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NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Spatial and Temporal Distributions in Sandy Soils with Seepage Irrigation: I. Ammonium and Nitrate

^a Southwest Florida Resear. and Educ. Center, Univ. of Florida, 2686 State Rd. 29 N, Immokalee, FL 34142
^b Horticultural Sciences Dep., Univ. of Florida, 1241 Fifield Hall, Gainesville, FL 32611

^* Corresponding author (shinjiro{at}ifas.ufl.edu).

Tomato (Lycopersicon esculentum Mill.) in southwest Florida is typically grown on fumigated, raised beds with polyethylene mulch under seepage irrigation. An average grower's N rate currently exceeds the University of Florida's Institute of Food and Agricultural Sciences (UF-IFAS) recommendation (224 kg N ha^–1 maximum). Excess nutrients are subject to runoff and leaching, which raises environmental concerns in Florida watersheds. A field study was conducted to elucidate N spatial distribution in tomato beds during the 2006 spring and winter growing seasons with 224 and 358 kg N ha^–1 rates. Ammonium N was highest for both seasons during 0 to 1 wk after planting (WAP) at the 0- to 10-cm depth in the fertilizer band, but rarely moved vertically. Lateral movement of NH₄⁺–N was observed through 7 WAP, however, probably due to diffusion. Nitrate N at 0 to 10 cm in the band peaked during 3 to 4 WAP, indicating about 3 wk of nitrification in the spring; however, this process was shortened to 1 to 2 wk in the winter, probably due to greater bacterial activity with warmer temperatures in the beginning of the winter than the spring (average 8°C in the first 3 wk). Both lateral and vertical movements of NO₃^––N were observed in the spring, even at the 20- to 30-cm depth. A rise and subsequent fall of the water table level during 5 to 8 WAP particularly enhanced NO₃^––N downward movement, which was attributed to greater diffusivity of NO₃^––N than NH₄⁺–N. Minimizing water table fluctuations and applying a reduced N rate are critical to reduce NO₃^––N leaching loss.

Abbreviations: UF-IFAS, University of Florida's Institute of Food and Agricultural Sciences • WAP, weeks after planting

This article has been cited by other articles:

				S. Sato, K. T. Morgan, M. Ozores-Hampton, and E. H. Simonne Spatial and Temporal Distributions in Sandy Soils with Seepage Irrigation: II. Phosphorus and Potassium Soil Sci. Soc. Am. J., May 1, 2009; 73(3): 1053 - 1060. [Abstract] [Full Text] [PDF]