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A Technical Guide for Wine Producers
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Vine roots play an important role in determining wine quality
E Archer1 & J JHunter2
Introduction
During the 2004 harvest general climatic conditions did not favour optimal ripening of grapes. It was abnormally dry and frequent heat waves were detrimental to normal ripening. After the rain of 1 March the chemical grape composition of some vineyards recovered, while that of others did not. In an effort to discover the reason(s) for this phenomenon an investigation into the canopy characteristics as well as the root distribution patterns of certain selected vineyards was launched. Vineyards that recovered as well as vineyards that did not recover were included in this investigation.
Results
The canopy characteristics and root distribution of the vineyards are indicated in Figs. 1 & 2.
 Figure 1. A good and well-buffered root system provides sufficient lateral shoot development for enough young leaves during ripening. A = Sufficient laterals in the canopy. B = Active leaves during ripening mainly on laterals. C = At ripening most active leaves occur on laterals. D = Active leaves on laterals in top part of the canopy contribute to optimal ripening.
 Figure 2. Insufficient root distribution provides no buffer capacity and results in very limited lateral shoot development. Centre: The result of incorrect soil preparation. Right: Too small trellis and leaf-roll contribute to insufficient and inefficient young leaf surface area. Vines with well developed and distributed root systems, containing fine roots in particular (Fig.1; Table 1), supported canopies that are characterized by sufficient lateral shoot development. The lateral shoots were responsible for a significant number of young leaves in the canopy during ripening. Our research in the past clearly showed the importance of younger leaves to sustain and improve grape composition during this period. Together with a quality root system, a high portion of young leaves in the canopy (on primary shoot ends and lateral shoots) increases the buffer capacity of the vine against unfavourable environmental conditions that may have a detrimental effect on grape composition and eventual wine quality. This favourable leaf age composition in the canopies was responsible for an improvement in grape composition after the rain (ñ30mm) on 1 March 2004 (Table 3). The quality of the root system clearly impact on general canopy characteristics in that it is very difficult (if not impossible) to obtain a positive relation between younger and older leaves with root systems that contain insufficient numbers of fine roots.
Vines with poorly developed root systems, especially fine roots (Fig. 2; Table 2), supported canopies characterized by insufficient lateral shoot development. The result was very few or no young leaves in the canopy during ripening; therefore grape composition could not be improved or sustained during the late stages of ripening, even after the rain on 1 March 2004 (Table 3). The composition of grapes on vines with few or no fine roots and the resulting absence of young leaves, kept on deteriorating after the rain and it produced wine with inferior quality because the canopy simply continued to senesce at a higher rate. In contrast, young leaves in high quality canopies were most active during this time and continued to feed both the grapes and the root system. The ratio between fine and thick roots (Tables 1 & 2) may be a way in which the quality of a root system can be quantified. The ratio of > 3,5 for good and < 3,0 for poor quality root systems obtained in this study coincide with results of other root studies done in different vineyards in the past (data not shown). It will be interesting to validate these values with root studies in the future, especially if it can be combined with an investigation into the hormone producing capacity of fine and thick roots. Conclusion The quality of the vine root system is important for the eventual quality of the grapes and wine. Root system quality is affected by the method and efficiency of chemical and physical soil preparation before planting. Proper soil preparation is the only way in which a well-composed root system can be obtained and it is especially the fine root system that plays a decisive role in the qualitative performance of vines during warm, dry summers. There is undoubtedly a direct relationship between the vine root system and top growth and this study shows that it is easier to obtain a quality canopy for vines with a quality root system than for those on inefficient roots.
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