Soil structural decline - Soil Essentials: Managing Your Farm's Primary Asset - page 132

By stock
The pressure of stock feet on wet soil can severely damage soil structure by causing
compaction and pugging. This is especially so if plant growth is poor and not
many roots are present to hold the soil together.
By salt
The sodium in salt will bind to clay particles and replace the calcium that helps
hold the soil together. This causes the clay to disperse, and the detached clay
particles then clog the pore spaces. This reduces the aeration and the permeability
of the soil that restricts water movement and plant root growth. Salt in the soil
reduces the ability of plants to take up water, and the sodium in the salt can be
toxic to plants, depending on how concentrated it is in the soil.
Note . Irrigating sodic soils with slightly salty water can retain good soil
structure, but crop production will be limited by sodium toxicity.