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Horticulture 1000
HT1033 - Soils 3 - Lime
Increasing organic matter Cultivation


Lime is finely ground limestone, which is calcium carbonate. Lime is effective more quickly as a soil conditioner and to raise pH when it is finely ground.

Dolomite lime can also be used. It is a kind of  limestone that contains magnesium as well as calcium.

Advantages of adding lime

  • Adding  lime makes acid soils less acidic. A less acidic soil will make more nutrients available to plant roots and therefore improve plant growth.
  • Lime improves soil structure. When lime is added to clay soil, the tiny clay  particles group themselves around the lime particles and together form  larger particles. The process is called flocculation because it reminded someone of a flock of sheep  coming together. Flocculation creates more air spaces, so the soil drains  better. The soil is easier to cultivate and for roots to grow in. If humus  is present, it binds the larger particles into crumbs and so produces a  good crumb structure.
    Lime improves soil structure
  • Liming  encourages the activity of soil organisms like earthworms and bacteria.  Very acid or very alkaline soils reduce the activity of soil, which is  needed to decompose organic material.
  • Liming  can make some nutrients more available to plants. For example, if the soil pH is above 6, phosphates are more available.
  • Lime  supplies calcium to the soil that is needed for plants' cell walls.

Applying lime

In a home garden:

Adding lime to soil
  • dig the soil
  • sprinkle lime over it
  • rake it into the surface    layer of the soil
  • water the soil with a sprinkler    or hose
  • leave the plot for two weeks    before planting.

On a commercial property:

Adding lime to soil
A truck, tractor or quad    motorbike will be used to apply the lime. Aeroplanes are also sometimes used.

The amount of lime that is used depends on the:

  • soil pH
  • plants that are being grown
  • soil texture.

Complete Activity 5A in your workbook

Key points   Key points

Lime is  considered to be a soil conditioner. It can be used to raise the pH of a soil  to make it less acidic. It will also flocculate clay particles so they will  form crumbs rather than clods.

In a soil with a pH of  about 6–6.5 most minerals are dissolved in soil water and can be used by  plants.

By adding lime  to the soil, plant growth is improved because:

  • nutrients are available
  • soil structure is improved and therefore drainage and  aeration is improved
  • micro-organisms activity is encouraged.

What's next?

Go to: 6 Cultivation.

Increasing organic matter Cultivation