Grape vine nutrient requirements and acquisition

Adequate amounts of the appropriate nutrients are required to support proper growth of the grape vine, fruit development, and fruit maturity and those nutrients are obtained from the soil by the plant.  The table below shows the mineral requirements of the vine plant, the role of each mineral, acceptable ranges of each mineral in the soil, and the impact of mineral deficiency on the vine.

Source: Compiled from LGRGP.org and others

Soil is comprised of air, water, mineral particles (a mix of clay, silt, and sand), organic matter (decomposing plant material), and organisms (bacteria, algae, fungi, earthworms, insects, etc.).  Most of the solid soil matter is comprised of mineral particles while fully half of the overall content is pore space (in general a 50-50 mix of air and water).  Organic matter is: (i) critical in holding soil particles together; (ii) a reservoir of nutrients and water; and (ii) a food source for soil organisms.

Soil-based nutrients are resident either in the soil solution (water and dissolved minerals in the soil pores) or in the soil matrix (mineral particles and organic matter).  Two problems present themselves, however: (i) the concentration of nutrients in the soil solution is low and (ii) the nutrients that are resident in the soil matrix is immobile.  Plant roots have developed adaptions to allow growth into the soil matrix and capture of the nutrients needed for metabolic activity (Dr. Paul Schreiner, USDA-ARS) and we will discuss these later.

Soil composition affects the availability of nutrients for soil uptake.  Soil pH is a measure of the acidity (3.5 - 6.5) or alkalinity (7.4 - 9.0) of soil which, through its influence on nutrient solubility and micro-organism activity, affects the number and types of nutrients in the soil. Soil pH between 6 and 7 is considered optimal for vine plant growth as most of the needed nutrients and micro-organisms are available in that range.  The optimal soil type also has a moderate content of low cation exchange capability (CEC) clay (Clay minerals act as harbors for nutrients because the positive ions of the nutrients are trapped by the negative charge of the clay minerals.  The abundance and types of minerals determine whether the clay is classed as low- or high-CEC.).

Roots have developed a number of physical and chemical adaptations to allow them access to an immobile nutrient set resident in the soil matrix (Dr. Schreiner).  The first adaptation is the root size and structure.  The vine plant deploys an always-growing, three-part root structure to meet its needs for anchoring, water- and nutrient-acquisition, nutrient storage during plant dormancy, and hormone production.  As it relates to nutrition, the plant deploys quick-growing, short-lived roots close to the surface to aid in moisture collection and primary roots for nutrient uptake (The woody roots (anchoring and transport) take up limited amounts of nutrients due to the presence of a waxy coating designed to keep ions in.).  According to UCDavis, about 60% of a vine plant's root structure is located within two feet of the surface but individual roots can grow as deep as 20 feet depending on soil permeability, water table levels, and rootstock variety.

Source: bccs.bristol.ac.uk

The second adaptation is the formation of symbiotic relationships with arbuscular mycorrhizal fungi (AMF), a non-specific fungi which extends its apparatus beyond the plant's zone of influence in order to retrieve minerals such as Phosphorous and Zinc and, in return, utilizes plant-derived carbon for its growth and reproduction.  Both the plant and fungi benefit from this relationship.

A third adaptation is the ability to secrete protons, organic acids, and enzymes and release these into the surrounding soil in order to increase the solubility -- and absorbability -- of certain ions.

In order to effect nutrient transfer, the roots of the plant has to be in direct contact with the soil matrix and the nutrients have to be delivered to the root surface.  Nutrients reach the root surface in a combination of three ways: interception, bulk flow, and diffusion.

Source: baileybio.com

Only a small fraction of the plant's nutrient needs are met by interception.  In this case, as the root grows into new areas, it displaces nutrients resident in the soil matrix.  Once on the root surface, the nutrients transit through the root's plasma membrane using available ion-selective channels.  The transfer is effected as the ions flow from areas of high concentration to areas of low concentration.

Bulk flow is the movement of nutrients towards the root as a result of transpiration water uptake.  Water enters a vineyard through precipitation or irrigation and that water either runs off, flows to levels beyond which it can be accessed by the vine plant, or remains in the rooting zone where it is available for the plant's use.  The plant uses water as an internal distribution vehicle (in addition to other functions) and facilitates this by expelling water through pores (stomata) in the leaves.  As water is transpired from the leaves, replacement water is drawn in at the roots.  This replacement water moves undiluted nutrients to the root surface but also carries dissolved nutrients into the roots as a part of its transit. Nitrogen is the nutrient most frequently acquired by the roots in this manner.

