Behaviour of two training systems for mechanical pruning combined with different nitrogen fertilizations on cv. Colombard

Abstract

Context and purpose of the study – Today winegrowers involved in mechanical winter pruning are applying this viticultural technique on two main training systems, the free cordon, appearing to be the more efficient, and the trellised vertical shoot positioning (VSP) system. The main reasons for maintaining the trellis are generally due to common habits in vineyard management, risk of wind damage for the shoots, or risk of decrease in photosynthesis potential. The aim of the study was to assess the effects of the two training systems on vine. In addition, different nitrogen fertilization levels were applied on the two systems to evaluate the best combination to achieve yield and grape quality.

Material and methods – Free cordon and spur pruned VSP system were compared during 3 vintages, from 2016 to 2018, on a rainfed cv. Colombard, planted in 2012 in Gascony vineyard, south-west of France. The trial was run on a young plot, planted in 2012, with a production goal of around 15 tons per hectare. Four strategies of nitrogen fertilization were applied on each system including soil mineral supplies (40N and 80N/ha) and foliar spraying (25N/ha) combined with green manure on each treatment (control). Total foliar area, yield, pruning weight, nitrogen and water status were controlled each year. Grapes composition at harvest and wine quality also allowed to compare the different treatments.

Results – The results showed different behavior of the vine according to the training systems. Total leaf area and yield were significantly lower for the free cordon system each of the tree years, regardless of nitrogen fertilizations. With the same leaf-fruit ratio, in 2017 and 2018, the free cordon grapes contained less sugar than VSP grapes. To explain some of these differences, discussion will take place around plot’s age and on plant development delay due to higher height of the supporting wire for free cordon system. Also, in our conditions, the rainfed free cordon development appeared to be very dependent on the height and period of shoot trimmings. The different fertilization strategies induced significant results on chlorophyll index of the leaves every year and on yeast assimilable nitrogen of grapes after the second year. The berries from the control treatment presented the lowest concentration of nitrogen and the foliar treatment the highest. But, the nitrogen fertilization supplies did not modify yield and pruning weight for both systems. The three-year treatments were not sufficient to induce major differences in these cases.