Agronomy: Growing Continuous Beans: Cover Crops

Planting cover crops can lessen the risk of yield drag on second-year soybeans, and planting them after soybean harvest gives you an opportunity to plant earlier in the fall and into low residue and good soil conditions.

There is some interest in growing more soybeans and even planting some fields back to second-year soybeans. There is some risk of yield drag (4 to 5%), so growers interested in this rotation need to plant soybeans back into their better, well-drained fields; select varieties with good disease resistance and seedling vigor; and treat the seed with a full seed treatment package.

Soil conditions must be right, so must be well-drained. Also, to lessen the risk of disease or emergence issues, plant into warmer, drier soils. And this may mean planting a bit later or the end part of your soybean planting window.

Of course, the major risks are due to soil borne pathogens and pathogens that overwinter on the residue. That is why selecting a defensive variety and the right seed treatment are so important. Genetics and seed treatment can be used to protect the seed against early season soil borne pathogens like Pythium, Phytophthora, Fusarium and Rhizoctonia.

As the crop grows other diseases can become more prevalent including bacterial blight, stem canker, pod and stem blight, Septoria brown spot, frogeye leaf spot and white mold. These pathogens overwinter on the residue and can infect the following soybean crop. That is where fungicides come into play to protect again fungi that impact the plant late in the season. This is something you can decide later based on weather conditions, disease outbreak elsewhere in the county or region, and by scouting fields.

Cover crops provide a number of soil and crop benefits that can make planting back to second-year soybeans less of risk.

First: Cover crops can dry out the soil quicker in the spring, but you have to keep the cover as a green and growing cover. If you terminate it, it will turn into a matt and seal off the soil and it’ll stay cooler and wetter, creating more stressful conditions.

Second: Green cover crops have active roots systems leaking a myriad of molecules that stimulate beneficial pathogens in the soil that will outcompete and suppress pathogenic fungi that prey on seeds and seedlings.

Third: In my experience planting into a green cover even improves on planting into soybean stubble. Everyone knows how nice the seed bed is after soybeans. Well, add in a green cover with its active roots and biologically active soil and the seedbed is even nicer, resulting in a very good stand. But if you end up planting into a matt of cover-crop residue don’t expect those same results.

If you are thinking that the economics and potential of planting some field back to soybeans is favorable, then incorporate these steps into your practices and perhaps you can even zero out any potential yield drag.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or leave a comment below.