Soil Fertility and Nutrient management (1+1)

Calcareous soil

• Calcareous soils are those that contain enough free calcium carbonate (CaCO3) and give effervescence visibly releasing CO2 gas when treated with dilute 0.1 N hydrochloric acid. The pH of calcareous soil is > 7.0 and also regarded as an alkaline (basic) soil.

Formation
The soil is formed largely by the weathering of calcareous rocks and fossil shell beds like varieties of chalk, marl and lime stone and frequently a large amount of phosphates. Soils are often very fertile, thin and dry. They are found in large part of arid and semiarid regions, which may prove very fertile when sufficient moisture for crops is available.
Soils also can become calcareous through long term irrigation with water contains small amounts of dissolved CaCO3 that can accumulate with time. Calcareous soils can contain from 3% to >25% CaCO3 by weight with pH values with a range of 7.6 to 8.3.

Management of Calcareous soil
Fertilizer management in calcareous soils is different from that of non calcareous soils because of the effect of soil pH on soil nutrient availability and chemical reactions that affect the loss or fixation of some nutrients. The presence of CaCO3 directly or indirectly affects the chemistry and availability of nitrogen (N) Phosphorus (P), Magnesium (Mg), Potassium (K), Manganese (Mn), Zinc (Zn) and iron (Fe). The availability of copper (Cu) also is affected.
Application of acid forming fertilizers such as ammonium sulphate and urea fertilizers, sulphur compounds, organic manures and green manures is considered as effective measures to reduce the pH of soil to neutral pH value.