Excessive water is one of the largest contributors to the inefficient use of nitrogen in Kentucky. Because of this, nitrogen is often lost by both leaching and,denitrification. The amount, of these losses can be great depending on soil type and weather. Well-drained soils in Kentucky have been shown to lose less nitrogen than poorly drained soils. The nitrogen lost from well drained soils is usually due, to leaching. The nitrogen in the soil, even soon after applying non-nitrate forms of fertilizer N, is mostly in the water soluble nitrate form. When more water falls onto a well-drained soil than the soil can hold, then both water and nitrogen move through the soil below the root zone and are lost for plant use. On poorly-drained soils, the mostly likely method of nitrogen loss is due to denitrification. Nitrogen loss by this mechanism is due to the soil becoming saturated with water (waterlogged) and forcing the air out of the soil. In an effort to survive, some of the microorganisms in the soil take oxygen from nitrate. This process (denitrification) turns the nitrogen into a gas that will diffuse out of the saturated soil and be lost ,into the air. It usually occurs when the soil temperature is above 50°F and the soil is saturated for more than a two day period. If nitrogen fertilizer has been added to the soil prior to the existence of the above conditions, then fairly large amounts of nitrogen can be lost. These conditions are most prevalent in Kentucky on poorly drained soil in April and May. In the past, most farmers have tried to manage this problem by adding excess fertilizer nitrogen to still obtain maximum yields after the loss has been sustained. This management practice may not be economically feasible in the future if nitrogen prices continue to escalate. An alternative management practice used by many farmers is to reduce the amount of nitrogen lost by simply delaying the application of nitrogen until the conditions for denitrification have little chance of occurring. This usually means that the nitrogen is applied in late May or June after the corn has been planted and the risk of waterlogged soil conditions is greatly reduced. To determine the magnitude of such factors, we began an experiment on a poorly drained bottom soil in 1970 to determine 1) the proper rates of preplant nitrogen 2) effectiveness of sidedressing nitrogen and 3) effect of soil tiling on the above two factors.
Murdock, Lloyd W.; Kavanaugh, John; Miller, Harold F.; Thomas, Grant; and Rasnake, Monroe, "Efficiency of Nitrogen Use with Corn on a Tiled and Untiled Soil" (1982). Agronomy Notes. 84.