Deconstructing the Masseto (Bolgheri, Tuscany) vineyard: Irrigation management

This post is the final in a series that sought to characterize Ornellaia's  Masseto vineyard using both publicly available data as well as reasoned supposition. Previous posts in the series covered soils, scion and rootstock, disease and virus management, training systems and pruning practices, and nutrient monitoring.   This post examines irrigation management.

Water is extremely important to the functioning of the vine plant but too much, or too little, can have adverse effects on the plant, with run-on effects on fruit quality.

One of the important viticultural philosophies in many new world grape-growing environments is that controlled water deficits, and the resultant vine stress, can improve wine quality while “full-potential water use” will most likely result in “heady canopies” and insufficient light getting through to the fruit as a consequence. Research carried out by UCDavis' Dr Terry Prichard on berry size and vine balance shows that:

• For a given berry size, vines grown with low irrigation have a higher anthocyanin concentration (between 15% and 33%) than those grown under higher irrigation conditions
• There is a higher concentration of skin tannins in low- versus high-irrigation environments
• Water deficits result in lower yields which, in turn, results in lower veggie characteristics and fruitier wines.

Water sources for the vine include stored soilwater, effective in-season rainfall, and any water that is added by the viticulturist. Vine water stress is created when this available water supply is reduced beyond the vines climatic needs.  In areas where irrigation is allowed, viticulturists use controlled irrigation to induce vine water stress. In this scenario, the soil water resources are utilized for the plants needs up through bud break and then amounts less than required are provided to the plant (This would include effective rainfall plus irrigation). This limited water access creates a stress situation for the vine, which, in turn, results in the quality enhancements that the viticulturist seeks. This controlled-irrigation option is not available to the Masseto vineyard because irrigation is not allowed in Bolgheri except under emergency conditions. That is, the soil will provide for the vine's needs with stored soil water and the vines will dive deeper -- a stressed situation -- in search of additional water when the near-in sources have been depleted. In the remainder of this document we will explore the implications of this situation for the Masseto vineyard.

According to Orlandini et al. (Water Use in Italian Agriculture: Analysis of rainfall patterns, water storage capacity, and irrigation systems), Tuscany gets about 22 billion cubic centimeters of precipitation annually with yearly values ranging from 2000 mm in the northwest to 500 mm in Maremma to the south. Overall, regional water requirements are 760 million cubic meters with agriculture demanding a paltry 150 million cubic meters. During April 2004, 92 mm of rain fell in Florence and effective rainfall (rainfall during the growing season) ranged between 53.6 and 78.5, depending on the conversion schema chosen. Precipitation is not the problem then. According to Orlandini et al., there is enough precipitation to supply the region’s water needs but the “temporal and spatial distribution can be responsible for severe water deficits” (see table below).

                           Effects of Severe Water Stress on the Grape Vine

Stage	Effects
Bud Break	Water stress infrequent at this stage Moderate levels -- uneven bud break and stunted shoot growth Severe levels -- poor flower cluster development; reduced pistil and pollen viability; nutrient deficiencies
Post-Berry Set	Severe levels -- flower abortion and cluster abscission; reduced canopy development; impact on following season’s crop potential
Post-Fruit Set	Restrict berry cell division and enlargement resulting in smaller fruit and lower yields Reduced shoot development Reduced yield potential Reduced fruit soluble-solids accumulation Higher pH fruit Decreased acidity Reduced color development in red varieties
Post-Harvest	Reduced root growth with resulting decreased nutrient uptake and micronutrient deficiencies the following spring

Source: Wample and Smithyman, Regulated deficit irrigation as a water management strategy in vitis vinifera production in Deficit Irrigation Practices, ftp://ftp.fao.org/agl/aglw/docs/wr22e.pdf%20.

Orlandini et al., recommend two solutions to addressing these emergency water deficit situations: (i) landforms and (ii) water repositories. The clayey soils of Bolgheri have an infiltration rate of .5 mm/hr and, coupled with the fact that terraced vineyards show runoffs of .72 g/l, while sloped vineyards experience runoffs of 4.18 g/l, point to terraced vineyards as a mechanism for slowing the runoff and keeping the water around to allow the max possible infiltration into the clayey soils.

A practice in the Italian farming community is the development of farm ponds to capture precipitation to hold for emergency situations. There are a total of 2462 farm ponds in Tuscany, up from 1707 in 1980 (Orlandini, et al.). A 1985 study has shown that the average farm pond can hold about 30,000 cubic meters of water, an optimal dimension for cost and maintenance. Allowed emergency irrigation is 60 mm/ha  which amounts to 780 cubic meters including losses and efficiency (Orlandini, et al.). A pond of 30,000 cubic meters can irrigate 30 ha, making it more than adequate to meet the emergency irrigation needs of the Masseto vineyard.

Masseto does support terraced vineyards and my guess is that they would have at least a 30,000 cubic meter farm pond to allow increased precipitation retention and to meet any emergency irrigation needs that may present.

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