI have shown up across portions of central Brazil and central Argentina. Brazil may be explained by the late start to the wet season rainfall and delays to the start of soybean planting. Plants are smaller than they normally would be for this time of year because of it, thus they have general low NDVI, but not extreme in too many areas outside of northern Sao Paulo, where precipitation has been more limited. The lower NDVI in Brazil may be just because plants are slower developmentally, not that they have poor health.

The same cannot be said of the patch in Argentina. The country dealt with significant drought coming out of winter and that significantly hurts wheat and early corn plants. An area from the state of Cordoba to northwest Buenos Aires -- a significant portion of the very fertile Pampas region -- is an area with perhaps spotty, but very low NDVI values. Unlike Brazil, corn and soybean planting in this region has been fairly normal as reported by the Buenos Aires Grain Exchange. In this regard, the lower NDVI values likely indicate poorer crop vigor than normal.

While October rains came in to ease a lot of the drought concerns, they did not eliminate the deep-soil moisture deficits. And over the past two weeks, rainfall has been moving through at a much slower pace. Systems came through every couple of days in October; now they stretch out to about once per week. Rainfall with these systems has been fair, but not enough to build soil moisture across a vast area. And for some areas, rains have been few and far between. Scattered showers have left some areas dry and when systems are only coming through once per week, getting missed by one system means going at least two weeks without rain.

This slower pace to storms continues as a system goes through the Pampas region of Argentina over the weekend, Nov. 16-17, then into southern Brazil for early in the week, Nov. 17-19. As the system passes through, only scattered showers are forecast for the Pampas region and some areas are bound to be drier. Pockets of dryness could start to raise concerns as corn and soybean planting continues to increase as the month passes. The next storm system may not move through until the following weekend, leaving those areas that do miss out concerned about the development of their crops.

Despite all this, the weather is still largely favorable for most areas of South America and longer-range models do show an increase in rainfall for Argentina later in November and into early December. The threat of La Nina developing in the tropical Pacific Ocean does create more concern for later in the season, as it is typically associated with hot and dry conditions for Argentina and southern Brazil.

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John Baranick can be reached at john.baranick@dtn.com

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