The following is a summary of a recent article that appeared in the Journal of Animal Science (Sept 2001).  The title of the paper is "Effects of nitrogen fertilization and harvest date on yield, digestibility, fiber, and protein fractions of tropical grasses".  This paper was published by a group from the Univ. of Florida.  Tifton 85 bermudagrass and Pensacola bahiagrass were fertilized at 5 different rates: 0, 35, 70, 105, and 140 pounds of N per acre.  Hay was cut at 28-day intervals:  harvest 1 was early June, harvest 2 was late June, 3 was July, 4 was August and harvest 5 was in September.  Results were as follows:

                                                                   N rate                                                                  Harvest date
Bahiagrass                                0        35        70        105         140                            1        2          3          4          5
    Yield (lb/ac/cutting)            686     1255    1320    1302        1223                        887    1268    1376    1102    1168
    IVOMD (%)                     52.1      51.7     51.2    51.9         52.6                        54.3     53.8     48.8     51.2    51.5
    CP (%)                               9.0      10.5     12.5    14.1         15.2                        12.4     11.5     12.0     12.0    13.4

                                                                   N rate                                                                  Harvest date
Bermudagrass                           0        35        70        105         140                            1        2          3          4          5
    Yield (lb/ac/cutting)            585     1386    1626    1644        1613                       1235    1760    1593    1142   1124
    IVOMD (%)                     58.0      56.3     56.0    57.2         60.0                        61.0     58.6     54.3     57.4    56.2
    CP (%)                               9.8      10.9     13.8    15.8         18.1                        14.6     13.2     12.4     13.2    14.9

    For yield, both grasses were optimized at a nitrogen rate of 70 pounds per acre.  IVOMD is similar to TDN which is an index of the energy content of the forage and N rate did not effect this; however, cutting date did.  This would have been even more dramatic if the cutting interval had exceeded 4 weeks.  N rate did continually effect the protein content of the hay and kept increasing with increasing application.
    A lactating cow requires approximately 62% TDN and 11% crude protein in her diet.  Thus, to me, the take home message is that these two grasses can be fertilized with 70 pounds of N per acre and this will optimize yield and quality as long as a short cutting interval is practiced.  Obviously, these results will vary with location and are highly dependent upon rainfall.  I should also note that this was over two years, one dry and one wet.  That is certainly similar to Alabama!!  Drought - Flood - Drought - Flood!!!  As always if you have questions or comments please let me know.