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ARS Home » Research » Publications at this Location » Publication #70720
Title: GROUNDWATER NITRATE UNDER FLORIDA CITRUS GROVES

Author
item Wutscher, Heinz

Submitted to: International Society of Citriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/17/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Groundwater nitrate nitrogen was monitored at five sites across the Florida citrus belt. Nitrate nitrogen levels varied widely even when approximately the same amount of fertilizer was applied, indicating that local conditions are the overriding factor governing the amount of nitrate in the groundwater. Water draining away from citrus groves is very low in nitrate or contains no nitrate at all. Levels above the 10 ppm NO3-N standard set for all groundwater are apparently confined to the soil under the trees where drinking water is rarely drawn from. It appears that sweeping Best Management Practices limiting nitrogen application to very low levels in all places would be a mistake, placing an unnecessary burden on citrus growers.

Technical Abstract: Groundwater drawn from test wells and drainage ditches at five sites located diagonally across the Florida citrus growing area was monitored every 30 days for 12 months for pH, electrical conductivity, NO3-N, P, K, Na, and Cl. Nitrate-nitrogen levels varied widely from site to site and multiple wells in one location showed that nitrate can vary greatly within a 4 ha area, from 2 to 28 mg L-1. At two locations on deep sand in the center of the peninsula NO3-N varied from 19 to 44 mg L-1. On the lower west coast, in sandy soil over hard pan at 2.5 m, the NO3-N in groundwater varies sharply between sampling dates from 3 to 43 mg L-1. On the upper west coast, on sandy soil (6m deep) over clay, groundwater NO3-N exceeded 19 mg L-1 only once (15 mg L-1 in November). Analysis of the water in adjacent drainage ditches and other bodies of water contained consistently less than 7 mg L-1, indicating that the higher levels appear to be confined to under the trees. Responses to variations in nitrogen application were slow or nonexistent. It appears that NO3-N levels in groundwater under Florida citrus groves are primarily governed by localized conditions.