Source: talktalk.co.uk

Diffusion is the mechanism whereby nutrients move toward the roots as a result of agitation caused by the concentration gradient that develops near the root surface as a result of nutrient uptake.  Phosphorous and Calcium are the nutrients most susceptible to this type of capture.

In addition to the above mechanisms, as mentioned previously, the plant can utilize AMF to reach beyond its depletion zone in order to bring Phosphorous to the root interface.

While the above treats "naturally" occurring nutrients, the viticulturist will fertilize if he/she determines that a nutrient deficiency exists.  The nutrients added to the soil will make their way into the plant in exactly the same manner.


©Wine -- Mise en abyme

The influence of soils on grape vine growth

The Douro (Portugal) and Carso (Friula-Venezia Giulia, Italy) wine regions are separated by the land mass that is Portugal and Spain, the full width of the Mediterranean Sea, and the Italian land mass but they have in common a lack of a "native" soil.  Even with this challenge, both regions still manage to produce high-quality wines.  I will detail the challenges presented to both regions and the solutions of choice but will precede that discussion with some background on soils and their role in the production of quality wine.

According to Christopher Bargman (Geology and wine in South Africa, Geoscientist 15(4), April 2005), soil is the major influence on the growth of the vine plant as it provides: (i) a supply of water; (ii) anchorage in the ground; and (iii) a source of nutrition.  According to education.mhusa.com, " soil is more than just dirt."  It is, instead, "... a complex system of decomposed rocks that have been enriched over time by decomposed organic matter."  The classic soil profile is shown below.

Source: westone.wa.gov.au

Adequate amounts of the appropriate nutrients are required to support proper growth of the vine, fruit development, and fruit maturity.  The table below shows the mineral requirements of the vine plant, the role of each mineral, acceptable ranges of each mineral in the soil, and the impact of mineral deficiency on the vine.

Source: Compiled from LGRGP.org and others

The key factors in nutrient availability are soil type, soil composition, and root structure.

The soil type dictates the quality of nutrients present and the adequacy of water drainage.  Our soil-type page shows the different types of soil that are of interest to the viticulturist.  The optimal soil type has a moderate content of low cation exchange capability (CEC) clay (Clay minerals act as harbors for nutrients because the positive ions of the nutrients are trapped by the negative charge of the clay minerals.  The abundance and types of minerals determine whether the clay is classed as low- or high-CEC.).

Soil composition affects root growth and development and the availability of nutrients for soil uptake.  Areas of interest here are soil pH, texture, and drainage.

Soil pH is a measure of the acidity (3.5 - 6.5) or alkalinity (7.4 - 9.0) of soil which, through its influence on nutrient solubility and micro-organism activity, affects the number and types of nutrients in the soil. Soil pH between 6 and 7 is considered optimal for vine plant growth as most of the needed nutrients and micro-organisms are available in that range.  Alkaline or acidic soils can be chemically treated to bring them closer to optimal.

Soil texture refers to the nature, size, shape, orientation, and arrangement of particles.  In our soil-type page we showed that sand, silt, and clay have standalone properties which are transformed when the soils are combined.  Clay forms flexible elastic bridges between soil particles to maintain soil structure and preserve porosity.  Pebbles and rocks in clay-rich soils break up the soil, providing pathways for water and root penetration.  Deep, rich soils will provide high-vigor growth and large, watery grapes.

Drainage Water is needed to transport nutrients to the vine plant roots.  Sandy, well-drained soils with little or no clay mineral content may provide inadequate amounts of nutrition, leading to reduced grape quality and a vegetal taste in the wine. Soils which retain too much water will exclude the oxygen needed for the nitrogen cycle.

Root Structure The roots of the vine plant: i) anchor the vine; ii) absorb water and nutrients; iii) store nutrients that nourish the plant during dormancy; and iv) produce hormones that control plant functions. The vine deploys a three-part structure to meet these varied needs.  First, quick-growing, short-lived roots deployed close to the surface are tasked with moisture collection.  Second, subterranean roots provide the anchoring function.  The principal roots are tasked with nutrient delivery and storage.  According to UCDavis, about 60% of the root structure of a vine plant can be found in the first two feet of the surface but individual roots can grow as deep as 20 feet depending on soil permeability, the level of the water table, and the rootstock variety.

Now that we understand the role of soils in the wine grape environment, we can go on to the next step in the Douro and Carso wine regions comparison.