|VAN KEUREN, ROBERT|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/1999
Publication Date: N/A
Interpretive Summary: Responsible stewardship of our natural resources is important to all, whether they are directly involved in agriculture or not. One aspect of this responsibility is to manage fertilizer use so that crop productivity can be achieved in an environmentally friendly manner. When nitrogen (N) fertilizer is applied in excess of crop needs, it has the potential to leach into groundwater supplies. The impacts on groundwater quality by th use of different rates and kinds of N fertilizer on pastures and grasslands have been studied near Coshocton, OH. For 5 years, 50 lbs/acre of nitrogen was annually applied as ammonium nitrate (NH4NO3) to large lysimeters (6 x 14 ft by 8 ft deep, undisturbed soil blocks which are instrumented so that water and chemicals can be collected from the bottom and analyzed). For the next 11 years, (NH4NO3) and a slow release N fertilizer were annually applied to lysimeters at a rate of 150 lbs/acre of N. Nitrate-N (NO3-N) concentrations in the water coming out of the bottom of the lysimeters wer below 3 ppm during the first 5 years, but they increased to over 20 ppm during the eighth year of the greater ammonium nitrate application. With the slow release N fertilizer, the percolate N concentrations rose only to 6 ppm. Within 2 years after no fertilizer was applied, NO3-N concentrations in the percolate fell to approximately 1 ppm. Although more NO3-N leached through the soil under NH4NO3 than the slow release fertilizer treatment, the combined total N loss from leaching and gaseous loss was similar with the two fertilizer treatments. This information will enable university extension and NRCS personnel to advise producers on options for more efficient and environmentally sound N fertilizer use.
Technical Abstract: Large, undisturbed, monolithic lysimeters (8.1 m**2 surface area) were used in a multi-year study of NO3 leaching under forages. For 5 years, 56 kg N/ha was annually applied (as NH4NO3). During the next 11 years, NH4NO3 was applied to a lysimeter (Y101B) and methylene urea, a slow release fertilizer, was applied to another lysimeter (Y101D) at an annual rate of 168 kg N/ha. Nitrate-N concentrations in the percolate from these 2.4 m-deep lysimeters were measured weekly. The soil is a well-drained silt loam on a 23% slope. Nitrate transport varied seasonally with the greatest amounts being moved during the late winter/early spring. Nitrate-N concentrations were below 3 mg/L during the first 5 years. Even though NO3-N levels increased steadily with the high NH4NO3 treatment, the greatest increases occurred during the eighth year of treatment, and reached levels above 20 mg/L. With the methylene urea, NO3-N concentrations remained relatively constant until after 8 years of the higher treatment, reaching concentrations of 6 mg/L. Following the 11 years of high fertilizer treatments, no N fertilizer was applied for 5 years. Within 2 years, the NO3-N concentrations in each lysimeter fell to approximately 1 mg/L. More NO3-N leached through the soil under the NH4NO3 treatment than the methylene urea treatment, but the combined total N loss from leaching and volatilization was similar with the two fertilizer treatments.