Nitrate levels are highest in soils that have finer textures, such as clay and silt, rather than those with rough textures, such as sand. Because nitrates are moved through soil by water, sandy soil often loses nitrates due to leaching, and heavy, coarsely textured soil loses nitrates due to denitrification, a process in which anaerobic bacteria in the soil converts nitrates to gaseous forms of nitrogen. Leaching and denitrification can cause nitrate pollution of water supplies and should be considered when deciding whether or not to apply additional nitrogen to soil. Source: Normal Soil Nitrate Levels by Tori Leigh
Growers are concerned that plants will be able to get enough nitorgen from the soil converting nitrates to a gaseous form. If you are considering soil testing for nitrates, make sure you not only pull soil samples form the surface, 0-6 inches but consider going deeper.
Both surface (0-8 inches) and subsurface (below 8 inches) samples are needed to accurately estimate nitrate-nitrogen in the root zone, because nitrogen in the nitrate form moves easily with water and will leach into the subsoil. Nitrate-nitrogen in the root zone is readily used by plants. For most soils and annual crops, roots will reach a depth of 4 feet or more. To accurately predict nitrate-nitrogen in the root zone, subsurface samples should be collected to a depth of 3 feet. A 2-foot sample is the minimum sampling depth recommended for nitrate-nitrogen, and will not predict plant available nitrate-nitrogen as accurately as a deeper sample. For crops with shallow root zones, such as dry beans, canola and millet, a 2-foot sample is adequate. If rooting depth is limited because of coarse sand or gravel, rock or a high water table, sample to the depth possible. Nitrogen fertilizer recommendations for several crops grown in Nebraska are based on the amount of nitrate-nitrogen in the root zone determined from subsurface samples, as well as organic matter content in the surface sample. If subsurface samples for nitrate-nitrogen aren?t taken, nitrogen recommendations for crops will be based on historical average values of nitrate-nitrogen in the root zone, and the accuracy of fertilizer recommendations may decrease. Source: Guidelines for Soil Sampling, Nebraska IANR
In addition to crops, nitrates in water streams are getting a lot of publicity, especially in Iowa. Make sure you, as a land owner know the levels in your own soil and water streams so you can be prepared if you are ever called on to produce those type of numbers to your State Natural Resources Department.
Picture Source: Producer.com