Nitrogen is a vital nutrient for plant growth, but its uptake and utilization are influenced by complex environmental factors and chemical processes in the soil, which are sensitive to moisture and temperature. This makes it a challenge to calculate the correct amount of nitrogen-based fertilizer to apply, presenting risks to groundwater and our atmosphere when it is not applied properly.
Although nitrogen makes up 78 percent of the atmosphere, most plants cannot absorb it directly from the air. Instead, they absorb it through their roots in the nitrate form, when nitrogen is bonded to oxygen. Nitrification, a process carried out by soil microorganisms, converts ammonium into nitrites and then nitrates, making it digestible for plants.
Nitrates have great mobility in the soil and heavy rains can leach them deep in the ground. If nitrates enter the groundwater, water can become toxic for humans. Fertilizers can also run off the fields and enter surface waters. Excessive nutrient concentrations deteriorate water quality, a process known as eutrophication. Further, excessive soil moisture intensifies denitrification, which converts the remaining nitrates back into nitrogen gas and returns them to the atmosphere. Another type of nitrogen loss after fertilizer application is called volatilization. This process involves the loss of the ammonia gas into the atmosphere. The extent of the loss depends on weather conditions, the type of fertilizer, and the method of application. Nitrate fertilizers can help minimize volatilization. In contrast, higher nitrogen losses are typical for fertilizers containing urea, especially when they are applied on the soil surface in hot weather with insufficient moisture.
