Hemp is a legume, meaning it has the unique ability to extract nitrogen from the atmosphere and deposit it in the soil. This process, known as nitrogen fixation, leaves the soil with more nitrogen than before hemp was cultivated. Studies have shown that hemp produces biomass at a rate 20% higher than that of crimson clover and shaggy pea. Not only is hemp resistant to plant root nematodes, but it actively suppresses them.
In just 60 to 90 days, hemp can produce up to 120 pounds of nitrogen per acre and can reduce weeds by up to 90%.Hemp has many benefits for soil health. It adds nutrients such as nitrates and potassium, which increases fertility and field performance. In a controlled study, wheat planted in a field a year after hemp showed a significant increase in yields. Hemp also has deep taproots that extract nutrients and water from deep under the surface of fields, aerate the soil and improve its structure, and add biomass.
Hemp is even able to withstand hot, dry summers and continues to grow until the first frost. Although hemp is generally safe for animals, it's important to proceed with caution once the plants start to flower. Hemp contains alkaloids in quantities that warrant special treatment. If grown with trees, hemp can be cut with a hedge trimmer and the waste can be scattered around the bases of the trees. The method used to cut and incorporate the crop can affect the rate of decomposition and mineralization of nitrogen. Hemp is not adapted to poorly drained soils, so establishment and production will be significantly lower in those soils.
Hemp has been one of humanity's most durable and productive crops for 12,000 years, but unfortunately processing industries needed to produce fiber from this crop are not present in the United States. It is also important to consider the schedule of the following direct-seeded crops when using hemp as a cover crop due to allelochemical effects of residues in crop seeds.