A disclaimer before we start:
We do NOT recommend planting soybeans back-to-back year after year.
Planting any crop back-to-back year after year increases the potential for pests and problems to build up. You may not see these problems after one year, but eventually, something will become an issue and it may be a problem that is difficult to control.
However, we understand that in some places in North Carolina rotation every year is not an option. Also, current economics may drive some growers to plant more soybeans this year, leaving no room for rotation. Below are some things to do and things to watch out for if you decide to plant soybeans back to back.
- Remember that yields will likely be lower if soybeans are planted back to back versus rotating with another crop. Numerous studies across the nation have demonstrated the yield advantages of crop rotation. In two long-term rotation studies carried out by NCSU in the Blacklands (Washington County) from 1972-1993 and in the Piedmont (Cleveland County) from 1985-1994 soybean yields were increased by about 5 bu/acre following corn compared to following soybeans.
- Be aware that certain pests may create more problems in back-to-back soybeans than they would if another crop was planted in the same field. Be prepared to scout your fields more often and potentially spend more money on herbicide, insecticide, and fungicide applications. Also, seed treatments may be a good investment for back-to-back soybeans to help combat seedling diseases that may have built up in the soil.
Nematodes: Soybean cyst nematode populations increase in long-term soybean cropping systems. The only way to monitor the population is through a nematode assay.
Insects: You are more likely to see problems with three-cornered alfalfa hopper, Dectes stem borer, bean leaf beetle, and stink bugs. Be on the lookout for these when you scout!
Diseases: Diseases that overwinter in crop residue are likely to be a problem for back-to-back soybeans. Keep an eye out for stem canker, Cercospora, frogeye leaf spot, and Septoria brown spot.
Weeds: Rotating crops allows you to diversify your weed management strategy by allowing use of different herbicides and tillage practices. With soybeans back-to-back, a good pre-emergent with multiple modes of action and overlapping residuals are critical.
- Don’t forget the importance of fertilization. Oftentimes, growers rely on carryover fertilizer for soybeans when rotated with corn. Soybean after soybean will likely require additional fertilizer, especially K. Soil testing is the best way to determine what your fields need, but if you didn’t soil test, use the removal chart below.
- Plant a different variety than was planted in the field last year. Every variety has a weakness and planting the same variety on the same land two years in a row will expose that weakness. Also, be sure to select a variety with a strong disease resistance package as disease pressure may be greater with second-year soybeans.
Conley, Shawn P. 2016. Best Management Practices for Growing Second Year Soybeans. http://thesoyreport.blogspot.com/2016/12/best-management-practices-for-growing.html.