Monday, November 13, 2006 - 8:00 AM
68-3
Nitrate Uptake Efficiency of Bermudagrass During Growth and Dormancy Cycles.
Benjamin Wherley1, Wei Shi1, Daniel Bowman2, and Thomas Rufty1. (1) North Carolina State University, Campus Box 7620, Raleigh, NC 27695, (2) Dep. of Crop Science, North Carolina State Univ., North Carolina State Univ., Raleigh, NC 27695, United States of America
Golf course fairways are increasingly being used for effluent disposal sites in the southeastern U.S. Application approaches must be developed that allow for efficient uptake of nitrogen and phosphorus in the effluent by the grass systems and minimize losses to the environment. Experiments were conducted to determine the nitrate assimilatory capacity of a Tifway bermudagrass system during seasonal growth and dormancy cycles. Bermudagrass cores, obtained from established field plots maintained at golf course fairway height, were placed in controlled environment chambers and fed solutions containing 40 A% 15N-nitrate at a rate of 4.9 g m-2. The fate of 15N was determined by periodic harvests and analysis of enrichments in different plant and soil fractions (8 in all). Results indicate that nitrate assimilation was highly variable during the different seasons. Nitrate uptake by bermudagrass was most rapid during summer months when rapid growth was occurring, with ~ 67% taken into the plant within 3 days and >80% within 10 days. The opposite was true in winter months, as ~80 to 90% of the nitrate remained in soil for up to 16 days. During the transition out of dormancy in spring, nitrate uptake efficiency rapidly increased and approached the summer peak 4 weeks after ‘green-up’ began. Nitrate uptake markedly declined when the bermudagrass growth slowed and dormancy approached in the fall. When growing, the bermudagrass strongly out-competed soil microbes for the nitrate, as a relatively small portion (< 12%) of applied 15N was present in the soil microbial fraction. Immobilization of nitrate by the microbial population was greatest in spring, before bermudagrass root systems were fully developed. The results clearly indicate that the ability of a bermudagrass system to assimilate nitrate differs widely among seasons, which should influence effluent storage/dispersal strategies.