Tuesday, November 14, 2006 - 2:45 PM

Coastal Bermudagrass Response to N Sources and Rates.

Vincent A. Haby, Maria L. Silveira, and Allen T. Leonard. Texas Ag Experiment Station, Texas A&M Univ, PO Box 200, Overton, TX 75684

Although N is an important agronomic input for productive bermudagrass pastures, increasing costs and environmental problems associated with improper fertilization have prompted the need to re-examine optimum rates and efficient sources to supply pastures with N.  Ammonium nitrate has been the primary N source for grass pastures on the Coastal Plain of the southern US; however, the importance of urea has increased.  The objectives of this study were to examine the effectiveness of various N sources, combinations, and rates relative to Coastal bermudagrass [Cynodon dactylon (L.)  Pers] dry matter yields (DMY) and N uptake efficiency on Gallime (Glossic Paleudalf) and Lilbert (Plinthic Paleudult) soils.  Urea-ammonium nitrate (UAN), urea, urea + Ca, ammonium nitrate (AN), ammonium sulfate (AS) and combinations of UAN with B and S were evaluated.  Nitrogen sources were applied to supply 0, 45, 90, and 130 kg N ha-1 for each harvest.  Bermudagrass plots were timely harvested during three years, and plant tissue was analyzed for total N and S.  Soil samples (0- to 90-cm) were collected at the end of the third year.  Dry matter yields varied across years due to inconsistent rainfall distribution during the three-year study.  Nitrogen sources and combinations showed significant effects on bermudagrass production at only one of the experimental sites.  For this site, average DMY follow the order: AN ≥ AS = UAN + AS.  However, the latter two N sources were not significantly different from the other sources.  The interaction between N sources and rates on DMY was not significant (P ≤ 0.05).  Yields, N, and S concentrations were significantly increased with higher N rates, while N uptake efficiency significantly declined.  Nitrogen promoted soil acidity, with AS showing the lowest pH at any N application rate.