Cover Crops May Protect Corn From Cooler Temperatures

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu and Cory Whaley, Agriculture Agent, whaley@udel.edu

The weather outlook in Georgetown includes no air temperatures (currently) in the 30s through April 21st. With that outlook, soybean and corn planting can probably start next week. Although there can still be a random late freeze, the probability really drops after April 15th in our region.

The preferred soil temperature for corn germination is 50°F, which allows the seed to begin root and shoot growth. Many of the weather stations on DEOS have soil temperature as an option, so you can track current conditions. Since April 1st, soil temperatures have ranged from 47-53°F in Newark and 47-55°F in Georgetown. Soil temperature does not change as rapidly as air temperature, so we would expect the daytime temperatures over the next week to keep soils above 50°F, even when nighttime temperatures dip into the 40s.

 

Figure 1. Fully exposed corn had more visible damage than corn planted into standing rye.

Figure 1. Fully exposed corn had more visible damage than corn planted into standing rye.

 

However, if soil temperatures at your closest weather station are barely above 50°F, germination will still be delayed and won’t necessarily get you ahead. Over the past two seasons, corn in Georgetown has taken 10 to 13 days to emerge when planted April 21st– 24th and only 5-9 days to emerge when planted mid-May.

If balancing multiple fields and crops requires earlier planting, selecting well-drained soils may provide warmer soil temperatures. Cover crops may also benefit earlier planted fields. In May 2020 cold temperatures (33-35°F) caused damage to plots at the Carvel Research center, but corn at V1-V2 appeared to be protected by cover crop residue (Figure 1). Using drone imagery, ground cover (measured by NDVI) was lowest in plots with no cover crops over the entire growing season. This difference was mostly apparent in June (cover crop NDVI = 0.5, no cover crop =0.35), revealing slower growth in plots without cover crops. Final yields in plots with no cover crops were also 20 bushels lower. This does not mean that cover crops could protect from temperatures reaching 28°F but may point to protection from frosts when temperatures are in the low 30s. So, if you are going to plant early, cover crops may provide extra protection from cold temperatures. This does not eliminate the need to consider previous slug damage in fields with cover crops, which may also cause a reduction in yield.

Print Friendly, PDF & Email