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Managing Cover Crops for Soil Moisture Goals

Too much or too little water is typically the biggest factor limiting soybean yield. However, the vast majority of US soybeans are produced without irrigation or artificial drainage. In these systems, producers may consider using cover crops to change soil moisture dynamics and optimize soil water availability for the soybean crop.

Planting Green: Delaying cover crop termination until soybean planting or a few weeks after planting

Early Season Effects on Soil Moisture

When cover crops are actively growing in the spring, they are using soil water and therefore reducing soil moisture ahead of soybean planting. When planting green:

  • The cover crop has more time to grow and take up water (Figure 1A). 
  • Delaying termination even for just two weeks can result in substantial cover crop growth and soil drying.

Mid to Late Season Effects on Soil Moisture

After the cover crop is terminated, it forms a mulch that can help conserve soil moisture for the soybeans later in the season. This effect is greater with planting green because more biomass (mulch) is accumulated compared to when the cover crop is terminated early. Further, with planting green, the cover crop typically has a higher carbon to nitrogen (C:N) ratio, which makes for a longer lasting mulch. Planting green can mitigate soybean drought stress in mid-to-late season (Figure 1B).

A figure with 2 panels, A on the left and B on the right. In panel A there is a figure with soil moisture in % volume on the y axis and months (May through October) on the x axis. Soil moisture for the early termination treatment is signified in yellow in the graph. Soil moisture for the planting green treatment is signified in green in the graph. There is a vertical line before May that signifies the early termination timing and a vertical line just after May that signifies the planting timing. Soil moisture for both treatments is closely aligned, but was greater for the early termination treatment until June. Panel B is a graph with drought stress on the y axis and the two treatments on the x axis. the first point on the left is the early termination treatment, while the second point on the right is the planting green treatment. The drought stress value is greater for the early termination treatment.
Figure 1. Data from an experiment in Pennsylvania demonstrates that (A) planting green reduced soil moisture ahead of soybean planting, compared to when the cover crop was terminated early. Later in the season, soil moisture differences disappeared and soybean drought stress (B), estimated via grain carbon isotope composition, was lower with planting green than when the cover crop was terminated early. Adapted from Kaur.

Tips for Planting into Cover Crop Residue

  • Make planter adjustments such as using
    • Downforce
    • Row Cleaners
    • Aggressive Disk Openers
  • Roll-crimp and plant in the same direction the cover crop was rolled

Effects of termination time on soybean yield

Across 28 trials conducted in the Midwest comparing early termination and planting green and including the absence of a cover crop, there was no consistent effect (positive or negative) on soybean yield. Similarly, across 14 trials conducted in Pennsylvania, soybean yields were not different whether the cover crop was terminated early or delayed until soybean planting.

These results indicate that the decision on when to terminate a cover crop is not a one-size-fits-all but rather an adaptive decision considering field conditions, weather, and goals. 

Understanding how soil moisture and other production factors respond to cover crop management is the first step to possibly translating these responses into increased yield and/or profitability.

Other Considerations for Planting Green

Compared to early termination, planting green is often associated with:

a thermostat with a snowflake to show a cold temperature.

Cooler soil at planting, which may hamper emergence in early planting scenarios

a gloved hand pulling a plant out of the ground.

Better weed suppression, especially with summer annuals

a bottle with a N on the body to indicate Nitrogen.

Nitrogen tie-up early in the season*

A magnifying glass next to a plant in a mount of soil.

Increased seedling disease*

*Negative effects have been observed in corn but not soybeans

Key Takeaways

  • Cover crop termination time affects soil water availability for the soybean crop.
  • Compared to early termination (typically 2-4 weeks before soybean planting), planting green can help reduce soil moisture ahead of soybean planting as well as conserve soil moisture later in the crop season.
  • Cover crop termination time can impact other production factors in addition to soil moisture and producers must consider the whole system when deciding when to terminate.

Author: Daniela Carrijo, Pennsylvania State University. December 2024

Read the factsheet here.

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