Which is the primary cause of increased soil acidity?

The primary cause of increased soil acidity is the application of nitrogen fertilizer. When nitrogen fertilizers are used in agricultural practices, they often contain ammonium or urea forms of nitrogen. These forms can lead to the production of nitric acid when they are transformed into nitrate by soil microorganisms. This process lowers the pH of the soil, making it more acidic over time.

Additionally, the continued use of these fertilizers can exacerbate soil acidification, especially in areas with high rainfall, as leaching can remove basic cations (like calcium and magnesium) that help to buffer soil pH against acidity. Therefore, the application of nitrogen fertilizer is a significant factor contributing to the overall acidity level in soils, particularly in intensive farming systems.

While soil erosion and the decomposition of natural organic matter can influence soil health and nutrient levels, they do not primarily drive soil acidity. Similarly, crop rotation is a practice designed to improve soil health and manage nutrients, and it does not inherently increase soil acidity. Thus, the application of nitrogen fertilizer stands out as the most direct contributor to increased soil acidity.