Hi, I’m Anne Verhallen, Soil Management
Specialist with the Ontario government. In this segment on soil structure, I’ll show
you how your crop rotation and tillage choices influence soil aggregate stability.
Soil aggregates are small crumbs or chunks of soil. Often you will see large clods of
soil but these break down further to these smaller aggregates.
Soil particles or basically the sand, silt and clay particles are held together by complex
sugars and other materials released by plant roots and soil life to form aggregates.
But are they stable? Can the aggregates resist the action of water?
Here we have four jars filled with water. In front of each is a large chunk of soil.
The chunks are all the same soil type but they have come from different management systems.
The soil chunks have all been dried so that they are all starting at the same moisture.
One is from continuous soybeans under conventional tillage, the second is from a corn/soybean
rotation also using conventional tillage. When I say conventional tillage in this case
I mean the soil is plowed. The third is also from a corn/soybean rotation
but is no-tilled. The fourth sample is from a more diverse crop rotation of corn/soybeans
and winter wheat with red clover underseeded in a no-till system.
These mesh baskets will hold the chunks under the water and allow us to observe the strength
of the aggregates. Watch as the water enters the pores of these
soil chunks. The stable aggregates stay together while soils with less stability will start
to melt apart. Generally the soils with more diverse crop
rotations will return more residue to the soil and build stronger, more stable aggregates.
Reducing tillage or using no-till helps to maintain soil organic matter and sustains
active soil life. In turn this helps to build stronger soil aggregates. Using both reduced
tillage and a diverse rotation will achieve this faster.
So which soil has the most stable aggregates? You can tell by looking for the clearest water.
Stable aggregates resist erosion and soil compaction. They also build a better soil
structure which is critical for emerging plants, the roots of growing crops and water infiltration.
For more information on soil structure and building stable soil aggregates, please visit
our website or give us a call.