SOIL COMPOSITION

  • Mineral-45%
  • Water-25%
  • Soil Gases-25%
  • Organic matter-5%

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  • Macrospore-Earthworms & root channels(drainage)
  • Microspore-water holding capacity,mineral

PLANT NUTRIENTS

  • soil nutrients are positively charged ions (cation) & negativly charged ions (anions).
  • Clay & organic matter particles are negatively charged ,Cations adsorbed to these particles,soil capacity to hold these cations is the CATION EXCHANGE CAPACITY(CEC).
  • CEC measures the no.of adsorption sites in a soil to adsorb & release cations.
  • low CEC soils leach & store less nutrition.

BULK DENSITY

Bulk density isdefined as the dry weight of soil per unit volume ofsoil.

Table 1. General relationship of soil bulk density to root growth based on soil texture.
Soil Texture Ideal bulk densities for plant growth (g/cm3) Bulk densities that restrict root growth (g/cm3)
Sandy < 1.60 > 1.80
Silty < 1.40 > 1.65
Clayey < 1.10 > 1.47
  • Soil’s ability to function for structural support, water and solute movement, and soil aeration
  • Bulk density is also used to convert between weight and volume of soil.
  • It’s expressed as gram per cubic centimeter(g/cm3).

HOW DOES BULK DENSITY AFFECT PLANT GROWTH ?

  • Highly bulk density (HBD)is an indicator of low soil porosity , poor plant growth , restrictions to root growth ,poor movement of air & water.
  • HBD can cause compaction & compaction can result in shallow plant rooting.
  • HBD is not good for plant growth.
     

     

     

    BULK DENSITY MEASUREMENT IN LABORATORY METHODS.

     

     

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    Lower bulk density is always better for plant growth

    SOIL TEXTURE is defined by size distribution or mass fractions ofsoil primary particles (individual grains and particles).

    ● Primary mineral particles formed through physical andchemical weathering of parent material and refractory organicsubstances make up the solid phase.

    ● Particle size distribution and shape are the most importantcharacteristics affecting:

    – pore geometry

    – total pore volume (porosity)

    – pore size distribution

    – solid surface area

     

    SOIL STRUCTURE-

    The arrangement of the solid parts of the soil and of the pore space located between them. It is determined by how individual soil granules clump, bind together, and aggregate, resulting in the arrangement of soil pores between them. Soil structure has a major influence on water and air movement, biological activity, root growth and seedling emergence.

     

      There are different types of soil is formed.

    1. Loam : proportion of sand , silt and clay feel approximately equal.
    2. Sandy loam : it is very fine loam to very coarse.feel is quite sandy or tough. But contains some silt and small amount of clay.
    3. Silt loam : silt is dominant size particle in silt loam.feels quite smooth or floury.
    4. Silty clay loam :silty clay loam is smooth to dry when moist. (slick or sticky) silt 7 clay are present in silty Clay loam but silt is dominant part of soil.
    5. Clay loam : clay dominants a clay loam smooth when dry & slicky when wet. Silt & sand usually are present in noticeable amount in this soil texture.
    6. Clay : clay has fine texture.absence of sand or silt.clay holds its from whemn wet & pressed between the thumb & middle of forefinger a ribbon forms that can be several inches long.
    7. Clay are very hard & dry.

     

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