Shinjiro Sato, Monica Ozores-Hampton, and Kelly Morgan. Southwest Florida Research and Education Center, University of Florida, 2686 SR 29 N, Immokalee, FL 34142
Tomato (Lycopersicon esculentum Mill.) production in southwest Florida’s sandy soils is typically conducted on fumigated, raised bed covered with polyethylene-mulch under seepage irrigation. A state-wide average nitrogen (N) application rate by tomato growers (300 kg N ha–1) currently exceeds those recommended by the University of Florida’s Institute of Food and Agricultural Sciences (UF-IFAS; 224 kg N ha–1 maximum). Excess nutrients are subject to leaching and have increasingly raised environmental concerns in some Florida watersheds because of adoption by the State of vegetable Best Management Practices (BMP). A field study was conducted to elucidate N spatial distribution on a commercial tomato farm during the 2006-spring growing season (18-wk period) with 224 and 358 kg N ha–1 applied at planting. Ammonium (NH4+)-N in the top-band and top-center of the bed were highest 0 and 3 wk after transplanting (WAT), respectively, then gradually decreased thereafter. Lateral movement of NH4+-N was likely by transpiration-driven mass flow. Time frame of significant decreases of soil NH4+-N coincided with rapid increases of total N accumulation by tomato plants. Nitrate (NO3–)-N in the top-band peaked during 3–4 WAT, implying about 5–6 wk of nitrification process after application. A rise and subsequent drop of water table during 5–8 WAT caused NO3–-N to move downwards, possibly being explained by greater mobility or diffusivity of NO3–-N compared to NH4+-N. However, most NO3–-N remained in the top-band at the end of the growing season. Estimated potential N leaching was 14% and 28% of the low and high application rates, respectively. Monitoring, particularly NO3–-N, movement relative to soil water content or water table shift is critical in minimizing leaching loss of this nutrient.
Presentation