Authors: Ignacio A. Ciampitti, Mary Knapp

Temperatures fell below freezing in parts of Kansas on Oct. 13 (Figure 1). Temperatures were well below freezing in north central Kansas and some areas of the central section of Kansas. This situation will shorten the grain filling period for grain sorghum that is not yet mature, and impact immature soybeans, which could be an issue especially for double crop or late-planted beans.

Low temperatures on Oct. 13 were close to or above 40 degrees F in the southern part of the state.

As discussed in an article in last week’s Agronomy eUpdate, the risk of damage to summer row crops is a function of the current developmental stage of the crop as well as the minimum temperature and the duration of the cold temperatures.

Figure 1. Lowest minimum temperatures measured on October 13.

The coldest temperatures on Oct. 13 were observed in the north central part of Kansas, with a duration of more than 4 hours (Figure 2). The freeze also extended to central and western areas of the state and also east to the counties of Republic, Marshall, Nemaha, Clay, Riley, Brown, and Doniphan. The duration of the sub-freezing temperatures varied from 2 to more than 4 hours.

For double crop or late-planted soybeans, exposure to temperatures below 32 degrees F will end grain filling if not yet mature, affecting test weight and seed quality (primarily protein levels). As the crop approaches maturity, the impact of a freeze event on soybean yields declines.

Figure 2. Total hours of air temperatures below 32 degrees F measured on October 13.

For grain sorghum, just more than 50% has reached maturity in the North Central District. Therefore, the probability of some sorghum being impacted and yields affected is high for this area. Temperatures below 32 degrees F will interrupt grain filling, impacting seed size (test weight) and seed quality, and make the harvest process more difficult (slowing the drying down process). A freeze at the soft- or hard-dough stage (before grain matures) will result in lower weight and chaffy seeds.

As with soybeans, the impact of a freeze event on grain sorghum yields declines as the crop approaches maturity.

Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist

Mary Knapp, Weather Data Library