5.2 - soil texture

soil is made up of:

• sand → largest particles so water passes quickly

• silt → finely ground particles of parent rock → medium particles

• clay → smallest particles → retain water

highly productive soil characteristics

• adequate humus content to retain moisture

• optimal pH 5.5-7.0 for plant growth

• rich microbiota

• presence of sufficient nutrients and minerals

• balanced drainage

• deep soil layers provide better plant support

loam soils

soil with balanced mixture of sand, silt and clay

• most productive

determining soil properties

• organic matter

  • mass before and after burning

• water storage capacity

  • mass before and after drying in over

• infiltration

  • drainpipe test

• bulk density

  • volume of soil before and after dried in oven

• soil colour

• soil pH

• soil texture

  • sifting through increasingly smaller sieves

  • a feel test

  • jar test → separating layers

  • texture triangle

bulk density definition

how densely packed the soil particles are including air spaces

negative feedback loop in soil

growth of decomposer population → reduced organic material → reduced growth in population

positive feedback loop in soil

growth of decomposer population → higher potential for reproduction → …

carbon release from soils forms

• as CO2

  • due to global warming → temp → microbial respiration

  • due to mechanical cultivation → disturbance → oxidation → metabolism of aerobic microorganisms

  • due to drainage

• as methane CH4

  • due to global warming