Definition - What does Soil Structure mean?
In the context of viticulture, soil structure refers to the how the individual solid soil components layer and arrange themselves with pore space. The composition of soil and pore space is known as soil aggregates. Soil structure is determined not only by the soil texture and soil composition but also by microbial activity in the soil, growth of roots, activity of animals as well as temperature and moisture.
WineFrog explains Soil Structure
The soil structure in a vineyard plays a large role in determining the health of the vine and the fruit that it bears. Soil needs to be nutrient rich, but also loose enough to allow water to reach the roots and for the roots to grow. Soil that is compacted will not distribute water properly or allow for proper root development. A porous soil with balanced structure allows roots to easily grow and expand while also storing and distributing hydration and nutrients.
Soil is composed of silt, sand and clay, but the amounts and distribution of the aggregates is what determines the soil structure. Aggregates determine soil structure by their shape, size and stability; the shape of the aggregate largely determines stability. Aggregate shapes include: single grains, blocky, prismatic, granular, crumb or structureless. Aggregate structure determines how porous the soil is, which determines how easily the soil can absorb, store and distribute water. The structure of the aggregate is determined by the composition of the soil as well as all factors that affect soil; for instance, it is possible for the structure of the surface soil to be compacted due to rainfall, which can overtime reduce the amount of water absorbed into the sub soil.
The roots of grape vines naturally create porous structure and deposit organic matter, as they grow and die in the sub soil. To promote balanced soil aggregates vineyard managers can add organic material to the soil which promote a crumb-like or granular soil structure and promotes microorganism activity which supports the sub soil structure.