Soil structure refers to the size, shape and stability of soil particles and the size between the groups of particles, or aggregates. It determines the ability of the soil to hold moisture, nutrients and air and to resist erosion or compaction. Canterbury soils lack soil bonding compounds, so tend to have a naturally weak structure.

Poor soil structure means greater soil instability- leading to more erosion problems. It can also lead to soil compaction, thereby increasing the rate of runoff of water and other materials like fertisiler and the nutrients from animal manure.

The Cause

Cultivation and cropping damages soil structure by crushing the aggregates by removing organic matter from the soil. Organic matter ensures aggregate stability.

Burning off vegetation and grazing can reduce the organic matter of the soil leading to less stable soil. The continual use of heavy machinery can also lead to problems with soil compaction and "pugged" soils are common where waterlogged soil is tramped by stock.

The Options

In Canterbury, the main sustainability issue associated with soil structure deterioration is soil erosion, so the management options are the same as in the induced erosion section below.

provide information and advice on maintaining a good soil structure
provide information and advice in the preparation of property plans that identify vulnerable areas and encourage appropriate cultivation practices and shelter belt planting
help with preparing codes of practice for cultivation, earthworks, grazing and vegetation removal
prepare rules to control land use in the areas at greatest risk and to control high impact land use activities