The use of cover crops in vineyards can help control the yield and quality of grapes and wine
Correct management of soil and irrigation is a vital factor in modern viticulture, due to the influence of the water balance of the vineyard on wine quality and the environmental impact of agricultural practices on vineyard soils. In order to innovate in this area, the NEIKER-Tecnalia technological centre is carrying out research on the influence of temporary cover crop and different irrigation regimes –for the typical flat and sloping soils of Rioja Alavesa region– on yield, vine vigour and grape and wine quality. The initial results when cover crops are planted show a reduction in the water availability of the vineyard, reflected in a reduction of yield and vigour, as well as in an improvement of the quality parameters of the must and wine. The results of the study can be used to help grapegrowers acquire a better understanding of their vineyards and adjust their management practices so as to obtain the highest possible quality.
The study took place in 2008 on a plot in Rioja Alavesa region (Bodegas y Viñedos Zuazo y Gastón), within the Denominación de Origen Calificada Rioja. The vineyard consists of double cordon espaliered Tempranillo vines. Two typical soils of Rioja Alavesa region were identified: sloping soil with an average depth of 70 cm and very exposed to erosion and flat soil with an average depth of 150 cm that tends to accumulate soil eroded from the slopes (Figure 1). The trial studied how different management practices affected the yield, vigour and quality of the grape and wine obtained. Different irrigation regimes were tried, along with two soil management programmes: conventional tillage and the use of temporary cover crop. The conventional tillage consisted of using machines four or five times a year (chisel and rotary), while the cover crop consisted of planting barley between the vine rows to compete with them and protect the soil against erosion.
Five different treatments were implanted during the study: ‘slope with conventional tillage and usual irrigation’; ‘slope with cover crop and usual irrigation’; ‘slope with conventional tillage and half usual irrigation’; ‘flat with cover crop and no irrigation’ and ‘flat with conventional tillage and no irrigation’ (Figure 1).
NEIKER-Tecnalia staff carried out in-depth monitoring of the vineyard, measuring the pruning weight (related to vigour), the yield and berry weight, at the grape harvest. Measurements were also taken of the shoot diameter (Ø) and the stem water potential (Ψstem) at solar midday, in order to observe the growth and water status of the vineyard. In addition, must quality parameters were also analyzed as the sugar content, total acidity, malic acid, tartaric acid and pH, as well as quality parameters related to the skin (after alcoholic fermentation of the wine): colour intensity, total polyphenol index, anthocyanins and potassium.
The results obtained (Tables 1 and 2) show that the ‘flat with conventional tillage and no irrigation’ treatment gave the highest values of vigour, yield and berry weight and lower values for sugar content and pH (acidity was higher), and lower levels for wine quality parameters, especially significant being the total polyphenol index. However, the ‘slope with cover crop and usual irrigation’ treatment showed the highest values for wine quality parameters and the lowest for productivity. In this trial, largely due to the significant topographic differences, more humidity was seen in the flat area than on the sloping area during the whole crop cycle. This is backed up by the shoot diameter and the stem water potential measurements, up to the point of registering water stress levels in the ‘slope with cover crop and usual irrigation’ treatment.
In general terms, it should be pointed out that, except for acidity, the parameters studied in this trial were similar for the ‘slope with conventional tillage and usual irrigation’ and ‘flat with cover crop and no irrigation’ treatments. This means that soil with lower qualitative potential such as the flat soil can produce grapes of a similar quality to soils on slopes, which in principle produce higher quality grapes. Therefore, the use of cover crops could be an example of differential management that can lead to enhanced control of yield and quality. Something that could well be of interest for grapegrowers seeking to better plan and manage their vineyards.
Thus, the results obtained show that control of the vineyard is a key factor in the final quality of both grape and wine. The use of cover crops may be a tool that reduces the water availability to the vine and, moreover, helps to retain soil in sloping areas, reducing the risk of erosion.
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