Why Are Nitrates Susceptible to Leaching in Soils?

Nitrates

• Nitrification is the chemical process of turning ammonia into nitrate. Both molecules contain nitrogen that is available to plants. Nitrate does not bond well with soil particles. Because it is free in the soil, it is easily washed out of the soil. Leaching of nitrates is due to their poor adhesion to soil particles and susceptibility to dissolving in water.

Leaching

• Most nitrogen fertilizer is a form of salt. Salt dissolves easily in water. The more rain or irrigation an area receives, the more it will be leached of nutrients. Leaching is the carrying away of nutrients in the soil by water. Soils in tropical climates are highly leached because they receive massive amounts of water. Heavy rains and flooding can significantly reduce the amount of nitrogen available to plants.

Pollution

• Nitrates that are leached from the soil can pollute ground water. Nitrogen pollution is the cause of blue baby syndrome, a condition where blood is unable to carry enough oxygen. Sandy soils are especially susceptible to leaching. Soils with a high percentage of clay are less permeable to water and may be subjected to erosion. Erosion of surface soils can carry away enough nitrates to contaminate groundwater. Agricultural soils that are subjected to the intensive use of chemical fertilizers can also pollute groundwater, especially if there are heavy rains.

Reducing Nitrogen Loss

• Fertilizer is expensive. Make sure you know how much nitrogen your plants require before fertilizing. Overfertilizing is harmful to the environment. If your soil is not deep until bedrock, nitrates that leach from it will get to groundwater sources quicker than in a deep soil. Use organic sources of nitrogen as much as possible. Compost and decayed manure are excellent sources of slow-releasing plant-available nitrogen.