Cover crops help build soil carbon, reduce erosion, and can offset crop nitrogen fertilizer requirements. But when it comes to nitrous oxide (N2O) – a greenhouse gas that contributes about half the total warming effect from agriculture in Canada – there is a question mark surrounding their benefit.
The primary driver of nitrous oxide emissions from agricultural soils is denitrification, which is promoted by wet soils, ample available mineral nitrogen (e.g. nitrate), the presence of carbon sources and freeze-thaw cycles. Cover crops influence each of these conditions. A 2014 meta-analysis found that cover crops decreased N2O emissions in 40 per cent of studies and increased them in the other 60 per cent.
The following factors determined cover crop effects on emissions:
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