Duration and Setting
Twenty minutes to 24 hours in the classroom.

Summary
This activity enables students to conduct experiments on soil to determine the best use of the soil and then develop a plan to improve the soil's function to suit their needs.

Student outcomes
This activity will enable students to:

• Observe the stability of soil aggregates in water and the impact of soil aggregation on soil function
• Assess what they can do to improve the function of their soil

Background notes for teachers

Soil's ability to aggregate (or clump together) is important for plant growth. Pores within and between soil aggregates allow water and oxygen to move into plant roots freely, which is essential for optimal plant growth.

Soil aggregates, when immersed in water, break open (slake) and disperse easily, indicating that the soil is prone to waterlogging and/or crusting. You can help with this by adding gypsum to improve the stability of aggregates. Organic matter can also help bond the aggregates together so they do not slake and disperse as easily.

This simple experiment will show if your soil has the ability to allow water and oxygen to move through the soil to root cells where it is needed to keep the plant alive.

Slaking - only relevant for surface soil. Problems associated with slaking include crusting, reduced air and water movement into surface soil.

Dispersion - more of a chemical effect due to too much exchangeable sodium (compared to calcium) attached to clay particles. This forces clay particles to swell and separate - giving a 'milky' solution. If this occurs in surface soils, they are likely to crust and seal - restricting plant emergence and water and air movement.

next» Healthy Soil for Your Plants - Part 2