Quantification of N2-fixation from Medicago polymorpha L. grown as cover crop in vineyard

Cover crops in vineyards help the reduction of chemical inputs and soil erosion risk as well as the improvement of soil fertility. In a two-year experiment carried out in Sardinia (Italy), the nitrogen (N) fixed by burr medic (Medicago polymorpha L.) grown as cover crop in a vineyard was quantified. The potential of N fixation in burr medic was estimated by the 15N isotopic dilution method. In late spring, dry matter legume forage mass ranged from 3.7 to 4.0 t ha-1, in 2012-13 and 2013-14, respectively. On average, the aerial fixed N was 120 kg ha-1 year-1 and represented about twice of the total N in grapevine organs (leaves, fruits and canes). If burr medic below-ground N is also taken into account, legume contribution to the total N of grapevine could be even higher. Results indicated that the N requirements from the annual organs of the grapevine could be potentially covered by atmospheric N via legume cover crop, compared to soil tillage treatment in vineyards.