Different Cover Crops Affect Nitrogen Fluxes in Mediterranean Vineyard

Core Ideas Burr medic cover crop supplied 125 kg ha–1 year–1 of fixed N to the vineyard. Twice the N needs of grapevine annual organs were satisfied by legume cover crop. Legume cover crop promoted + 25% of total N compared to grass cover crop. Compared to traditional soil tillage, the establishment of cover crops in Mediterranean vineyards has several advantages such as better soil fertility; however, vigor and N concentration of grapevine [Vitis vinifera (L.)] organs may be affected. A 3‐yr experiment was performed in Sardinia (Italy) to: (i) quantify the N fixation ability by burr medic [Medicago polymorpha (L.)] grown in a vineyard and its potential benefit for grapevines; (ii) compare the effects of different management systems (grass or legume cover crop vs. soil tillage) on grapevines. Total N fixed by burr medic was 125 kg ha−1 yr−1 and it was twice as high as the N contents of grapevine annual organs. Soil tillage promoted higher cluster and cane dry matter (+38% and +31%), compared to cover crop treatments. Legume cover crop induced higher N concentration in leaves and canes. The N content detected in grapevine annual plant growth with the legume cover crop reached 61 kg ha−1 yr−1. According to an indirect 15N dilution approach, the higher 15N enrichments detected in organs of grapevines, did not indicate that legume N was utilized by grapevine. However, lower 15N enrichment was occasionaly detected, indicating 6 and 13% of N derived from legume in clusters and canes, respectively. Compared to grapevines with grass cover, the N contribution from legume cover, estimated by the N‐difference method, induced 24, 24, and 31% of N increase in leaves, clusters, and canes, respectively. The increases corresponded to 10% of legume fixed N.