Estimating the contribution of nitrogen from legume cover crops to the nitrogen nutrition of grapevines using a [sup.15]N dilution technique

• Published in: Plant and soil 2010-09, Vol.334 (1-2), p.247
• Main Authors: Ovalle, Carlos, del Pozo, Alejandro, Peoples, Mark B, Lavin, Arturo
• Format: Article
• Language: English
• Subjects: Agricultural industry; Beans; Fertilizers; Grapes; Legumes; Methods; Mimosaceae; Soil management; Vineyards; Wine industry; Wineries
• ISSN: 0032-079X
• DOI: 10.1007/s11104-010-0379-1

Cover cropping is increasingly being used as a form of sustainable soil management in grapevine (Vitis vinifera L.) production. The objective of the current study was to determine the effect of a legume cover crop on a set of growth and production variables of a vineyard, and to quantify the relative importance of legume nitrogen (N) as a source of N for the vine plants and to compare this to the current recommended practice of annually applying 40 kg fertilizer-N [ha.sup.-1]. The study was carried out in a 5-yr-old vineyard cv. Cabernet Sauvignon at the Cauquenes-INIA Experimental Center in one of the wine production areas of Chile. The treatments were: control without cover crop (C); a legume mixture of early maturing cultivars of subterranean clover (Trifolium subterraneum L.) and burr medic (Medicago polymorpha L.)(EMC); or a legume mixture of late maturing cultivar of subterranean clover and balansa clover (T. michelianum Savi) (LMC). Average inputs of legume N generated by the EMC and LMC treatments represented 112 and 161 kg above-ground legume N [ha.sup.-1][year.sup.-1], respectively. Grape dry matter production was increased significantly (P [less than or equal to] 0.05) by 48-61% and the amount of N accumulated in grape bunches was enhanced by 74-105% after 2 years of legume cover crop. However, no significant (P>0.05) effects of cover cropping were observed on vine leaf, canes, roots or trunk biomass. To estimate the relative contribution of legume and fertilizer N to the N nutrition of grapevines [sup.15]N-enriched fertilizer (10 atom% [sup.15]N excess) was applied to the soil in micro-plots within all treatments as two split applications of 20 kg N [ha.sup.-1]. The [sup.15]N composition of vines grown with or without cover crops were subsequently compared. Any measured reduction in the [sup.15]N enrichment of the tissues of cover cropped vines relative to the nil cover crop control was assumed to have resulted from the uptake of legume N. Recovery of [sup.15]N in vine plant parts was used to calculate the efficiency of use of fertilizer N. Surprisingly the [sup.15]N data indicated that the fruit had the lowest reliance upon legume N for growth (only 7-13% cf 14-56% of the N in other organs), even though grape bunches were the only plant part to positively respond to the cover cropping treatments. This suggested that either the temporal patterns of N mineralization in soil and N uptake by vines over the growing season was such that much of the