Iowa State University Research Shows Extra Cover Crop Growth Prior to Soybeans Provides Benefits
By Michael Castellano and Daren Mueller
AMES, Iowa — Research at Iowa State University, funded by the United Soybean Board (USB), suggests that an additional period of cover crop growth prior to soybeans results in high cover crop biomass production, nitrogen retention and has no negative effect on yield.
Iowa State University associate professor in agronomy, Mike Castellano, has been working on the project over the last three years to show the effect of cover crops preceding soybeans. The study consisted of three major experiments that included corn and soybean systems with and without the cover crop, winter cereal rye. The cover crop prior to corn was terminated about seven to 10 days before planting corn, while the cover crop prior to soybeans was terminated at two different times; the same day the cover crop was terminated in corn and approximately three weeks later, the day before soybean planting.
Winter cereal rye that grew an extra three weeks prior to soybean planting produced about 300 to 400 percent more biomass with a 100 percent increase in nitrogen retention, when compared with the early terminated cover crops.
“The extra three weeks of cover crop growth is like getting three to four years of cover crop production in the system and organic matter into your soil,” said Castellano. “This is clearly a way to speed up the process of receiving the benefits of biomass production.”
The study also showed that cover crops left in the field for an additional three weeks before soybean planting increased the nitrogen in the cover crop from 40 pounds per acre to over 80 pounds per acre.
“It really goes to show that you get a lot of bang for your buck in those extra three weeks,” said Castellano. “And despite letting the cover crop grow an extra three weeks, we saw the same soybean yields.”
While the research so far has demonstrated what an extra period of growth can do for cover crop biomass, the overall goal of the research is to link the amount of cover crop biomass directly to economic benefits.
“At the present time, we can say with confidence that we can retain a lot more nitrogen in the system and lose less to the environment with increased biomass production,” said Castellano. “In the short term, that’s a great benefit for water quality challenges. In the long term, adding that biomass and keeping that nitrogen in the system will build soil health.”