What is the major immediate loss of nitrogen from manure spread on the surface?

The major immediate loss of nitrogen from manure spread on the surface is due to volatilization. When manure is applied to the soil surface, the ammonia contained in the manure can be lost to the atmosphere as a gas. This process typically occurs rapidly and is influenced by factors such as soil temperature, surface pH, and moisture.

Volatilization is particularly significant with surface applications because when the nitrogen is not incorporated into the soil, it is more susceptible to escaping as ammonia, which can occur within a matter of hours to days after application. Reducing volatilization losses is an essential practice in nutrient management, as it not only influences the nitrogen availability for crops but also helps in reducing air pollution and ensuring economic efficiency of fertilizer use.

Denitrification, while it can lead to nitrogen loss, primarily occurs in saturated soils where conditions are anaerobic and is a slower process rather than an immediate loss. Leaching pertains to the movement of nutrients through the soil profile into groundwater, which is a longer-term issue rather than an immediate one after surface application. Oxidation refers to the chemical reaction that can occur with various nutrients, but it is not a primary mechanism for immediate nitrogen loss from surface-applied manure. Thus, volatilization is the most relevant process