Grapevine Uptake of ¹⁵N-Labeled Nitrogen Derived from a Winter-Annual Leguminous Cover-Crop Mix

Abstract

A winter-annual leguminous cover-crop mix was labeled with ¹⁵N-depleted ammonium sulfate fertilizer and tilled into every other alley of a Chardonnay vineyard on 5-C rootstock. The cover crop-derived nitrogen was detected in the grape leaves four weeks after cover-crop incorporation. There were two main periods of grapevine nitrogen uptake from the decomposing cover crop: from 4 to 6 weeks and again from 16 to 20 weeks following incorporation. The percent of grape-leaf nitrogen derived from labeled cover crop (%Ndfcc) reached 0.28% by the end of the growing season. The results of this preliminary study indicate that leguminous cover crops have the potential to supply nitrogen to grapevines during the times of peak nitrogen demand in early spring and fruit set. In this tilled vineyard, the overall contribution of cover-crop nitrogen to total grape-leaf nitrogen content was small compared to previous studies that have measured cover-crop nitrogen uptake by younger grapevines or annual crops.