Carbon and nitrogen movement in legumes
Forage mixtures (dead plant material placed on fields and pastures) are an important way to return essential elements such as carbon and nitrogen to pastures and fields. Legumes efficiently fix nitrogen through their roots, but what is not known is whether that nitrogen is efficiently transferred into the soil through forage. The EU-funded 'Root longevity and the impact on soil N fertility' (LEGUME ROOT IMPACT) project aimed to develop new methods to estimate how long legume roots last in forage mixtures. It also aimed to measure nitrogen and carbon transfer to the soil. An initial experiment was conducted to test whether radioactive labels could be used to track different chemical elements. Researchers found that bicarbonate with a single carbon-14 atom (a radioactive isotope) could be used to effectively label clover leaves. A similar process was used for tracking nitrogen atoms. Researchers found that over eight months, no significant movement in carbon and nitrogen was observed from the roots of clover plants. They concluded that a longer experimental period would be needed to estimate root longevity. In contrast, they found that nitrogen and carbon readily moved from the leaves of decaying clover into the soil. It is clear that movement of elements from leaves to soil plays a more important role than movement from the roots. Despite not fulfilling all of the desired outcomes of the project, LEGUME ROOT IMPACT improved our understanding of the movement of elements from forage mixture into soil. In the long term, this will support further studies dedicated to bettering sustainable farming practices and decreased use of fertilisers.
Keywords
Legume, forage mixture, nitrogen, carbon, soil, roots, sustainable farming
