Double Crop Soybeans or Cover Crops


Approaching mid-July, some farmers are still debating whether to plant soybeans after wheat harvest. Double crop soybeans are risky but high soybean prices, early summer planting and good weather favor farmers taking the risk. As summer progresses, the risk of failure increases on double crop soybeans. Cover crops are often planted from June to October with good results depending upon the species and weather. Planting cover crops after mid-July becomes a much safer proposition.

Let’s start with looking at our current crops. For the most part, corn looks great this year while soybeans are average at best, depending upon the field. Corn was planted when the soil was dry and then it started to rain and soybeans where planted. Soybeans suffered from seed corn maggot and/or wire worms, and then if the soil was vertically tilled, standing water and pathogens (fusarium, phytophthora, etc) began a problem. In some fields, soybean struggled with slow growth due to small puckered and/or cupped leaves. Usually this is an indication of herbicide damage which looks like 2-4D. However, if 2-4D was not used, what could be the problem?

Last year, the weather was exceeding dry from summer through early spring. Herbicides generally break down fairly quickly with adequate moisture, heat, and biological activity. When soils remain dry, some herbicides stay attached to the soil particles for long periods. Soluble herbicides will inhibit weed germination and also break down, but herbicides in a dry soil stay attached to the soil particles, do not inhibit weed germination, and do not break down quickly. Herbicide carryover then becomes an issue. R

esicore is corn herbicide that is a combination of acetochlor (Harness, Group 15 herbicide), mesotrione (Callisto, group 27 herbicide) and clopyralid MEA salt (Stinger or Curtail, group 4 herbicide). Group 15 herbicides include Dual, Zidua, and Harness which may cause these symptoms under dry conditions. These products usually break down fairly quickly but in fields that were very dry and or had low soil organic matter (SOM), farmers are seeing patchy issues with soybean growth, depending upon soil type and moisture. Soils with higher SOM and moisture generally have less issues because they have higher microbial diversity, they hold more water, and the SOM buffers the soil. Improving soil health and SOM helps prevent or least reduce some herbicide carryover issues.

Wheat prices are still high, so wheat has become a profitable crop to raise again. For both soybeans and cover crops, harvesting the straw is recommended to increase plant growth. Some farmers like to keep the straw to increase SOM. However, most SOM comes from your roots. The straw tends to tie up nitrogen and it slows down either soybean or cover crop growth. If you harvest the straw, as long as you plant another crop you are gaining live roots to improve your SOM and keep microbial populations healthy. Leave 4-6” of upright wheat stems to reduce soil drying and to protect the soil from erosion. 

Since USDA-NRCS has changed their cover crops rules, cover crops can now be mowed, hayed, or grazed. Grass cover crops like sorghum or Sudan varieties, oats, barley, and cereal rye can be sown and harvested. These grass cover crops will also benefit from manure applications. Manure can be applied either before the crop is sown or apply after the cover crop is at least 3-4 inches tall. Liquid manure may burn the leaves and slow down plant growth.

Legumes like hairy vetch (prefers well drained soils) winter peas, cowpeas, crimson clover, and Balansa clover can be planted now to obtain 100-200# of nitrogen for next year’s corn crop. Most legume and clovers need to be established between Mid-July and Mid-September to get a good crop. Early planting generally improves establishment and nitrogen content. Winter peas planted August 1st may yield 150# N while those planted in September only yield 50-75# N depending upon the stand. 

Brassicas like daikon radish, kale, rape, turnips, and Ethiopian cabbage can also be planted early. Buckwheat and sunflower are great pollinators. Buckwheat goes to seed within 45-60 days and is great for loosing the top 3-4 inches of soil. Sunflowers are deep rooted and improve drainage. Farmers often plant 5 to10-way cover crop mixtures to get multiple benefits. For the H20 program, at least 50% of the mixture needs to be a cover crop that survives the winter. After wheat harvest, planting cover crops is a great way to improve soil health.