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Eric Harmsen, Joel Colon, Carmen Lis Arcelay and Dionel Cadiz

EVALUATION OF PERCOLATION AND NITROGEN LEACHING FROM A SWEET PEPPER CROP GROWN ON AN OXISOL SOIL IN NORTHWEST PUERTO RICO. Agricultural and Biosystems Engineering Department University of Puerto Rico – Mayagüez Campus. Eric Harmsen, Joel Colon, Carmen Lis Arcelay and Dionel Cadiz.

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Eric Harmsen, Joel Colon, Carmen Lis Arcelay and Dionel Cadiz

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  1. EVALUATION OF PERCOLATION AND NITROGEN LEACHING FROM A SWEET PEPPER CROP GROWN ON AN OXISOL SOIL IN NORTHWEST PUERTO RICO Agricultural and Biosystems Engineering Department University of Puerto Rico – Mayagüez Campus Eric Harmsen, Joel Colon, Carmen Lis Arcelay and Dionel Cadiz

  2. This Material Is Based on Research Supported by USDA/CSREES Grant No. CBAG-82 in Tropical/ Subtropical Agriculture Research

  3. BACKGROUND • Nitrate leaching through the soil profile can result in a significant loss of fertilizer N, and may be a source groundwater contamination. • Highly weathered soils may exhibit substantial anion exchange capacity (AEC), which retards the movement of anions such as NO3- through the profile. • However, AEC decreases as soil pH increases by agronomic practices such as liming.

  4. OBJECTIVE • To evaluate the effects of liming and fertigation on the leaching of nitrogen through a highly weathered tropical soil

  5. Study Area – NW Puerto Rico

  6. Field Study • 2002 and 2003 at the UPR Experiment Station at Isabela, PR, using sweet peppers (Capsicum annuum, “Biscayne”) as the test crop. • 2 lime levels (Lime or No lime); 2 fertigation frequencies (Weekly or Bi-weekly). • Soil samples collected every two weeks at 20 cm increments, down to 80 cm. • Analyzed for NH4+ and NO3- concentrations by steam distillation (Mulvaney, 1996).

  7. Experimental Layout

  8. Estimating Nitrogen Leaching • LNO3 = 0.01 ρb NO3 PERC / θvol • LNH4 = 0.01 ρb NH4 PERC / θvol

  9. Water Balance Perc = (R-RO)+Irr-ETc + S Perc = Deep percolation (R –RO) = Rainfall – Runoff Irr = Irrigation based on ETpan ETc = Evapotranspiration based on Penman-Monteith method. S = Change in stored water

  10. IRR = ETpan = Kc Kp Epan IRR = ETpan = Evapotranspiration based on pan Kc = Crop coefficient Kp = Pan coefficient Epan = Pan evaporation

  11. ETc = Kc ETo ETc = Evapotranspiration based on Penman- Monteith method. Kc = Calibrated crop coefficient ETo = Reference evapotranspiration

  12. Calibration of the Water Balance Equation • Calibration variables: (RO/R) • Calibration target: average soil moisture content

  13. RESULTS

  14. Properties of the Coto Clay

  15. Evapotranspiration – 2003 Season

  16. Calibrated Soil Moisture Content RO/R = 0.25 2002 2003

  17. Estimated Percolation 2002 2003

  18. Soil Nitrate Concentration at 60-80 cm Depth 2002

  19. Nitrate, ammonium and nitrate plus ammonium (Total) leached during Year 1 and 2 for the four experimental treatments

  20. Percent of Nitrogen Leached Relative to Applied

  21. How much N was leached during the flooding events? • The estimated amount of nitrogen lost (average of all treatments) on April 6, 2002 and April 10, 2003 was 19.6 kg/ha and 20.1 kg/ha, respectively. • For years 1 and 2 this represented 34% and 60% of the total N lost by leaching during the two seasons, respectively.

  22. The method used in this study may underestimate nitrogen losses, because the contribution of unsaturated flow to the percolation was not considered 2003

  23. Conclusions • No clear difference in nitrogen leaching was observed for the lime and no-lime treatments. • No clear difference in nitrogen leaching was observed between the fertigation treatments. • The average percent of nitrogen (nitrate plus ammonium) leached during the 1st and 2nd season, relative to the amounts applied, were 26% and 15%, respectively.

  24. Conclusions cont. • Leaching events were associated with large rainstorms, suggesting that leaching of N would have occurred regardless of the irrigation scheduling method used. • During the first and second seasons, respectively, 34% and 60% of the total N lost by leaching occurred during a single day (April 6 in 2002 and April 10 in 2003) when flooding was observed in the study areas. • The N leaching results from this study may be underestimated because the contribution of percolation from unsaturated flow was not considered.

  25. Future Work • Estimate N leaching rates using the Darcy velocity results, estimated from the tensiometers. • Calibrate and validate a numerical model (HYDRUS-2D) to simulate water and nitrogen movement. • Use the numerical model to develop best management practices in terms of maximizing N uptake and minimizing N leaching.

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