Planting green ‘a work in progress’

HARRINGTON, Del. — Planting green, the practice of delaying cover crop termination until after planting the season’s cash crop, has gotten more attention in recent years as a method of weed suppression and adding biomass to the soil.
As with any new system, there are still a lot of kinks to work out. In the agronomic session of Delaware Ag Week, Dr. Eugene Law, a postdoctoral researcher stationed in USDA’s Beltsville, Md., research station, shared data and observations about planting green and managing pests.
In this three-year “Common Experiment 2”, through the national network, Precision Sustainable Agriculture, agronomists, pathologists and entomologists were involved in strip trials conducted with cover crops on 233 plots in 17 Eastern states, including Delaware, Maryland and Virginia.
Results of the delayed termination include more biomass and more effective pest management, Law said.
In a survey done in 2019-20, 70 percent of farmers observed improved weed control, 68 percent saw improved soil moisture conditions, 27 percent had improved disease management and 17 percent saw improved slug management.
Tests were done with soybeans first, Law said, because there was less concern about stand density since soybean plants can fill in voids in the row. Soybeans are more adapted to environmental stress and there is greater need for weed suppression.
Caution was called for with corn because population loss is yield loss, Law continued.
A corn crop also requires an estimate of nitrogen credits/debits and faces greater risk of early season pests, particularly invertebrates.
The design of the experiment with cereal rye termination called for four treatments: no cover crop, 14-21 days pre-plant; three to seven days pre-plant; and one to three days post-plant.
“We measured biomass at termination,” Law said. “The later we planted, the more biomass.”
In Delaware, Maryland and Virginia, biomass was more than double at three to seven days pre-plant compared to the earlier termination and more than three times as much at three to seven days post-planting.
Observations with corn seedling disease revealed planting green — termination three to seven days post-planting — resulted in more radicle root rot in most locations. There was greater root rot associated with Pythium populations on radicles and seminal roots. Precision planting cereal rye (more than 19 centimeters spacing away from the corn row) can reduce root rot incidence.
Planting green resulted in less corn stalk rot than having no cover crop in most locations.
Slugs can be a big problem. They feed on the cover crop residue, and without a gap in available plants, move on to eat corn plants.
However, part of the experiment was to quantify both bad and good bugs. The higher slug activity and damage incidence when planting green was offset by higher predation rates in the Mid-Atlantic States.
As for weeds, there were significant reductions in weed density with later termination of the cereal rye cover crop. Lower weed biomass was seen than with no cover crop, but not at 14 days pre-plant.
There were no yield increases observed with green planting. There were a few instances in yield drag in the Mid-Atlantic though this was more common in the Midwest, due to precipitation and moisture, Law said.
In summary, Law said planting green does increase cover crop biomass; risks greater incidence of root rot; shows evidence of top-down control of pests; and shows reductions in weed pressure relative to fallow but not at 14 days pre-plant. Yield drag was not observed in corn in the Mid-Atlantic, but can be variable, he added.
Law said future work will address these questions:
Does delaying cover crop termination increase the number of spring field working days?
Can the risk of water-related yield drags be offset by long-term gains in yield stability due to soil health improvement?
Can the risk of water-related yield drags be offset by cost savings from reduced pesticide inputs?
“It’s still a work in progress,” he said. “We need a couple more years to experiment.”