In agriculture, dolomite powder is sometimes applied to certain soils. What is the main purpose of applying dolomite in agricultural fields?

Introduction / Context:
Soil pH strongly influences nutrient availability and crop growth. Many agricultural soils tend to be too acidic, especially in regions with high rainfall and intensive cultivation. Farmers sometimes apply liming materials such as limestone or dolomite to correct soil acidity. This question asks you to identify the main purpose of applying dolomite powder to agricultural land, which is a common practice in soil management.

Given Data / Assumptions:

• Dolomite is a mineral composed mainly of calcium magnesium carbonate (CaMg(CO3)2).
• The options mention effects on soil pH and specific nutrients like phosphorus and nitrogen.
• We assume that the soil in question is acidic enough to require treatment, which is a common reason for using dolomite.

Concept / Approach:
Dolomite is a liming material that contains both calcium carbonate and magnesium carbonate. When applied to acidic soils, these carbonates react with hydrogen ions in the soil solution, thereby neutralising acidity and increasing soil pH. This process is similar to the action of agricultural lime (calcium carbonate). By raising the pH, dolomite reduces problems associated with strong acidity, such as aluminium toxicity and poor availability of certain nutrients. Dolomite also supplies calcium and magnesium as secondary nutrients. However, it is not primarily used to directly add phosphorus or nitrogen; those nutrients typically come from specific fertilisers like superphosphate (for phosphorus) and urea or ammonium fertilisers (for nitrogen). Therefore, the main purpose of applying dolomite powder is to increase soil pH and reduce acidity, not to directly supply phosphorus or nitrogen.

Step-by-Step Solution:

Verification / Alternative check:
Agronomy and soil science textbooks list dolomitic lime alongside calcitic lime as standard liming materials. They describe recommended application rates based on soil pH, buffer capacity, and crop requirements. Extension bulletins for farmers explain that dolomite is selected when soils are deficient in magnesium as well as being acidic, so that both pH correction and magnesium supply can be addressed. None of these sources describe dolomite as a primary phosphorus or nitrogen fertiliser. Instead, they stress its role in neutralising acidity and improving soil structure and nutrient availability. This confirms that increasing soil pH is the main purpose for applying dolomite powder.

Why Other Options Are Wrong:

To lower the pH of alkaline soil and increase soil acidity is wrong because dolomite is a liming material that raises pH; it is not used to make soil more acidic.

To directly increase the phosphorus content of the soil is incorrect because dolomite does not contain significant phosphorus; phosphate fertilisers are used for that purpose.

To directly increase the nitrogen content of the soil is also wrong because nitrogen is supplied by nitrogenous fertilisers and organic manures, not by dolomite.

Common Pitfalls:
Students sometimes confuse the roles of different soil amendments and assume that any powdered mineral applied to soil must be a nutrient fertiliser. Another pitfall is not clearly remembering the difference between liming agents (which raise pH) and acidifying agents (which lower pH). To avoid these mistakes, associate dolomite and limestone with liming: they are applied mainly to neutralise acidic soils and increase soil pH, with dolomite also supplying magnesium as an added benefit.

Final Answer:
Therefore, the main purpose of applying dolomite powder is to increase the pH of acidic soil and reduce soil acidity.