Explanation
The correct answer is (d) Calcium carbonate.
Alkalinity refers to the soil's capacity to neutralize acids and maintain a higher pH level. If the soil has low alkalinity or is acidic, adding substances that increase alkalinity can help correct the pH balance.
Among the options provided, calcium carbonate is commonly used to correct soil alkalinity. Calcium carbonate, also known as agricultural lime or limestone, is a natural mineral that contains calcium and carbonates. When added to acidic soil, calcium carbonate reacts with the acids and releases calcium and carbonate ions, which help raise the soil pH and increase alkalinity.
Vermicompost (option a) is organic matter that is produced through the process of vermicomposting. While vermicompost can improve soil fertility and structure, it does not directly affect soil alkalinity.
NPK fertilizers (option b) typically contain nitrogen (N), phosphorus (P), and potassium (K), which are essential nutrients for plant growth. While they can influence soil fertility, NPK fertilizers do not directly impact soil alkalinity.
Gypsum (option c) is calcium sulfate, and it can be used to improve soil structure and water infiltration. However, gypsum does not directly affect soil alkalinity.
Therefore, the correct answer is (d) Calcium carbonate.
