Soil organic matter is a primary source of what nutrient for crops?

Soil organic matter is indeed a primary source of nitrogen for crops. This organic matter contains decomposed plant and animal materials that contribute to the nutrient reservoir in the soil. As it breaks down, organic matter releases nitrogen in forms that plants can absorb, primarily as ammonium (NH4+) and nitrate (NO3-). This process enhances soil fertility, promoting healthy crop growth, as nitrogen is essential for plant development, particularly for cell structure and enzymatic functions.

In contrast, the other nutrients listed, such as phosphorus, potassium, and calcium, are typically derived from mineral sources and do not rely to the same extent on the decomposition of organic matter for availability. While organic matter can improve the overall nutrient-holding capacity and environmental conditions of the soil, nitrogen uniquely ties to the transformation and turnover of organic matter in the soil ecosystem.