Canadian research on pulse crops shows that growing the crops to maturity and harvesting for seed actually creates more nitrogen in the soil than using the pulse as a green-manure crop, according to a news release from the American Society of Agronomy.
When grown to maturity, the crop's roots in the soil have more time to fix nitrogen. Researchers say that growers should be aware that nitrogen is released for several years after the pulse crop is grown, so they should only grow a pulse crop about every fourth year to avoid excess nitrogen runoff. The study also found pulse crops increase the amount of carbon in soil.