Organic Framing

Liming

• Application of lime raises the soil pH to a desirable level.
• The quantity of liming material to be applied depends on soil pH, soil texture, capacity and type of liming material.
• On an average, hydrated lime Ca(OH)2 at the rate of 5 t/ha is applied in the field and is thoroughly mixed in soil.
• The gap between lime application and crop sowing is atleast two or three months.

Liming materials

1. Calcium limestone (CaCO3) (more than 90% use in India).
2. Dolomite (rich in Mg).
3. Quick lime (CaCO).
4. Slaked lime Ca(OH)2.
5. Coral shell lime.
6. Chalk CaCO3.
7. Blast furnace slag CaSiO3 and Ca2SiO4.
8. Miscellaneous sources like wood ashes, etc.

Biological Reclamation

• Use of organic materials and crops

Soil amendments

• Soil amendments are substances that influence plant growth favourably by changing the soil pH, increasing the nutrient availability, improving the physical conditions of the soil and counteracting the effects of injurious substances.
• There are three types of soil amendments.
  1. Materials used for amending acidic soils. E.g. Lime
  2. Materials used for ameliorating alkali soils. E.g. Gypsum and phosphogypsum.
  3. Soil aggregating agents or soil conditioners to stabilise soil aggregates and to form granular structures. E.g. Poly-electrolytes, including polyvinylites, polyacrylates, cellulose gums, lignin derivatives and silicates.

Gypsum

• Gypsum is dehydrated calcium sulphate (CaSO4.2H2O) and used as a popular amendment for the reclamation of alkali soils.
• Pure gypsum contains 18.6% S and 23.2% Ca. Commercial agricultural grades (70-80%) contain 13-15% S and 16-19% Ca.
• The sulphur in gypsum is in plant available sulphate form and its solubility is comparable to that of SSP.
• Most of the gypsum mines are located in Rajasthan.

Phosphogypsum

• It is a byproduct of phosphoric acid production.
• The CaSO4 in phosphogypsum is available as dehydrate (CaSO4.2H2O), hemihydrate (CaSO4.1/2 H2O) and anlydrate (CaSO4) or in combination of dehydrate and hemihydrate.
• Phosphogypsum is high grade gypsum with 80-90% purity. It may also contain traces of iron, manganese, zinc and copper.
• This fertilizer is of great importance in alkali soils as a source of S.

Lime and Liming Materials

• Calcium oxide (CaO) is the only material to which the term lime may be correctly applied.
• It is also called as unslaked lime, burned lime or quick lime (CaO).
• It is most effective with high neutralising value or calcium carbonate equivalent (CCE) of 179% compared to pure CaCO3.
• Complete mixing of this material into the soil is very difficult. Calcium hydroxide [Ca(OH)2] is a white powder and called slaked lime or hydrate lime [Ca(OH)2]. The other common liming materials are calcium carbonate (CaCO3), calcite or calcium-magnesium carbonate [CaMg (CO3) 2] or dolomite.
• Limestone is mined by open pit method. Most of the agricultural limestones have the CCE value of 90-98% because of impurities present.