Physical Fertility

Many soil physical properties influence plant growth. If you have looked at the Hydrological Cycle and Soil Structure sections, you will be familiar with some of these.

However, there are just four physical attributes of soil that affect plants directly. All others do so via their influence on one or more of these four properties. Drag the four labels corresponding to the key soil physical properties to the boxes.

 

Soil Tempreature

Temperature influences biochemical reactions taking place in the soil, including those within plants. Seeds have an optimum temperature range for germination, and root and shoot growth rates are also affected. Soil temperature is mainly determined by climate, but is influenced by factors like surface cover (plants, stubble) and soil colour

 

Aeration

Plant roots need oxygen for respiration. Exchange of O₂ and CO₂ requires continuous air-filled pore space between the roots and the soil surface. In the absence of oxygen, roots are unable to take up water and nutrients, and plants wilt. Waterlogging is the main cause of poor soil aeration. Some plants have adapted to living in waterlogged soil (e.g., rice and marsh plants) and are able to transport oxygen from the leaves to the roots.

Water Availability

Plants must take up water to balance losses by transpiration. Nutrients are carried with the transpiration stream, and water is essential to all plant physiological processes. For annual crops like cereals, yield is directly related to the amount of water transpired. There is more on water availability in the module on Water Retention and Potential in the Hydrological Cycle section.

 

Soil Strength

Plants need the soil to be firm enough for support, but not so hard that elongation of roots is impeded. If root growth is restricted, plants have a smaller volume of soil to explore for water and nutrients. The formation of hard surface crusts can also restrict the emergence of seedlings. There is a module on Soil Strength in the Soil Structure section