Vineyard Soil – Dirty Talk
When working in the world of wine people wax lyrically all the time about vineyard soil. The fact is soil is our life support system and without it life would be near impossible. It’s ability to retain water and nutrients, fix nitrogen, decompose organic matter and house countless organisms makes it a vital part of the earth’s ecosystem. Whether some chap in red trousers can taste it in a wine isn’t so important, however having detailed knowledge of your soil so that you can create and manage a healthy, sustainable soil is crucial to the success of planting and managing any vineyard. Here are some terms that you may find useful.
Soil Parent Material
Parent material is another name for weathered rock and over millions of years ancient rocks and coastlines are developed into soil through physical and chemical actions, influencing soil texture, structure, drainage and chemistry.
- Mineral particles (sand, silt & clay)
- Water (containing plant nutrients)
- Organic matter (living, decomposing or dead organic compounds
- Pores (air spaces)
Soil Organic Matter
It is estimated that 1,000,000,000 bacteria live in 1g of soil. It’s these microbes that break down plant residues and green manures releasing carbon dioxide to form humus. Organic matter will help to provide a balanced ecosystem for microbes and insects by improving soil structure, water retention/drainage and nutrient availability, symbiotically improving plant health and growth.
A sequence of horizons (layers) that can be identified by differences in colour, texture, structure and thickness. The arrangement of these horizons is known as the soil profile. Soil scientists categorise these horizons using letters (O, A, B, C & E) however when analysing vineyard soils we are most interested in the A horzion (top soil) and B horizon (sub soil).
Soil texture is defined as the proportion of sand, silt and clay particles that make up the mineral fraction of soil. Scientists use the proportions of these fractions to identify the soil texture triangle.
The particle size affects the surface area in comparable volumes, with smaller particles being able to retain a greater volume of water and nutrients, this when combined with the organic matter content can have a number of effects and influences on crop performance.
- Sand (0.06-2.0mm)
- Silt (0.002-0.06mm)
- Clay (<0.002mm)
Soil structure is the physical condition of the soil and best describes how the soil constituents bind to aggregates or structures. There are different grades and classes used to categorise soil structure all of which will have an effect on soil fertility, water holding capacity, root development and plant growth.
Bulk density is the weight of a soil in a given volume and reflects water movement, root growth and nutrient uptake with compact soils having a higher bulk density. Soil compaction affects root growth and microbial activity and can be caused by machinery use, heavy rainfall, animals and poor soil management. Reducing tillage, introducing cover crops and appropriately timing machinery operations can all help relieve soil compaction, improving bulk density.
Available Water Capacity (AWC)
The available water capacity of the soil is measured as the volume of water held against gravity, available for root uptake. It is the water held between field capacity (water held after drainage) and the wilting point (minimum soil moisture required to prevent wilting). AWC levels will vary depending on soil texture.