Campbell Scientific Sentek TriSCAN® Manual v 1.2a User Manual

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TriSCAN Manual Version 1.2a

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texture in governing how much water and air move in soil and therefore their availability to crops. Roots
penetrate more easily and rapidly in soils that have stable aggregates, than in similar soil types that have no
or highly developed structures. The effectiveness of soil moisture, air and nutrient utilization, is related to the
efficiency of root colonization of the entire soil profile.

Soil depth

The effective depth of soil affects the extent of root penetration. The deeper the soil, the greater the volume
of soil that is available for gaseous exchange and water and nutrient uptake. Drainage is also affected by
effective depth.

Soil compaction

Soil compaction from farm machinery can change pore size and distribution resulting from the natural
arrangement of the sand, silt and clay particles. This can cause reductions in water infiltration rates, and air
and water permeability within the soil profile. The resultant impact upon the effectiveness of root penetration,
air exchange and nutrient and water uptake, affects plant growth efficiency and hence water and nutrient
uptake.

Salinity

Salinity lowers osmotic potential, reducing the efficiency with which nutrients and water are taken up by the
plant. The dominance of the contributing ions can result in a nutrient imbalance causing deficiencies of
essential macro and micro nutrients. The reduced plant health and vigour affect crop water use.

Water tables & drainage rate

Poor drainage can lead to the development of water tables and/or cause a temporarily saturated soil profile.
The presence of impermeable soil layers can cause the formation of perched water tables, which saturate
parts of the root zone. Efficient gaseous exchange becomes impossible, and plant health and water use is
reduced.

Organic Matter

The presence of organic matter and humus increases the cation exchange capacity (CEC), water-holding
capacity and structural stability of soils. This influence is predominantly in the top soil, although lamellae
(thin organic matter layers further down the profile) can be important properties.

Type of clay

Clays are highly variable in their water-holding capacity, CEC (ability to hold and release nutrients) and
stability (shrink-swell potential). At the one end of the spectrum, the so-called smectite-type clays have high
CEC’s, water-holding capacities and low stability. Highly weathered (kaolinite or oxide) clays, at the other
extreme, are stable with relatively lower CEC’s and water-holding capacities. Most soils have a mixture of
clay types depending on parent material and climate. At present TriSCA N is only recommended for
predominantly sandy soils.

Soil chemistry

Acid, alkaline, sodic (soils characterized by a dominance of sodium ions) or nutrient deficient conditions
impact on expected soil chemical properties. For example:

•

pH conditions change CEC; the availability of nutrients (by changing their form) and the solubility of
ions.

•

High levels of sodium can lead to structural collapse.

Rocks and stones

Stones and rocks within a soil profile occupy part of the soil volume and hence reduce the soil water storage
capacity. Very stony soils have a substantially lower water holding capacity than soils of the same texture
that are free of stones.