Apparent Recovery of Fertilizer N by Coastal Bermudagrass on a Swelling Clay Soil1
- D. E. Kissel,
- Larry Bartek and
- L. J. Zatopek2
The apparent recovery of N fertilizer by Coastal bermudagrass [Cynodon dactylon (L.)] growing on swelling clay soils has usually been quite low (approximately 40 to 50%), possibly due to biological immobilization of large quantities of applied N fertilizer. The objective of this study was to determine if the net immobilization might be reduced after several years of continued fertilization, thereby improving the recovery of N by Coastal bermudagrass.
The 6-year study was set up with variable N rates (NH4NO3 was the N source), some applied only the first 3 years of the study, some applied only the last 3 years and some fertilized throughout the study. Measurements were taken of N removed in forage, soil NO3−-N at the 504 kg N/ha rate, and soil organic N at the end of the study.
Immobilization (as determined by the increase in soil organic N) accounted for over 50% of the applied N, about equal to the amount of N going into the harvested portion of the grass. Other potential losses of N such as leaching and denitrification were apparently insignificant. There was no indication of inorganic N accumulation in the later years of the study. However, some improvement in N availability was noted in the last three years of the study on those plots receiving fertilizer throughout the 6-year study. The results from this study suggest that immobilization of fertilizer N on Coastal bermudagrass pastures would be a substantial sink for applied N fertilizer for an unknown but large number of years. Continuous generous fertilization programs would result in a gradual buildup of soil organic N with a resulting gradual improvement in N recovery by forage.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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