• In order to understand compaction, we must first understand the makeup of soils. Soil consists of organic matter, minerals and pore space. The mineral fraction consists of a combination of sand, silt and clay particles. These particles do not fit together tightly but are surrounded by open pore spaces. The pores are important because they hold the air and water. Compaction pushes the particles together thus reducing the pore space and the capacity of the soil to hold adequate amounts of air and water. (Kansas State Univ.)
  
  

• Root penetration through the soil decreases as compaction increases. At 300 psi most root growth stops. Reduction of root percentage penetration is an almost linear relationship as compaction increases from 0 to 300 psi. (Penn State University)
  
  

• Degree of compaction can be determined using a Penetrometer.
  
  

• A moderate amount of compaction in the root zone is desirable in order to provide adequate seed to soil contact.
  
  

• Freeze and thaw cycles only reduced compaction in the top 2 – 5 inches of the soil. Compaction beyond this depth was not affected by freeze – thaw cycles. (Univ. Of Minnesota)
  
  

• Soil compaction can significantly reduce potato yields. Deliberate compaction reduced yields by 54% in the Red River Valley, by 21% at Grand Forks Minnesota, and 35% at Morris Minnesota. (Univ. Minnesota)
  
  

• Roots require air for biological activities such as respiration. Pore space is necessary for gaseous exchange- 10 – 20 % of the soil component should be air. (Ohio State Univ)
  
  

• Nearly 80 % of the compaction caused by wheeled traffic occurs in the first pass. (Ohio State Univ.)
  
  

• Effects of Moisture “canola and mustard are the poorest adapted to a dry rooting zone. Therefore, these crops in dryland areas are best suited for production on fallow where the soil profile is recharged with moisture at seeding....The amount of water that can be stored varies widely among soils depending on the number and size of pore spaces they contain, and the depth to layers of soil difficult for water to penetrate. The number and size of pore spaces in a soil depend on its texture, organic matter content and structure.” (Canola Council Ch 4)
  
  

• “Besides limiting yields, soil compaction has been identified as a key factor that aggravates or increases the soil emission of nitrous oxide (N₂O). Because soil compaction results in a lower soil oxygen status, reduced root growth rates, and reduced nutrient absorption rates...any nitrate  present in the surface soil under warm, wet to near saturated conditions...which is not rapidly absorbed by the roots ...can be quickly converted by certain soil microorganisms to N₂O. Even mild compaction can increase N₂O emissions by more than 20%.” This of course represents a loss to your fertilizer investment. (Plant Nutrition Today Summer 2008)
  
  

• “Soil compaction is like a silent thief whose robbery is not discovered until the symptoms of damage are severe. It increases soil bulk density, decreases soil porosity, lowers total water holding capacity, lowers the plant-available water capacity, causes significant resistance to root penetration and root elongation. It can severely limit soil infiltration of rainfall and irrigation water and contribute to increased runoff loses. (Plant Nutrition Today Summer 2008)
  
  

• “More than a century cultivating at the same depth and at different soil moisture contents has left most southern Australian soils compacted. Compaction reduces yield and economic viability of many farms. The South Australian Research and Development Institute (SARDI) established a long term conservation tillage trial in 1978 and took us 16 years to realise that that poor water use efficiency in South Australian red-brown earth was mainly associated with subsoil problems. We also found that the use of no-till, without first removing compaction, would take more than 15 years to satisfactorily repair compacted sub-soil.” (Malinda and Darling, Australian Crop Science Symposia 2004)
  
  

• “Conventional seed bed tillage did not alleviate the negative effects of compaction on crop growth even though most of the compaction occurred in the plough layer” (aprox 6”)   (Carefoot and Lindwall)
  
  

• High productivity of crops depends on the efficient use of rainfall and available water held in the soil profile. The amount of water available to plants is the difference between the water held at field capacity and the permanent wilting point. Each soil has a finite capacity to hold water that is plant available and this capacity varies with soil type. Soil texture, soil structure, bulk density and organic carbon content all contribute to this capacity.

