The Scoop on Soil Testing for Nitrogen Nitrogen can be added to soil in many forms. It can be applied as nitrates, ammonium, urea, etc. Soon after the nitrogen is added and if there is some moisture present, the indiginous bacteria called nitrosomonas and nitrobacter convert all forms of nitrogen to the nitrate form. The clays in South Carolina soils also have a negative charge and since similar charges repel, the nitrates are not attracted to the clays like the posit ively charged calcium, magnesium and potassium ions.
Nitrates are also very soluble in water.
As a result, the nitrate ions are very mobile in the soil and move through quite readily as water percolates down into the soil. If a soil is sandy, nitrates move through the soil even faster due to the large pore space and faster percolation of water. These factors are the reason for environmental and health concerns regarding nitrate movement into groundwater. Because of nitrogen's rapid conversion to the nitrate form and its subsequent movement through the soil, it makes the soil test for nitrogen quite difficult to interpret. By the time you receive soil test results for nitrate nitrogen, it may have alre ady moved through the soil if some rain had fallen between sample collection and reporting of lab results.