Agronomic and Nitrate Leaching Impacts of Pelletized versus Granular Urea
| dc.contributor.author | Shah, Sanjay Bikram | en |
| dc.contributor.committeechair | Wolfe, Mary Leigh | en |
| dc.contributor.committeemember | Dillaha, Theo A. III | en |
| dc.contributor.committeemember | Mostaghimi, Saied | en |
| dc.contributor.committeemember | Persaud, Naraine | en |
| dc.contributor.committeemember | Borggaard, Jeffrey T. | en |
| dc.contributor.committeemember | Alley, Marcus M. | en |
| dc.contributor.department | Biological Systems Engineering | en |
| dc.date.accessioned | 2014-03-14T20:17:06Z | en |
| dc.date.adate | 2000-10-24 | en |
| dc.date.available | 2014-03-14T20:17:06Z | en |
| dc.date.issued | 2000-08-02 | en |
| dc.date.rdate | 2001-10-24 | en |
| dc.date.sdate | 2000-10-06 | en |
| dc.description.abstract | Agronomic and water quality impacts of urea particle size were evaluated through field and laboratory experiments and mathematical modeling. In a two-year field study, corn silage yield, corn nitrogen (N) removal, and nitrate-N (NO₃⁻-N) leaching from urea pellets (1.5 g each) and granules (0.01-0.02 g each) applied at 184 kg-N/ha were compared. A control treatment (no N) and two other N application rates (110 and 258 kg-N/ha) were also included. Urea particle size impact on dissolution rate, dissolved urea movement, mineralization, and N0³-N leaching were evaluated in the laboratory. A two-dimensional (2-D) mathematical model was developed to simulate the fate of subsurface-banded urea and its transformation products, ammonium (NH₄⁺)and NO₃⁻. With 184 kg-N/ha, corn silage yield was 15% higher (p = 0.02) and corn N removal was 19% higher (p = 0.07) with pellets than granules in the second year of the field study. In the absence of yield response at 110 kg-N/ha, reason for higher yield at 184 kg-N/ha with pellets was unclear. Greater N removal reduced NO₃⁻-N leaching potential from pellets compared to granules during the over-winter period. No urea form response to yield or corn N removal was observed in the first year. In 23 of 27 sampling events, granules had higher NO₃⁻-N concentration in the root zone than pellets, with average nitrate-N concentrations of 2.6 and 2.2 mg-N/L, respectively. However, statistically, NO₃⁻-N leaching from the root zone was unaffected by urea form, probably due to high variability within treatments masking the treatment effects. In October 1997, pellets retained 16% more (p = 0.04) inorganic-N in the top half of the root zone than granules, due to slower nitrification in pellets as was determined in the mineralization study. Slower NO₃⁻-N leaching allowed for greater N extraction by plants. Pellets had lower dissolution, urea hydrolysis, and nitrification rates than granules; however, nitrification inhibition was the dominant mechanism controlling N fate. The model took into account high substrate concentration effects on N transformations, important for simulating the fate of band-applied N. The model exhibited good mass conservative properties, robustness, and expected moisture and N distribution profiles. Differences in measured field data and model outputs were likely due to uncertainties and errors in measured data and input parameters. Model calibration results indicated that moisture-related parameters greatly affected N fate simulation. Sensitivity analyses indicated the importance of nitrification-related parameters in N simulation, particularly, their possible multiplicative effects. Need for extensive model testing and validation was recognized. The validated 2-D N model could be incorporated into a management model for better management of subsurface-banded granular N. However, the 2-D model is not appropriate for simulating the three dimensional N movement from pellets. | en |
| dc.description.degree | Ph. D. | en |
| dc.identifier.other | etd-10062000-15170004 | en |
| dc.identifier.sourceurl | http://scholar.lib.vt.edu/theses/available/etd-10062000-15170004/ | en |
| dc.identifier.uri | http://hdl.handle.net/10919/29201 | en |
| dc.publisher | Virginia Tech | en |
| dc.relation.haspart | etd.pdf | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | corn silage yield | en |
| dc.subject | mathematical modeling | en |
| dc.subject | pellet | en |
| dc.subject | tension lysimeter | en |
| dc.subject | subsurface banding | en |
| dc.title | Agronomic and Nitrate Leaching Impacts of Pelletized versus Granular Urea | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Biological Systems Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Ph. D. | en |
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