101 Questions answered
A Hidden Barrier to Crop Growth
The most obvious answer is the soil is too hard for crop roots to grow through,but compacted soil creates other problems for crop roots.
When soil becomes compacted, the peds (aggregates) are squashed together to make bigger peds,increasing soil strength and reducing pore space. The same mass of soil fills a smaller space.
Bigger aggregates mean there is less surface area for microorganisms to colonise and for nutrients to adsorb to.
Fewer pores means:
- Less oxygen. Roots and beneficial soil microbes need oxygen:
- Anaerobic bacteria love compacted soils due to the lack of oxygen. They can produce toxic compounds such as hydrogen sulphide that can limit root growth and predispose plants to root diseases.
- Higher risk of waterlogging:
- Can eventually kill plant roots.
- Nitrogen can be lost as a gas through denitrification.
- Lower water holding capacity means less water is available for roots to use.
- Roots release ethylene and concentrations build up in the reduced pore space. Too much ethylenestunts roots and inhibits root function, affecting overall plant health.
- Plants are more susceptible to pathogen attack because of all of the above – overall reduced roothealth from stress and stunted root growth.
What does this mean for roots?
Dense soil is physically harder for roots to push through, causing less root branching and a less dense root system. It is now harder for the roots to access water and nutrients for two reasons:
- Being a smaller root system, they can’t explore as far, and
- Because there are fewer pores and less surface area, there is less water and nutrients to find.
The lack of pore space also means less oxygen for crop roots and a higher risk of waterlogging, leading to nitrogen losses, more anaerobic bacteria, and a weakened root system that is more susceptible to disease.
