Influencing grapevine yield
High wine grape yields are obtained on the most freely drained soils where water is not limiting. Vines will grow across a wide range of soil pHs, but extremes will render many nutrients unavailable and thereby restrict yield.
Physical or nutritional manipulation of the vine to allow light into the canopy will ensure maximum growth potential and high yields. The aim of any grower is a high yielding wine grape crop that satisfies the wine-maker. However, many vineyard managers and wineries believe that a high yielding wine grape crop cannot produce a quality wine.
We believe this apparent conflict has not been rigorously tested. There are many examples around the world of vineyards producing top quality wine from high yielding grapes that have been provided with a balanced nutritional programme.
Targeted optimum production of a top quality wine comes from controlling the number of grape bunches. Best seasonal growth occurs during long, dry, hot summers and when winters offer a cool respite. The use of fungicides, or canopy manipulation, will reduce the incidence of yield-sapping diseases such as Botrytis during high-pressure years.
Crop nutrition and wine grape yield
Nitrogen is one of the most important nutrients governing grape crop yield. It promotes strong, early growth and bunch and berry weight. However, high nitrogen availability in the later stages of vine development can delay maturity and increase disease risks as the grapes are close to harvest.
Potassium is also needed in large quantities, often at higher doses than nitrogen in grapes grown for wine. High levels of potassium are required to produce the best wine grape yields. However, as with nitrogen, the balance between the supply for growth and lower potassium-levels in the grape is critical. Analysis of soil potassium-levels in the vineyard soil is essential to predicting the potassium needs for the grape crop.
Calcium is important for wine grape yield, through increasing disease tolerance and reduced berry rot. Low calcium content can also increase berry drop.
Magnesium is needed to maintain photosynthesis and the synthesis of proteins required for high yields.
Of the micronutrients, boron and zinc are the most important for fruit set and final yield and need to be available in higher quantities than other trace elements.
Iron is important for early leaf production to ensure better berry development and grape yield. Manganese can play a similar role.
