A weekly report prepared by the staff of the Ministry of Agriculture and Food (OMAF) and the Ministry of Rural Affairs (MRA). If you require further information, regarding this report, call the Elora Resource Centre at 519-846-0941. Office hours: 8:30am to 5pm. For technical information, call the Agricultural Information Contact Centre at 1-877-424-1300 or visit the OMAF website: www.ontario.ca/omaf and/or the MRA website: www.ontario.ca/mra
IS YOUR SOIL IN GOOD PHYSICAL SHAPE?
Soil health is broken down in to three components: physical, biological and chemical. Each component is important, but the physical component can have a significant impact on yield. Physical aspects break down into two main areas: soil structure, including aggregate stability, and available water capacity.
Aggregate stability is a measure of how well clumps of soil stay together when they are subjected to a test with water or simulated rainfall. Soil aggregates with good stability will mostly stay intact during the test. Soils with poor stability will breakdown into individual particles.
Soil with poor aggregate stability is prone to water erosion. When raindrops hit the soil the individual particles are easily broken away and washed down the slope and potentially off the field. The same is true for wind erosion. Particles are more easily broken off and blown with the wind. Poor aggregate stability also increases crusting. The rain hits the soil surface breaking the aggregates apart and spreading them across the soil surface filling the soil pores. When the soil dries, it is a solid layer that slows water movement and makes it difficult for crops to emerge.
Soil structure refers to the way soil particles cling together to form aggregates. When individual particles are aggregated, they form larger, relatively stable primary structures. It also encompasses how particles are bound together and the spaces or pores in between. Structure has a significant effect on soil water properties and the ability of soil to resist erosion. Good soil structure increases porosity, aeration, and drainage while permitting easier root penetration, all of which are important on soils with limited internal drainage, such as clays. Conversely, poor soil structure in the topsoil produces hard, massive clods, which makes a poor seedbed for germinating crops.
Poor structure in the subsoil results in dense, compact properties which limit root and moisture penetration. Clay particles tend to cling tightly together and resist separation more than sand particles. As organic matter decomposes to humus, a variety of compounds are released which “glue” soil particles together.
Soil structure is formed by:
• drying and wetting or shrinking and swelling, creating cracks and planes of weakness for roots
• freezing and thawing
• removing water, root exudates or organic materials that bind soil particles and the formation of root channels
• animals like worms and beetles, moving soils, mixing and releasing organic materials
• microorganisms breaking down plant and animal residues
• tillage reducing the size of aggregates, an artificial way of creating structure in some soils, generally not long lived
Tillage breaks down soil structure, so minimum tillage or no tillage is the best. Increasing organic matter in the soil with manure, or other organic materials such as compost, along with a diverse crop rotation and cover crops will improve soil structure.
Soil compaction is a part of the soil profile that has poor structure. The compacted layer lacks good structure, making it difficult for roots to grow through and for air and water to move through. Taking measures to minimize compaction, such as keeping axel loads below five tons per axel, reducing traffic in the field, making sure the soil is fit and using radial tires and reduced tire pressure, will help prevent the problem.
Plant growth depends on the water stored in the soil. Available water capacity is a measure of the soil water that is available to the plant. Water is stored in the soil in the pores and in organic matter. Adding organic matter, such as manures and composts, is a good way to improve the water holding capacity of sandy soils.
Soil that is in good physical shape will have good soil structure. A well-structured soil will allow water to move through the soil, air to enter the soil, will not crust and favours good root growth.
Minimizing tillage and compaction, using a multi-crop rotation including cover crops and adding organic materials such as manure and composts, will greatly improve the structure of the soil.
RECENTLY RELEASED PUBLICATIONS
–Guide to Fruit Production 2014/15;
–Guide to Weed Control, 2014/15, Publication 75;
–Thrips in Greenhouse Crops: Biology, Damage and Management, 14-001/002;
–Fungus Gnats and Shore Flies in Greenhouse Crops 14-003/004;
–Maintenance of a Subsurface Drainage System 13-037/38;
–Field Crop Protection Guide, Publication 812.
