Not all the terrain of the same vineyard has the same properties. Research undertaken by Neiker-Tecnalia (the Basque Institute for Agricultural Research and Development) confirmed that, over the same zone of cultivated land, there are plots with soils of different characteristics, a fact which gives rise to significant differences in the production of the grape and in the quality of the must. Knowing these differences enables the winegrowers to carry out zoning on their vineyards with the goal of better adapting to the needs of fertilisation, irrigation and treatment of the vine. Likewise, it enables carrying out a selective harvest, with plots producing batches of different qualities.
The research, led by doctor in Biology, Ms Olatz Unamunzaga, aimed to establish a zoning of a vineyard, according to the properties of the soil, as well as studying the productive behaviour and quality of wine. The study enables establishing a series of criteria that help to link the behaviour of a vineyard with the properties of the different soils found on the various plots of the vineyard under study.
The research was carried out on a vineyard of eight hectares located in Oion (in the Basque province of Araba-Álava) and belonging to Bodegas y Viñedos Zuazo y Gastón. The researchers established a sampling of more than 190 points distributed systematically at various plots of the vineyard, spread over different topographies and orientation. Apart from the properties of the terrain and soil, different parameters related to the robustness and productivity of the vines were measured, such as the weight of the pruned wood, the production per each unit of vine, the number and weight of the bunches of grapes, the weight of the grape, and the quality of the must.
The Neiker-Tecnalia study showed that erosion processes in the soil influences the horizontal and vertical distribution of its properties and, in particular, the depth of it. The variability of the physical properties enabled identifying four types of soil: a) deposition soil, with a depth greater than 110 cm and an irregular distribution of in-depth organic material; b) argillite soil, with a depth of between 85 and 100 cm and characterised by a reddish-coloured clayey layer at 50-80 cm depth; c) limolite soil with a depth of between 50 and 100 cm and an in-depth clay content of 270-380 g per kg; and d) sandstone soil with a depth of between 25 and 80 cm and with a high content of in-depth sand (300 g per kg).
Amongst other results, it was shown that soils with the greatest capacity for retention of water (deposition and argillite soil) were those that developed the most robust vines. Hydric availability affected the unit production of the vine and the number of grape bunches on the deposition soil, although it was observed that, after one year of high production and number of grape bunches, there was a considerable drop in these variables the following year.
The research also revealed that the best conditions for obtaining a higher degree of probable alcohol are in years where there is less hydric availability during the setting to the véraison (onset of ripening) periods (middle of June to end of July) and greater hydric availability during ageing (August-September). This effect was clearly reflected with the different types of soil.
The temperature during the month of September prior to the harvest was one of the most influencing factors on the malic acid content of the must. High temperatures favoured the combustion of malic acid and, thus, the loss of this acid. The temperature of the grape bunch was influenced by the temperature of the air and the shade afforded.
The parameter values related to the grape skin (such as the antocyanes, polyphenol index and colour intensity) were greater on the sandstone soil, with a colour intensity up to four times greater than on the other soils.
The Neiker-Tecnalia research was carried out at a vineyard complying with the handling and management rules set down by the Denominación de Origen Calificada Rioja, which determines a maximum production limit. This involves an evermore exhaustive control of the vineyard in order that the limit fixed is not passed and, in this way, balance plant development and production, with the aim of obtaining maximum quality. This balance is closely related to the specific conditions of the soil, climate, cultural practices and piping systems which, in turn, are linked with the variety of the grape.
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