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

• Published in: Soil Science Society of America journal Vol. 73; no. 3; pp. 1044 - 1052
• Main Authors: Sato, Shinjiro, Morgan, Kelly T, Ozores-Hampton, Monica, Simonne, Eric H
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.05.2009; Soil Science Society of America; American Society of Agronomy
• Subjects: agricultural runoff; Agricultural sciences; Agronomy. Soil science and plant productions; Ammonium; ammonium nitrogen; application rate; Biological and medical sciences; Crop diseases; Earth sciences; Earth, ocean, space; Exact sciences and technology; Farms; Fertilizers; Florida; Fundamental and applied biological sciences. Psychology; Growing season; horticultural soils; Leaching; Moisture content; nitrate nitrogen; Nitrification; nitrogen fertilizers; nutrients; raised beds; Sandy soils; seasonal variation; Soil science; soil water content; Soils; Solanum lycopersicum var. lycopersicum; Spatial distribution; Spring; subsurface irrigation; Surficial geology; Tomatoes; Water depth; Water table; Water table fluctuations; weeks after planting; Winter; Florida; Macronutrient(mineral); physical properties; Monovalent cation; temporal distribution; textures; Nitrogen compounds; ammonium; Inorganic ion; sandy soils; Earth science; Inorganic element; Inorganic cation; irrigation; percolation; Spatial distribution; Inorganic nitrogen; Water engineering; Soil science; soils
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2008.0206

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.