Agronomic and Nitrate Leaching Impacts of Pelletized versus Granular Urea
MetadataShow full item record
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 N03-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 N03-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, N03-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 N03-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.
- Doctoral Dissertations