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'Planting Green' Has Advantages if Done Correctly

by Brook Wilke
Kellogg Biological Station farm manager

Published: Friday, January 22, 2021

The following is from Brook Wilke, Kellogg Biological Station farm manager.

A recent trend among no-till and organic crop producers is to plant corn and soybeans into living cover crops, and then terminate the cover crops during or after planting. This practice has become commonly known as "planting green" and can provide a number of benefits including weed suppression, soil moisture management and soil health improvement.

Similarly, skeptics might also point out a number of potential drawbacks to planting green as well. But by recognizing these challenges and managing for them, this practice can be successfully adopted.

Perhaps the most commonly used scenario is to plant soybeans into a cereal rye cover crop that was seeded the previous fall. Organic farmers pioneered this particular practice decades ago in an attempt to include more no-till practices in organic crop systems, but recent development of herbicide-resistant weeds has led to renewed interest among conventional farmers as well. We've been able to explore this practice over the past couple of decades at the Kellogg Biological Station and are excited to share some observations that may be relevant if you are considering "planting green."

If weed control is your primary objective, prioritize the cereal rye cover crop to obtain a good stand with vigorous spring growth. A dense cereal rye "mat" is necessary to reduce weed pressure for an extended period after planting. Even though cereal rye can survive the winter when planted very late in the fall, earlier fall planting will lead to more spring biomass.

Plant a minimum of 60 pounds of rye seed per acre, but up to 100 pounds per acre can be justified, especially if aerial or broadcast seeding is used. You may also consider fertilizing the rye with manure or a moderate amount of synthetic nitrogen to boost the rye biomass.

Organic farms must allow the rye to reach the heading stage in order to kill it by roller/crimping or mowing. However, conventional farms have a wide range of possible termination times depending on planting goals and weather opportunities. In other words, you can plant green when the rye is 6 inches tall, or 60 inches tall, or anywhere in between, and terminate the rye with a herbicide after planting.

In general, the larger the rye gets, the more challenging it is to manage, but the greater the potential benefit becomes.

The benefits of allowing the cereal rye to reach the heading stage include soil resilience to heavy rain events after planting (a.k.a. less soil crusting), reduced weed pressure in the soybean crop, moisture reduction at planting time, moisture retention later in the season and taller soybean plants. In extremely wet spring conditions, a dense stand of cereal rye can remove soil moisture and provide some support for equipment that allows fields to be planted that would otherwise need to be left fallow.

There are also several challenges or drawbacks to letting the rye grow tall and dense before planting and termination, including: delaying soybean planting which may reduce yield potential in some years, rye residue can be a challenge at harvest time (e.g. plugging up in combine header), reduced soil temperatures at planting, and difficulty closing the seed trench during planting.

Luckily, soybeans can produce surprisingly high yields from low populations, so some stand loss due to problems at planting may not substantially reduce yield.

Armyworms feed heavily on cereal rye and may attempt to eat the soybeans after the cereal rye is dead. However, soybeans are not a sustainable food source for armyworms and any damage to the young soybean plants is not expected to affect yield. If you observe this temporary feeding on the soybeans, don't rush to apply an insecticide.

If the rye is terminated early, there is no need to further manage the residue. However, there are additional benefits from knocking down the rye with a cultipacker, roller, roller/crimper or mower if you allow it to reach the heading stage before termination. If left standing, the rye residue will remain partially erect for the entire summer and may cause challenges during soybean harvest.

Another option is to mow and bale the rye residue for livestock feed prior to soybean planting. This method reduces the weed suppression benefits of the rye residue, but the root residue remains for soil health benefits.

My overall recommendation is that cereal rye cover crops don't need to be terminated weeks before soybean planting. Planting green can be a useful practice for managing weeds, conserving moisture and minimizing crusting from heavy rain events. Delaying termination past the rye boot stage can add additional weed control and moisture retention benefits, but can also result in additional challenges due to large amounts of residue and soybean stand reductions.

If delaying rye termination past the boot stage, I would recommend rolling or mowing the rye at the time of planting.

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