| Summary: | Grapevines must have 16 of the 118 known elements to grow normally, flower, and produce fruit. These essential elements, listed in table 3.1, are also called nutrients and as such are divided into • Macronutrients, which are required in relatively large concentrations • Micronutrients, which are required in smaller concentrations Box 3.1 discusses the different ways of calculating nutrient concentrations in soil, plants, and liquid. Vines draw most of their nutrients from the soil, and so table 3.1 also shows the common ionic form of each element in soil. Ions, the charged forms of elements, are introduced in box 2.4, chapter 2. For example, carbonic acid (H2CO3), which is a compound of carbon (C), hydrogen (H), and oxygen (O), dissociates in water into the ions H+ and HCO3−. This is a chemical reaction that can be written in shorthand form as . . . H2CO3 ↔ H+ + HCO3− . . . The double arrow shows that the reaction can go either forward (to the right) or backward (to the left), depending on the concentrations of H+ and HCO3− relative Concentration (symbol C)a is the amount of a substance per unit volume or unit weight of soil, plant material, or liquid. For example, the concentration C of the element nitrogen (N) can be expressed as micrograms (μg) of N per gram of soilb, noting that . . . 1 μg N/g = 1 mg N/kg = 1 part per million (ppm N) (B3.1.1) . . . An amount is the product of concentration and weight. For example, the total amount of N of concentration C (measured in μg/g) in a soil sample of 100g is . . . 100C μg or 0.1C mg (B3.1.2) . . . Because all soil and plant materials contain some water, analyses are best expressed in terms of oven-dry (o.d.) weights. The o.d. weight of a soil sample is obtained by drying it to a constant weight at 105ºC; for plant material the drying temperature is 70ºC. The amount of a nutrient is often expressed per hectare (ha) of vineyard.
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