Nitrogen partitioning among vine organs as a consequence of cluster thinning

Abstract

Context and purpose of the study ‐ Agroscope is investigating the impact of yield on nitrogen (N) partitioning in grapevine and on must composition. The mechanism of N assimilation, partitioning and 15 mobilization from the reserves is studied through foliar application of N isotope‐labelled urea over a two‐year period. The final scope is to optimize fertilizer use efficiency and grape composition. Here are summarized the results from the first year of experimentation.

Material and methods ‐ Two blocs (control and test) of 12 homogeneous potted grapevines each (Vitis vinifera L. Chasselas) were grown under field conditions. During summer 2017, cluster thinning allowed to create a large yield gradient (from 0.5 to 2.5 kg/m2 of soil). Vegetative development—canopy weight, leaf area, photosynthesis activity—and yield parameters —bud fruitfulness, bunch and berry weights, number of bunches and total yield per vine— were measured. All the vines were excavated at harvestand the organs were separated (roots, trunk, canopy, pomace and must), with the aim of monitoring N partitioning in the plant. The test bloc received 20 kg/ha of foliar‐applied 15N labelled urea at veraison. Total organic carbon and nitrogen and their stable isotope compositions were determined in each organ, using EA‐IRMS. The musts were analysed for their content of soluble sugars, acids, NH4+ and amino acids.

Results ‐ Grapevine compensated higher N demand from the grapes by assimilating more N through leaves and roots and mobilizing more N from reserves. The foliar supply of urea limited N mobilization from the roots, preserving the reserves for the following year. Must amino‐acid profiles varied significantly with the yield. Yield had no impact neither on vegetative development nor on grape maturation. With increasing yield, N concentration remained constant in the canopy and grapes at harvest, to the detriment of the N content in roots. Urea assimilation was positively correlated with the yield (r = 0.68, P = 0.029). Urea supply had a positive impact on yeast assimilable nitrogen concentration in the must only under higher yield conditions.