The soil variability that we evidenced within the Pomerol vineyard (first part) in France (near to Bordeaux) led us to compare the behaviour of Merlot noir, which is the main local cultivar in this area. This study was conducted on four sites, which belong to the main soil map units of the area. Soils (FAO) were: a deep (A) and a shallow (C) planosols with abrupt textural changes between uppest sandy-gravelly horizons and sandy clay (A) or heavy clay (C) deeper layers, a very sandy well-drained neoluvisol (B), and a very stony cambisol with a temporary watertable (D). Water uptake by vines was assessed by leaf water potential measurements undertaken from June to September. Both observations on shoot elongation and leaf water potential measurements were performed together. The year 1995 exhibited a mild winter, then followed by both temperature and insolation higher than mean values. The rainfall in summer was less than the mean value, and the climatic water balance was negative. As a consequence, the vine phenology exhibited a very early development. Various water behaviours were observed amongst the four experimental plots: some were strongly linked to c1imatic events whereas others showed regulating mechanisms attributable to inherent soil properties such as texture and structure. The vine on soil D exhibited the greatest variations in water potential, showing significant periods of droughtiness during summer. On this soil, the variations in leaf water potential were strongly linked to rainfall events in summer. The vine on soil B kept the less negative values of water potential in relation to the very deep root development which was observed in this light and well-drained sandy material. The vine on soil A had a high water uptake during the period of shoot development, but showed a significant reduction of water availability in august. The most progressive regulation of water uptake was observed on soil C, and could be attributed to the elongation of roots with shrinking during summer in the deep c1ayey horizons. The water behaviour variability was mainly linked both to textural and structural soil properties intluencing soil water retention, aeration, and rooting development. The longest shoots were observed in soil (A) where the elongation speed was the highest. On soil (B) shoot elongation was signiticantly reduced, although water supply was the highest. This was attributed to a low nutrient availability in this very sandy soil. The elongation speed in site (D) was rather chaotic, and was related to marked variations in water supply. The lowest shoot elongation was observed in the shallow planosol (C). Preliminary results on grape quality are showed, and seem to be consistent with these behaviours.
These results are consistent with previous studies on various vines of the Bordeaux region which have already shown that various soil properties might induce a control on water behaviour in soil and thus might result in similar consequencies for water availability for vines. The discussion points out the important role played by water uptake control mechanisms on vintage quality in this area.
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