Weather-Station Data Shows Risk to Argentine Soybeans

Unseasonably cold weather hit parts of Argentina’s soybean-growing regions, bringing some light frosts that could delay the plants’ development. Soybeans in the Southern growing province of La Pampa and Buenos Aires experienced near freezing temperatures. The Feb. 26 temperature in the city of Bahia Blanca was the lowest on record for that day since 1956, according to NOAA/NCDC’s GHCN daily weather-station data. It was the lowest temperature in at least 20 years for any day in February.

The graph on the left shows daily observed minimum temperatures at the Bahia Blanca weather station over 20 years stacked together so as to compare calendar days. The darker blue line shows 2019 values, and Feb 26. 2019, stands out at 2.5 degrees Celsius. The graph on the right shows dry areas across the Southwestern part of the primary crop regions.

The region’s relatively dry soil magnified the impact of the colder than normal temperatures. The soybeans are mostly in the pod-filling stage, which is a vulnerable part of the growth cycle. Although the minimum temperatures did not quite get cold enough for long enough to cause serious damage, pod filling and development could be delayed and possibly impacted.

Temperatures just below 0 degree Celsius can damage leaves. The soybean plant is somewhat more tolerant to freezing than other crops such as corn. A light frost is likely to only damage the leaves in the upper canopy of the plant. A thick canopy can retain heat radiating from the soil, especially if it’s moist, and keep the lower portions of the plant a few degrees warmer. Pods and seeds can continue to develop with minimal impact on yields. Temperatures a few degrees below zero for an extended period can damage stems, pods, and seeds, significantly impacting yield. An example of a killing freeze occurred in Northern US states during late August 2004. It resulted in multidecade lows for soybean yields in many counties. Argentina’s recent weather in soybean-growing regions was far from that severe, but daily minimum temperatures are important to monitor as early frosts can negatively impact crops before they are fully mature. Farther south there were reports of sub-zero temperatures in Rio Colorado province. The frost damaged horticulture there, including pumpkins, tomatoes, peppers, and other fruits and vegetables.

Daily minimum temperatures for Argentina are obtained from GHCN, or Global Historical Climatology Network, a new data source added to the Gro database. It provides daily observations of climate, including daily rainfall, minimum and maximum temperature, and snowfall, from more than 75,000 weather stations in roughly 180 countries, with some archive records dating from 1763.