Title : What Is Soil Compaction?
Visit Count : 2330 Time(s)
Upload Date : 8/2/2016 - 3 Year(s) ago
Category : agricultural technical notes
Tuesday, August 2, 2016
Visit Count : 2330 Time(s)
Upload Date : 8/2/2016 - 3 Year(s) ago
Category : agricultural technical notes
Simply put, soil compaction is the loss of pore space within a soil profile caused by the compression of soil particles due to natural, human, and animal activities. Soil compaction has been found to occur at any depth up to 24" and is generally categorized in three specific groups.
1. Surface Soil Compaction (Hardened, cracked, soil found on the surface)
2. Sub-Surface Soil Compaction (Compacted layers found 10" deep and above)
3. Deep Soil Compaction (Compacted layers found below 10" deep)
Ideal, non-compacted, soils will be composed of 45% mineral particles, 5% organic matter, and 50% pore space (25% water and 25% air). As the soil is compacted by moving soil particles closer together, pore space is dramatically reduced. This restricts water flow within the soil, reduces air pockets, and inhibits proper root development.
The Causes of Compaction
As farming practices continue to evolve, compaction has become harder to reduce and prevent. The use of heavier equipment, multiple field operations, operating in less than ideal conditions due to time constrictions, and the consolidation of crops used in a rotation, all provide elements for "more extensive and deeper compaction" Additionally, since farmers cannot easily see if they have compacted soil, many are not aware that they have a problem; and some older methods believed to help solve compaction problems have been proven ineffective when tested.
1. Wheel compaction from heavy equipment
Researchers agree that the primary cause of soil compaction remains tires from heavy equipment running through the field. Tractors alone have increased in weight over the past 70 years from less than 3 tons to about 20 tons. Although heavier machines may not produce more compaction near the surface when compared to lighter machines, they produce compaction deeper within the soil structure. Additionally, dual tractor tires do not prevent compaction, they may reduce the depth of compaction, but they also double the area affected.
2. Multiple Field Operations
Those growing corn on corn face a residue challenge that can take multiple tillage operations to overcome. Because of these heavy residue crops being planted year after year, tandem and offset disk use is increasing. These tillage processes create a thin layer of compaction with each pass you make through the field. "Continuous moldboard plowing or disking at the same depth will cause serious tillage pans (compacted layers) just below the depth of tillage in some soils." Additionally, newer seed hybrids that are more resistant to disease and climate conditions often leave behind tougher residues that do not break down as easily and often require additional tillage. These extra passes through the field will cause additional compaction within a soil profile, but can be taken care of by varying the depth of tillage over time or through "special tillage operations."
3. Time limitations
The average number of acres a person is able to farm has dramatically increased over the past few years. Although larger machinery assists in making this possible, producers are finding that time constraints are forcing them to operate in a manner that promotes soil compaction.1 The best example of this is operating on soils that are too wet because time allows no other choice. Soils are weaker when they are wet and "considerable compaction" often takes place due to this practice. The question of "how wet is too wet?" can be difficult to answer. There are varying maximum moisture contents for every soil type and infrastructure situation which, if exceeded can be "severely compacted with minimal effort."
4. Less Diversification in Crop Rotations
The crops you plant can have a dramatic effect on the susceptibility your field has to developing compaction due to the organic matter and root penetration that they provide to the soil structure. Since organic matter is a key component in soil composition, having less of it will weaken the soil and cause compaction to develop more easily. Growing potatoes year after year is a good example of a practice that will decrease organic matter in the soil structure. Because potatoes are a low residue crop, organic matter from previous years will disappear and the potato crop will not provide enough residue to replenish it.
"Organic matter is the fuel, short-term building blocks of soil structure, and supply warehouse for living things in the soil. As organic matter decomposes and mineralizes without adequate replacement, soil becomes more compacted. Bulk density increases and aggregate stability declines as organic matter is “burned “ out of the soil."
Lessened crop diversification has also eliminated the use of deep rooted, perennial crops in some areas. The root systems from these crops help to reduce the effects of compaction by recreating porous areas in the soil structure.
http://www.ext.colostate.edu/mg/gardennotes/215.html
http://www.extension.umn.edu/agriculture/tillage/soil-compaction/
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex13331
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