Calcium Nitrate Tetrahydrate (Ca(NO₃)₂·4H₂O) is a highly water-soluble inorganic salt composed of calcium, nitrate nitrogen, and four molecules of crystallization water. It is one of the most important calcium fertilizers used in modern agriculture and is also widely applied in construction, wastewater treatment, chemical manufacturing, and environmental management.

In agricultural production, people often tend to judge whether crop nutrition is sufficient simply by the amount of fertilizer applied. However, from the perspective of plant physiology, what determines crop growth and final yield is not merely the quantity of fertilizer input, but rather the balance, synergy, and utilization efficiency of nutrient elements.