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Physical fertility - soil structure

Well-structured soils allow air, water and roots to move freely through the spaces within and between soil aggregates. These soils have many aggregates and their friability makes them crumble easily in your hand.

Poorly structured soils have fewer, more closely packed aggregates, which are difficult to crumble. High bulk density and smaller pore sizes limit water and air entry and movement through these soils and restrict root growth.

The activities of soil invertebrates, micro-organisms and plant roots play a crucial role in soil structure by creating stable pores and aggregates. The burrowing activity of worms and other invertebrates create a network of large pores and channels, especially in the topsoil. Roots create similar networks of macropores, resulting in lower bulk density, improved infiltration and drainage, and better aeration of the soil.

The major factors influencing soil structure and physical fertility include soil texture, clay mineralogy, organic activity and physical disturbance.

Maintaining sufficient ground cover throughout the year is the most important way to build and maintain soil structure. Any activity that promotes healthy plant growth and builds up litter and soil organic matter (such as applying fertiliser or rotational grazing) will encourage plant root growth.

Activities that compact or damage soil structure (such as pugging or cultivation), or reduce the supply of litter and soil organic matter (such as overgrazing) have a negative impact on soil structure.