What is the major nitrogen loss mechanism in poorly drained soils?

In poorly drained soils, the major nitrogen loss mechanism is denitrification. This process occurs primarily under anaerobic conditions, which are prevalent in waterlogged or poorly drained environments where oxygen levels are low. During denitrification, soil bacteria convert nitrate (NO3-) into nitrogen gas (N2) or nitrous oxide (N2O), which are released into the atmosphere.

This mechanism is particularly significant in wetlands or fields that retain water, as the saturation of the soil creates an environment conducive to these anaerobic microbial processes. As a result, denitrification can lead to substantial losses of nitrogen, which can negatively impact nutrient availability for plants and contribute to environmental issues such as the emission of greenhouse gases.

Other options, such as volatilization and leaching, do occur but are not the primary mechanisms in poorly drained soils. Volatilization typically refers to the loss of ammonia through surface reactions, while leaching involves the downward movement of dissolved nutrients in water. Nitrogen fixation, on the other hand, is a process by which atmospheric nitrogen is converted into a form usable by plants, but it does not represent a loss mechanism. Thus, denitrification stands out as the major mechanism responsible for nitrogen loss in these specific soil conditions.