Many farmers who grow soybean and corn also integrate crop rotation strategies to avoid the continuous corn yield cost, but scientists from the US have given a new reason to use crop rotation. Evidence suggests that rotating crops increases yield and lowers greenhouse gas emissions compared to monoculture corn or soybean.
The corn yield penalty is a known effect of continuously growing corn over years of harvesting, which was evaluated in a 6-year study undertaken by the University of Illinois (ACES). This penalty causes reductions in yield as a result of corn residues in the soil introducing a number of physical, chemical and biological effects such as soil temperature, moisture levels and nitrogen concentrations which can all negatively influence crop yields for several years.
Scientists at ACES have studied greenhouse gas emissions and measured crop yields over a 20-year period to determine the beneficial impact of using crop rotation practices in comparison to continuous corn and soybean farming.
“I think farmers in today’s world are looking for reasons to avoid growing in a monoculture. They’re looking to diversify and rotate their systems. If they’re doing that partially out of a concern for the environment, well, it lowers greenhouse gasses. And it could potentially result in a substantial yield increase,” says Geven Behnke, a research specialist in the Department of Crop Science, ACES.
The results of this study determined that crop rotating with corn and soybean produced an average yield benefit of more than 20% as well as a cumulative reduction in nitrous oxide emissions of roughly 35%. Nitrous oxide in an extremely long-lasting greenhouse gas, with a global warming potential (how much heat the gas traps in the atmosphere) of around 300 times higher than that of carbon dioxide.
In agriculture, it is produced as a by-product of natural bacterial processed breaking down nitrate in the soil known as denitrification. This process can be affected by factors such as fertiliser application and timing, with studies reporting that fertilised crops take up less than 50% of the total nitrogen applied from chemicals, thus leaving an excess in the soils available for this bacterial process.
As well as the reduction in nitrogenous gas production by 35% using crop rotation practices, in terms of crops which receive less fertiliser application such as soybean, the study found that rotation did result in an overall increase in crop yield by 7%.
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