In order for plants to access this water (and nutrients) their roots must be able to the volume of soil in which the water is held. Soils dry out from the top down therefore optimum productivity is typically found where plant root have the freedom to penetrate the deeper subsoil layers which contain water and nutrients. Any soil conditions that limits the volume of soil that roots can exploit will reduce the plants access to water and nutrients. These limiting conditions can be chemical (salinity) or physical (compaction) in nature. (Baldock, O’Leary, Sadras; CSIRO Summer 2002)

• Mechanical impedance refers to the resistance offered by the soil matrix against deformation by growing roots. Except for cracks and macropores that provide niches for root growth root elongation in soils is only possible to the extent to which the root pressure exceeds the mechanical resistance of the soil.
  
  There are many and various reasons for differences in root response to soil strength between plant species, the difference in the average diameter of roots being one of them. For a given soil bulk density the mechanical impedance increases as the soil dries out. This is because soil particle mobility decreases...and accordingly root elongation is suppressed. However in compacted soils at a given bulk density this effect can be even greater in wet compared to dry soils indicating that factors other than mechanical impedance are involved (oxygen deficiency, elevated concentrations of ethylene).
  Typical responses of roots to increased soil strength include inhibition of elongation rate of    the main axis, enhanced formation of lateral roots which are initiated closer to the apex with a higher density per unit root length.
  
  A reduction in root growth in the zone of high soil strength (compaction) is often compensated for by higher growth rates in loose soil above or below the compacted zone. ...Despite the various compensatory reactions of root systems in compacted soil, plants usually grow poorly in soils of high bulk density. Insufficient water and nutrient supply might play a role but often both shoot growth and transpiration are first reduced regardless of the plant nutrient and water status. In compacted soils shoot growth is also more often depressed than root growth, suggesting root- derived hormone signals in response to soil compaction.  (Mineral Nutrition of Higher Plants, P.528 – 530, Marschner)
  
  

• Restriction of the rooting volume...has inhibitory effects on shoot growth similar to those of soil Compaction
  

  Under root restriction stress there is a very a very similar decline in root and shoot dry weight. A reduction in leaf elongation rates is the most distinct response to root restriction stress, and this reduction is primarily the result of reduced cell division and not so much of cell size. (Mineral Nutrition of Higher Plants, P.530 – 531, Marschner

• Compaction as measured by surface bulk density could be significantly (0.31 g/cm) increased by with eight passes of a standard tractor. (Al-Ghazal  2002 Spatial Variability of measured Soil Properties)
  
  

• In solonetzic soils a hard “Ped” is caused by a reaction between the soil and soil salts, generally sodium sulphates, although bicarbonates and sulphate salts of magnesium and calcium are also present. These columnar structures occur in the B horizon. Water, air and roots are incapable of penetrating these structures.
  
  

• The main problem of most Solonetz soils is the very limited penetration of water through the B horizons. (Univ. Alberta)
  
  

• In Alberta the Bnt horizon starts at 3 – 7 inches and goes to a depth of 7 – 13 inches. (U. Alberta)
  
  

• A recent (Feb. 2002 Can. J. Soil Science) research paper “Longevity of deep ripping on Solonetzic and associated soils” (in Alberta) showed;
          1.  A significant increase in yield of wheat, barley, oats and canola at 6 of 10 sites over a 16 year 
              period,all  sites had a mean overall yield increase
          2. The yield increase ranged from 4 – 41% with mean grain yield higher for the deep  ripping 
              treatment  at all sites.
          3. Deep ripping improved the movement of water through the hard pan layer.
          4. Deep ripping is a physical treatment and had no effect on the soil chemistry.
  
  

Benefits of NonInversion Tillage With Agrowplow

• Greater depth of rooting for the crop.

• Roots are able to access nutrients that were made unavailable in the zone of compaction.

• No mixing of the soil horizons.

• Greater depth of moisture penetration.

• Greater rooting depth with improved access to stored nutrients.

• Elimination of wet spots caused by poor moisture penetration / reduced water logging.

• Improved storage of moisture to a greater depth.

• Improved nitrogen storage / maintenance.

• Improved biological activity.

Compiled by;
Dennis Laughton
Agrowplow Soil Care Systems International Pty. Ltd.
403 860 7199
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