Effect of crop load on production to quality balance

Abstract

In a vineyard located at Alcains (Beira Interior, Portugal), planted in 2004 with ‘Trincadeira’, ‘Touriga Nacional’, ‘Aragonez’ and ‘Alfrocheiro’ all grafted on ‘SO4’ rootstock, spaced 3×1 m, and trained as a single vertical curtain, the effect of crop load in vine production and quality was studied by non-linear fitting of crop load (expressed as weight of grapes per weight of pruning wood, leaf area or canopy volume units) and sugar content (TSS), at different sampling timings. Pruning wood and canopy volume per vine were obtained by direct measurements, while leaf area per vine was obtained by multiplying bud number in pruned wood by average leaf area for each cultivar (average of 50 individual leaf scans). A model based on differential income with TSS was constructed. TSS was influenced by harvest time and crop load, but not by cultivar. When compared for identical crop load levels, the range of TSS values clearly overlaps for all cultivars regardless of the unit used for crop load. On the other hand, total acidity showed a strong relation with cultivar, but not with crop load. From these results, TSS seems to be mainly influenced by environmental factors and vineyard practices, not by genetic determinism. Therefore, canopy and crop load management appears to be critical to maximize production and to regulate sugar accumulation, respectively; and thus: (1) crop load effects should not be ignored in experimental designs; (2) production and quality (TSS) are not incompatibles, since crop load will be adjusted to vine capacity; (3) in colder and wetter regions, it is possible to anticipate harvest by cluster thinning (finishing it before autumn rains); (4) in warmer and dryer places, it is possible to delay harvest with higher crop loads, to improve phenol ripening without excessive TSS; (5) production, quality and economic revenue, can be modelled in function of crop load, to manage optimal crop load for each vine ecosystem or “terroir”.