Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 1997
Publication Date: N/A
Interpretive Summary: In efforts to eliminate nitrate pollution of groundwater, blanket limitations of nitrogen fertilization have been proposed. It has become clear, however, that the amount of nitrogen applied is not always related to the nitrate level in the groundwater under a citrus grove. It appears that groundwater nitrate under groves with a high water table is lower than when the water table is deep in the soil profile. The reason is a high rate of denitrification under anoxic conditions, the conversion of nitrate to nitrogen gas. Clay in the soil keeps the water table high and seems to explain the difference in groundwater nitrate between two sites with similar climatic conditions and fertilization.
Technical Abstract: Groundwater nitrate concentrations remained sharply different at two sites in the central part of the Florida peninsula over a two-year observation period. Nitrogen fertilization patterns, both quantity and application methods, and rainfall were approximately the same at both sites. The soil at the low groundwater nitrate site, at depths of 0 to 120 cm, had a higher cation exchange capacity and contained more ammonium acetate-extractable K, Ca, and Mg. It also had a greater organic matter content, contained more clay in the 90 to 120 cm layer and more nitrate in the 1 to 30 cm layer. There was a sharp difference in depth to groundwater. At Site 1 (high nitrate levels) the water table remained steady at 4 m, while at Site 2 (low nitrate levels) it ranged from 0.9 to 1.1 m in the two wells monitored. The aquifer at Site 1 was unconfined, but was confined at Site 2 by increasing clay contents with depth.