1. Nitrogen Spatial Distribution in a Sandy Soil Cropped with Tomatoes under Seepage Irrigation Shinjiro Sato (shinjiro@ifas.ufl.edu) Monica Ozores-Hampton Kelly Morgan Southwest Florida Research and Education Center University of Florida Soil Science Society of America Annual Meeting November 4-8, 2007, New Orleans, LA

2. #1 vegetable crop in FL 70% of the production in South Florida with >16,000 ha in 2006 Grown primarily in sandy soils (mostly >95% sand) 3 growing seasons a year (fall, winter, and spring) under intensive irrigation and fertilizer managements Tomato Production in Florida

3. Irrigation and Fertilization Seepage irrigation is most commonly practiced with fumigated raised beds with polyethylene mulch. State-wide average N-P-K fertilizer usage: 300-200-555 kg ha -1 UF-IFAS recommendation for high yields: 224-168-252 kg ha -1

4. Questions ?? How is N (NH 4 + and NO 3 - ) spatially distributed in tomato beds and redistributed throughout the growing season? Do different N application rates affect the N distribution in beds and leaching potential at the end of the growing season?

5. Field Experiment A grower’s tomato field in east of Immokalee, FL 2006-spring (Jan-May) and 2006-winter (Oct-Feb 07) growing seasons (only spring data presented) UF-IFAS or growers’ N-P-K fertilizer rates: 224 or 358-140-667 kg ha -1 applied 3 plots (replicates) for each rate Holopaw sand (loamy, siliceous, active, hyperthermic Grossarenic Endoaqualfs)

6. Soil Sampling Fertilizer furrow 80cm 12cm Tomato bed cross-section diagram 20cm 3 depths: top (0-10 cm) middle (10-20 cm) bottom (20-30 cm) On weeks after planting (WAP): 1,2,3,4,5,6,7,8, 10,12,14,16, and 18 Sampling from one side of fertilizer bands (band) and center of tomato bed (center) between 2 tomato plants (15 cm apart)

7. Rainfall and Water Table Depth WAP 1 3 5 7 10 16

8. Ammonium Distribution (224 kg N ha -1 ) (mg/kg)1 WAP4 WAP 8 WAP18 WAP

9. Ammonium Distribution (358 kg N ha -1 ) (mg/kg)1 WAP4 WAP 8 WAP18 WAP

10. Nitrate Distribution (224 kg N ha -1 ) (mg/kg)1 WAP4 WAP 8 WAP18 WAP

11. Nitrate Distribution (358 kg N ha -1 ) (mg/kg)1 WAP4 WAP 8 WAP18 WAP

12. Potential N Leaching (kg N ha -1 ) Initial N applied224358 Biomass N uptake (at 120 d)192250 Total N in bed (on 18 WAP)2534 Potential N leaching774 % leaching of initial N applied3.1%20.7%

13. Conclusions NH 4 + distributed more laterally than vertically and remained mostly in upper 20 cm or within tomato bed (unlikely leaching). NO 3 - distributed both laterally and vertically to below tomato bed, especially when water table fluctuated (potential leaching). Different N application rates resulted in different N concentrations in tomato bed but similar distribution patterns throughout the growing season. Higher N application caused higher potential for N (most likely NO 3 - ) leaching.

14. Acknowledgement Co-authors Grower Florida Department of Agriculture and Consumer Services (No. 12280) Soil Lab at SWFREC

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